title: Induction of beta-lactamase and methicillin resistance in unusual strains of methicillin-resistant Staphylococcus aureus.
abstract: Two unusual, heterogeneously-resistant, strains of Staphylococcus aureus appeared resistant to oxacillin, but susceptible to methicillin by disc diffusion methods. In agar dilution tests, both strains were oxacillin-resistant. One was susceptible to methicillin, and the other gave a paradoxical reaction, with growth only on plates containing low (0.5, 1 and 2 mg/l) and high (32 and 64 mg/l) concentrations of antibiotic. Induction of methicillin resistance was tested by inoculating each strain on to agar plates containing an inhibitory concentration of methicillin (8 mg/l), and then placing discs containing inducers (oxacillin, nafcillin, methicillin and CBAP [2-(2'-carboxyphenyl) benzoyl-6-aminopenicillanic acid]) on the agar surface. Colonies grew only around discs containing effective inducers. Oxacillin and CBAP were much more potent inducers of methicillin resistance and beta-lactamase than was nafcillin or methicillin. These data suggest that the mechanism that regulates induction of the low-affinity penicillin binding protein (PBP-2') may be altered in these strains. Similar mechanisms appear to induce both beta-lactamase and methicillin resistance.
authors.affiliation: Department of Medicine, Miriam Hospital, Providence, RI 02906.
authors.forename: J M
authors.initials: JM
authors.lastname: Boyce
authors.forename: A A
authors.initials: AA
authors.lastname: Medeiros
authors.forename: E F
authors.initials: EF
authors.lastname: Papa
authors.forename: C J
authors.initials: CJ
authors.lastname: O'Gara
mesh_terms: D001426:Bacterial Proteins; D002352:Carrier Proteins / Q000096:biosynthesis; D002455:Cell Division / Q000187:drug effects; D002969:Clavulanic Acids / Q000494:pharmacology; D004352:Drug Resistance, Microbial; D004790:Enzyme Induction; D006602:Hexosyltransferases; D008712:Methicillin / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D002267:Muramoylpentapeptide Carboxypeptidase / Q000096:biosynthesis; D009254:Nafcillin / Q000494:pharmacology; D010068:Oxacillin / Q000494:pharmacology; D010397:Penicillanic Acid / Q000494:pharmacology / Q000031:analogs & derivatives; D010403:Penicillin Resistance; D046915:Penicillin-Binding Proteins; D010458:Peptidyl Transferases; D013211:Staphylococcus aureus / Q000235:genetics; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D002969:Clavulanic Acids; D046915:Penicillin-Binding Proteins; C063561:2-(2'-carboxyphenyl)benzoyl-6-aminopenicillanic acid; D009254:Nafcillin; D010397:Penicillanic Acid; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase; D001618:beta-Lactamases; D008712:Methicillin; D010068:Oxacillin