Major differences exist in frequencies of virulence factors and multidrug resistance between community and nosocomial Escherichia coli bloodstream isolates.

Escherichia coli is a major cause of bloodstream infections and death due to sepsis. It is the most frequent Gram-negative bacterial pathogen recovered from cultures of blood from both community-acquired and nosocomial cases. We set out to determine the relationships between E. coli virulence factors (VFs), phylogenetic groups, and antibiotic resistance and whether bacteremia cases had a community, health care-associated. or nosocomial origin. Isolates from consecutive episodes of E. coli bacteremia in 303 patients presenting to a university hospital were screened for their VFs, phylogenetic group, and antibiotic resistance. The majority of VFs present in the collection were equally distributed between antibiotic-susceptible and multiple-drug-resistant (MDR) isolates, but the overall VF score was higher for isolates of community and health care-associated origin than those of nosocomial origin (P = 0.0002 and P = 0.0172, respectively); the papA, papG allele II, hlyA, and hek VFs were more prevalent in this cohort. Most isolates belonged to phylogenetic group B2, which harbored a greater proportion of antibiotic-susceptible isolates than MDR isolates (P = 0.04). The community, health care-associated, or nosocomial origin of E. coli bacteremia determines the virulence capacity of an isolate better than the phylogenetic group does. This study provides new insights into the relationships between the pathogenesis and epidemiology of E. coli bacteremia.