Increase in resistance of methicillin-resistant Staphylococcus aureus to beta-lactams caused by mutations conferring resistance to benzalkonium chloride, a disinfectant widely used in hospitals

Methicillin-resistant Staphylococcus aureus (MRSA) has been found worldwide and is one of the major nosocomial agents. Appearance of MRSA resistant to benzalkonium chloride, a disinfectant widely used in hospitals, has been reported. To determine if the disinfectant might be related to increases in resistance to beta -lactams, we selected strains of MRSA which showed resistance to low concentrations of oxacillin (MIC, 2 to 32 mu g/ml), isolated mutants resistant to benzalkonium, and then monitored the resistance to oxacillin. MRSA mutants resistant to benzalkonium chloride showed a higher resistance than parent strains to various beta -lactam antibiotics including cloxacillin, moxalactam, flomoxef, and cefmetazole, as seen in the case of oxacillin.