Antimicrob Agents Chemother, 1991 Sep, 35(9), 1760 - 4 Beta-lactamase of Mycobacterium fortuitum: kinetics of production and relationship with resistance to beta-lactam antibiotics; Fattorini L et al.; The kinetics of both intracellular and extracellular beta-lactamase production and the relationship between extracellular enzyme and in vitro susceptibility of Mycobacterium fortuitum to beta-lactam antibiotics have been studied . To this end we used a panel of stable nitrosoguanidine-induced mutants of M . fortuitum derived from the parental strain ATCC 19542 and differing in beta-lactamase production from 0.0001 to 278 U/liter in Mueller-Hinton broth . For overproducers of beta-lactamase (mutants A188, B180, C207, D316, and E31), MICs of benzylpenicillin, amoxicillin, ampicillin, and cephaloridine progressively increased with the amount of enzyme released into the medium, whereas MICs of imipenem and cefoxitin did not . The resistance of the mutants to amoxicillin was reduced up to 32-fold by clavulanic acid, whereas that to ampicillin was reduced 8-fold by sulbactam . These data suggest that the enzyme participated in the mechanisms of resistance to the beta-lactam antibiotics . However, for a mutant of M . fortuitum (gamma 27) with virtually nonexistent beta-lactamase production, the antibiotics still had relatively high MICs (for instance, benzylpenicillin and cephaloridine had MICs of 64 and 32 micrograms/ml, respectively) . This suggests that, aside from beta-lactamase production, other mechanisms such as cell wall permeability and/or affinity for penicillin-binding proteins could coexist in M . fortuitum and explain its natural resistance to beta-lactam antibiotics. Antimicrob Agents Chemother, 1991 Jun, 35(6), 1261 - 3 Human serum enhances the postantibiotic effect of fluoroquinolones against Staphylococcus aureus; Davidson RJ et al.; The postantibiotic effect (PAE) of fluoroquinolones against Staphylococcus aureus was determined in Mueller-Hinton broth and normal human serum . At both 4X and 10X the MIC, serum significantly increased the duration of the PAE in all strains tested (P less than 0.05) . Reducing the pH of the serum from 7.9 to 7.2 had no effect on the PAE . Heat treating the serum (56 degrees C, 30 min) reduced the PAE of ciprofloxacin at 10X the MIC approximately 25% (P less than 0.05) . The PAE of cloxacillin was reduced approximately 80% in serum, and PAE experiments with gentamicin and cephalexin produced findings similar to those obtained with the fluoroquinolones . Serum increased the MICs of ciprofloxacin and norfloxacin less than twofold and increased the MIC of pefloxacin approximately fourfold . We conclude that normal human serum considerably increases the PAE of fluoroquinolones against S . aureus. J Infect Dis, 1991 Jun, 163(6), 1369 - 73 Resistance of Staphylococcus aureus recovered from infected foreign body in vivo to killing by antimicrobials; Chuard C et al.; Because persistence of infections associated with prosthetic material despite the use of appropriate antibiotics is a major clinical problem, the antimicrobial susceptibility of bacteria responsible for a chronic subcutaneous tissue cage infection in rat was investigated ex vivo . Three to 6 weeks after the initiation of infection, suspensions of two strains of Staphylococcus aureus recovered from the foreign body surface and surrounding fluid were exposed to either oxacillin, vancomycin, fleroxacin, gentamicin, or rifampin . The MBCs of these bacteria were markedly elevated, in most cases 128 to greater than 256 times higher than the MBC of batch culture S . aureus in either logarithmic or stationary phase . Kinetic studies showed the bacteria did not grow when incubated for 2 h in Mueller-Hinton broth, possibly reflecting dormancy . Their killing was slow and incomplete by all antibiotics at greater than 8 times their MIC . These data provide direct evidence of a decreased susceptibility of S . aureus to the killing effect of antimicrobials during chronic foreign body infections in vivo. Antimicrob Agents Chemother, 1991 Jun, 35(6), 1089 - 92 Comparative effect of protein binding on the killing activities of teicoplanin and vancomycin; Bailey EM et al.; The effect of protein binding on the activity of teicoplanin against Staphylococcus aureus was evaluated . Bactericidal rates of teicoplanin in cation-supplemented Mueller-Hinton broth (SMHB) and in a 1:1 mixture of pooled human serum and cation-supplemented Mueller-Hinton broth (PHS-SMHB) were compared with those of vancomycin . Eight concentrations of each drug ranging from 15 to 150 micrograms/ml were studied in two series which correspond to the concentrations in serum achieved with low- (6 mg/kg of body weight once daily) and high-dose (30 mg/kg once daily) teicoplanin . Overall, the bactericidal rate of teicoplanin was lower than that of vancomycin . In the presence of serum, the bactericidal rate of teicoplanin in PHS-SMHB was lower than that in SMHB, often resulting in only one log10 drop in CFU over a 24-h period . There was no statistical difference in the bactericidal rates of high- and low-concentration teicoplanin in either medium . Additionally, concentration-dependent killing in SMHB was not evident with either agent . The bactericidal rates of teicoplanin and vancomycin in a 1:1 mixture of serum ultrafiltrate and SMHB at 60 micrograms/ml were also studied . It was noted that the bactericidal rate of neither agent was affected by the presence of serum ultrafiltrate . This finding is consistent with teicoplanin's high degree of protein binding (reported to be greater than 90% in undiluted serum) and further substantiates the hypothesis that only the free drug is active against microorganisms . These data support protein binding as being a factor in teicoplanin activity against S . aureus. J Antimicrob Chemother, 1991 Apr, 27(4), 481 - 9 Antimicrobial effects of lomefloxacin in vitro; Chambers ST et al.; The MIC of lomefloxacin was determined for 554 isolates from the urinary tract . Some of the more resistant strains of Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, and Pseudomonas aeruginosa were studied in a dynamic in-vitro model in order to study dosing strategies . The model simulated, in Mueller-Hinton broth, the profile of plasma lomefloxacin concentrations in volunteers . Bacteria were exposed to a range of lomefloxacin concentration profiles achievable by oral dosing . The first dose of lomefloxacin was rapidly bactericidal in a dose-dependent manner for all strains . On re-exposure, a dose-dependent inhibitory effect was observed . Drug-resistant mutants were readily isolated from all bacteria tested on lomefloxacin-containing plates . These occurred at a high frequency in P . aeruginosa (10(-1)), but less frequently in K . pneumoniae (10(-3)) . P . mirabilis (10(-5)), and E . coli (10(-6)) . The number of resistant mutants isolated tended to be lower with use of higher drug concentrations . The results suggest that lomefloxacin dosing regimens ensuring maintenance of a high serum concentration: MIC ratio will result in maximal antibacterial effects and minimal problems with resistant strains. Immun Infekt, 1991 Feb, 19(1), 3 - 7 {Effect of cyclic nucleotides on beta-lactamase production and outer membrane proteins of clinical Xanthomonas maltophilia isolates}; Cullmann W; Resistance of clinical Xanthomonas maltophilia isolates to beta-lactam compounds is influenced considerably by the nutrient medium employed for sensitivity testing; the organisms were much more resistant to beta-lactams when susceptibility testing was performed in Mueller-Hinton broth as compared to Isosensitest broth as the nutrient medium . Consequently, the influence of cyclic nucleotides was studied on beta-lactamase expression and outer membrane proteins in more detail . The exogenous supply of 5 mmol/l c-AMP or its lipophilic derivative c-AMP-N6,O2-dioctanoyl resulted in a marked reduction of enzyme production as compared to the control assay; 0.5 mmol/l c-AMP-S or 1 mmol/l c-GMP did not exhibit any effect . The analysis of the outer membrane proteins of Xanthomonas maltophilia revealed the single band of a 40 kdal protein which was expressed independently of the experimental conditions, thus confirming the classification of this pathogen as Xanthomonas maltophilia . The reduction of beta-lactamase expression in the presence of either c-AMP or c-AMP-N6,O2-dioctanoyl cannot be explained at present . The above findings emphasize again the problem of in-vitro susceptibility testing . To avoid false sensitive results, the use of Mueller-Hinton broth is recommended. Infection, 1991, 19 Suppl 3, S167 - 9 MICs of ciprofloxacin and trimethoprim for Escherichia coli: influence of pH, inoculum size and various body fluids; Aagaard J et al.; The influence of pH, inoculum size, human urine and prostatic extract on the MICs of ciprofloxacin and trimethoprim for Escherichia coli was investigated . There was no influence by the bacterial inoculum size within wide ranges on either drug . An increase in pH had a variable influence on the MICs of trimethoprim for E . coli but lowered those of ciprofloxacin considerably . Human prostatic extract increased the trimethoprim MIC for E . coli but lowered those of ciprofloxacin as compared to Mueller Hinton broth . Human urine increased the MICs of both drugs for E . coli. Chemotherapy, 1991, 37(3), 218 - 23 Influence of human urine on the in vitro activity and postantibiotic effect of ciprofloxacin against Escherichia coli; Zhanel GG et al.; The purpose of this investigation was to study the effects of human urine on the minimum inhibitory concentration (MIC) and the postantibiotic effect (PAE) of ciprofloxacin against Escherichia coli . MICs and the PAE were performed in Mueller-Hinton broth (MHB; pH 7.3 and 5.5) and in human urine (pH 5.5 and 7.3) . In urine, pH 5.5, MICs increased 64-fold (from 0.016 to 1.024 micrograms/ml) and the PAE was abolished (from 101.6 to 3.7 min), when compared to MHB, pH 7.3 . An acidic pH demonstrated the greatest effect on reduced susceptibility and PAE . Using ciprofloxacin concentrations adjusted for a higher MIC obtained in pH-adjusted urine and MHB, PAE values were similar for urine and MHB (approximately 280 min at 40 x MIC) . This study demonstrated that the MIC and PAE of ciprofloxacin against E . coli are influenced by human urine and in particular its pH. Chemotherapy, 1991, 37(3), 186 - 95 Teicoplanin combined with various antibiotics and human blood against a multiple-drug-resistant strain of Staphylococcus aureus; Traub WH et al.; Neither teicoplanin nor vancomycin at 2, 1 and 0.5 micrograms/ml consistently killed inocula of representative isolates of a multiple-drug-resistant (MDR) strain of Staphylococcus aureus in the presence of 65% (v/v) of fresh, defibrinated human blood, although both antibiotics sterilized tube contents in Mueller-Hinton broth (MHB) . With added human blood, teicoplanin (1 microgram/ml) combined with rifampin (1 microgram/ml) was the most effective in vitro combination, followed by teicoplanin (1 microgram/ml) + amoxicillin (8 micrograms/ml) + clavulanate (3 micrograms/ml), ampicillin (8 micrograms/ml) + sulbactam (8 micrograms/ml), cefamandole (8 micrograms/ml), fosfomycin (4 micrograms/ml + 25 micrograms/ml glucose-6-phosphate), imipenem (8 micrograms/ml), netilmicin (4 micrograms/ml), trimethoprim + sulfamethoxazole (1/19 micrograms/ml) and vancomycin (1 microgram/ml), respectively . Conversely, teicoplanin (1 microgram/ml) combined with fusidic acid (0.5 micrograms/ml) and ofloxacin (4 micrograms/ml), respectively, proved ineffective with 65% (v/v) added human blood . In concurrent control tubes, however, all drug combinations were bactericidally active in MHB against the MDR strain of S . aureus. Drugs Exp Clin Res, 1991, 17(2), 101 - 4 In vitro activity against aerobes and anaerobes of trospectomycin versus spectinomycin; Gismondo MR et al.; The general antibacterial properties of trospectomycin (TRO) were compared with those of spectinomycin (SPEC) in an in vitro study using a collection of recent clinical isolates: 50 Gram-positive and 25 Gram-negative aerobes and 30 Gram-positive and 15 Gram-negative anaerobes . Minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were determined for all strains by microtitre using serial dilutions in Mueller-Hinton broth for aerobes and Brucella broth for anaerobes . The final inoculum in each well was 10(5) cfu/ml . This study shows that none of the Gram-negative organisms was sensitive to TRO; the most sensitive were streptococci aerobic strains; TRO exhibited antibiotic activity against all anaerobes tested, which was not seen with SPEC, and also exhibited bactericidal activity . The MICs of Staphylococcus epidermidis and Bacteroides fragilis tested with TRO and SPEC were not significantly affected by the size of bacterial inoculum tested, and the nature of the growth medium did not alter the susceptibility tests. Jpn J Antibiot, 1990 Oct, 43(10), 1685 - 97 {Antibacterial activity of imipenem in combination with ampicillin against methicillin-resistant strains of Staphylococcus aureus}; Saionji K et al.; Imipenem (IPM) and beta-lactams have been reported to possess a synergistic relationship in their activities against methicillin (DMPPC)-resistant strains of Staphylococcus aureus (MRSA) . The purpose of this study was to determine activities of IPM and ampicillin (ABPC) singly and in combination against MRSA . Activities of the 2 antibiotics against 19 strains of S . aureus resistant to DMPPC were investigated by means of the checkerboard method, the disk diffusion technique and the killing-curve method . MICs of DMPPC against these strains determined using the agar dilution method were greater than or equal to 100 micrograms/ml and MICs of IPM and ABPC ranged from 12.5 to 100 micrograms/ml and from 12.5 to 50 micrograms/ml, respectively, when used singly . The following results were obtained with the checkerboard method: Synergistic effects and additive effects were found against 13/19 and against 6/19 strains, respectively, and no antagonistic effect was found according to the FIC (fractionary inhibitory concentration) index . The disk diffusion technique indicated synergistic results . Killing-curves with the following drug concentration combinations were examined in Mueller-Hinton broth against 5 fosfomycin(FOM)-resistant and 5 FOM-susceptible stains: (1) IPM 12.5 micrograms/ml, (2) ABPC 