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In Vitro Activity of Caspofungin Combined with Sulfamethoxazole against Clinical Isolates of Aspergillus spp.. Aya Yekutiel, 2004.Caspofungin (CAS) inhibits fungal cell wall synthesis . Sulfamethoxazole (SMX) inhibits folate biosynthesis and is active in vitro against Aspergillus spp . We studied the activities of the combination of CAS and SMX against 31 Aspergillus isolates and compared them with that of SMX combined with amphotericin B (AMB) or itraconazole (ITC) . MICs and minimal effective concentrations (MECs) were determined by the NCCLS broth microdilution method . With MIC endpoints, the combination of SMX and CAS showed synergy or synergy to additivity against 29 of 31 isolates . With MEC endpoints, synergy to additivity was found against 12 of 31 isolates and indifference was displayed against the rest of them . SMX in combination with AMB or ITC was not truly synergistic, while synergy to additivity was found for SMX-AMB and SMX-ITC against 17 of 31 and 3 of 12 isolates, respectively . No antagonism was found with any of the drug combinations . Further analysis of the synergy of CAS and SMX was performed by detailed measurement of hyphal length by microscopy and time-dependent 2,3-bis(2-methoxy-4-nitro-5-[(sulfenylamino)carbonyl]-2H-tetrazolium hydroxide (XTT)-based hyphal damage experiments . With MEC endpoints, the combination of CAS and SMX was characterized by a greater than 50% decrease in hyphal length compared to the hyphal lengths achieved with double the concentration of each drug alone . The XTT-based hyphal damage studies showed a statistically significant (P < 0.05) reduction in viability with CAS and SMX in combination compared to the viabilities achieved with double the concentration of each drug alone . These findings support the synergy results found by using MIC endpoints and suggest that visual MEC measurements may not be sufficient to identify the synergistic interactions seen by more sensitive, quantitative methods . Animal models are required to validate the significance of the synergy of CAS and SMX against Aspergillus spp . observed in vitro . Penicillin-Binding Proteins 1a and 1b Form Independent Dimers in Escherichia coli. Xavier Charpentier, 2002.We report here that PBP1a can dimerize but does not interact with PBP1b to form PBP1a/PBP1b heterodimers in Escherichia coli . These findings support the idea of a relevant involvement of dimerization of both PBP1a and PBP1b during murein synthesis and suggest the existence of different peptidoglycan synthesis complexes . Anabaena sp . Strain PCC 7120 hetY Gene Influences Heterocyst Development. Ho-Sung Yoon, 2003.The filamentous cyanobacterium Anabaena (Nostoc) sp . strain PCC 7120 responds to starvation for fixed nitrogen by producing a semiregular pattern of nitrogen-fixing cells called heterocysts . Overexpression of the hetY gene partially suppressed heterocyst formation, resulting in an abnormal heterocyst pattern . Inactivation of hetY increased the time required for heterocyst maturation and caused defects in heterocyst morphology . The 489-bp hetY gene (alr2300), which is adjacent to patS (asl2301), encodes a protein that belongs to a conserved family of bacterial hypothetical proteins that contain an ATP-binding motif . Carbon and Hydrogen Isotopic Fractionation during Anaerobic Biodegradation of Benzene. Silvia A. Mancini, 2003.Compound-specific isotope analysis has the potential to distinguish physical from biological attenuation processes in the subsurface . In this study, carbon and hydrogen isotopic fractionation effects during biodegradation of benzene under anaerobic conditions with different terminal-electron-accepting processes are reported for the first time . Different enrichment factors (  ) for carbon (range of -1.9 to -3.6 ) and hydrogen (range of -29 to -79) fractionation were observed during biodegradation of benzene under nitrate-reducing, sulfate-reducing, and methanogenic conditions . These differences are not related to differences in initial biomass or in rates of biodegradation . Carbon isotopic enrichment factors for anaerobic benzene biodegradation in this study are comparable to those previously published for aerobic benzene biodegradation . In contrast, hydrogen enrichment factors determined for anaerobic benzene biodegradation are significantly larger than those previously published for benzene biodegradation under aerobic conditions . A fundamental difference in the previously proposed initial step of aerobic versus proposed anaerobic biodegradation pathways may account for these differences in hydrogen isotopic fractionation . Potentially, C-H bond breakage in the initial step of the anaerobic benzene biodegradation pathway may account for the large fractionation observed compared to that in aerobic benzene biodegradation . Despite some differences in reported enrichment factors between cultures with different terminal-electron-accepting processes, carbon and hydrogen isotope analysis has the potential to provide direct evidence of anaerobic biodegradation of benzene in the field .
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