Sensitivities to biocides and distribution of biocide resistance genes in quaternary ammonium compound tolerant Staphylococcus aureus isolated in a teaching hospital

In this study, the minimum bactericidal concentrations (MBCs) of 5 biocides (benzalkonium chloride, glutaraldehyde, sodium hypochlorite, povidone iodine and ethanol) for 56 clinical quaternary ammonium compound (QAC) tolerant S. aureus strains following exposure for 5, 30 or 180 min, collected from a teaching hospital in China, were examined. The distributions of the biocide resistance genes qacA/B, smr, qacH and qacG were investigated by polymerase chain reaction. Following 5 min exposure of benzalkonium chloride and povidone iodine, 7.1% (4/56) and 7.1% (4/56) isolates, respectively, exhibited MBC values higher than their in-use concentrations for mucosa and wound disinfection. The MBC values of all the isolates studied for glutaraldehyde, sodium hypochlorite and ethanol were lower than the in-use concentrations in all contact times. The qacA/B gene was found in 94.6% (53/56) of QAC tolerant S. aureus. The frequencies of smr (3.6%, 2/56) and qacH (7.1%, 4/56) were low and qacG was not detected. The results suggested that clinical QAC tolerant S. aureus isolates of China had the possibility to survive in proper in-use concentrations of some biocides at proper contact time, and qacA/B is the most prevalent disinfectant resistant gene in this type of bacteria.