25 micrograms/ml, (3) IPM 12.5 micrograms/ml + ABPC 25 micrograms/ml, (4) IPM 6.25 micrograms/ml + ABPC 25 micrograms/ml, (5) IPM 6.25 micrograms/ml + ABPC 12.5 micrograms/ml, (6) IPM 6.25 micrograms/ml + ABPC 12.5 micrograms/ml + FOM (fosfomycin) 25 micrograms/ml, (7) IPM 12.5 micrograms/ml + ABPC 25 micrograms/ml + FOM 50 micrograms/ml, (8) FOM 50 micrograms/ml . The following results were obtained with the killing-curve method; (1) Synergistic effects were found against 8/10 strains and no antagonistic effect was found with the combinations of IPM and ABPC . (2) Synergistic effects were found against 3/5 strains and no antagonistic effect was found with the combinations of IPM, ABPC and FOM against 5 FOM-susceptible strains . Conclusions: IPM in combination with ABPC produced synergistic effects against MRSA . This combination therapy should be evaluated in treating MRSA infections. J Clin Microbiol, 1990 Sep, 28(9), 2145 - 7 Mueller-Hinton broth undergoes visible oxidative color changes in the presence of peroxidase and hydrogen peroxide; Galeazzi L et al.; In the presence of peroxidase and hydrogen peroxide, Mueller-Hinton broth undergoes a slow but clearly detectable color change from pale yellow to dark yellow or brown . An investigation of this phenomenon led to the conclusion that it is the result of the oxidation of tyrosine, a major component of the broth . Indeed, tyrosine has long been known to oxidize upon treatment with peroxidase and hydrogen peroxide . The observations reported here, besides being curious for the clinical microbiologist, might deserve attention for the possible implications in the medium color darkening which sometimes happens during microbial growth. J Antimicrob Chemother, 1990 Jul, 26(1), 131 - 44 Resistance to aminoglycoside antibiotics in gram-negative bacilli and staphylococci isolated from blood . Report from a European collaborative study . The ESGAR Study Group (European Study Group on Antibiotic Resistance); Dornbusch K et al.; The incidence of resistance to gentamicin, tobramycin, amikacin and netilmicin was determined by the microdilution method in Mueller-Hinton broth among blood culture isolates consecutively collected in 37 laboratories in 14 European countries . The distribution of bacteria was similar in each laboratory, Escherichia coli and staphylococci predominating . Resistance levels varied between laboratories but they were higher to all four antibiotics in Southern Europe than in Central and Northern Europe . Aminoglycoside resistance was usually associated with production of aminoglycoside-modifying enzymes, ANT(2"), AAC (3)-V, AAC (6')-I predominating in Gram-negative bacilli and APH (2") + AAC (6') and ANT (4')-I in staphylococci. Jpn J Antibiot, 1990 May, 43(5), 757 - 60 {Influence of Mueller-Hinton broth on the in vitro activities of cefuzoname, flomoxef, imipenem, and minocycline against Staphylococcus aureus}; Fujita S et al.; The influence of Mueller-Hinton (MH) broth (from BBL Microbiology Systems, and Difco Laboratories) of minimum inhibitory concentrations (MIC) of cefuzoname (CZON), flomoxef (FMOX), imipenem (IPM), and minocycline (MINO) for 100 strains of Staphylococcus aureus was investigated . Antibacterial activity of MINO was stronger than any other antibiotics . MICs of CZON for 16 strains (14 of 50 methicillin-resistant S . aureus (MRSA), 2 of 50 methicillin-sensitive S . aureus) were greater than or equal to 4-fold greater when tested in BBL MH broth than when tested in Difco MH broth, thus, different media altered categories of some strains (8 of 50 MRSA) from susceptible to resistant . MICs of FMOX in the BBL MH broth for 12 of 50 MRSA strains rose greater than or equal to 4-fold compared to the Difco MH broth . On the other hand, MICs of IPM and MINO were affected very little by the different brand of MH broth used. Pathol Biol (Paris), 1990 May, 38(5), 446 - 9 {Post-antibiotic effect of imipenem, amikacin and ciprofloxacin against various strains of Serratia marcescens}; Bollet C et al.; The authors compared the post-antibiotic effect (PAE) of imipenem, amikacin, ciprofloxacin, and latamoxef against Serratia marcescens ATCC 13880 (type strain) and against 12 clinical strains belonging to Grimont's most frequent biotypes: A2a, A3a, A3b, A4a, A4b, A5, A6a, A8a, A8b, A8c, TT, TCT . PAE was determined by measuring bacterial growth kinetics after one hour exposure to concentration of 2 x MIC of 10(6) CFUs in Mueller-Hinton broth . Drug removal was by 10-3 dilution of the exposed culture . A PAE was consistently present with imipenem (range 0.8-2.9 hrs), amikacin (range 1.0-4.9 hrs), ciprofloxacin (range 1.4-2.8 hrs) . The duration of PAE did not correlate with MIC or Grimont's biotypes. Jpn J Antibiot, 1990 Mar, 43(3), 379 - 87 {Antibacterial activities and electron microscopic studies of imipenem in combination with fosfomycin against methicillin and fosfomycin resistant strains of Staphylococcus aureus}; Saionji K et al.; Imipenem (IPM) and fosfomycin (FOM) have been reported to possess a synergistic relationship in their activities against both methicillin (DMPPC)-susceptible and -resistant strains of Staphylococcus aureus . However it was not concluded whether these antibacterial activities were bacteriostatic or bactericidal . The purpose of this report is to elucidate this point clearly . Activities of the 2 antibiotics against 15 strains S . aureus resistant to both DMPPC and FOM were investigated by means of the killing-curve method and electron microscopic studies . MICs of DMPPC and FOM against these strains determined using the agar dilution method were greater than or equal to 50 micrograms/ml and MICs of IPM by the broth dilution method ranged from 12.5 to 50 micrograms/ml . The killing-curves with the following drug concentration combinations were examined in Mueller-Hinton broth: 1 . FOM 25 micrograms/ml, 2 . FOM 25 micrograms/ml + IMP 1/2 MIC, 3 . IPM 1MIC, 4 . FOM 25 micrograms/ml + IPM 1 MIC and 5 . FOM 25 micrograms/ml + IPM 2MIC . Morphological changes produced in 1 strain by 2 of the combinations, 2 . FOM 25 micrograms/ml + IPM 1/2 MIC and 4 . FOM 25 micrograms/ml + IPM 1MIC, were observed using scanning and transmission electron microscopy . The following results were obtained; (1) The synergistic effects were found in 6/15 strains (40%) and no antagonistic effect was found . (2) Electron microscopic observation showed that IPM in combination with FOM caused lysis of the cells . Conclusions: IPM in combination with FOM produced bactericidal and bacteriolytic effects on DMPPC-resistant S . aureus (MRSA) . This combination therapy should be evaluated for FOM resistant MRSA infections. Eur J Clin Microbiol Infect Dis, 1990 Feb, 9(2), 133 - 5 Comparison of four methods for testing high-level aminoglycoside resistance in enterococci; Yagupsky P et al.; In a prospective study the prevalence of high-level aminoglycoside resistance (MIC greater than or equal to 2,000 micrograms/ml) among 62 clinically significant enterococci was investigated . A total of 10(5) organisms were inoculated a) onto a plate containing 2,000 micrograms/ml of gentamicin or streptomycin; b) into a microtube for dilution MIC determinations for gentamicin, amikacin, tobramycin and streptomycin; and c) into a single tube containing 500 micrograms/ml of gentamicin, amikacin, tobramycin or streptomycin in supplemented Mueller-Hinton broth . In addition, tubes containing 500 micrograms/ml of gentamicin, amikacin, tobramycin or streptomycin were inoculated with five enterococcal colonies ("crude" method) . For 45 of the 62 isolates, MICs of gentamicin, amikacin and tobramycin were less than or equal to 500 micrograms/ml, while 17 (27%) showed high-level resistance . The MICs of streptomycin were less than or equal to 500 micrograms/ml for 42 of 62 isolates, and greater than or equal to 2,000 micrograms/ml for 20 (32.3%) . For 8 of the 17 (47%) isolates showing high-level gentamicin resistance, MICs of streptomycin were less than or equal to 500 micrograms/ml . There was complete agreement between the results of the plate method, the microtube dilution MIC and the tube inoculated with 10(5) CFU, but the crude method gave discordant results for two isolates . It is concluded that a tube containing 500 micrograms/ml of aminoglycoside is a simple, accurate and inexpensive method for determining high-level aminoglycoside resistance. Antimicrob Agents Chemother, 1990 Jan, 34(1), 98 - 101 Significance of "extravascular" protein binding for antimicrobial pharmacodynamics in an in vitro capillary model of infection; Dudley MN et al.; The effect of protein binding in an "extravascular" space on antimicrobial pharmacodynamics was studied in an in vitro capillary model of infection . Simulated 500-mg oral doses of dicloxacillin (approximately 96% bound) or cephalexin (less than 5% bound) were administered every 6 h for four doses . A 10-fold-higher dose of dicloxacillin was also studied to determine the effect of drug concentration on the reduction of bacterial killing in the presence of protein . Staphylococcus aureus ATCC 25923 was inoculated into peripheral chambers filled with either Mueller-Hinton broth or Mueller-Hinton broth plus 25% human serum . Serial samples for bacterial counts were collected over 24 h . The presence of serum in the chambers significantly reduced bacterial killing by dicloxacillin but not by cephalexin during the first 6 h (two-way analysis of variance, F = 6.04, P less than 0.05) but not at 24 h . Reduction of dicloxacillin activity in serum-containing chambers persisted with the higher dose . These data suggest that despite attaining higher total drug concentrations in protein-containing extravascular spaces with highly bound drugs, protein binding reduces bactericidal activity during the early stages of treatment in this model. J Lab Clin Med, 1989 Dec, 114(6), 724 - 7 The effect of sodium on amiloride-tobramycin synergy in Pseudomonas cepacia; Cohn RC et al.; Amiloride combined with subinhibitory concentrations of tobramycin is synergistic against Pseudomonas cepacia in vitro . It is known that amiloride blocks transmembrane sodium (Na+) flux in eukaryotic cells, but the mechanism of action in bacteria is unknown . Amiloride-mediated Na+ gradient changes might affect transcellular tobramycin transport, resulting in synergy between these two drugs . To examine this hypothesis, we studied the effect of extracellular {Na+} on amiloride-tobramycin synergy with a reference strain of P . cepacia . Control growth in Mueller-Hinton broth (MHB) alone, MHB supplemented with 200 mmol/L NaCl, and MHB dialyzed against a Na+-free solution was determined by absorbance at 650 nm over 3 hours . Inhibition in the presence of amiloride, tobramycin, or a combination was expressed as percentage of control growth . Growth in the presence of tobramycin alone was significantly higher in MHB + NaCl than in MHB or dialyzed MHB (81% +/- 5%; vs 57% +/- 5%; 35% +/- 4%; mean +/- SEM, respectively, p = 0.003) . Growth in the presence of amiloride alone was not significantly different in the three media (84% +/- 4%; 80% +/- 3%; 80% +/- 1%; respectively, p = 0.746) . Percent control growth was significantly lower when the two drugs were combined, but results were not statistically different among the three media (3.5% +/- 3%; 0.2% +/- 0.8%; 4% +/- 1%; respectively, p = 0.604) . We conclude that growth inhibition of P . cepacia in the presence of tobramycin is antagonized by increasing extracellular {Na+} . This antagonistic effect of {Na+} is reversed by amiloride . Changes in {Na+} do not appear to directly affect amiloride-tobramycin synergy in P . cepacia. J Infect Dis, 1989 Oct, 160(4), 616 - 23 Use of serum ultrafiltrate in the serum dilution test; Leggett JE et al.; Although pooled human serum diluent is advocated in the serum dilution test, its use may compensate for protein binding defects in patients and yield nonrepresentative titers . To test this hypothesis, comparison was made of serum ultrafiltrate (molecular weight cutoff less than or equal to 30,000) serially diluted into either pooled serum ultrafiltrate or Mueller-Hinton broth with patient serum samples diluted into pooled human serum in 111 assays from 55 patients and 6 volunteers . Of 111 bactericidal titers in ultrafiltrate and/or Mueller-Hinton broth, 101 were within a single twofold dilution of titers in pooled human serum . Nine of 10 discordant titers involved highly bound drugs and were usually higher in ultrafiltrate than in pooled human serum . In seven additional volunteers with renal failure, titers in ultrafiltrate and in each volunteer's serum were higher than those diluted in pooled human serum (P = .002) . Recommended methods using pooled serum diluent may not accurately predict actual bactericidal titers in patients with abnormal protein binding. Microbiologica, 1989 Oct, 12(4), 297 - 306 Killing rate and serum bactericidal activity of oxacillin, rifampin and ciprofloxacin against Staphylococcus aureus; Moretti MV et al.; The bacterial activity of oxacillin, rifampin and ciprofloxacin was examined at two concentrations by the serum bactericidal rate (SBR) technique against 5 strains of methicillin-susceptible Staphylococcus aureus . The activity of oxacillin plus ciprofloxacin and oxacillin plus rifampin was also determined for 5 strains of staphylococci examining in vitro the SBR and the serum bactericidal activity (SBA) . We simulated SBR and SBA in vitro using pooled human serum containing know concentrations of antimicrobial agents . The rate at which the antibiotics kill S . aureus did not rise by increasing the concentrations over the MBC . The oxacillin-ciprofloxacin combination was indifferent when tested by the rate of killing, whereas an antagonistic interaction was frequently observed with the oxacillin-rifampin combination . The SBA was determined by two methods: the technique of the Mayo Clinic that uses Mueller-Hinton broth (MHB) as the diluent and the method of Stratton in which the diluent was prepared with MHB supplemented with Ca++ and Mg++ and combined with 50% pooled human serum . The activities of oxacillin and rifampin were decreased in the presence of human serum . These results were attributed to the high protein binding of these antibiotics . Rifampin in combination with oxacillin showed antagonism against S . aureus also by the SBA method . The inhibitory activity of drugs in combination remained substantially the same