title: Evidence of Naturalized Stress-Tolerant Strains of Escherichia coli in Municipal Wastewater Treatment Plants.
abstract: Escherichia coli has been proposed to have two habitats-the intestines of mammals/birds and the nonhost environment. Our goal was to assess whether certain strains of E. coli have evolved toward adaptation and survival in wastewater. Raw sewage samples from different treatment plants were subjected to chlorine stress, and ∼59% of the surviving E. coli strains were found to contain a genetic insertion element (IS30) located within the uspC-flhDC intergenic region. The positional location of the IS30 element was not observed across a library of 845 E. coli isolates collected from various animal hosts or within GenBank or whole-genome reference databases for human and animal E. coli isolates (n = 1,177). Phylogenetics clustered the IS30 element-containing wastewater E. coli isolates into a distinct clade, and biomarker analysis revealed that these wastewater isolates contained a single nucleotide polymorphism (SNP) biomarker pattern that was specific for wastewater. These isolates belonged to phylogroup A, possessed generalized stress response (RpoS) activity, and carried the locus of heat resistance, features likely relevant to nonhost environmental survival. Isolates were screened for 28 virulence genes but carried only the fimH marker. Our data suggest that wastewater contains a naturalized resident population of E. coli We developed an endpoint PCR targeting the IS30 element within the uspC-flhDC intergenic region, and all raw sewage samples (n = 21) were positive for this marker. Conversely, the prevalence of this marker in E. coli-positive surface and groundwater samples was low (≤5%). This simple PCR assay may represent a convenient microbial source-tracking tool for identification of water samples affected by municipal wastewater.
  
  
  
  The results of this study demonstrate that some strains of E. coli appear to have evolved to become naturalized populations in the wastewater environment and possess a number of stress-related genetic elements likely important for survival in this nonhost environment. The presence of non-host-adapted strains in wastewater challenges our understanding of using E. coli as a microbial indicator of wastewater treatment performance, suggesting that the E. coli strains present in human and animal feces may be very different from those found in treated wastewater.
authors.affiliation: School of Public Health, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Shuai
authors.initials: S
authors.lastname: Zhi
authors.affiliation: School of Public Health, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Graham
authors.initials: G
authors.lastname: Banting
authors.affiliation: School of Public Health, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Qiaozhi
authors.initials: Q
authors.lastname: Li
authors.affiliation: Environment Canada, Burlington, Ontario, Canada.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Edge
authors.affiliation: Agriculture and Agri-Food Canada, London, Ontario, Canada.
authors.forename: Edward
authors.initials: E
authors.lastname: Topp
authors.affiliation: School of Public Health, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Mykola
authors.initials: M
authors.lastname: Sokurenko
authors.affiliation: School of Public Health, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Candis
authors.initials: C
authors.lastname: Scott
authors.affiliation: School of Public Health, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Shannon
authors.initials: S
authors.lastname: Braithwaite
authors.affiliation: Water Quality Services, Calgary, Alberta, Canada.
authors.forename: Norma J
authors.initials: NJ
authors.lastname: Ruecker
authors.affiliation: School of Public Health, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Yasui
authors.affiliation: Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada.
authors.forename: Tim
authors.initials: T
authors.lastname: McAllister
authors.affiliation: Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Linda
authors.initials: L
authors.lastname: Chui
authors.affiliation: School of Public Health, University of Alberta, Edmonton, Alberta, Canada Environmental Microbiology Program, Provincial Laboratory for Public Health, Edmonton, Alberta, Canada norman.neumann@albertahealthservices.ca.
authors.forename: Norman F
authors.initials: NF
authors.lastname: Neumann
mesh_terms: D000220:Adaptation, Biological; D015373:Bacterial Typing Techniques; D002713:Chlorine / Q000378:metabolism; D016000:Cluster Analysis; D004251:DNA Transposable Elements; D004202:Disinfectants / Q000378:metabolism; D004926:Escherichia coli / Q000145:classification* / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D005838:Genotype; D050296:Microbial Viability / Q000187:drug effects; D010802:Phylogeny; D020641:Polymorphism, Single Nucleotide; D013312:Stress, Physiological; D062065:Wastewater / Q000382:microbiology*; D018508:Water Purification
chemical_list: D002713:Chlorine; D004251:DNA Transposable Elements; D004202:Disinfectants; D062065:Wastewater