Zinc oxide nanoparticles restore susceptibility to chlorhexidine and benzalkonium chloride in methicillin-resistant Staphylococcus aureus isolated from burn infections.

Decolonization of methicillin-resistant S. aureus (MRSA) is one of the main challenges in burn wards. In this study, the antibacterial and antibiofilm effects of zinc oxide (ZnO) nanoparticles in combination with chlorhexidine (CHG) and benzalkonium chloride (BCC) were investigated against MRSA isolates. Reduced susceptibility to CHG and BCC was detected in 56% (n = 18) and 25% (n = 8) of isolates, respectively. The most common efflux-associated genes linked to biocide resistance were norC (75%), norB (65%), norA (20%), and qacA/B (15%). The combinations of ZnO nanoparticles with biocides significantly reduced the minimum inhibitory concentrations and enhanced the biofilm inhibitory effect of the biocides. This study confirms the potential of ZnO nanoparticles to enhance the antibacterial and antibiofilm activities of the examined biocides. The involvement of ZnO nanoparticles in efflux pump inhibition is also suggested.