as the single more active one. J Clin Microbiol, 1989 Oct, 27(10), 2277 - 85 Wide variability in Pseudomonas aeruginosa aminoglycoside results among seven susceptibility testing procedures; Staneck JL et al.; Seven commonly used antimicrobial susceptibility testing methods were used to test the susceptibility of 150 isolates of Pseudomonas aeruginosa against gentamicin, tobramycin, amikacin, carbenicillin, and piperacillin . Results were compared with respect to the susceptibility characteristics of the population of isolates as defined by each method . Conventional methods included agar disk diffusion and agar dilution, carried out in accordance with current recommendations of the National Committee for Clinical Laboratory Standards, as well as broth microdilution testing with cation-supplemented Mueller-Hinton broth (CSMHB) . Methods in which instrumentation was used for result determination included the Autobac I, Avantage, Sensititre Autoreader (using a breakpoint panel at 18 h of incubation), and Vitek (AMS-240, using the GNS susceptibility card) . When necessary for comparison, MIC data were converted to categorical interpretations (susceptible, intermediate, and resistant) . With respect to gentamicin, no significant differences were noted among the results of disk diffusion, broth microdilution, Sensititre Auto breakpoint, or Vitek methods which characterized 60 to 67% of isolates as susceptible, 16 to 22% as intermediate, and 13 to 17% as resistant . In contrast, agar dilution, Autobac, and Avantage, although yielding gentamicin results similar to those of one another, were each significantly different in result reporting from the other four methods above for gentamicin results, and they characterized the Pseudomonas population largely as susceptible (88 to 97%), with 0 to 6% intermediate and only 3% to 6% resistant . More isolates were characterized as being resistant to gentamicin in the Avantage test if an assay broth supplemented with increased amounts of calcium was used . Cation impregnation of Autobac disks did not appreciably change Autobac results . The geometric mean MIC of gentamicin was 4 micrograms/ml lower in the agar dilution method than in the CSMHB microdilution method, despite monitoring of the agar for cation content through performance disk diffusion testing with P . aeruginosa ATCC 27853 . Tobramycin activity was greater than gentamicin activity, and susceptibility to tobramycin ranged from 89 to 97%, with few statistically significant differences noted among the seven methods studied . Differences in MIC distribution and geometric mean MIC between agar dilution and CSMHB microdilution testing were minimal and suggested less of a cation influence on tobramycin than gentamicin results . Although amikacin was also more active than gentamicin (83 to 99% of isolates were susceptible), differences in the amikacin results among methods tended to reflect the same trends in reporting as seen with gentamicin testing, with the exception that results of Avantage testing were similar to those of disk diffusion, CSMHB microdilution, Sensititre, and Vitek . A difference in geometric mean MIC of 5 micrograms/ml between CSMHB testing and agar dilution testing suggested the influence of divalent cations on amikacin results . Few highly significant differences were noted among methods when isolates were tested against carbenicillin and piperacillin, except that Avantage piperacillin results (66% susceptible) and Autobac piperacillin results (98% susceptible) were noticeably different from the percent piperacillin susceptibility (range, 85 to 92%) measured by the other methods . Method-dependent variability among aminoglycoside susceptibility results, particularly when testing gentamicin, prevents meaningful comparison of Pseudomonas susceptibility trends among hospitals when different methods are used and promotes confusion and frustration among clinical microbiologists and clinicians owing to the uncertainties of clinical meaning of these data. Antimicrob Agents Chemother, 1989 Sep, 33(9), 1526 - 30 Hyperoxia and the antimicrobial susceptibility of Escherichia coli and Pseudomonas aeruginosa; Muhvich KH et al.; We have tested the ability of hyperoxia (98% O2-2% CO2 at 2.8 atmospheres absolute {ca . 284.6 kPa}) to enhance killing of Escherichia coli (serotype O18 or ATCC 25922) by nitrofurantoin, sulfamethoxazole, trimethoprim, gentamicin, and tobramycin . We have also looked for interactions between hyperoxia and the aminoglycosides against Pseudomonas aeruginosa ATCC 27853 . Hyperoxia significantly enhanced bacteriostatic activity of nitrofurantoin and trimethoprim as measured by MIC testing . The possibility exists that these effects might be due to the method required to tests MICs under hyperoxic conditions rather than to the effect of hyperoxia itself . In addition, hyperoxia enhanced killing of bacteria by trimethoprim as measured by MBC testing . Hyperoxia decreased numbers of E . coli by 1.3 log10 and P . aeruginosa by 2.7 log10 in cation-supplemented Mueller-Hinton broth medium . The bacteriostatic effects of hyperoxia did not affect MICs of gentamicin or tobramycin . The lack of interaction between hyperoxia and gentamicin or tobramycin was confirmed by determining the number of viable bacteria remaining after 24 h of exposure to hyperoxia by using a pour plate method . We conclude that hyperoxia potentiates the antimicrobial activity of the reduction-oxidation-cycling antibiotic tested (nitrofurantoin) and of one of the antimetabolites tested (trimethoprim) . Hyperoxia does not enhance the bactericidal effects of gentamicin and tobramycin, which require oxidative metabolism for transport into bacterial cells. Kansenshogaku Zasshi, 1989 May, 63(5), 457 - 62 {Studies on determination of minimum bactericidal concentrations of penicillin-G for beta-hemolytic streptococci}; Takizawa Y et al.; Minimum bactericidal concentrations (MBC) of penicillin-G were determined for 94 isolates of beta-hemolytic streptococci: 37 group A; 40 group B; 6 group C; and 11 group G . Our experiments focused on the influence of technical variable factors on the outcome of the MBC test such as inoculum preparation, manner of inoculation, technique of sampling for survivors, growth phase of inoculum, final concentration of inoculum, and time of incubation . The results were summarized as follows: 1 . The mean MBC, ranged from 0.0145 microgram/ml (group A) to 0.084 microgram/ml (group B) . The MBC/MIC ratio ranged from 1- to 4-fold (3 strains: 2 group A, 1 group C), showing no penicillin-G tolerance . 2 . Logarithmic-phase inocula used were prepared by incubating 10 ml Mueller-Hinton broth (MHB) in water bath at 37 degrees C for 4 to 5 h after adding 0.01 ml of 24 h-incubated cultures . 3 . 0.1 ml of logarithmic-phase inocula were released on the surface of penicillin-containing MHB (1 ml) without shaking or splashing . 4 . It was important to resuspend the organisms by vortexing 4 h before tubes were sampled so that any organisms contaminating glassware above the meniscus were exposed to antibiotic . 5 . No carry-over effect was observed with 0.01 ml samples . 6 . Effect of bacterial growth phase on outcome of MBC test was not confirmed . 7 . All tests used final volumes of 1.1 ml of MHB containing 10(5) cells/ml and 24-h incubation time. Antimicrob Agents Chemother, 1989 May, 33(5), 776 - 7 Production and induction of beta-lactamase during growth of Pseudomonas aeruginosa in biological fluids; Letendre ED et al.; beta-Lactamase production in biological fluids was evaluated by using an antibiotic-resistant Pseudomonas aeruginosa strain . Enzyme production was low in plasma or ascitic fluid and high in urine . Induction of beta-lactamase by imipenem was studied by using an inducible P . aeruginosa strain . Induction was lower in biological fluids than in Mueller-Hinton broth. J Antimicrob Chemother, 1989 Mar, 23 Suppl C, 43 - 52 Comparative in-vitro activity of the penem FCE 22101 against recent European blood culture isolates; Dornbusch K et al.; Recent blood culture isolates (462 strains of Gram-negative bacilli and 288 strains of staphylococci) collected in 30 European laboratories were tested for susceptibility to five beta-lactam antibiotics by a microdilution method in Mueller-Hinton broth . The penem FCE 22101 and imipenem were very active against the Gram-negative bacilli, except the pseudomonads, FCE 22101 being four- to 16-fold less active (MIC50 2 mg/l; MIC90 8 mg/l) than imipenem MIC50 0.5 mg/l; MIC90 2 mg/l) . Ceftibuten and ceftazidime were also active (MIC50 0.25 mg/l; MIC90 greater than 16 mg/l) . The MIC of piperacillin (MIC50 8 mg/l; MIC90 greater than 64 mg/l) were two- to 16-fold reduced in the presence of the beta-lactamase inhibitor YTR-830 against these bacteria . Only imipenem and piperacillin inhibited the pseudomonads (MIC50 4 and 8 mg/l respectively; MIC90 16 mg/l and greater than 64 mg/l), with two-fold reduction in MIC50 of piperacillin in the presence of YTR-830 . The staphylococci were very susceptible to FCE 22101 and imipenem (MIC50 less than or equal to 0.25 mg/l) except some cefazolin-resistant strains . In Staphylococcus aureus penem resistance was better expressed after bacterial growth at 30 degrees C . Some strains of Staph . epidermidis were susceptible to FCE 22101 but resistant to imipenem . The cephalosporins were not active against the staphylococci, and the presence of YTR-830 caused a four- to 16-fold reduction in MIC of piperacillin. Antimicrob Agents Chemother, 1989 Jan, 33(1), 35 - 40 Enhancing effect of serum ultrafiltrate on the activity of cephalosporins against gram-negative bacilli; Leggett JE et al.; A few studies have suggested that the inhibitory effect of serum on activity of broad-spectrum cephalosporins is less than that predicted by the degree of protein binding . Microdilution MICs of ceftriaxone, cefoperazone, moxalactam, and ceftizoxime were therefore determined against ATCC and clinical strains of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus in Mueller-Hinton broth containing either human albumin (as 0, 2.5, or 5% solution) or heat-inactivated human serum (as 0, 25, 50, or 95% solution) . Arithmetic linear dilutions were used to improve accuracy . For standard bacterial strains, MICs in the presence of 5% albumin were higher than in broth alone by multiples of 10.9 to 21 for ceftriaxone, 5.5 to 16.4 for cefoperazone, 1.9 to 3.7 for moxalactam, and 1.1 to 1.4 for ceftizoxime, as expected by their protein binding . MICs in the presence of 95% serum were similar to those in 5% albumin for all four drugs against S . aureus and P . aeruginosa but were 2.2- to 4.8-fold lower (P less than 0.001) against E . coli and K . pneumoniae . Similar findings were observed at lower protein concentrations and with clinical isolates, except that for some strains of P . aeruginosa MICs were lower in serum than in albumin . Individual sera from five subjects gave comparable results . The addition of serum ultrafiltrate to albumin-containing solutions reduced MICs of ceftriaxone and cefoperazone 1.6- to 7.4-fold against E . coli and K . pneumoniae (P less than 0.01) but did not alter the MICs for S . aureus . Serum may contain an ultrafiltrable component(s) that enhances the activity of third-generation cephalosporins against many gram-negative bacilli. Antimicrob Agents Chemother, 1988 Nov, 32(11), 1614 - 8 Bactericidal activity of oxacillin against beta-lactamase-hyperproducing Staphylococcus aureus; Woods GL et al.; The bactericidal activity of oxacillin against beta-lactamase-hyperproducing strains of Staphylococcus aureus for which the MIC by MicroScan was 1 or 2 micrograms/ml after incubation for 24 h was evaluated by MBC studies and kill kinetics methods . MBC and kill kinetics tests were both performed using Mueller-Hinton broth (MHB), with and without 2% NaCl supplementation, and incubation at 30 and 35 degrees C . When MBC testing was performed with salt-supplemented MHB, the oxacillin MBC/MIC ratio was greater than 8 for 17 and 16 of 17 S . aureus isolates at 30 and 35 degrees C, respectively . With unsupplemented MHB, the MBC/MIC ratio was greater than 8 for nine and six strains at 30 and 35 degrees C, respectively . Five representative strains were selected for kill kinetics studies under the four different test conditions . Oxacillin appeared more bactericidal by the kill kinetics method than by MBC testing . Moreover, salt supplementation did not affect the results of kill kinetics studies as dramatically as it did the MBC results . Thus, bactericidal testing results are markedly influenced by the technique employed, and further in vivo studies are necessary to fully evaluate the efficiency of oxacillin against beta-lactamase-hyperproducing strains of S . aureus. Antimicrob Agents Chemother, 1988 Nov, 32(11), 1648 - 54 Bactericidal activity of M14659 enhanced in low-iron environments; Mochizuki H et al.; The bactericidal activity of M14659 against Escherichia coli in low-iron environments was investigated and compared with that of ceftriaxone and ceftazidime . The bactericidal activity of M14659 against E . coli in Mueller-Hinton broth was enhanced 30- to 20,000-fold by addition of transferrin, which is an iron-binding protein, whereas the activity of ceftriaxone or ceftazidime was much less strongly affected . This enhancement by transferrin was completely inhibited by saturating the iron-binding capacity of transferrin with FeCl3 . M14659 was taken up markedly into bacterial cells in the presence of transferrin, and its uptake was inhibited by the protonophore dinitrophenol, which inhibits active-transport systems coupled to an energized membrane such as the iron transport systems of E . coli . The bactericidal activity of M14659, which chelates Fe3+, was also enhanced in the presence of other iron-binding compounds such as lactoferrin and alpha,alpha'-dipyridyl or in iron-deficient Mueller-Hinton broth (Fe3+ concentration, less than 2 nM) supplemented with FeCl3 at 0.1 to 1.0 microM, but not in unsupplemented iron-deficient Mueller-Hinton broth . The E . coli used in this study was confirmed to derepress iron transport systems in the presence of transferrin, lactoferrin, and alpha,alpha'-dipyridyl and in the iron-deficient Mueller-Hinton broth supplemented with FeCl3 at 0 to 1.0 microM . M14659 also showed an excellent antibacterial activity in vitro against other gram-negative bacteria in the low-iron environments . These findings indicate that M14659 may be actively taken up with Fe3+ into bacterial cells, probably through the iron transport systems under conditions of low iron and, thus, kills bacteria effectively. Jpn J Antibiot, 1988 Oct, 41(10), 1390 - 406 {Influence of human albumin on bactericidal or antibacterial activities of cephems and monobactams}; Saionji K; Influence of human albumin on bactericidal or antibacterial activities of 11 beta-lactams were examined . The 11 beta-lactams included second generation cephems (cefsulodin, cefotiam and cefmetazole), third generation cephems (ceftazidime, latamoxef, cefmenoxime, cefoperazone, cefotetan and cefpiramide) and monobactams (carumonam and aztreonam) . The micro-broth-dilution method was used to determine antibacterial activities . Bactericidal activities were determined using the time-kill method . Used in the broth-dilution method were 2 media, MUELLER-HINTON broth (MHB) and the same medium supplemented with 5 g human albumin/d1 (MHB-A) . The first experiment was to compare minimum inhibitory concentrations (MICs) determined in MHB were compared with those in MHB-A of 6 antibiotics against Staphylococcus aureus FDA 209P JC-1, of 7 antibiotics against Escherichia coli ATCC 25922 and of 5 antibiotics against Pseudomonas aeruginosa NCTC 10490 . MICs using MHB-A were higher than MIC using MHB for 2 of the 6 antibiotics against S . aureus, and for all the 7 antibiotics against E . coli, and for 3 of the 5 antibiotics against P . aeruginosa . The second experiment was done to compare MICs of 5 antibiotics determined in MHB-A with those determined in MHB against 10 clinical isolates of S . aureus, of 6 antibiotics against 10 clinical isolates of Klebsiella pneumoniae and of 6 antibiotics against 10 clinical isolates of P . aeruginosa . The results obtained in the second experiment were varied for different antibiotics and different strains of organisms, and same antibiotics produced different results for different strains . MICs determined in MHB-A were lower than those in MHB for antibiotics with relatively low protein binding rates against 22 of 170 isolates tested (12.9%), whereas the former was higher than the latter against 103 out of 170 isolates tested (60.6%) . MICs of antibiotics with relatively high protein binding rates showed an opposite trend . In the third experiment, time-kill curves were determined in the 2 media for 5 antibiotics against S . aureus FDA 209P JC-1, for 6 drugs against E . coli ATCC 25922 and for 5 drugs against P . aeruginosa NCTC 10490 . The concentrations of these antibiotics used were 1/2 x MIC, 1 x MIC and 2 x MIC . MICs determined in the first experiment were used here . Time-kill curves determined in MHB-A didn't reflect MICs determined in MHB . Using MHB-A, antibiotics with lower MICs determined in MHB-A showed bactericidal activities in lower concentrations . Human albumin influenced antibacterial or bactericidal activities of beta-lactams.(ABSTRACT TRUNCATED AT 400 WORDS) J Antimicrob Chemother, 1988 Oct, 22 Suppl D, 199 - 207 In-vitro activity of fleroxacin against isolates causing complicated urinary tract infections and concentrations in seminal and prostatic fluid and in prostatic adenoma tissue; Naber KG et al.; Fleroxacin is a new fluoroquinolone with a broad antibacterial spectrum and a serum half-life of about 8-12 h . Eighty percent of 400 isolates from complicated or hospital-acquired urinary tract infections were inhibited by a concentration of 1 mg/l and 95% by 4 mg/l . As with other quinolones, fleroxacin is less active in acid urine (pH 5.4) than in Mueller-Hinton broth (pH 7.4) . In 12 healthy volunteers the concentrations of fleroxacin were measured in plasma and seminal and prostatic fluid 2, 4 and 12 h after an oral dose of 400 mg . The mean plasma concentrations of three or four volunteers at each time were 4.2, 3.6 and 1.2 mg/l, respectively . The corresponding prostatic fluid/plasma ratios were 0.30, 0.27 and 1.96, respectively . By concomittant administration of ioxitalamic acid it could be demonstrated that in samples obtained 12 h after administration urinary contamination must be considered . Fleroxacin is concentrated in seminal fluid by a median ratio of 1.7 . In 13 elderly patients the prostatic fluid and prostatic adenoma tissue concentrations were determined one to four hours following oral administration of 400 mg . The concentrations in prostatic fluid were similar to those of volunteers . The tissue concentrations exceeded plasma concentrations by only about 10% (median) . Fleroxacin is very active against isolates causing complicated UTI . Concentrations in seminal and prostatic fluid and prostatic adenoma tissue are sufficiently high to treat bacterial prostatitis or vesiculitis caused by susceptible bacterial strains. J Clin Microbiol, 1988 Sep, 26(9), 1675 - 8 Salt-supplemented medium for testing methicillin-resistant staphylococci with newer beta-lactams; Jorgensen JH et al.; The addition of 2% NaCl to cation-supplemented Mueller-Hinton broth (CSMHB) was evaluated for microdilution testing of the susceptibility of staphylococci to five cephalosporins, imipenem, amoxicillin-clavulanate, and ticarcillin-clavulanate . With Staphylococcus aureus, NaCl improved the recognition of methicillin (oxacillin) resistance to cefamandole, imipenem, or ticarcillin-clavulanate . Resistance to amoxicillin-clavulanate was readily determined, irrespective of the presence of added salt . The addition of 2% NaCl to CSMHB did not significantly improve detection of resistance to any of the beta-lactams among coagulase-negative staphylococci . Since the addition of NaCl did not have significant adverse effects on tests with coagulase-negative staphylococci, the routine addition of 2% NaCl to oxacillin or methicillin tests with staphylococci may be justifiable on the basis of convenience or standardization . However, addition of NaCl to susceptibility tests of other beta-lactams does not consistently improve recognition of resistance among staphylococci and thus cannot be recommended for routine use. J Med Microbiol, 1988 Jun, 26(2), 143 - 6 Profiles of amino-acid utilisation and production amongst strains of Branhamella catarrhalis; Bezjak V et al.; Utilisation and production of amino acids by isolates of Branhamella catarrhalis was studied by ion exchange chromatography after cells had been grown in nutrient broth and Mueller-Hinton broth . The profiles of amino acids used and produced by each strain were compared by a single linkage cluster algorithm . The results of this study reflect the biochemical and physiological heterogeneity amongst strains of B . catarrhalis. Pathol Biol (Paris), 1988 Jun, 36(5 Pt 2), 608 - 12 {In vitro effect of combinations of netilmicin and amikacin with fosfomycin and pefloxacin on 31 strains of heterogeneous methicillin- resistant Staphylococcus aureus}; David C et al.; The Minimal Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) of 31 strains of Staphylococcus aureus resistant to methicillin and gentamicin were determined towards aminoglycosides: netilmicin (N) and amikacin (A) . The results of the study showed a large discordance between the technic using dilution in Mueller-Hinton broth and the technic using agar diffusion with antibiotic discs . The level of sensitivity appears to decrease by dilution . The problem of using these aminoglycosides in combination with other antibiotics as fosfomycin (F) and pefloxacin (P) was faced . In vitro, antibacterial activity of combinations {N-F}, {N-P} and {A-F}, {A-P}, was studied by microtiter checkerboard method . The antibacterial effects of these combinations were evaluated by determination of Fractional Bactericidal Indices (FBC-indices) . The combination netilmicin or amikacin with pefloxacin has an additive bactericidal effect in most cases, without discrimination between the different aminoglycosides (FBC #0.82) . Netilmicin or amikacin in combination with fosfomycin are found to be additive or moderately synergistic (FBC #0.53) . No occurrence of antagonism was observed. Antimicrob Agents Chemother, 1988 Feb, 32(2), 170 - 4 Characterization of resistance phenotype and cephalosporin activity in oxacillin-resistant Staphylococcus aureus; Mateos-Mora M et al.; Forty isolates of methicillin-resistant Staphylococcus aureus were tested versus oxacillin at 30 and 35 degrees C with and without 2% NaCl supplementation of Mueller-Hinton broth and classified as having resistance that was low (MIC, less than or equal to 16 micrograms/ml) or high (MIC, greater than or equal to 32 micrograms/ml) and temperature or NaCl dependent . Only three isolates had low-grade resistance at both 30 and 35 degrees C; for two isolates the MICs at 35 degrees C were greater than or equal to 4 X the MICs at 30 degrees C . NaCl usually increased the MICs two- to fourfold . Efficiency of plating studies were performed on strains selected for their level of oxacillin resistance and according to temperature-related difference in MICs . Most strains appeared to represent the heterogeneous resistance phenotype . Cefamandole MICs were little affected by temperature but increased with NaCl . With three exceptions, cefamandole MCBs were less than or equal to 4 X MICs . For only six isolates were cefuroxime MICs less than or equal to 16 micrograms/ml . Four strains that were susceptible to both cefuroxime and cefamandole were selected for time-killing curve studies at inocula of 10(7) CFU/ml . At 8 X MIC, cefuroxime failed to reduce the concentration of any strain by greater than or equal to 3 X log10 CFU/ml . Killing of greater than or equal to 3 X log10 CFU/ml was achieved by cefamandole at 4X and 8 X MIC in one strain, at 8 X MIC only in two strains, and by neither 4 X nor 8 X MIC in one strain . Within therapeutically attainable blood levels, cefuroxime is essentially inactive and cefamandole is variably bactericidal against oxacillin-resistant s . aureus. J Clin Microbiol, 1988 Jan, 26(1), 54 - 6 Toxic effect of calcium alginate swabs on Neisseria gonorrhoeae; Lauer BA et al.; Calcium alginate (CA)-tipped swabs have been reported to interfere with the recovery of herpes simplex virus, Chlamydia trachomatis, and Ureaplasma urealyticum and may cause cytotoxicity in cell culture . To determine whether CA swabs also inhibit the growth of Neisseria gonorrhoeae, we carried out a series of experiments using either CA swabs that were toxic or nontoxic in a cell culture cytotoxicity assay or nontoxic rayon or cotton swabs . Leaving a toxic CA swab in 3 ml of Mueller-Hinton broth inoculated with 10(4) CFU/ml caused rapid killing within 6 h at 37 degrees C; colony counts of five strains were less than 1% of those of Mueller-Hinton broth controls . When the tips of toxic CA swabs were inoculated directly and kept at 37 degrees C without holding medium, the swabs were sterile at 6 h . If the same swabs were placed in Amies medium with charcoal, organisms could still be recovered at 6 h . Toxicity was less at room temperature than at 37 degrees C . Inhibition of growth of N . gonorrhoeae was not seen with rayon or cotton swabs . The toxic component was neither the CA fiber nor the aluminum wire but probably the glue used to attach the fibers . We concluded that some lots of CA swabs kill N . gonorrhoeae in vitro . Survival of N . gonorrhoeae is improved with nontoxic swabs, particularly cotton swabs, and Amies medium with charcoal regardless of swab type. Vet Rec, 1987 Dec 5, 121(23), 533 - 6 Experimental reproduction of porcine proliferative enteritis; Mapother ME et al.; Conventional crossbred pigs from different sources and of different weights were examined for susceptibility to porcine proliferative enteritis . The ileal mucosa of pigs with the disease was emulsified and suspended in Mueller-Hinton broth . Pigs weighing 15, 120 and 200 lb (6.8, 54.5 and 91 kg) (four pigs per group) were stressed and inoculated orally with 80 ml of emulsified proliferative ilea . Severe lesions of porcine proliferative enteritis were detected in three of the four pigs weighing 6.8 kg . Mild lesions were detected in two of the four pigs in each of the other two groups . Gross lesions consisted of reticulation of the serosa, and hyperaemia and thickening of the mucosa with either fibrin or blood clots adherent to the mucosal surface . Inflammation, numerous mitotic figures and epithelial cell proliferation were observed microscopically in the crypts . Silver stained sections revealed numerous comma-shaped organisms in the crypts of infected epithelial cells . Using this method, serial reproduction of the disease was accomplished through the passage of fresh and previously frozen inocula . The virulence of the freshly prepared inoculum increased with passage through the host, whereas the inoculum prepared from tissue that had previously been frozen showed a decrease in infectivity and virulence . These data provide strong evidence for the infectious nature of this disease. J Med Microbiol, 1987 Nov, 24(3), 267 - 74 Expression of H1 outer-membrane protein of Pseudomonas aeruginosa in relation to sensitivity to EDTA and polymyxin B; Said AA et al.; During growth in magnesium (Mg++)-deficient mineral media, Pseudomonas aeruginosa cells synthesise large amounts of H1 outer-membrane protein and are resistant to polymyxins and EDTA . It has been suggested that H1 protein replaces Mg++ as an outer-membrane-stabilising component in Mg++-deprived cells, thereby removing the EDTA target and blocking an adsorption site for polymyxins . Induction of H1 protein synthesis also occurred in P . aeruginosa cells grown in Antibiotic No . 