Effect of combination of oxacillin and non-β-lactam antibiotics on methicillin-resistant Staphylococcus aureus

The in-vitro activity of oxacillin combined with non-β-lactam antibiotics, bacitracin, vancomycin, enduracidin, tunicamycin, flavomycin, fosfomycin, and cycloserine, was investigated in 23 methicillin-resistant and 15 methicillin-susceptible Staphylococcus aureus strains. In the presence of a non-β-lactam antibiotic (0.25 MIC), the MICs of oxacillin for methicillin-resistant S. aureus (MRSA) strains and methicillin-susceptible S. aureus (MSSA) strains were lowered. This effect was most marked with MRSA strains, and bacitracin, flavomycin, and tunicamycin increased the susceptibility of MRSA to oxacillin by greater than 200-fold