Molecular Characterization of Staphylococcus epidermidis Isolates Recovered from Patients Admitted to a Referral Hospital in Iran

[Background]Coagulase-negative Staphylococci (CoNS), especially Staphylococcus epidermidis, are considered as commensal bacteria of human skin and oral-nasal mucosa. Because of having many various virulence factors as well as the emergence of the multidrug-resistant (MDR) strains, this microorganism is regarded as a major cause of hospital-acquired bacteremia and invasive nosocomial infections.[Objectives]Due to the significance of S. epidermidisassociated infections in different health care units, the aim of this study was to determine the molecular epidemiology of S. epidermidis in true infection-associated isolates.[Methods]In our cross sectional study, a total of 183 S. epidermidis strains was collected during 8 months. Only 40 strains, which were identified as “true” infection-associated strains, were assessed via antibiotic susceptibility testing and pulsed field gel electrophoresis (PFGE) typing. Finally, strains with specific assigned pulsotypes were also analyzed by multilocus sequence typing (MLST).[Results]Specimens were most commonly obtained from the bloodstream, wound, and catheter. More than half (75%) of the tested strains were found to be resistant to cefoxitin and ciprofloxacin (60%), while 45% of strains showed resistance to tetracycline. Using PFGE, 3 clones (A, B and C) were identified. According to MLST, the frequency of ST2 and ST5 was more prominent than the other STs.[Conclusions]In accordance with the life cycle of S. epidermidis, molecular characterization of invasive isolates is essential for controlling the epidemic strains in health care units.