Influencc of B-lactamase inhibitors on the activity of oxacillin and four quinolone agents against resistant staphylococcus aureus

ABSTRACT

The influence of some Beta-lactamase inhibitors on the activity of four quinolones against 78 isolates of methicillin-resistant Staphylococcus aureus [MRSA] was tested by the minimum inhibitory concentration [MIC] method. All 78 strains were found by the rapid chromogenic cephalosporin method to be Beta-lactamase producer. The addition of 8 ug/ml of tazobactam to oxacillin had decreased the MICs from 8 to 32 folds, while the addition of 8 ug/ml of clavulanic acid had decreased the MICs only two fold. The addition of 2 ug/ml of clavulanic acid, sulbactam, and tazobactam to levofloxacin did not affect the MICs at all. The only effect observed was a two-fold decrease of the MICs when we added 8 ug/ml of the three inhibitors. The addition of 2 ug/ml of the three inhibitors to ofloxacin, lomefloxacin, and ciprofloxacin did not improve the MICs at all and 8 ug/ml decreased the MISs from two-fold to four-fold. The results of this study suggest that Beta-lactamase production plays a role in resistance to the four quinolones tested in those MRSA strains of low-level quinolone resistance