Virulence determinants in vancomycin-resistant Enterococcus faecium vanB: clonal distribution, prevalence and significance of esp and hyl in Australian patients with haematological disorders.

European studies have suggested that the esp gene and other virulence factors have roles in vancomycin-resistant Enterococcus faecium (VREfm) infections. The aim of this study was to examine the relationship between the spectrum of clinical disease and putative virulence factors in vanB VREfm isolates. A multiplex polymerase chain reaction was used to amplify potential virulence genes (asa1, gel E, cylA, esp and hyl) in VREfm isolates obtained from an Australian population of haematology patients. Clonality was assessed by pulsed-field gel electrophoresis (PFGE) and automated ribotyping. Infection, requirement for intensive care unit (ICU) admission and all-cause 30-day mortality were used as clinical indicators of organism virulence. Forty-one VREfm vanB isolates (41 patients; 14 infected and 27 colonised only) were analysed. Thirty-five of these isolates were typed by PFGE, 31 of which were represented by three clusters. The esp gene was identified in 22 of 27 (81.5%) screening and 11 of 14 (78.6%) infection-associated isolates. One isolate was hyl gene positive, and no isolate contained asa1, gel E or cylA genes. VREfm infection was independently associated with host factors (underlying diagnosis of acute myeloid leukaemia, age <or=60 years) but not with presence of the esp gene. ICU admission was negatively associated with presence of the esp gene (OR: 0.05; 95% CI: 0.01-0.61; P=0.02). There was no association between 30-day mortality and host factors or the presence of the esp gene. When compared to European and US reports, a high esp gene prevalence and low hyl gene prevalence was observed in polyclonal VRE isolates obtained from this immunocompromised population.