Reduced susceptibility of methicillin-resistant Staphylococcus aureus to cetylpyridinium chloride and chlorhexidine

Sensitivities of 120 strains of Staphylococcus aureus to methicillin, cetylpyridinium chloride (CPC) and chlorhexidine (CH) were measured by the agar dilution technique. The MICs for CPC and CH were less than or equal to 2 mu g/ml in 93 and 83% of methicillin-sensitive S. aureus respectively, and > 2 mu g/ml in 81 and 83% of methicillin-resistant S. aureus (MRSA), respectively. Overall, the MICs for CPC and CII were 5-10 times greater in the methicillin-resistant than in the methicillin-sensitive strains (p < 0.001), The MICs for CPC and CH also predicted the relative susceptibilities of S. aureus strains to the bactericidal action of these agents in growth and time-kill studies. The possibility that antiseptics and disinfectants contribute to the selection and maintenance of multiply resistant MRSA is considered.