Résumé : Introduction Staphylococcus epidermidis (SE) is a major cause of catheter-related bloodstream infections (CRBSI). Recent studies suggested the existence of well adapted, highly resistant, hospital-associated SE clones. The molecular epidemiology of SE in the Belgian hospitals and community has not been explored yet.Objectives We compared a set of 33 SE isolates causing CRBSI in hospitalized patients with a set of 33 commensal SE isolates. Analyzed factors 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 confronted to clinical data.Results CRBSI SE isolates were significantly resistant to more antibiotics than commensal SE 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 SE 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 of which were due to an ica positive multi-resistant isolate belonging to ST2 or ST54.Conclusions SE isolates causing CRBSI were more resistant and more often ica positive than commensal SE isolates, that were genetically heterogeneous and susceptible to the majority of antibiotics tested. Clinically severe CRBSI were due to isolates belonging to two closely related MLST types, ST2 and ST54.