Phylogenetic groups and extraintestinal virulence genes of inflow Escherichia coli entering a municipal drinking water treatment facility (St. Paul, MN, USA).

Extraintestinal pathogenic Escherichia coli (ExPEC), a leading cause of urinary tract infections, sepsis and neonatal meningitis, circulates between diverse hosts and the environment. Consequently, identifying ExPEC reservoirs and transmission pathways has potentially great public health importance. Here, we used PCR-based methods to characterize 104 E. coli isolates from inflow water to the St. Paul, MN (USA), municipal drinking water treatment plant. Isolates were analysed for major phylogenetic groups and multiple extraintestinal virulence genes. Additionally, from the 65 (of 104) water samples that yielded multiple E. coli colonies, we screened E. coli population DNA for virulence genes. Thirty-three percent of isolates represented virulence-associated groups B2 and D, and 8% (95% CI: 3%, 15%) qualified molecularly as ExPEC. The ExPEC isolates, all from group B2 or D, had a median virulence gene score of 11.0 and collectively contained all but four of the 28 studied extraintestinal virulence genes. Population DNA screening increased the proportion of samples positive for individual virulence genes and, presumptively, for ExPEC [14% (95% CI: 10%, 30%) vs. 8%, P=0.03]. These findings identify a previously underappreciated potential mechanism for community-wide dissemination of ExPEC and underscore the importance of consistent disinfection of municipal drinking water.