Comparative killing kinetics of methicillin-resistant Staphylococcus aureus by bacitracin or mupirocin

The in vitro activities of bacitracin and mupirocin were compared for seven different strains of methicillin-resistant Staphylococcus aureus. Six of seven strains showed bacitracin minimum inhibitory concentrations (MICs) of 0.5 to 1.0 units/mL, and all seven had mupirocin MICs of 0.5 to 2 micrograms/mL. Time-kill studies revealed 2.6- to 4.5-log reduction in 24 hours with strains susceptible to bacitracin (4 units/mL) and 0 to 2.2 reduction with mupirocin (16 micrograms/mL). Bacitracin should be considered further for in vivo studies because of enhanced bacteriocidal effect and lower cost.