title: Biochemical analysis of the ceftazidime-hydrolysing extended-spectrum beta-lactamase CTX-M-15 and of its structurally related beta-lactamase CTX-M-3.
abstract: The extended-spectrum beta-lactamase CTX-M-15 confers resistance to ceftazidime, unlike the majority of CTX-M-type enzymes. Kinetic parameters were determined from purified CTX-M-15 and CTX-M-3, which differ by the single amino acid substitution Asp-240 to Gly, according to the Ambler numbering of class A beta-lactamases. Relative molecular masses of CTX-M-15 and CTX-M-3 were approximately 29 kDa and pI values were 8.9 and 8.4, respectively. CTX-M-15 had higher affinities for beta-lactams (lower K(m) values) than those of CTX-M-3 but catalytic efficiency (k(cat)/K(m) values) was variable depending on the beta-lactam substrate. Only CTX-M-15 showed a measurable catalytic efficiency for ceftazidime. Clavulanic acid and tazobactam were good inhibitors of both enzymes. MICs of beta-lactams for Escherichia coli reference strains expressing cloned beta-lactamase genes in the same genetic background were similar except for ceftazidime. This work underlines the fact that some CTX-M enzymes may hydrolyse ceftazidime and thus confer resistance to this expanded-spectrum cephalosporin in Enterobacteriaceae.
authors.affiliation: Service de Bactériologie-Virologie, Hôpital de Bicêtre, Assistance Publique/Hôpitaux de Paris, Faculté de Médecine Paris-Sud, 94275 Le Kremlin-Bicêtre, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Poirel
authors.forename: Marek
authors.initials: M
authors.lastname: Gniadkowski
authors.forename: Patrice
authors.initials: P
authors.lastname: Nordmann
mesh_terms: D002442:Ceftazidime / Q000737:chemistry / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000302:isolation & purification; D006801:Humans; D006868:Hydrolysis; D008826:Microbial Sensitivity Tests; D018440:beta-Lactam Resistance / Q000502:physiology; D001618:beta-Lactamases / Q000737:chemistry* / Q000494:pharmacology*
chemical_list: D002442:Ceftazidime; C473109:beta-lactamase CTX-M-15; C417271:beta-lactamase CTX-M-3; D001618:beta-Lactamases