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 (MIC50) values for both antiseptics. qac-positive strains exhibited significantly increased BAC MIC50 (1 vs. 0.25 µg/mL; p < 0.001). Biofilm-forming isolates (16.4%) had three-fold higher BAC MIC50 (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.