3 Broth (Ab3B), although this medium is not Mg++-deficient . Generally, significant induction of H1 protein did not occur in P . aeruginosa cultures grown in other complex media such as Proteose Peptone and Nutrient Broth, which contained less Mg++ than Ab3B, nor in Isosensitest Broth or Mueller Hinton Broth, which contained higher Mg++ concentrations . H1-protein-induced P . aeruginosa cells from Ab3B cultures, unlike those from Mg++-deficient mineral-broth culture, remained fully sensitive to polymyxin B and, with one exception, to EDTA . It is concluded that induction of H1 protein does not itself confer resistance to polymyxin B, and has no more than a minor role in EDTA resistance . Other cell-wall changes, such as phospholipid modifications and the absence of Mg++, probably account for the resistance of Mg++-deprived cells. J Clin Microbiol, 1987 Oct, 25(10), 1897 - 901 Reliability of high-content disks and modified broth dilution tests for detecting staphylococcal resistance to the penicillinase-resistant penicillins; Barry AL et al.; In vitro susceptibility tests were performed with 271 isolates of Staphylococcus species (204 Staphylococcus aureus), including 110 strains resistant to the penicillinase-resistant penicillins . Disks containing 5 or 10 micrograms of methicillin, 1 or 4 micrograms of oxacillin, and 1 or 4 micrograms of nafcillin were evaluated . After a full 24 h of incubation at 35 degrees C, tests with 1-microgram oxacillin disks provided optimal results . Use of the more potent oxacillin, nafcillin, or methicillin disks only increased the number of false-susceptible test results . For broth microdilution tests, 2% NaCl should be added to cation-supplemented Mueller-Hinton broth, and MICs should be recorded after a full 24 h at 35 degrees C . Microdilution tests with oxacillin in broth with 2% NaCl were more reliable than similar tests with methicillin. Antimicrob Agents Chemother, 1987 Oct, 31(10), 1549 - 52 Comparative activity of CGP 31608, nafcillin, cefamandole, imipenem, and vancomycin against methicillin-susceptible and methicillin-resistant staphylococci; Sachdeva M et al.; The activity of CGP 31608 for 53 strains of Staphylococcus aureus and 48 strains of S . epidermidis, both methicillin susceptible and resistant, was compared with that of vancomycin, nafcillin, cefamandole, and imipenem . Microdilution MICs were determined in Mueller-Hinton broth with or without 2.5% NaCl at an inoculum of 3 x 10(5) CFU/ml with a 20-h, 37 degrees C incubation . The MICs of imipenem and CGP 31608 for methicillin-resistant strains were lower than the MICs of nafcillin or cefamandole for these strains; these differences diminished in the presence of 2.5% NaCl . Subpopulations were detected in strains of methicillin-resistant S . aureus and S . epidermidis that were resistant to all the beta-lactam antibiotics tested at 5 micrograms/ml . This resistant subpopulation produced progeny that were uniformly resistant to high concentrations of each of the beta-lactams. Antimicrob Agents Chemother, 1987 Oct, 31(10), 1514 - 8 Influence of cation supplements on activity of netilmicin against Pseudomonas aeruginosa in vitro and in vivo; Barry AL et al.; In vitro studies were performed with 74 Pseudomonas aeruginosa isolates which were collected during a multicenter trial . The isolates were obtained from 70 patients who had been treated with netilmicin as the only antipseudomonal antibiotic . Clinically, 83% of the patients were cured or improved, and 64% of the Pseudomonas isolates were eliminated by chemotherapy . The 74 clinical isolates and 38 additional isolates with known mechanisms of aminoglycoside resistance were tested in three separate laboratories by disk diffusion methods and by microdilution tests with three broth media (Mueller-Hinton broth with full, half, and no cation supplements) . Isolates that responded to netilmicin therapy and those that failed to respond were all susceptible by the disk test, and most were susceptible by microdilution tests with unsupplemented broth . However, over half of the clinical isolates appeared to be resistant when cations were added to the broth medium . Strains capable of producing enzymes that inactivate netilmicin were resistant by all methods tested . Broth dilution and agar dilution results were most comparable when half of the recommended cation supplements was added to Mueller-Hinton broth . Further consideration should be given to reducing the concentration of cations that are added to Mueller-Hinton broth when netilmicin susceptibility tests are being performed . However, additional studies with other aminoglycosides are needed before appropriate testing conditions can be standardized. J Clin Microbiol, 1987 Sep, 25(9), 1753 - 6 Quantitative antimicrobial susceptibility test for Streptococcus pneumoniae using inoculum supplemented with whole defibrinated sheep blood; D'Amato RF et al.; The National Committee for Clinical Laboratory Standards recommends the use of lysed horse blood-supplemented Mueller-Hinton broth for determining the quantitative antimicrobial susceptibility of Streptococcus pneumoniae . This procedure may be difficult for laboratories using previously prepared or commercial MIC systems . Therefore, a study was undertaken to determine whether previously prepared microdilution trays containing Mueller-Hinton broth without blood could be used for determining the antimicrobial susceptibility of S . pneumoniae by adding whole defibrinated sheep blood to the bacterial suspension used to inoculate the trays . The presence of alpha-hemolysis was used as an indicator of bacterial growth . One hundred isolates of S . pneumoniae selected to represent a distribution of susceptibility patterns were tested by the National Committee for Clinical Laboratory Standards method and the sheep blood-supplemented-inoculum method . Greater than 94% agreement between the two methods was achieved . The sheep-blood-supplemented-inoculum procedure was highly reproducible and easy to perform and provides an acceptable alternative for determining the MICs for S . pneumoniae for laboratories using previously prepared or commercial microdilution systems. J Dairy Sci, 1987 Sep, 70(9), 1946 - 51 Effects of milk on activity of antimicrobics against Staphylococcus aureus isolated from bovine udders; Owens WE et al.; Addition of milk to Mueller-Hinton susceptibility test medium permitted measurement of milk effect on agar disc diffusion zone diameters obtained from Staphylococcus aureus herd isolates and stock strains . Milk reduced zone diameters for all antimicrobics tested when compared with zones obtained by standard methods . Antimicrobics most affected included novobiocin, streptomycin, gentamycin, tetracycline, and vancomycin . Growth curves of a reference strain of Staphylococcus aureus in Mueller-Hinton broth with and without milk indicated no effect on growth rate of the organism, suggesting the observed effect was due to the action of milk on the antimicrobics being tested . The described method offers a simple in vitro test for milk effects on antimicrobic activity. Diagn Microbiol Infect Dis, 1987 Aug, 7(4), 279 - 81 A simple broth-disk elution test for screening methicillin-resistant (heteroresistant) staphylococci; Otero JR et al.; Forty-six strains of Staphylococcus aureus and 47 strains of unspeciated coagulase-negative staphylococci were inoculated in tubes containing a cation-supplemented Mueller-Hinton broth with 4% (wt/vol) NaCl . A critical concentration of methicillin (10 micrograms/ml) or oxacillin (6 micrograms/ml) was achieved in each tube by adding the appropriate number of antibiotic disks . Growth was interpreted as resistance . Results obtained with fully resistant or fully sensitive strains showed complete agreement with the reference method . Four strains with intermediate sensitivity (two S . aureus and two coagulase-negative staphylococci) were classified as resistant by the broth-disk elution test. Eur J Clin Microbiol, 1987 Aug, 6(4), 378 - 85 In vitro susceptibility to aminoglycoside antibiotics in blood and urine isolates consecutively collected in twenty-nine European laboratories . European Study Group on Antibiotic Resistance. {Resistance of Listeria monocytogenes to cefotaxime and ceftriaxone combined with an aminoside} Borderon E, Borderon JC, Feron JF, Thieffry JC, Tescher M, Farid IA. The in vitro antibacterial activity of cefotaxime and ceftriaxone-aminoglycoside combinations was studied against 20 clinical isolates of Listeria monocytogenes, and compared with the activity of the antibiotics alone . Minimal bacteriostatic and bactericidal concentrations (MBCs) as well as killing curves were determined using different parameters . In all cases, the MBCs of gentamicin and netilmicin were shown to be lowered by addition of CTX or CTR . Using Mueller-Hinton broth the values of MBCs obtained were achievable in the CSF . However, the clinical bearing of these results remained to be discussed. Antimicrob Agents Chemother, 1987 May, 31(5), 808 - 10 Failure to demonstrate a consistent in vitro bactericidal effect of trimethoprim-sulfamethoxazole against enterococci; Najjar A et al.; Controversy exists as to the in vitro and in vivo activities of trimethoprim-sulfamethoxazole (TMP-SMX) against enterococci . In this study, we investigated the in vitro activity of TMP-SMX in the type of Mueller-Hinton broth previously reported to give the lowest MICs and MBCs with enterococci . In all instances, MICs were less than or equal to 0.5 microgram/ml . The majority of tests showed MBCs of greater than 32 micrograms/ml, although there was some effect from varying the inoculum and the length of incubation after subculturing . Minor differences were noted when tests were repeated and between the results from microdilution and macrodilution tests and those obtained by the time-kill method . These results, as well as other reports, suggest that TMP-SMX should not be considered a reliable bactericidal agent against enterococci. Diagn Microbiol Infect Dis, 1987 Apr, 6(4), 335 - 42 Occurrence and reproducibility of the "skip" phenomenon in bactericidal testing of Staphylococcus aureus; Gresser-Burns ME et al.; A "skip" phenomenon, in which subcultures to determine bactericidal endpoints show discordant results, can make bactericidal testing of Staphylococcus aureus difficult to interpret . Either a single or several consecutive concentrations may be skipped, with insignificant growth from these concentrations, but heavy growth from higher antimicrobic concentrations . Replicate macrodilution minimum bactericidal concentration testing of cephalothin against S . aureus was investigated to determine the frequency and reproducibility of the skip phenomenon in this test . In preliminary testing, the skip phenomenon occurred at 24 hr in 11 of the 30 tests performed on ten S . aureus strains . Incubation of tubes for 48 hr before subculture markedly reduced the number of tests containing a skip tube (four of 30) . The skip phenomenon was not reproducible either within concurrent replicate testing or on repeat testing of the same isolate on subsequent days . The ten strains were retested in replicative trials using the macrodilution test comparing Mueller-Hinton broth (MHB) and MHB supplemented with Tween 80 . The number of skips occurring in the supplemented broth test was the same (two of 22) at 24 hr as nonsupplemented broth . For reproducible results, macrodilution minimum bactericidal testing requires performance of the test in duplicate, with repeat subculture at 48 hr if the skip phenomenon occurs in both trials at the 24-hr subculture . Killing curves performed on these isolates did not appear to demonstrate any relationship between the skip phenomenon and the paradoxical effect described by Eagle. Am J Clin Pathol, 1987 Apr, 87(4), 525 - 8 Rapid identification of Staphylococcus epidermidis; Woods GL et al.; A panel of Minitek sugar disks, consisting of trehalose, mannitol, xylose, and sucrose, was evaluated for its ability to identify blood culture isolates of Staphylococcus epidermidis (SE) . Using a heavy suspension of organism in Mueller-Hinton broth, 50 microL was pipetted onto each disk in wells of a flat-bottomed microtiter tray . The tray was covered, incubated in a moist chamber in non-CO2 at 35 degrees C, and examined after 5 and 24 hours . A color change of yellow or orange was positive; no color change (red) was negative . Expected reactions for SE were as follows: negative trehalose, mannitol, and xylose; positive, sucrose . On evaluation of 227 coagulase-negative staphylococci (CNS) at 5 and 24 hours, the panel had a sensitivity of 94 and 96%, specificity of 92 and 89%, predictive value of positive tests of 97 and 96%, and predictive value of negative tests of 84 and 87% . This panel offered an inexpensive and convenient method for differentiating SE from the other CNS in five hours. Zentralbl Bakteriol Mikrobiol Hyg {A}, 1987 Mar, 263(4), 572 - 6 {The effect of magnesium on the formation of toxic shock syndrome toxin 1 (TSST-1) by Staphylococcus aureus}; Dickgiesser N et al.; The influence of magnesium on the production of toxic shock syndrome toxin-1 (TSST-1) by Staphylococcus aureus was examined . As media we used: Standard-I-Nutrient Broth, Todd Hewitt Broth, Mueller-Hinton Broth, Isosensitest Broth and a chemically defined liquid medium . The magnesium content of these media was determined using flame photometry and was subsequently changed using magnesium sulfate to the magnesium concentrations as shown in table 1 . In each of these media the TSST-1 positive S . aureus strains MN8 and T 40 were grown at 37 degrees C, 18 h, vigorously shaken . Then the colony forming units (cfu) were determined . Toxin assays were performed by immunodiffusion after concentrating the culture fluids 100-fold using ethanol precipitation . Concentrations of toxin per milliliter were determined by comparison with standard toxin preparations using hyperimmune-TSST-1 antisera as described . The cfu and the amount of TSST-1 produced are shown in table 1 . No link could be demonstrated between TSST-1 production and magnesium concentration of the media used . Our results are in agreement with the ones published by Schlievert and disagree with the results from Mills. Boll Ist Sieroter Milan, 1987, 66(1), 31 - 7 {Demonstration of methicillin-resistant Staphylococci using the broth microdilution method}; Rossi A et al.; The increasing incidence of methicillin resistant staphylococci rendered more important the problem of their detection, by the susceptibility tests, particularly by the broth microdilution methods . The effects of the addition of 2% NaCl to the Cation Supplemented Mueller Hinton Broth (CSMHB) on the MICs of penicillinase resistant penicillins (PRP) and of other antibiotics have been studied on 100 strains of staphylococci isolated by pathological materials . In 13% of the studied strains the MIC of oxacillin in CSMHB plus 2% NaCl was at least 4 times greater than the value found in the absence of NaCl . In the same experimental conditions a ratio between MICs equal or greater than 4 dilutions resulted in 69% of the strains for the gentamicin and in 93% of the strains for the amikacin . Such variation in the value of MIC determined a change in the