EFFECT OF BETA-LACTAMASE ON MINIMUM INHIBITORY CONCENTRATIONS OF METHICILLIN IN METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS

A study was undertaken to determine whether the production of penicill in-binding protein-2' (PBP-2') and the production of beta-lactamase we re related to the minimum inhibitory concentrations of methicillin (DM PPC) in various strains of methicillin-resistant Staphylococcus aureus . The amount of PBP-2' produced by the low-level resistant strain L20A was small and the strain became resistant to DMPPC as a result of ina ctivation of DMPPC by beta-lactamase. The largest amount of PBP-2' pro duced was in a moderately resistant strain L21A but the MIC was not hi gh since the strain was not capable of producing beta-lactamase and th e population of cells was heterogeneous. The amount of PBP-2' produced in the high-level resistant strain L457A was lower than that in strai n L21A but the MIC was high as a result of the production of beta-lact amase. Production of PBP-2' was essential for resistance to methicilli n but production of beta-lactamase had a major effect on the MIC.