Biofilm-forming Staphylococcus epidermidis expressing vancomycin resistance early after adhesion to a metal surfaceBiofilm-forming Staphylococcus epidermidis expressing vancomycin resistance early after adhesion to a metal surface バイオフィルム形成表皮ブドウ球菌は金属表面付着後早期にバンコマイシン抵抗性を発現する
We investigated biofilm formation and time of vancomycin (VCM) resistance expression after adhesion to a metal surface in Staphylococcus epidermidis. Biofilm-forming Staphylococcus epidermidis with a VCM MIC of 1μg/mL was used. The bacteria were made to adhere to a stainless steel washer and treated with VCM at different times and concentrations. VCM was administered 0, 2, 4, and 8 hours after adhesion. The amount of biofilm formed was evaluated based on the biofilm coverage rates (BCRs) before and after VCM administration, bacterial viability in biofilm was visually observed using the fluorescence staining method, and the viable bacterial count in biofilm was measured. The VCM concentration required to decrease BCR significantly compared with that of VCM-untreated bacteria was 4μg/mL, even in the 0hr group. In the 4 and 8hr groups, VCM could not inhibit biofilm growth even at 1,024μg/mL. In the 8hr group, viable bacteria remained in biofilm at a count of 104 CFU even at a high VCM concentration (1,024μg/mL). It was suggested that biofilm-forming Staphylococcus epidermidis expresses resistance to VCM early after adhesion to a metal surface. Resistance increased over time after adhesion as the biofilm formed, and strong resistance was expressed 4-8 hours after adhesion.