category of susceptibility (from sensitive to intermediate or resistant and from intermediate to resistant) in 10% of the strains for the oxacillin, in 28% for the gentamicin and 41% for the amikacin . To improve detection of methicillin resistant staphylococci without altering the MICs of other antibiotics (aminoglycosides), it is necessary to perform the broth microdilution tests with CSMHB and with CSMHB plus 2% NaCl . CSMHB plus 2% NaCl will be used for testing PPR and cephalosporin, while CSMHB for the other antibiotics. Int J Clin Pharmacol Res, 1987, 7(3), 203 - 5 In vitro activity of aztreonam, cefuroxime and ceftazidime against gram-negative rods isolated from hospital patients with urinary tract infection; Webb G et al.; The in vitro activity of aztreonam, cefuroxime and ceftazidime was determined against 2,372 Gram-negative rods (including Pseudomonas spp.) isolated from hospital patients with urinary tract infections during 1985 . Minimum inhibitory concentrations (MICs) were determined using an agar incorporation technique in Mueller-Hinton agar . The inoculum used was approximately 10(5) colony forming units (cfu) contained in 10 microliter Mueller-Hinton broth, which was applied to the surface of the agar plates using a multipoint inoculator . Following inoculation plates were incubated aerobically at 37 degrees C for 18 h . The MIC of each antimicrobial for each organism examined was determined as the lowest concentration of the antimicrobial which completely inhibited growth of the inoculum . The minimum concentration required to inhibit the growth of 90% (MIC90) of the bacterial isolates in each genus or species examined was also determined . In general the antibacterial spectrum of aztreonam was comparable to that of ceftazidime and superior to that of cefuroxime . Against Escherichia coli, which accounted for 72% of the isolates examined, aztreonam (MIC90 less than or equal to 0.25 microgram/ml) was slightly more active than ceftazidime (MIC90 0.5 microgram/ml) and considerably more active than cefuroxime (MIC90 8 micrograms/ml) . Aztreonam was active against Pseudomonas spp . (MIC90 16 micrograms/ml), although somewhat less so than ceftazidime (MIC90 4 micrograms/ml) . Cefuroxime showed low activity against this genus (MIC90 greater than 128 micrograms/ml). Antonie Van Leeuwenhoek, 1987, 53(6), 413 - 9 Comparison of meningococcal outer membrane protein vaccines solubilized with detergent or C polysaccharide; Poolman JT et al.; Outer membrane proteins (OMPs) were isolated from meningococcal strain H44/76 (B:15:P1.16) by detergent extraction of bacteria . A final product containing class 1 (P1.16), 3(15), 4 OMPs and 5% (w/w) lipooligosaccharide was obtained . Two experimental vaccines were prepared: OMP-detergent and OMP-C polysaccharide . The OMP-detergent vaccine tended to show a better bactericidal: ELISA ratio for the antibodies induced as compared to the OMP-C polysaccharide vaccine . The vaccine induced bactericidal antibodies appeared for the greater part to be directed against the class 1 OMP (P1.16) . By comparison of cultures grown in Mueller Hinton Broth with and without 0.25% (w/v) glucose, it was found that monoclonal antibodies against the serotype OMP (class 2 or 3) were not bactericidal against meningococci grown in MHB without glucose . Antibodies against class 1 OMP and lipooligosaccharide were not influenced by this . A new major outer membrane protein (appr . 40 kd) is described that may function as a cation-specific porin. Drugs Exp Clin Res, 1987, 13(2), 63 - 7 The post-antimicrobial suppressive effect of quinolone agents; Neu HC et al.; A post-antimicrobial effect (PAE) was seen with all of the new 4-quinolones studied: ciprofloxacin, ofloxacin, Cl-934, Ro 23-6240, A-56619 and S-25930 . The post-antimicrobial suppression of growth was for 4-8 h in the case of Escherichia coli, Klebsiella pneumoniae, Serratia marcescens and Pseudomonas aeruginosa . PEA was demonstrated both in Mueller-Hinton broth at pH 7.4 and in urine at pH 5.5 with a Mg2+ concentration of 9.5 mM . Resistant organisms, with MICs greater than 4 micrograms/ml, showed a PAE after a 2-h exposure to 200 micrograms/ml of 4-quinolones . This demonstrates that PAE is seen for 4-quinolones even under conditions in which they are less active. Antimicrob Agents Chemother, 1987 Jan, 31(1), 104 - 7 In vitro susceptibility of gram-positive cocci to paldimycin; Pohlod DJ et al.; Paldimycin (U-70138F) is a new antimicrobial agent with activity against gram-positive cocci . Clinical isolates of staphylococci and streptococci were tested . MICs were higher in Mueller-Hinton broth than in nutrient broth . Change in pH had minimal effect on the MICs in either broth . When inoculum size was varied, an inoculum effect was observed . The gram-positive cocci tested were generally more susceptible to paldimycin than to vancomycin. J Clin Microbiol, 1986 Nov, 24(5), 764 - 9 Evaluation of laboratory tests for detection of methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis; Coudron PE et al.; Few studies evaluating susceptibility testing of methicillin-resistant staphylococci have included isolates of Staphylococcus epidermidis, a known pathogen in many types of serious infections . We tested 175 S . epidermidis and 95 Staphylococcus aureus isolates to determine the most sensitive procedures for detecting methicillin-resistant staphylococci . Reference procedures included agar dilution with methicillin and 4% NaCl in the agar and broth microdilution with methicillin and 2% NaCl in cation-supplemented Mueller-Hinton broth . After 24 h of incubation, the results from both methods correlated well and were within 1 log2 dilution for all isolates tested . Only one-half of all resistant isolates (92 of 183) were detected at 18 h by using the standard disk diffusion technique with 5-micrograms methicillin disks, and even fewer were detected with 10-micrograms methicillin disks and newly recommended zone-size criteria . However, the standard disk diffusion method with 4% NaCl in the agar increased the sensitivity and specificity for identification of the proper phenotype to greater than 92% . The spread plate and new spot techniques, both using agar with 4% NaCl, were also sensitive methods . Of 47 S . epidermidis isolates tested against oxacillin, 6 (13%) were oxacillin susceptible but methicillin resistant . Two automated systems, the Automicrobic system (Vitek Systems) and MicroScan (American MicroScan), as well as two broth screening systems available from Remel and Austin Biological Laboratories, failed to detect several resistant isolates, depending on the species. J Clin Microbiol, 1986 Oct, 24(4), 600 - 6 Microtiter broth dilution method for yeast susceptibility testing with validation by clinical outcome; Radetsky M et al.; There is no ideal laboratory procedure or culture medium in current use for susceptibility testing of pathogenic yeasts . Six candidate growth media (RPMI 1640 with L-glutamine, yeast nitrogen base, Casamino Acids medium, Mueller-Hinton broth, Sabouraud dextrose broth, and minimum essential medium-Eagle salts) were screened by spectrophotometric absorbance for nucleic acid and protein . From these, two media were selected: a chemically defined growth medium (RPMI 1640 with L-glutamine) and a chemically complex medium (Casamino Acids) . MICs of four antifungal agents (5-fluorocytosine, miconazole, ketoconazole, and amphotericin B) for 84 clinical isolates of various Candida species were then determined with both media in agar dilution and microtiter broth dilution systems . The resultant MICs were correlated with clinical outcome for those isolates obtained from patients treated with single antifungal agents, and susceptibility cut points were calculated . Derived MIC cut points for susceptibility were validated in a murine model of systemic candidiasis . RPMI 1640 with L-glutamine was found to have the lowest absorbance values for both nucleic acid and protein, while Casamino Acids medium was highest in both categories . We found that RPMI 1640 with L-glutamine was superior to Casamino Acids medium in the yield of MICs which correlated with actual clinical and animal outcome data . While there were no significant differences in MICs when RPMI 1640 medium was used, the microtiter broth dilution technique was superior to agar dilution in efficiency and ease of performance . We conclude that a microtiter broth system containing RPMI 1640 medium with L-glutamine is a simple, precise, and economical technique for susceptibility testing of pathogenic Candida species . We also suggest that the validation of susceptibility cut points with patient and animal outcome data make this microtiter broth system a preferential method for yeast susceptibility testing. J Clin Microbiol, 1986 Sep, 24(3), 435 - 9 Serum bactericidal testing with the Autobac system; Sanders SJ et al.; Current methodology for the serum bactericidal test requires a minimum of 48 h . A procedure was devised for performing this test with the Autobac system (General Diagnostics, Div . Organon Inc., Raleigh, N.C.) in a shortened time span . All titers obtained with the Autobac were compared against results obtained with a standardized tube dilution procedure . The Autobac low-thymidine eugonic broth performed comparably to the tube dilution diluent, a 1:1 ratio of pooled human serum and cation-supplemented Mueller-Hinton broth (99.2% correlation between bactericidal endpoints) . Over 300 tests were conducted by using stock reference bacterial strains, clinical isolates, pooled human serum seeded with antimicrobial agents, and serum from patients on antimicrobial therapy . With the Autobac procedure, serum inhibitory titers can be reported in 3 to 4 h (93.4% correlation with the tube dilution procedure) . Serum bactericidal titers can be obtained in 24 h without the necessity of subculturing (95.6% correlation) . With the exception of staphylococci tested against penicillin, serum bactericidal titers can be obtained in 3 to 4 h (88.4% correlation) . The Autobac procedure can provide the clinical laboratory with a rapid, reliable method for performing the serum bactericidal test. Diagn Microbiol Infect Dis, 1986 Sep, 5(3), 245 - 53 Susceptibility testing of methicillin-resistant Staphylococcus aureus with three commercial microdilution systems; Robinson A et al.; The antimicrobial susceptibilities of 100 methicillin-resistant Staphylococcus aureus isolates were determined concurrently by API Uniscept KB, Micro-Media, MicroScan, standardized disk diffusion, and reference broth microdilution to evaluate whether these commercial microdilution systems would reliably defect methicillin-resistant S . aureus . The methicillin minimal inhibitory concentration for all isolates was greater than or equal to 16 micrograms/ml as determined by the reference minimal inhibitory concentration panels containing 2% NaCl supplemented Mueller-Hinton broth . Using the breakpoints established by the National Committee for Clinical Laboratory Standards for reporting susceptible and resistant methicillin results, there was 100% agreement between the reference methods and API Uniscept KB at 24 hr . The Micro-Media and MicroScan systems had 47% and 8% very major discrepancies at 24 hr, respectively . At 48 hr, these two systems exhibited 15% and 0% very major discrepancies . Micro-Media and MicroScan were in agreement with the reference microdilution method (+/- 1 log2 dilution) for 62% and 68% of the strains at 24 hr, respectively and 88% and 85% of the isolates at 48 hr, respectively . The results of this study indicate that API Uniscept KB would provide a practical and reliable method for the detection of methicillin-resistant S . aureus. Curr Eye Res, 1986 Jul, 5(7), 503 - 10 Relationship between proteases and descemetocele formation in experimental Pseudomonas keratitis; Twining SS et al.; Proteases are involved in the pathogenesis of Pseudomonas aeruginosa infections of the cornea . Although there are many potential roles for these enzymes, involvement in corneal stroma destruction with subsequent descemetocele formation and/or corneal perforation is an important example . This study examined the relationship of elastase and alkaline protease to corneal destruction as indicated by descemetocele formation . The protease content of the overnight Mueller-Hinton broth cultures of various strains of P . aeruginosa correlated with the production of descemetoceles both in the rabbit trauma model of Pseudomonas keratitis and upon intrastromal injection of filtrates of the overnight culture media . The levels of alkaline protease correlated better with descemetocele formation than those of elastase . The influx of inflammatory cells was not correlated with descemetocele formation within 24 to 48 hrs. Am J Clin Pathol, 1986 May, 85(5), 626 - 9 False susceptible penicillin G MICs for Streptococcus pneumoniae with a commercial microdilution system; Shanholtzer CJ et al.; A commercial minimal inhibitory concentration (MIC) panel that contains a broth of undisclosed formulation intended to support growth of streptococci unable to grow in Mueller-Hinton broth was found to give false susceptible MIC results for pneumococci . The authors encountered several Streptococcus pneumoniae isolates that showed resistance by the oxacillin disk diffusion test, but showed a susceptible penicillin G MIC when tested in an unsupplemented MIC panel . Seven isolates that showed penicillin G resistance by oxacillin disk diffusion testing were retested for penicillin G susceptibility with oxacillin disk diffusion, commercial MIC panels, Mueller-Hinton with blood agar dilution, and Mueller-Hinton with blood broth microdilution . Five of these isolates produced a button of growth in the commercial MIC panel growth control well, but no growth in the penicillin G-containing wells (0.06-4.0 micrograms/mL), suggesting a valid test system and susceptibility to penicillin G . When tested by the three standard methods, these seven isolates showed resistance (R) or relative resistance (I) to penicillin G . These data indicate that frozen MIC panels from this commercial source (American Micro Scan, Campbell, CA) are not reliable for detection of resistance to penicillin G in S . pneumoniae, and if these panels are used, results must be confirmed by another method. Antimicrob Agents Chemother, 1986 May, 29(5), 765 - 8 Artifacts in dilution pharmacokinetic models caused by adherent