pubmed-article:9301981 | pubmed:abstractText | 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. | lld:pubmed |