|
|
|
|
|
|
Combinations of Adefovir with Nucleoside Analogs Produce Additive Antiviral Effects against Hepatitis B Virus In Vitro. William E. Delaney IV, 2004.Combination therapies may be required for long-term management of some patients chronically infected with hepatitis B virus (HBV) . Adefovir is a nucleotide analog that has similar activity against wild-type and lamivudine-resistant HBV . In contrast to lamivudine, clinical resistance to the prodrug adefovir dipivoxil emerges infrequently . Based on its clinical efficacy and low frequency of resistance, adefovir dipivoxil may form an important component of combination regimens . We therefore investigated the in vitro antiviral efficacy of combinations of adefovir with other nucleoside analogs (lamivudine, entecavir, emtricitabine [FTC],and telbivudine [L-dT]) and the nucleotide analog tenofovir . Using a novel stable cell line that expresses high levels of wild-type HBV, we assayed the antiviral activity of each drug alone and in combination with adefovir . All two-drug combinations resulted in greater antiviral effects than treatments with single agents and could be characterized as additive by the Bliss independence model . Analysis using the Loewe additivity model indicated that adefovir exerted additive antiviral effects when combined with lamivudine, FTC, or L-dT and moderately synergistic effects when combined with entecavir or tenofovir . There was no evidence of cytotoxicity with any of the drugs when used alone or in combination at the tested doses . Characterization of Salmonella enterica Serovar Typhimurium from Marine Environments in Coastal Waters of Galicia (Spain). Jaime Martinez-Urtaza, 2004.Twenty-three Salmonella enterica serovar Typhimurium isolates from marine environments were characterized by phage typing, pulsed-field gel electrophoresis (PFGE) analysis, plasmid analysis, and antibiotic resistance, and the distribution of the different types in the coastal waters were subsequently analyzed . Five phage types were identified among the isolates (PT41, PT135, PT99, DT104, and DT193) . PT135 isolates were exclusively detected during the winter months from 1998 to 2000, whereas DT104 and PT41 isolates were detected exclusively in the summer months from 2000 to 2002 . XbaI PFGE analysis revealed 9 PFGE types, and plasmid profiling identified 8 plasmid types (with 1 to 6 plasmids) among the isolates . Only three isolates presented multidrug resistance to antibiotics . Two DT104 isolates were resistant to 8 and 7 antibiotics (profiles ACCeFNaSSuT and ACeFNeSSuT), whereas a PT193 isolate presented resistance to 6 antibiotics (profile ACFSSu) . In addition, four PT41 isolates were resistant to a single antibiotic . The detection of multidrug-resistant phage types DT104 and DT193 in shellfish emphasizes the importance of monitoring the presence of Salmonella in routine surveillance of live bivalve molluscs . Enterococcus faecalis Heme-Dependent Catalase. Lena Frankenberg, 2002.Enterococcus faecalis cells cannot synthesize porphyrins and do not rely on heme for growth but can take up heme and use it to synthesize heme proteins . We recently described a cytochrome bd in E . faecalis strain V583 and here report the identification of a chromosomal gene, katA, encoding a heme-containing cytoplasmic catalase . The 54-kDa KatA polypeptide shows sequence similarity to members of the family of monofunctional catalases . A hexahistidyl-tagged version of the catalase was purified, and major characteristics of the enzyme were determined . It contains one protoheme IX group per KatA polypeptide . Catalase activity was detected only in E . faecalis cells grown in the presence of heme in the medium; about 2 and 10 µM hemin was required for half-maximal and maximal production of catalase, respectively . Our finding of a catalase whose synthesis is dependent on the acquisition of heme in the opportunistic pathogen E . faecalis might be of clinical importance . Studies of cellular heme transport and heme protein assembly and in vivo synthesis of metalloprotein analogs for biotechnological applications are impeded by the lack of experimental systems . We conclude that the E . faecalis cell potentially provides such a desired system . Common and Distinguishing Regulatory and Expression Characteristics of the Highly Related KorB Proteins of Streptomycete Plasmids pIJ101 and pSB24.2. Matthew J. Ducote, 2003.The conjugative plasmid pIJ101 of the spore-forming bacterium Streptomyces lividans contains a regulatory gene, korB, whose product is required to repress potentially lethal