bacteria; Haag R et al.; Liquid cultures of a Pseudomonas aeruginosa strain in Mueller-Hinton broth diluted at rates higher than the bacterial growth rate showed the expected decrease in CFU only for 1 to 2 h . Later the CFU started to increase . This phenomenon can be explained by a hypothesis that assumes that the bacteria multiply in two different compartments . From the first compartment, which comprises bacteria homogeneously distributed in the broth, cells are eliminated at a rate that is dependent on the dilution and growth rates . Concomitantly, the second compartment is formed as a nondilutable adherent population on the surface of the culture vessel . Eventually, only cells stemming from that population appeared in the medium and were subsequently diluted . This hypothesis can be described mathematically by a linear combination of two exponential functions . The calculated values fit the experimental data well . Because similar CFU versus time curves were also found with other strains, care should be taken in interpreting results of experiments performed in liquid cultures and evaluated in terms of CFU . One should bear in mind that within a liquid culture an adherent population may exist, which differs in size according to selective influences (dilution, addition of antibiotics, etc.) . This may give rise to artificial and unexpected results. Diagn Microbiol Infect Dis, 1986 Apr, 4(4), 291 - 7 Penicillin tolerant group A streptococci; Krasinski K et al.; A penicillin (PCN) tolerant {minimal inhibitory concentration (MIC) less than or equal to 0.02, minimal bactericidal concentration (MBC) = 3.10 micrograms/ml} group A streptococcus (GAS) was recovered from the bone aspirate of a child with osteomyelitis . The penicillin therapy with 200,000 micron/kg X day, and subsequently ampicillin 360 mg/kg X day, resulting in a serum ampicillin concentration of 74 micrograms/ml, failed to achieve a serum bactericidal effect greater than 1:2 . Ninety-nine additional isolates of GAS obtained from 99 infants and children with pharyngitis were randomly selected for study . Organisms were screened for tolerance by macrobroth dilution determination at 0.05 and 1.0 microgram/ml of penicillin . Twenty-two of 100 organisms had MICs = 0.05 microgram/ml and MBCs = 1.0 microgram/ml; further tests were performed on these organisms . Twenty of the 22 strains (20% of all GAS) grown in Mueller-Hinton broth with 2% sheep blood were tolerant to penicillin at 24 hr, with MICs less than or equal to 0.02 and MBCs = 0.39 microgram/ml . When retested at 48 hr the MBCs of the 20 tolerant strains had decreased: three strains by twofold, three strains by fourfold, four strains by eightfold, one strain by 16-fold, and nine strains by 40-fold or greater . Seven strains were not tolerant after 48 hr of incubation . The detection of tolerance was media dependent; only nine strains were tolerant when grown in Todd-Hewitt broth . Tolerance to GAS was more frequent than generally suspected . The phenomenon of tolerance, and potentially delayed killing may alter prophylaxis and therapy of GAS disease and merits further investigation. Antimicrob Agents Chemother, 1986 Jan, 29(1), 152 - 4 Effect of NaCl supplementation of Mueller-Hinton broth on susceptibility of staphylococci to aminoglycosides; Campos JM et al.; The addition of NaCl to cation-supplemented Mueller-Hinton broth increased the MICs of gentamicin, amikacin, and netilmicin for coagulase-positive and -negative staphylococci in a concentration-dependent manner . At 2% NaCl, geometric mean MICs were elevated 14.1- to 25.6-fold . Mueller-Hinton broth containing added NaCl should not be used for testing the susceptibility of staphylococci to aminoglycosides. Acta Pathol Microbiol Immunol Scand {B}, 1985 Dec, 93(6), 379 - 82 Comparative in vitro activity of four beta-lactam antibiotics in surgical wound fluid against staphylococci; Sorensen TS; Minimal inhibitory and bactericidal concentrations (MIC and MBC) of methicillin, dicloxacillin, cephalothin and cefuroxime were determined against 26 strains of staphylococci, using a broth dilution method with surgical wound fluid (WF) and Mueller-Hinton broth (MH) as test media . The staphylococci were all clinical isolates; 17 strains were coagulase-positive and 9 were coagulase-negative . The MIC-values of dicloxacillin and cephalothin estimated in MH were lower than those estimated in WF . For methicillin and cefuroxime the MIC-values in the two media were similar . With regard to MIC-values, the two penicillins were identical in WF, as were the two cephalosporins, but the cephalosporins were found to be more active than the penicillins, with an average of one dilution step . As regards the MBC to MIC ratios, no differences were found neither between the two media nor between the four antibiotics. J Antimicrob Chemother, 1985 Nov, 16(5), 671 - 4 The effect of a range of antimicrobial drugs on the haemagglutination of two clinical isolates from urinary tract infections; Hales BA et al.; A range of nine common antimicrobial drugs were tested for their effect on adhesion of the mannose-resistant haemagglutination-positive Proteus vulgaris strain BH77 and Escherichia coli strain BH121, isolated from patients with urinary tract infections . Minimum inhibitory concentrations of the antimicrobials for these strains were determined in Mueller-Hinton broth and the effect of each antimicrobial, at the quarter MIC values, on the haemagglutination of the strains was then determined . Haemagglutination could only be prevented by inhibitors of protein synthesis . After the introduction of an R-plasmid into strain BH121 this effect was annihilated . When the new MICs were determined, the inhibition was still observed at the new quarter MIC values. J Clin Microbiol, 1985 Nov, 22(5), 886 - 7 Screening method for rapid detection of methicillin-resistant (heteroresistant) Staphylococcus aureus; Hansen SL et al.; A broth screening method was developed to detect methicillin-resistant (heteroresistant) strains of Staphylococcus aureus from primary plates . Lyophilized vials containing cation-supplemented Mueller-Hinton broth, 2% NaCl, and 10 micrograms of methicillin and 6 micrograms of oxacillin per ml were hydrated and tested with 129 methicillin-resistant and 35 methicillin-susceptible strains of S . aureus . With the addition of a tetrazolium indicator after 5 h of incubation, 96.9% of resistant strains were detected . No false-positive results occurred. J Clin Microbiol, 1985 Aug, 22(2), 212 - 5 Antimicrobial susceptibility testing of Francisella tularensis with a modified Mueller-Hinton broth; Baker CN et al.; A modified Mueller-Hinton broth was developed to perform antimicrobial susceptibility tests on Francisella tularensis . Adequate growth of the organism was obtained within 24 h of inoculation, and MICs could be read at that time . We tested 15 selected strains of F . tularensis and five reference quality control strains in this medium with 36 antimicrobial agents . The MICs of the aminoglycosides and tetracycline increased 1 to 3 dilutions in this medium compared with those in the usual medium, but the other antimicrobial agents were not consistently affected by the medium . Even though the medium caused an increase in MICs, the aminoglycosides and tetracyclines remained very active in vitro against F . tularensis . Other antimicrobial agents effective in vitro were chloramphenicol, erythromycin, ceftazidime, moxalactam, cefotaxime, ceftriaxone, and Sch 29482 (a cephalosporin). Antimicrob Agents Chemother, 1985 Aug, 28(2), 331 - 42 Antimicrobial activity of ciprofloxacin against Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus determined by the killing curve method: antibiotic comparisons and synergistic interactions; Chalkley LJ et al.; A derivative of quinolinecarboxylic acid, ciprofloxacin (BAY o 9867) was found to be an effective bactericidal agent against Pseudomonas aeruginosa and Escherichia coli . A bactericidal effect was achieved immediately after the addition of ciprofloxacin . At a concentration of 0.5 micrograms/ml, culture viability was reduced from 5 X 10(5) to about 5 X 10(3) CFU/ml within 15 min, and at 0.1 micrograms/ml, a greater than 10-fold reduction in viability resulted during the first hour after exposure . This bactericidal activity observed during the lag phase in Mueller-Hinton broth was also demonstrated in a nongrowing system . The antibiotics used in comparative studies, i.e., tobramycin, aztreonam, cefotaxime, and azlocillin, did not show this initial bactericidal activity, and ciprofloxacin prevented culture regrowth at lower concentrations . Staphylococcus aureus was not as susceptible to ciprofloxacin; killing occurred at a concentration of 0.5 micrograms/ml only after the onset of exponential growth in the control culture . Synergistic interactions were observed with ciprofloxacin in combination with tobramycin and azlocillin against P . aeruginosa and with cefotaxime and tobramycin against E . coli. Antimicrob Agents Chemother, 1985 Jun, 27(6), 908 - 11 In vitro antibacterial activities of antibiotics against Pseudomonas aeruginosa in peritoneal dialysis fluid; Shalit I et al.; Intraperitoneal antibiotics are used to treat Pseudomonas aeruginosa peritonitis, a serious complication of continuous ambulatory peritoneal dialysis . However, P . aeruginosa killing is often inefficient despite low MBCs . Broth dilution MIC/MBC and time kill curves of tobramycin, amikacin, netilmicin, azlocillin, piperacillin, ceftazidime, cefsulodin, and ciprofloxacin were determined in peritoneal dialysis fluid (PDF), buffered PDF, fluid recovered from patients on continuous ambulatory peritoneal dialysis (RPF), and cation-supplemented Mueller-Hinton broth . MBCs of all antibiotics were 8 to 16 times greater in PDF and RPF than in Mueller-Hinton broth or buffered PDF . Use of the time kill curve technique and Mueller-Hinton broth showed that aminoglycosides killed greater than or equal to 99.9% of P . aeruginosa at 1 h, ciprofloxacin killed greater than or equal to 99.9% at 2 h, and beta-lactams killed greater than or equal to 99.9% at 6 h . In contrast, killing was not demonstrated in PDF by any drug at 6 h and by aminoglycosides only at 24 h . Bactericidal activity was optimal in RPF for ciprofloxacin at 1 h and for aminoglycosides at 2 h; bactericidal activity was not demonstrated in RPF with any beta-lactam (no kill by penicillins; less than 99% kill by cephalosporins) . Slow bacterial growth, increased protein binding, and glucose concentrations and other inhibitors may interfere with beta-lactam activity in RPF . These considerations and reported clinical failures and toxicity of aminoglycoside therapy warrant further study of quinolones and drug combinations in P . aeruginosa peritonitis. Eur J Clin Microbiol, 1985 Jun, 4(3), 316 - 26 Colonization antigens and haemagglutination patterns of human Escherichia coli; Blanco J et al.; The haemagglutinating properties of 223 (35 enterotoxigenic and 188 non-enterotoxigenic) Escherichia coli strains with nine erythrocyte types were investigated; 153 strains were also tested for beta-haemolysis and colicin production and for the presence of CFA/I, CFA/II, K88 and K99 antigens . A selected group of strains was also examined by electron microscopy to determine the presence of fimbriae or fibrils and to establish the relationship between these, the haemagglutinating properties and the presence of colonization antigens . Generally, the haemagglutinating patterns yielded by the same strains grown in Mueller Hinton broth and on CFA agar differed considerably . Mannose-sensitive haemagglutinating (MSHA) patterns were more homogeneous than mannose-resistant haemagglutinating (MRHA) patterns . Forty-seven percent of the non-enterotoxigenic MRHA+ strains were haemolytic while only 6% of the remaining strains were (chi2 correction = 34.01; p less than 0.001) . CFA/I was only detected in the four enterotoxigenic MRHA+ strains which were positive only with human and calf erythrocytes when grown on CFA agar . CFA/II was detected in three of a total of six enterotoxigenic strains which were MRHA+ only with calf erythrocytes when grown on CFA agar . K88 and K99 antigens were not detected . All strains in which bacteria with fimbriae or fibrils were observed showed haemagglutinating activity . Thus, 18 (66.7%) of the 27 haemagglutinating strains grown on CFA agar showed fimbriae or fibrils while none of the 19 non-haemagglutinating strains did (chi2 correction = 18.10; p less than 0.001). Diagn Microbiol Infect Dis, 1985 May, 3(3), 185 - 91 Susceptibility testing with the sensititer breakpoint broth microdilution system; Doern GV et al.; The antimicrobial susceptibility profiles of a total of 318 aerobic and facultatively anaerobic bacteria (255 gram-negative bacilli and 63 gram-positive cocci) were determined, using a new commercially available breakpoint broth microdilution procedure (Sensititer Breakpoint System (SBS), Gibco Diagnostics, Inc., Madison, WI) that categorizes test results in the form of susceptibility categories: susceptible, intermediate, and resistant . Results obtained with the SBS were compared with those achieved with a standardized disk diffusion procedure . Among a total of 4,414 organism-antimicrobic comparisons, concordance between the results of the SBS and the disk diffusion procedure was observed in 3,888 cases (88.1%) . Four hundred twenty-three (9.6%) minor discrepancies, 45 (1.0%) major discrepancies, and 58 (1.3%) very major discrepancies were noted . Arbitration of major and very major discrepancies with a full-range minimum inhibitory concentration (MIC) procedure confirmed the results of the SBS in 53.4% of cases . A single organism-antimicrobial combination, the nonenterococcal streptococci tested against the aminoglycosides, yielded a significant number of very major errors which were arbitrated in favor of the disk diffusion result . These errors were probably due to poor growth of the test organism in the broth medium used for performing the SBS test (i.e., cation-supplemented Mueller-Hinton broth) . With this exception, the SBS was found to be at least as accurate as the standardized disk diffusion procedure. J Clin Microbiol, 1985 Mar, 21(3), 409 - 14 Feasibility study of disk diffusion susceptibility tests with Mueller-Hinton broth solidified with Gelrite, an agar substitute; Barry AL et al.; Feasibility studies were done to determine