title: Convergent in vivo and in vitro selection of ceftazidime resistance mutations at position 167 of CTX-M-3 beta-lactamase in hypermutable Escherichia coli strains.
abstract: We report on a novel CTX-M extended-spectrum beta-lactamase (ESBL), designated CTX-M-42, with enhanced activity toward ceftazidime. CTX-M-42 was identified in a hypermutable Escherichia coli nosocomial isolate (isolate Irk2320) and is a Pro167Thr amino acid substitution variant of CTX-M-3. By molecular typing of ESBL-producing E. coli strains previously isolated in the same hospital ward, we were able to identify a putative progenitor (strain Irk1224) of Irk2320, which had a mutator phenotype and harbored the CTX-M-3 beta-lactamase. To reproduce the natural evolution of CTX-M-3, we selected for ceftazidime resistance mutations in bla CTX-M-3 gene in vitro both in clinical isolate Irk1224 and in laboratory-derived hypermutable (mutD5) strain GM2995. These experiments yielded CTX-M-3 Pro167Ser and CTX-M-3 Asn136Lys mutants which conferred higher levels of resistance to ceftazidime than to cefotaxime. CTX-M-3 Asn136Lys had a level of low activity toward ampicillin, which may explain its absence from clinical isolates. We conclude that the selection of CTX-M-42 could have occurred in vivo following treatment with ceftazidime and was likely facilitated by the hypermutable background.
authors.affiliation: Institute of Antimicrobial Chemotherapy, Krupskaya str. 28, PO Box 5, Smolensk, Russia.
authors.forename: Marina N
authors.initials: MN
authors.lastname: Stepanova
authors.forename: Maxim
authors.initials: M
authors.lastname: Pimkin
authors.forename: Anatoly A
authors.initials: AA
authors.lastname: Nikulin
authors.forename: Varvara K
authors.initials: VK
authors.lastname: Kozyreva
authors.forename: Elena D
authors.initials: ED
authors.lastname: Agapova
authors.forename: Mikhail V
authors.initials: MV
authors.lastname: Edelstein
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002442:Ceftazidime / Q000494:pharmacology*; D018550:Cephalosporin Resistance; D019020:Directed Molecular Evolution; D004926:Escherichia coli / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D006801:Humans; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009154:Mutation; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D001618:beta-Lactamases / Q000737:chemistry / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D029968:Escherichia coli Proteins; D002442:Ceftazidime; C417271:beta-lactamase CTX-M-3; D001618:beta-Lactamases