Influence of sub-inhibitory concentrations of antiseptics on biofilm formation in S. epidermidis.

Clinical isolates of Staphylococcus epidermidis were evaluated for biofilm production/chemical nature, and for the effect of sub-inhibitory concentrations (sub-MICs) of ethanol and chlorhexidine on biofilm production. Moreover, some of the biofilm-positive samples were studied for the effect of sub-MICs of these antiseptics in the expression of icaA, icaR, sigB and sarA genes. Sub-MICs of ethanol (2 and/or 4%) led to an increase in biofilm production in almost all PIA-dependent and all PIA-independent strains tested, but did not induce biofilm production in primarily non- producers. Unlike ethanol, chlorhexidine sub-MICs determined reduction in biofilm production in biofilm-positive strains. In PIA-dependent strains, ethanol (1%) caused an increase in the relative expression of icaA and reduced expression of icaR, in addition to increased expression of global regulators (sarA and sigB), while the PIA-independent strain showed reduction in the expression of these global regulators. Unlike ethanol, chlorhexidine (0.5 µg/mL) determined increased expression of icaR and reduction of icaA in PIA-dependent strains, besides a reduction in the expression of sarA and sigB in the PIA-independent strain. The opposite effects of ethanol and chlorhexidine on the expression of icaA and icaR in PIA-dependent strains corroborated the phenotypic results obtained for biofilm production in isolates exposed to these antiseptics. The biofilm-inducing or -inhibiting effects of ethanol and chlorhexidine are of practical importance due to their widespread use as antiseptics in healthcare settings.