whether a new agar substitute, Gelrite gellan gum, could be used to prepare a solid Mueller-Hinton medium for disk diffusion susceptibility tests . Mueller-Hinton broth was combined with 0.43% of the gellan gum and 0.75% KCI . The resulting medium had performance characteristics similar to those of Mueller-Hinton agars; however, zones on the gellan gum media tended to be a little larger . Significant differences among Mueller-Hinton broths and among Mueller-Hinton agars from different manufacturers were documented: zones on different lots of the gellan gum were more consistent . The Mueller-Hinton broth-gellan gum medium appears to represent a satisfactory alternative to agar media . However, because somewhat larger zones were seen on the gellan gum plates, further study will be needed to develop quality control limits and interpretive zone size standards for tests on this new medium. J Clin Microbiol, 1985 Mar, 21(3), 366 - 70 Effects of storage temperature and pH on the stability of eleven beta-lactam antibiotics in MIC trays; Nickolai DJ et al.; Microdilution MIC test trays containing 11 beta-lactam antibiotics in Mueller-Hinton broth at pH 7.31 or 6.80 were prepared and stored at 4, -10, -25, and -70 degrees C . The drugs tested were ampicillin, ticarcillin, mezlocillin, piperacillin, azlocillin, cefazolin, cefotaxime, moxalactam, cefoperazone, ceftriaxone, and imipenem . MICs for Staphylococcus aureus ATCC 29213, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853 were determined at weekly intervals for up to 1 year . The data from the MIC determinations showed the stability of antimicrobial activity over time to be -70 degrees C greater than -25 degrees C approximately 4 degrees C much greater than -10 degrees C . The relative stability at 4 degrees C as compared with that at -10 degrees C cannot be explained by desiccation, as determined by changes in broth sodium concentrations . The relative instability at -10 degrees C may have been caused in part by a temperature fluctuation, resulting in intermittent freezing and thawing of the antibiotics . Some of the drugs appeared to be more stable when diluted in broth at pH 6.80, but endpoints were more difficult to read . Cefazolin and cefoperazone were stable at all four storage temperatures . Cefotaxime, moxalactam, and ceftriaxone also were relatively stable . The other drugs showed moderately rapid to rapid deterioration at each temperature except -70 degrees C . Storage at -25 degrees C is suitable for up to 3 months for many, but not all, beta-lactams; -10 degrees C appears to be unsuitable . Storage at -70 degrees C is recommended. Scand J Infect Dis, 1985, 17(1), 59 - 61 Antibiotic tolerance of Staphylococcus epidermidis; Watanakunakorn C; The phenomenon of antibiotic tolerance was studied in 50 strains of Staphylococcus epidermidis isolated from blood cultures . The antibiotics used for study were methicillin, nafcillin, oxacillin, cephalothin, cefazolin and vancomycin . The MICs and MBCs were determined in Mueller Hinton Broth (MHB) and Brain Heart Infusion broth (BHI) after incubation at 24 and 48 h at 37 degrees C . Tolerance was defined as the MBC/MIC ratio of greater than or equal to 16 . About one third of the strains were tolerant to vancomycin and another one third were tolerant to multiple betalactam antibiotics . However, cross tolerance between vancomycin and betalactam antibiotics occurred very infrequently (4 strains) . Tolerance was demonstrated for some strains in both MHB and BHI . Other strains were tolerant only in MHB or BHI . Similarly, some strains were tolerant at both 24 and 48 h . However, many strains were tolerant only at 24 and not at 48 h. Drugs Exp Clin Res, 1985, 11(7), 427 - 9 The comparative activity of twelve 4-quinolone antimicrobials and sulphadiazine against Neisseria meningitidis; Felmingham D et al.; The minimal inhibitory concentrations (MICs) of twelve 4-quinolone antimicrobials and sulphadiazine were determined for 160 clinical isolates of Neisseria meningitidis . The bacteria were recovered from nasopharyngeal carriers and cases of meningitis examined in The Gambia, West Africa, during the 1982-83 dry season . MICs were determined using an agar dilution technique in Mueller-Hinton agar supplemented with 10% lysed horse blood . The inoculum used was approximately 10(4) colony-forming units of each organism, contained in 10 microliters of Mueller-Hinton broth, which was applied to the agar plates using a multipoint inoculator . Following inoculation, plates were incubated for 18 h at 37 degrees C in an atmosphere enriched to 5% carbon dioxide . The MIC of each antimicrobial for each isolate examined was determined as the lowest concentration of the antimicrobial which completely inhibited growth of the inoculum . The minimum concentrations of each antimicrobial required to inhibit 50% (MIC50) and 90% (MIC90) of the isolates examined were also determined . The more recently synthesised 4-quinolones were very active against the isolates of Neisseria meningitidis, ciprofloxacin being marginally the most active (MIC90 0.008 micrograms/ml) . The activity of the 4-quinolone antimicrobials was unaffected by the MICs of sulphadiazine required by the organisms, which ranged from 0.5- greater than 64 micrograms/ml. Scand J Infect Dis, 1985, 17(2), 211 - 8 Trimethoprim and methenamine hippurate . A new theoretical combination for the treatment of urinary tract infections; Raisanen S et al.; The antibacterial interaction of methenamine hippurate (MH) and trimethoprim (TMP) was tested in vitro in 3 different media: urine, brain-heart broth and Mueller-Hinton broth . MH and TMP were found to have a synergistic interaction in chequer-board titration against 11/11 bacteria in urine . Low concentrations of MH (1/2 MIC) had an additive or synergistic effect with TMP against 14/14 bacteria in brain-heart broth and 20/26 bacteria in Mueller-Hinton broth . In addition, the growth of bacteria in urine from healthy subjects treated with TMP (200 mg), MH (1000 mg) or a combination of TMP + MH (200 + 1000 mg) twice a day for 5 days was compared . A synergistic or additive effect of TMP and MH was found against 14/16 strains . Antagonistic interaction was not found in any of the tests . Preliminary pharmacokinetic studies with TMP and MH showed no marked interaction between the drugs . The hydrolysis of MH to formaldehyde was inversely related to urinary pH, and at pH 5 most of the formaldehyde released from MH in urine was generated within 3 h . The results suggest that the combination of TMP and MH may be more efficient than TMP alone in the treatment of urinary tract infections. Drugs Exp Clin Res, 1985, 11(1), 39 - 48 In vitro antibacterial activity of imipenem against Pseudomonas and Staphylococcus species . Comparison with thirteen other antimicrobial agents; Cristiano P et al.; The in vitro antimicrobial activity of imipenem against recent clinical isolates of Pseudomonas spp . (94 strains) and penicillin-resistant Staphylococcus spp . (50 Staph . aureus and 50 coagulase-negative Staphylococcus) was assessed using the Mueller-Hinton agar dilution method . Results were compared with those simultaneously obtained for amikacin, netilmicin, tobramycin, norfloxacin, piperacillin, ceftazidime, ceftriaxone and azthreonam against Pseudomonas spp., and for rifampicin, clindamycin, netilmicin and cefoxitin, besides penicillin and methacillin, against Staphylococcus spp . About 50 and 90% of 84 Pseudomonas aeruginosa isolates were inhibited by concentrations of imipenem equal to or less than 2 and 8 mg/l respectively . The in vitro activity of imipenem was comparable to that of ceftazidime and norfloxacin, but superior to that of the aminoglycosides and all the other antibiotics tested, in terms of potency by weight . Among other Pseudomonas spp . only P . malthophilia (2 strains) proved resistant to imipenem . Rifampicin was the most active antibiotic by weight against Staph . aureus but imipenem was more active than clindamycin and, especially, netilmicin and cefoxitin . Imipenem was highly active also against coagulase-negative staphylococci, with some differences related to the high incidence of methicillin-resistant strains . MICs of imipenem in Mueller-Hinton broth correlated with those obtained in agar, unlike the aminoglycosides . There were no significant inoculum effects on MICs of imipenem and MBCs were within one twofold dilution of MICs in over 75% of assays. Drugs Exp Clin Res, 1985, 11(1), 23 - 7 Methicillin- and gentamicin-resistant Staphylococcus aureus: susceptibility to fosfomycin, cefamandole, N-formimidoyl-thienamycin, clindamycin, fusidic acid and vancomycin; Graninger W et al.; The in vitro activity of fosfomycin against 90 strains of methicillin- and gentamicin-resistant Staphylococcus aureus was studied in an in vitro microtitre system using Mueller-Hinton broth supplemented with glucose-6-phosphate . In parallel the antistaphylococcal activity of cefamandole, N-formimidoyl-thienamycin, clindamycin, fusidic acid and vancomycin was determined with the same organisms . The following MIC50 (MIC95) values were obtained: fosfomycin 8 (128) mg/l, cefamandole 8 (greater than 64) mg/l, clindamycin 0.25 (16) mg/l, fusidic acid less than 0.25 (less than 0.25) mg/l, vancomycin 1 (2) mg/l and N-formimidoyl-thienamycin 4 (16) mg/l . A high MIC/MBC ratio was noted for cefamandole, in contrast to fosfomycin. Drugs Exp Clin Res, 1985, 11(5), 317 - 29 Comparative in vitro studies with 4-quinolone antimicrobials; Felmingham D et al.; The minimal inhibitory concentrations (MICs) of nalidixic acid, pipemidic acid, cinoxacin, oxolinic acid, flumequine, pefloxacin, acrosoxacin, amifloxacin, norfloxacin, enoxacin, ofloxacin and ciprofloxacin were determined for a range of clinical isolates . MICs were determined using an agar dilution technique in Mueller-Hinton agar supplemented with 10% lysed horse blood . The inoculum used was approximately 10(4) colony forming units, contained in 10 microliters Mueller-Hinton broth, which was applied to the agar plates using a multipoint inoculator . Following inoculation, plates were incubated in conditions appropriate for the organisms under investigation . The MIC of each antimicrobial for each isolate examined was determined as the lowest concentration of the antimicrobial which completely inhibited growth of the inoculum . The minimum concentrations required to inhibit the growth of 50% (MIC50) and 90% (MIC90) of the organisms examined were also determined . All of the more recently synthesised 4-quinolones showed considerably greater activity than the parent compounds, nalidixic acid, pipemidic acid and cinoxacin, against the range of organisms used in this study . Ciprofloxacin and ofloxacin were the two most active of the 4-quinolones examined. J Antimicrob Chemother, 1984 Oct, 14(4), 349 - 57 Specificity of beta-lactamase induction in Pseudomonas aeruginosa; Dalhoff A et al.; The in-vivo induction of the chromosomally determined class Id beta-lactamase of Pseudomonas aeruginosa was studied in the granuloma pouch model in rats . Treatment of animals with carbenicillin, ticarcillin, piperacillin, azlocillin (100 mg/kg bd) and cefsulodin (40 mg/kg bd) resulted in Id beta-lactamase induction . beta-Lactamase induction was not only observed in those animals receiving beta-lactamase therapy, but also in the untreated control group, thus suggesting 'non specific' beta-lactamase induction by body fluids (such as serum or exudate) . These findings agree with the observation that commercially available complex media such as Mueller Hinton Broth, IsoS-ensitest Broth, Brain Heart Infusion and Diagnostic Sensitivity Test broth, respectively, also exhibited induction potency . Further experiments revealed that aromatic amino acids as well as histidine largely contributed to the phenomenon of 'non specific' induction of Id beta-lactamase in Ps . aeruginosa. J Clin Microbiol, 1984 Apr, 19(4), 473 - 6 Early detection of oxacillin-resistant staphylococcal strains with hypertonic broth diluent for microdilution panels; Dillon LK et al.; A total of 292 coagulase-positive and 111 coagulase-negative staphylococcal strains were tested in microdilution MIC panels containing 16 to 0.13 microgram of oxacillin per ml diluted in cation-supplemented Mueller-Hinton broth with and without an additional 2% NaCl . All strains were tested using the stationary-phase inoculum procedure with an incubation temperature of 35 degrees C . Test results were recorded after 16 to 20 h of incubation; staphylococcal strains susceptible to oxacillin (less than or equal to 2 micrograms/ml) were reincubated for 20 to 24 h, and endpoints were determined again . Oxacillin resistance was found in 27 (9%) of the 292 coagulase-positive strains and 39 (35%) of the 111 coagulase-negative strains . Of these resistant strains, 5 (19%) of the 27 coagulase-positive strains and 13 (33%) of the 39 coagulase-negative strains were detected 24 h earlier in cation-supplemented Mueller-Hinton broth with 2% NaCl than in cation-supplemented Mueller-Hinton broth without the additional NaCl . However, 9 (33%) of the 27 resistant coagulase-positive strains and 10 (26%) of the 39 resistant coagulase-negative strains were detected only after an additional 24 h of incubation . Oxacillin MICs for the 265 coagulase-positive susceptible strains and 72 coagulase-negative susceptible strains were not affected by the additional 2% NaCl . These results support the utility of adding 2% NaCl to the broth diluent for the early detection of oxacillin-resistant staphylococcal strains and the necessity of extended incubation for those strains which initially appear to be susceptible to oxacillin after only 16 to 20 h of incubation. J Clin Microbiol, 1984 Jan, 19(1), 85 - 6 Comparison of the suitability of three common bacterial media for susceptibility testing of trimethoprim-sulfamethoxazole; Ferguson RW et al.; The in vitro inhibitory activity of trimethoprim-sulfamethoxazole is inversely related to the amount of thymine and thymidine in the test medium; manufacturers must adequately control their media to avoid spurious antimicrobial susceptibility results . No differences were observed when commercial Mueller-Hinton broth and agar were compared with a semisynthetic broth medium by the use of microdilution and disk diffusion techniques. J Clin Microbiol, 1984 Jan, 19(1), 8 - 16 Influence of culture conditions on expression of the mucoid m