Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 2, 2004
Publication Date: May 1, 2005
Citation: Higgins, J.A., Karns, J.S., Shelton, D.R., Belt, K.T., Anelli, J. 2005. Tir- and stx- positive E. coli in stream waters in a metropolitan area. Applied and Environmental Microbiology. 71:2511-2519. Interpretive Summary: A team of USDA-ARS, USDA-Forest Service, and Center for Urban Environmental Research and Education (CUERE) researchers has been studying a variety of streams in the metropolitan Baltimore, DC area,for the presence of pathogenic E. coli bacteria (EPEC). The streams chosen for sampling represent forested, row crop agriculture, suburban, and urban watersheds. Detection of EPEC was accomplished by growing coliform bacteria from the water samples and using a polymerase chain reaction (PCR) assay to detect the tir gene (one important in pathogenesis in the mammalian intestinal tract) in the EPEC genome. A majority of the 782 samples assayed (442, 56%) were positive for the presence of EPEC. Analysis of the DNA sequence from 40 of the tir positive samples indicated that the EPEC had a high degree of similarity to established, disease-causing serotypes of E. coli. Comparison of EPEC prevalence between stream sites indicated that urban streams were more likely to contain EPEC than forested or agricultural-associated streams. Based on these results, the scientific team members believe that EPEC may be a common component of the gastrointestinal tract flora of the human population in the metro Baltimore, MD area.
Technical Abstract: Enteropathogenic Escherichia coli (EPEC) are a significant cause of diarrheal disease among infants and children in both the developing and developed worlds. A hallmark of EPEC pathogenesis is the ability to form attachment/effacing lesions on the intestinal epithelia, a process mediated by the translocated intimin receptor (Tir), a protein coded for by the extrachromosomal tir gene. While the mechanisms of EPEC virulence are comparatively well defined, less is known regarding its presence in the environment. From April, 2002 to August, 2003 we conducted weekly surveys of streams in the metropolitan Baltimore, Maryland area for the prevalence of EPEC using a PCR assay targeting a ~ 500 bp region of the tir gene. Coliforms testing positive for the presence of the tir gene were cultured from 442 of 782 samples (56%), with a greater prevalence associated with urban, polluted streams as compared to suburban and forested watershed streams. Sequence analysis of the tir amplicon, as well as the entire tir gene from three isolates, indicated that the EPEC present in the stream waters has a high degree of sequence homology with E. coli O157 and E. coli O26 serotypes. Our data indicate that EPEC are continually deposited into a variety of stream habitats, and suggest that this organism may be a permanent member of the gastrointestinal microflora of humans and animals in the metropolitan Baltimore area.