Antagonistic Effect of Colistin on Vancomycin Activity against Methicillin-Resistant Staphylococcus aureus in In Vitro and In Vivo Studies

As concerns arise that the vancomycin MIC of methicillin-resistant Staphylococcus aureus (MRSA) could be increased by concurrent colistin administration, we evaluated the effect of colistin on vancomycin efficacy against MRSA via in vitro and in vivo studies. Among MRSA blood isolates collected in a tertiary-care hospital, we selected representative strains from community-associated MRSA strains (CA-MRSA; ST72-MRSA-SCC mec IV) and hospital-acquired MRSA strains (HA-MRSA; ST5-MRSA-SCC mec II).