In vitro effect of pH and ethanol on biofilm formation by clinical ica-positive Staphylococcus epidermidis strains

Biofilm production is an important step in the pathogenesis of Staphylococcus epidermidis associated biomaterial infections. Staphylococcus epidermidis strains isolated from dialysis fluid (n = 9) and needle cultures (n = 14) were phenotyped and genotyped for extracellular polysaccharide production and were examined for their ability to produce slime in a medium at various pH levels (3, 5, 7, 9 and 12) and with ethanol supplementation (0, 2, 5, 10 and 15%) using a semi-quantitative adherence assay. A total of 23 clinical icaADBC positive S. epidermidis, one reference strain (S. epidermidis CIP 106510) used as positive control, and one icaADBC negative strain (E21) were investigated. Qualitative biofilm production analysis revealed that 15 of the 23 icaADBC positive strains (65.21%) produced slime on Congo Red agar plates. Quantitative biofilm was determined by measuring the optical density at 570 nm (OD570). The results show that the slime production depended on the pH value of the medium and the ethanol concentration. At highly acidic (pH 3) and alkaline (pH 12) levels, the OD570 was lower, while at pH 7 the adhesion was moderate, In addition the cells adhered strongly with 2% ethanol than with the other concentrations. Our results suggest that pH and ethanol were stress factors that led to S. epidermidis biofilm formation and also play a possible role in the pathogenesis of biomaterial-related infections.