Genetic characteristics and antimicrobial resistance of Staphylococcus epidermidis isolates from patients with catheter-related bloodstream infections and from colonized healthcare workers in a Belgian hospital

Abstract

Background: Staphylococcus epidermidis is a pathogen that is frequently encountered in the hospital environment. Healthcare workers (HCWs) can serve as a reservoir for the transmission of S. epidermidis to patients.

Methods: The aim of this study was to compare and identify differences between S. epidermidis isolated from 20 patients with catheter-related bloodstream infections (CRBSIs) and from the hands of 42 HCWs in the same hospital in terms of antimicrobial resistance, biofilm production, presence of the intercellular adhesion (ica) operon and genetic diversity (pulsed field gel electrophoresis (PFGE), multilocus sequence typing (MLST) and staphylococcal cassette chromosome (SCC) mec typing).

Results: S. epidermidis isolates that caused CRBSI were resistant to significantly more non-betalactam drugs than were isolates collected from HCWs. Among the 43 mecA positive isolates (26 from HCWs), the most frequent SCCmec type was type IV (44%). The ica operon was significantly more prevalent in CRBSI isolates than in HCWs (P < 0.05). Weak in vitro biofilm production seemed to correlate with the absence of the ica operon regardless of the commensal or pathogenic origin of the isolate. The 62 isolates showed high diversity in their PFGE patterns divided into 37 different types: 19 harbored only by the CRBSI isolates and 6 shared by the clinical and HCW isolates. MLST revealed a total of ten different sequence types (ST). ST2 was limited to CRBSI-specific PFGE types while the "mixed" PFGE types were ST5, ST16, ST88 and ST153.

Conclusion: One third of CRBSI episodes were due to isolates belonging to PFGE types that were also found on the hands of HCWs, suggesting that HCW serve as a reservoir for oxacillin resistance and transmission to patients. However, S. epidermidis ST2, mecA-positive and icaA-positive isolates, which caused the majority of clinically severe CRBSI, were not recovered from the HCW's hands.

Figure 1

Biofilm production and correlation with the presence of the ica A in S . epidermidis population among HVs (healthy volunteers), CRBSIs (catheter-related bloodstream infections) and HCWs (healthcare workers).