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

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.
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.
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).
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.
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.