Assessment of ica operon carriage and biofilm production in Staphylococcus epidermidis isolates causing bacteraemia in bone marrow transplant recipients

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The clinical significance of coagulase-negative staphylococci isolated from blood culture is typically assessed on the basis of a combination of clinical and microbiological criteria. However, these criteria are difficult to apply to haematology patients who are highly immunosuppressed and from whom blood cultures are obtained most frequently through a central venous catheter. This study analysed 112 episodes of Staphylococcus epidermidis bacteraemia that occurred in 79 bone marrow transplant recipients. In 73 (65%) episodes, only one blood culture set was positive for S. epidermidis, while 39 (35%) episodes grew S. epidermidis from multiple blood cultures. Nine patients had two or more episodes of bacteraemia with the same strain, as determined by pulsed-field gel electrophoresis (PFGE). The PFGE method also showed that 34 (31%) isolates belonged to seven clusters, indicating the persistence of certain clones in the environment. Of the 109 isolates analysed, 59 (54%) produced biofilm and 91 (83.5%) carried the ica operon. Isolates that produced biofilm were observed to colonise central venous catheters faster than non-biofilm-producing isolates (18 vs. 37 days; p 0.03). No clinical features were associated with carriage of the ica operon, but the ica operon was carried more frequently by the isolates that formed clusters.

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