Comparative epidemiology of Staphylococcus epidermidis isolates from patients with catheter-related bacteremia and from healthy volunteers

Abstract

Staphylococcus epidermidis is a major cause of catheter-related bloodstream infections (CRBSIs). Recent studies suggested the existence of well-adapted, highly resistant, hospital-associated S. epidermidis clones. The molecular epidemiology of S. epidermidis in Belgian hospitals and the Belgian community has not been explored yet. We compared a set of 33 S. epidermidis isolates causing CRBSI in hospitalized patients with a set of 33 commensal S. epidermidis isolates. The factors analyzed included resistance to antibiotics and genetic diversity as determined by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and SCCmec typing. Additionally, the presence of virulence-associated mobile genetic elements, the ica operon and the arginine catabolic mobile element (ACME), was assessed and compared against clinical data. CRBSI S. epidermidis isolates were significantly resistant to more antibiotics than commensal S. epidermidis isolates. The two populations studied were very diverse and genetically distinct as only 23% of the 37 PFGE types observed were harbored by both CRBSI and commensal isolates. ACME was found in 76% of S. epidermidis strains, regardless of their origin, while the ica operon was significantly more prevalent in CRBSI isolates than in commensal isolates (P < 0.05). Nine patients presented a clinically severe CRBSI, eight cases of which were due to an ica-positive multiresistant isolate belonging to sequence type 2 (ST2) or ST54. S. epidermidis isolates causing CRBSI were more resistant and more often ica positive than commensal S. epidermidis isolates, which were genetically heterogeneous and susceptible to the majority of antibiotics tested. Clinically severe CRBSIs were due to isolates belonging to two closely related MLST types, ST2 and ST54.

Fig 1

Dendrogram of PFGE profiles of 66 S. epidermidis isolates causing CRBSI (n = 33) or collected from the skin of healthy volunteers (n = 33). For each isolate represented, the year of isolation and the presence of the mecA gene, the ica operon, and the ACME are listed, as well as the number of cases of resistance observed, the MLST ST (when tested), and the SCCmec type (mecA-positive isolates). Additionally, for isolates causing CRBSI, severe clinical presentation, hospitalization unit, and attributable death are indicated. PFGE types shared by CRBSI and commensal isolates are represented in boldface. Abbreviations: HV, healthy volunteer; G, gastrointestinal surgery units; H, hematology unit; ICU, intensive care units; N-U, nephrology-urology units; P, pulmonary oncology. *, close to ST86; **, close to ST19; °, number of cases of resistance observed among the 12 non-β-lactam antimicrobials tested (Table 1).