Strong biofilm production but not adhesion virulence factors can discriminate between invasive and commensal Staphylococcus epidermidis strains.

Staphylococcus epidermidis is a leading cause of hospital-acquired infections, mostly associated with the use of medical devices in immunocompromised patients. It originates from the patient's own skin flora, which is subject to severe changes as a result of selective pressure exerted by the hospital environment. This notion led us to compare S. epidermidis isolates from catheter related infections (CRI), non-catheter related bacteremia (NCRB) and catheter hub cultures (commensal isolates). The collection comprised 47 CRI strains from the Bone Marrow Transplant Centre of Tunis, 25 NCRB strains and 25 commensal isolates from patients hospitalized in the same center. Antimicrobial resistance and virulence-associated genes (icaABC, aap, atlE, bhp, fbe, embp, and IS256), polysaccharide intercellular adhesin synthesis, and biofilm formation were investigated. The clonal relationship of strains was investigated by pulsed field gel electrophoresis. Whereas bhp, atlE, fbe, embp, and aap were almost ubiquitously amplified, resistance to oxacillin, kanamycin, tobramycin, gentamicin, cotrimoxazole, and fosfomycin, biofilm production, ica genes, and IS256 were significantly more frequent in invasive (CRI and NCRB strains) than in commensal strains. Moreover, strong biofilm production was significantly more frequent among CRI strains than in NCRB strains. In conclusion, when S. epidermidis is isolated from blood cultures, the detection of strong biofilm production may be significant with regard to judging whether the detected strain is an etiologic agent of CRI.