Mutant selection window of disinfectants for Staphylococcus aureus and Pseudomonas aeruginosa

•Mutant selection window (MSW) of various disinfectants against S. aureus and P. aeruginosa was determined.•0.05% sodium hypochlorite as used for environmental disinfection was inside the MSW for all strains.•0.5% chlorhexidine gluconate against P. aeruginosa exceeded all MSWs.•53.3% of P. aeruginosa were in the MSW at a concentration of 0.2% benzalkonium chloride.•Proper use of disinfectants means using them at a concentration that both kills micro-organisms and inhibits resistance. The aim of this study was to determine the mutant selection window (MSW) of various disinfectants against Staphylococcus aureus and Pseudomonas aeruginosa clinical isolates to determine the tendency of these strains to acquire resistance to disinfectants. A total of 60 S. aureus isolates [30 methicillin-resistant S. aureus (MRSA) and 30 methicillin-susceptible S. aureus (MSSA)] and 30 P. aeruginosa, including 2 multidrug-resistant P. aeruginosa (MDRP), were collected in Japan. The minimum inhibitory concentrations (MICs) and mutant prevention concentrations (MPCs) of disinfectants, including sodium hypochlorite (NaOCl), against these strains were established to determine the MSW. The MSW50, MSW80 and MSW100 for sodium hypochlorite against S. aureus and P. aeruginosa were 4×, 8× and 16× MIC, respectively. Strains surviving in the sodium hypochlorite MSW remained at a concentration of ≤0.3% (≤3072μg/mL). This is the first evaluation of the bactericidal activity against S. aureus and P. aeruginosa strains surviving in the MSW of disinfectants. Environmental disinfection at low concentrations of sodium hypochlorite does not kill micro-organisms. Proper use of sodium hypochlorite shows a bactericidal effect against various pathogenic micro-organisms and is inexpensive, making it frequently used globally.