Abstract: AIM: To study whether levofloxacin and Vancomycin combination can narrow mutant selection window(MSW)of single drug group in vitro, which contribute to new strategies for restricting the development of resistance and provide data for rational applications of available antibacterial drugs in clinic practice. METHODS: Minimal antibiotic concentration(MPC)and MSWs were determined by spreading 10¹⁰ CFU/mL coccus on agar plates at different drug concentrations.MPC was defined as the lowest concentration inhibiting 100% of the coccus population after 72 h incubation. RESULTS: MSW of levofloxacin and vancomycin for staphylococcus aureus strain ATCC29213 was 16 and 64 respectively;Vancomycin combined with levofloxacin(1MIC+8MIC, 2MIC+ 4MIC)decreased the MSW of levofloxacin to staphylococcus aureus ATCC29213 for 2-4 times;Levofloxacin combined with vancomycin(1MIC+16MIC, 2MIC+8MIC) decreased the MSW of vancomycin to staphylococcus aureus ATCC29213 for 4-8 times. CONCLUSION: Combinations of levofloxacin and vancomycin can decrease MSW to staphylococcus aureus, ATCC29213 compared with individual drug administration.

Key words: levofloxacin, vancomycin, staphylococcus aureus, mutant selection window