title: Distribution and expression of beta-lactamase genes among Aeromonas spp.
abstract: Clinical and environmental isolates of Aeromonas spp. (20 Aeromonas caviae, 33 Aeromonas veronii and 21 Aeromonas hydrophila) were examined for their ability to yield mutants derepressed for beta-lactamase production and for the distribution of the three chromosomally encoded beta-lactamase genes, ampS and cepS from A. veronii bv. sobria and cphA from A. hydrophila. Of these isolates, 100% and 96% of the isolates from A. hydrophila and A. caviae, respectively, yielded beta-lactamase derepressed mutants but only 38% of A. veronii isolates yielded the resistant phenotype at 37 degrees C. However, when tested at 30 degrees C, all isolates gave rise to the derepressed mutants, indicating a temperature effect on the control mechanism. All mutants had significantly higher beta-lactamase activity against ampicillin, oxacillin, cephaloridine and imipenem. Hybridization studies with cloned aeromonas beta-lactamase genes indicated that the cephalosporinase gene, cepS, is almost ubiquitous for the three species tested. The cphA gene cross-hybridized with all isolates of A. veronii and A. hydrophila but not to A. caviae isolates. In contrast, hybridization studies using ampS revealed that only 25% of A. caviae, 45% of A. veronii and 38% of A. hydrophila tested carried the ampS gene or one closely homologous to it. Nonetheless, strains that failed to hybridize with ampS showed two serine beta-lactamases when analysed by isoelectric focusing.
authors.affiliation: Bristol Centre for Antimicrobial Research and Evaluation, Department of Microbiology and Pathology, Medical School, University of Bristol, UK.
authors.forename: T R
authors.initials: TR
authors.lastname: Walsh
authors.forename: R A
authors.initials: RA
authors.lastname: Stunt
authors.forename: J A
authors.initials: JA
authors.lastname: Nabi
authors.forename: A P
authors.initials: AP
authors.lastname: MacGowan
authors.forename: P M
authors.initials: PM
authors.lastname: Bennett
mesh_terms: D000333:Aeromonas / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D016980:Aeromonas hydrophila / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015139:Blotting, Southern; D006801:Humans; D008826:Microbial Sensitivity Tests; D009154:Mutation / Q000235:genetics; D013696:Temperature; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism; D047090:beta-Lactams / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D001618:beta-Lactamases