期刊
ANTIMICROBIAL AGENTS AND CHEMOTHERAPY
卷 46, 期 6, 页码 1966-1970出版社
AMER SOC MICROBIOLOGY
DOI: 10.1128/AAC.46.6.1966-1970.2002
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The class C beta-lactamase from Enterobacter cloacae P99 confers resistance to a wide range of broad-spectrum beta-lactams but not to the newer cephalosporin cefepime. Using PCR mutagenesis of the E. cloacae P99 ampC gene, we obtained a Leu-293-Pro mutant of the P99 beta-lactamase conferring a higher MIC of cefepime (MIC, 8 mug/ml, compared with 0.5 mug/ml conferred by the wild-type enzyme). In addition, the mutant enzyme produced higher resistance to ceftazidime but not to the other beta-lactams tested. Mutants with 15 other replacements of Leu-293 were prepared by site-directed random mutagenesis. None of these mutant enzymes conferred MICs of cefepime higher than that conferred by Leu-293-Pro. We determined the kinetic parameters of the purified E. cloacae P99 beta-lactamase and the Leu-293-Pro mutant enzyme. The catalytic efficiencies (k(cat)/K-m) of the Leu-293-Pro mutant beta-lactamase for cefepime and ceftazidime were increased relative to the respective catalytic efficiencies of the wild-type P99 beta-lactamase. These differences likely contribute to the higher MICs of cefepime and ceftazidime conferred by this mutant beta-lactamase.
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