expression of the pIJ101 kilB gene . The KorB protein also autoregulates korB gene expression and may be involved in control of pIJ101 copy number . KorB (pIJ101) is expressed as a 10-kDa protein in S . lividans that is immediately processed to a mature 6-kDa repressor molecule . The conjugative Streptomyces cyanogenus plasmid pSB24.1 is deleted upon entry into S . lividans to form pSB24.2, a nonconjugative derivative that contains a korB gene nearly identical to that of pIJ101 . Previous evidence that korB of pSB24.2 is capable of overriding pIJ101 kilB-associated lethality supported the notion that pIJ101 and pSB24.2 encode highly related, perhaps even identical conjugation systems . Here we show that KorB (pIJ101) and KorB (pSB24.2) repress transcription from the pIJ101 kilB promoter equally well, although differences exist with respect to their interactions with kilB promoter sequences . Despite high sequence and functional similarities, KorB (pSB24.2) was found to exist as multiple stable forms ranging in size from 10 to 6 kDa both in S . lividans and S . cyanogenus . Immediate processing of KorB (pIJ101) exclusively to the 6-kDa repressor form meanwhile was conserved between the two species . A feature common to both proteins was a marked increase in expression or accumulation upon sporulation, an occurrence that may indicate a particular need for increased quantities of this regulatory protein upon spore germination and resumption of active growth of plasmid-containing cells . Genomic Changes Arising in Long-Term Stab Cultures of Escherichia coli. D. Faure, 2004.Genomic scans of clones isolated from long-term stab cultures of Escherichia coli K-12 showed the loss of two large segments of the genome, with each lost segment being approximately 20 kb long . A detailed analysis of one of the deletions, located between 5.4 and 5.9 min, revealed that similar deletions had arisen in several other stab cultures . All deletions of this type exhibited a right terminus ending precisely at an IS5A element and a left terminus that varied over an  5-kb range but was bordered in all but two cases by sequences belonging to the preferred consensus target sequence for IS5, YTAR . The ubiquity of such deletions in independent stab cultures and the increase in their frequency over time argue that they have a selective advantage . It is speculated that the loss of the crl locus is responsible for the selective advantage of the deletions .
The ars Detoxification System Is Advantageous but Not Required for As(V) Respiration by the Genetically Tractable Shewanella Species Strain ANA-3. Chad W. Saltikov, 2003.Arsenate [As(V); HAsO42-] respiration by bacteria is poorly understood at the molecular level largely due to a paucity of genetically tractable organisms with this metabolic capability . We report here the isolation of a new As(V)-respiring strain (ANA-3) that is phylogenetically related to members of the genus Shewanella and that also provides a useful model system with which to explore the molecular basis of As(V) respiration . This gram-negative strain stoichiometrically couples the oxidation of lactate to acetate with the reduction of As(V) to arsenite [As(III); HAsO2] . The generation time and lactate molar growth yield (Ylactate) are 2.8 h and 10.0 g of cells mol of lactate-1, respectively, when it is grown anaerobically on lactate and As(V) . ANA-3 uses a wide variety of terminal electron acceptors, including oxygen, soluble ferric iron, oxides of iron and manganese, nitrate, fumarate, the humic acid functional analog 2,6-anthraquinone disulfonate, and thiosulfate . ANA-3 also reduces As(V) to As(III) in the presence of oxygen and resists high concentrations of As(III) (up to 10 mM) when grown under either aerobic or anaerobic conditions . ANA-3 possesses an ars operon (arsDABC) that allows it to resist high levels of As(III); this operon also confers resistance to the As-sensitive strains Shewanella oneidensis MR-1 and Escherichia coli AW3110 . When the gene encoding the As(III) efflux pump, arsB, is inactivated in ANA-3 by a polar mutation that also eliminates the expression of arsC, which encodes an As(V) reductase, the resulting As(III)-sensitive strain still respires As(V); however, the generation time and the Ylactate value are two- and threefold lower, respectively, than those of the wild type . These results suggest that ArsB and ArsC may be useful for As(V)-respiring bacteria in environments where As concentrations are high, but that neither is required for respiration .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
