Prevalence of antiseptic-resistance genes in Staphylococcus aureus and coagulase-negative staphylococci colonising nurses and the general population in Hong Kong

Reduced biocide susceptibility in staphylococci is associated with quaternary ammonium compound (qac) gene-encoding efflux proteins. This study compared the prevalence of antiseptic-resistance genes (qacA/B, smr) in staphylococci colonising nurses and non-healthcare workers. Staphylococcus aureus and coagulase-negative staphylococci (CoNS) isolated from 249 nurses were compared for qacA/B and smr positivity with carriage isolates from non-healthcare workers. Associations between qac genes and antibiotic resistance were investigated and minimum inhibitory concentrations (MICs)/minimum bactericidal concentrations (MBCs) to benzalkonium chloride and chlorhexidine determined. Both genes had higher prevalence in CoNS from nurses (OR: 8.4; 95% CI: 5.4-13.2) and qacA/B was more common in nurses' S. aureus isolates than those of the general population (OR: 5.5; 95% CI: 2.7-11.2). Meticillin-resistant S. aureus (MRSA) carriage was low (3.2% nurses; 0.5% general population). The risk of harbouring qacA/B and smr was associated with presence of mecA (OR: 2.9; 95% CI: 1.8-4.8) and contact with MRSA-infected patients (OR: 2.0; 95% CI: 1.0-3.9) in S. aureus and CoNS. S. aureus with qac genes displayed significantly more antibiotic resistance and all gene-positive isolates had higher MICs and MBCs to antiseptics. Increased prevalence of antiseptic-resistance genes in staphylococci from nurses indicates that the hospital environment could exert selective pressure for carriage of these strains. The increased proportion of qac genes in meticillin-resistant strains suggests co-selection of these genes, as does the increased carriage of gene-positive strains by those in contact with MRSA-positive patients. Reduced antiseptic susceptibility may allow persistence of organisms in the presence of low level residues and contribute to survival of MRSA. (C) 2011 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.