Influence of beta-lactamase inhibitors on the activity of oxacillin against methicillin-resistant Staphylococcus aureus.
We studied the in vitro susceptibility to oxacillin of 46 isolates of methicillin-resistant Staphylococcus aureus (MRSA) isolates with a minimum inhibitory concentration (MIC) > 8 micrograms/ml of oxacillin, with and without adding clavulanic acid, sulbactam, or tazobactam in three different concentrations (2, 4, and 8 micrograms/ml). All 46 strains were found by the rapid chromogenic cephalosporin method to be beta-lactamase producers. For those strains with low-level resistance (MIC of 16 or 32 micrograms/ml), the MICs of oxacillin decreased four- to 32-fold and two- to 32-fold after adding sulbactam and tazobactam, respectively. For those with high-level resistance (MIC of > or = 64 micrograms/ml), the MICs either did not change or decreased only two-fold after we added one of three beta-lactamase inhibitors. The results suggest that beta-lactamase production probably plays a role in resistance to oxacillin in those MRSA strains of low-level oxacillin resistance.
Chang
S C
SC
Department of Internal Medicine, National Taiwan University Hospital, ROC.
Hsieh
W C
WC
Luh
K T
KT
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D019818:Clavulanic Acid; D002969:Clavulanic Acids / Q000494:pharmacology; D004347:Drug Interactions; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D010068:Oxacillin / Q000494:pharmacology*; D010397:Penicillanic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D013211:Staphylococcus aureus / Q000187:drug effects*; D013407:Sulbactam / Q000494:pharmacology; D000078142:Tazobactam; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D002969:Clavulanic Acids; D065093:beta-Lactamase Inhibitors; D019818:Clavulanic Acid; D010397:Penicillanic Acid; D001618:beta-Lactamases; D013407:Sulbactam; D000078142:Tazobactam; D010068:Oxacillin