Molecular epidemiology of Escherichia coli bacteremia in liver transplant recipients

The characteristics of Escherichia coli strains causing bacteremia in profoundly immunosuppressed patients such as transplant recipients are undefined. The phylogenetic group and the virulence genotype of 57 distinct E. coli strains that caused bacteremia in 53 liver transplant recipients were investigated, and the association of these characteristics with host factors and in-hospital mortality was examined. Phylogenetic groups A, B1, B2, and D accounted for 39%, 10%, 25%, and 26% of the isolates, respectively. The most prevalent virulence genes were fyuA (yersiniabactin system: 70%) and iutA (aerobactin system: 63%), whereas hlyA (alpha-hemolysin) and cnf1 (cytotoxic necrotizing factor 1) occurred in only 14% and 12% of isolates, respectively. Most virulence genes were significantly more prevalent among group B2 and D isolates, vs. group A and B1 isolates. The overall rate of in-hospital mortality after E. coli bacteremia was 20%. Predictors of mortality included onset of bacteremia within 30 days of transplantation or during the intensive care unit stay, and non-urinary source and cutaneous source, but not E. coli phylogenetic group or virulence profile. Compared with historical E. coli bloodstream isolates from non-transplant patients, those from liver transplant recipients are characterized by a higher prevalence of groups A and B1 isolates and reduced virulence gene content. This finding can be explained by the severely immunocompromised status of the patients and the predominance of abdominal-source bacteremic episodes. Time of onset and source of bacteremia, not bacterial characteristics, predict mortality.