Phenotypic and genotypic characterization of coagulase-negative staphylococci isolated in blood cultures from patients with haematological malignancies

Coagulase-negative staphylococci are the predominant aetiological agents in bacteraemic patients hospitalized for haematological malignancies. The aim of this study was to determine whether differences exist in the prevalence of icaAB genes and in the phenotypic and/or genotypic pattern between blood isolates of coagulase-negative staphylococci, interpreted as representing true bacteraemia, and contaminant isolates from patients with haematological malignancies. Eighty-two isolates representing true bacteraemia and 47 contaminant isolates were found among 76 patients. The most prevalent species in both groups of patients was Staphylococcus epidermidis (n=103; 80%). Biochemical typing using the Phene Plate system and genotyping using pulsed-field gel electrophoresis showed a tendency towards a more homogeneous pattern among isolates causing true bacteraemia compared with contaminant isolates. Two major genotypic groups of S. epidermidis were found in both the true bacteraemia group and the contaminant group, with concordant pulsotypes found as well. These groups may comprise isolates carrying specific virulence factors, but the prevalence of the icaAB genes did not differ between the true bacteraemia group and the contaminant group. No significant difference was seen between the two study groups regarding clinical symptoms or complications, use of central venous catheter, and levels of absolute neutrophil count or C-reactive protein.