Antiseptic Susceptibility and Sub-Inhibitory Concentration-Induced Biofilm Response in Staphylococcus epidermidis from Abdominal Surgical Site Skin

Background: Staphylococcus epidermidis , a commensal skin pathogen, is a key pathogen in surgical site infections (SSIs). This study characterized clinical isolates obtained from an abdominal operation to guide decolonization therapy. Methods: In total, 146 S. epidermidis isolates obtained from pre-operative skin swabs of patients undergoing gynecological procedures were analyzed. PCR was performed to detect mecA , efflux pump genes ( qacA/B , smr , etc.), and biofilm-associated genes ( icaA-D , aap ). Methicillin-resistant S. epidermidis (MRSE) isolates were typed by multi-locus sequence typing. Broth microdilution was used to assess susceptibility to benzalkonium chloride (BAC) and chlorhexidine digluconate (CHG). Biofilm formation was measured in the presence or absence of sub-inhibitory antiseptic exposure. Results: Of the isolates, 49.3% were MRSE, and 63.0% and 29.5% carried qacA/B and smr , respectively. MRSE showed higher minimum inhibitory concentration (MIC 50 ) values for both antiseptics. qac -positive strains exhibited significantly increased BAC MIC 50 (1 vs. 0.25 µg/mL; p < 0.001). Biofilm-forming isolates (16.4%) had three-fold higher BAC MIC 50 (p < 0.01). Sub-MIC exposure to BAC/CHG induced biofilm formation in prior non-producers (p < 0.05); among these, 81.3% were qac -positive, and 62.5% were MRSE. Conclusions: The high prevalence of MRSE and efflux genes contributed to antiseptic tolerance. Sub-inhibitory antiseptic concentrations may enhance biofilm formation in resistant strains, underscoring the need for optimized decolonization tactics to prevent SSI.