Mupirocin resistance in methicillin-resistant Staphylococcus aureus from a veterans hospital.

679 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) which occurred from 1986 and 1992 were retrospectively tested to determine the frequency of mupirocin resistance. With disk agar diffusion screening, 26 of 679 MRSA had zones of inhibition of < 18 mm using a 5 micrograms mupirocin disk. Minimal inhibitory concentrations (MICs) by agar dilution on the 26 suspect MRSA revealed that 9 were resistant. Of these 9, 1 had a MIC of 6.25, 4 of 12.5, 1 of 25, 1 of 500 and 2 of > 1,000 micrograms/ml. Although the overall incidence of mupirocin resistance was low in our hospital, 5 of the 9 resistant isolates occurred in 1992 and may signal a much more serious threat in the future.