title: Detection of extended-spectrum beta-lactamases in clinical isolates of Klebsiella pneumoniae and Escherichia coli.
abstract: Forty clinical isolates of Escherichia coli and 141 isolates of Klebsiella pneumoniae that either transferred ceftazidime resistance or showed sulbactam enhancement of oxyimino-beta-lactam susceptibility were tested by disk diffusion methodology for susceptibility to aztreonam, cefotaxime, ceftazidime, and cefoxitin. With standard 30 micrograms antibiotic disks, the fraction of these extended-spectrum beta-lactamase (ESBL)-producing isolates testing resistant by National Committee for Clinical Laboratory Standards criteria was lowest (24%) with cefotaxime disks. Forty percent of the E. coli and 29% of the K. pneumoniae isolates appeared susceptible with at least one oxyimino-beta-lactam disk. Ceftazidime and aztreonam disks were equivalent in differentiating ESBL production, and both were superior to cefotaxime disks. Over half the E. Coli and 29% of the K. pneumoniae isolates tested cefoxitin resistant. In 30 isolates, cefoxitin resistance was transmissible and due to a plasmid-mediated AmpC-type beta-lactamase. With a 5-micrograms ceftazidime disk, a breakpoint could be chosen with high sensitivity and specificity for ESBL-producing organisms. Present disk diffusion criteria underestimate the prevalence of ESBL-producing strains.
authors.affiliation: Lahey Hitchcock Clinic, Burlington, Massachusetts 01805, USA.
authors.forename: G A
authors.initials: GA
authors.lastname: Jacoby
authors.forename: P
authors.initials: P
authors.lastname: Han
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001398:Aztreonam / Q000494:pharmacology; D002439:Cefotaxime / Q000494:pharmacology; D002440:Cefoxitin / Q000494:pharmacology; D002442:Ceftazidime / Q000494:pharmacology; D004352:Drug Resistance, Microbial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification; D006801:Humans; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D010957:Plasmids / Q000235:genetics; D001618:beta-Lactamases / Q000032:analysis* / Q000096:biosynthesis / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D002440:Cefoxitin; D002442:Ceftazidime; D001618:beta-Lactamases; D001398:Aztreonam; D002439:Cefotaxime