title: Three beta-lactamases isolated from Aeromonas salmonicida, including a carbapenemase not detectable by conventional methods.
abstract: The beta-lactamases of seven strains of Aeromonas salmonicida subsp. achromogenes resistant to amoxicillin (MIC > 1024 mg/l) and responsible for furunculosis in farmed Atlantic salmon in Scotland were examined to establish the mechanisms of beta-lactam resistance. Separation of a cell-free extract on an isoelectric focusing gel stained with the chromogenic cephalosporin nitrocefin showed the presence of two beta-lactamases, one with a pI of 7.9 and the other with a pI of 6.0. Hydrolysis assays of cell-free extracts of these strains demonstrated carbapenemase, penicillinase and cephalosporinase activity. However, when the beta-lactamases were separated by anion exchange chromatography, the carbapenemase activity could not be retrieved in either of the peak fractions containing the separated enzymes that had been visualised by nitrocefin. Consequently, a novel carbapenemase was discovered which cannot be detected with nitrocefin.
authors.affiliation: Department of Medical Microbiology, Medical School, University of Edinburgh, UK.
authors.forename: M V
authors.initials: MV
authors.lastname: Hayes
authors.forename: C J
authors.initials: CJ
authors.lastname: Thomson
authors.forename: S G
authors.initials: SG
authors.lastname: Amyes
mesh_terms: D000333:Aeromonas / Q000187:drug effects* / Q000201:enzymology* / Q000302:isolation & purification; D000658:Amoxicillin / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins; D001431:Bacteriological Techniques; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D005393:Fish Diseases / Q000382:microbiology*; D005667:Furunculosis / Q000382:microbiology / Q000662:veterinary; D007525:Isoelectric Focusing; D008826:Microbial Sensitivity Tests; D008970:Molecular Weight; D012474:Salmon / Q000382:microbiology*; D013379:Substrate Specificity; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000302:isolation & purification* / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D000658:Amoxicillin; D001618:beta-Lactamases; C063912:carbapenemase