Study on mutant prevention concentrations of vancomycin alone and in combination with rifampicin or fosfomycin against MRSA

Aim To evaluate the mutant prevention concentrations of vancomycin alone and in combination with rifampicin and fosfomycin against Methicillin-resistant staphylococcus aureus(MRSA) in vitro,which provides evidence for new strategies for restricting the development of resistance.Methods The cells of 1010 colony forming units per milliliter coccus were enriched in broth.Mutant prevention concentrations of the above drugs for 10 strains of MRSA were detected with agar dilution method and the value of selectiveity index and drug-resistant frequencies were calculated.Results The selectiveity index of vancomycin alone for 10 strains of MRSA were 16~64,and selectiveity index of the combination application with rifampicin and fosfomycin for MRSA were 2~16 and 1~8 respectively.The selectiveity index for the combination application decreased 2 to 32-fold and drug-resistant frequencies were also significantly lower than the single application of vancomycin.Conclusion Combinations use of antimicrobial agents can decrease the mutant prevention concentration of MRSA and narrow the mutant selection window,so the emergences of resistant strains are decreased.