Prevalence and Persistence of Escherichia coli Strains with Uropathogenic Virulence Characteristics in Sewage Treatment Plants

We investigated the prevalence and persistence of Escherichia coli strains in four sewage treatment plants (STPs) in a subtropical region of Queensland, Australia. In all, 264 E. coli strains were typed using a high-resolution biochemical fingerprinting method and grouped into either a single or a common biochemical phenotype (S-BPT and C-BPT, respectively). These strains were also tested for their phylogenetic groups and 12 virulence genes associated with intestinal and extraintestinal E. coli strains. Comparison of BPTs at various treatment stages indicated that certain BPTs were found in two or all treatment stages. These BPTs constituted the highest proportion of E. coli strains in each STP and belonged mainly to phylogenetic group B2 and, to a lesser extent, group D. No virulence genes associated with intestinal E. coli were found among the strains, but 157 (59.5%) strains belonging to 14 C-BPTs carried one or more virulence genes associated with uropathogenic strains. Of these, 120 (76.4%) strains belonged to seven persistent C-BPTs and were found in all four STPs. Our results indicate that certain clonal groups of E. coli with virulence characteristics of uropathogenic strains can survive the treatment processes of STPs. These strains were common to all STPs and constituted the highest proportion of the strains in different treatment tanks of each STP.Community sewage treatment plants (STPs) receive waste from diverse sources, including residential, industrial, and recreational facilities (31). Waste generated from these facilities contains the liquid and fecal discharges of humans and animals, household wastes, industry-specific materials, and storm water runoff (31). These materials are treated through primary, secondary, and tertiary sedimentation processes (18). Following these processes, effluent is normally clear and thus often recycled for nonpotable use (20), with excess water released into receiving waterways. However, due to possible malfunctions or poor management of wastewater systems (1), effluent containing pathogenic bacteria can be discharged into receiving waterways (11, 34). It has been speculated that waters contaminated with feces are a great risk to human health, as they are likely to contain human-specific enteric pathogens, including Salmonella spp. (30), Shigella spp. (10), enteroviruses (12), hepatitis A virus (13), and pathogenic Escherichia coli (30).E. coli, while widely used as an indicator bacterium (30, 35), can actually be pathogenic and be responsible for both intestinal and extraintestinal diseases (16). Intestinal pathogenic strains of E. coli are rarely encountered in the fecal flora of healthy hosts. Extraintestinal pathogenic E. coli (ExPEC) strains commonly cause infections of any organ or anatomical site (28). The ability of these pathogenic bacteria to cause disease is due to their acquisition of specialized virulence factors, which commensal E. coli strains typically lack. These specialized virulence factors allow them to cause a broad spectrum of diseases (17, 28), such as gastroenteritis (34), diarrhea (16), urinary tract infections and meningitis (29), and soft tissue infections and bacteremia (28). E. coli strains belong to four main phylogenetic groups (A, B1, B2, and D) (2), with pathogenic strains belonging mostly to phylogenetic group B2 and, to a lesser extent, group D. Another phylogenetic group (group E) has also been identified; however, it is uncommon and is not widely used (5).Presently, chlorination is an extremely widespread practice aimed at reducing the pathogen load in the final effluent to levels low enough to ensure that the organisms will not cause disease when the wastewater is discharged (31). Despite this, some pathogenic strains of E. coli may survive to become a significant public health risk (14, 35). The aim of this study was to investigate the presence and survival of these pathogenic E. coli strains during the treatment processes of four community STPs with different capacities in South East Queensland, Australia.