ABSTRACT
Staphylococcus aureus, an important human pathogen, is particularly adept at producing biofilms on implanted medical devices. Although antibiotic treatment of nonsusceptible bacteria will not kill these strains, the consequences should be studied. The present study focuses on investigating the effect of vancomycin on biofilm formation by vancomycin-non-susceptible S. aureus. Biofilm adherence assays and scanning electron microscopy demonstrated that biofilm formation was significantly enhanced following vancomycin treatment. Bacterial autolysis of some subpopulations was observed and was confirmed by the live/dead staining and confocal laser scanning microscopy. A significant increase in polysaccharide intercellular adhesin (PIA) production was observed by measuring icaA transcript levels and in a semi-quantitative PIA assay in one resistant strain. We show that the release of extracellular DNA (eDNA) via cidA-mediated autolysis is a major contributor to vancomycin-enhanced biofilm formation. The addition of xenogeneic DNA could also significantly enhance biofilm formation by a PIA-overproducing S. aureus strain. The magnitude of the development of the biofilm depends on a balance between the amounts of eDNA and PIA. In conclusion, sublethal doses of cell wall-active antibiotics like vancomycin induce biofilm formation through an autolysis-dependent mechanism in vancomycin-non-susceptible S. aureus.