Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/25/2003
Publication Date: 5/20/2003
Citation: Higgins, J.A., Karns, J.S., Shelton, D.R., Belt, K. 2003. Prevalence and molecular characterization of enteropathogenic E. coli in streams along an urban-rural gradient in the Baltimore, Maryland Metropolitan Area [abstract]. American Society for Microbiology Annual Meeting. p. 125. Interpretive Summary:
Technical Abstract: We are interested in learning if enteropathogenic E. coli (EPEC) are prevalent in stream water samples taken from urban and suburban stations in Baltimore, MD, and if their occurrence might be associated with agricultural runoff drainage. Beginning in March, 2002, water samples were obtained at least biweekly from eight core stations along an urban-rural gradient in the metropolitan Baltimore area. These stations were located at hydrologic research catchments in the Gwynns Falls and Baismans Run watersheds, sites of the Baltimore Ecosystem Study, a long-term ecological research (LTER) project. Samples were also taken from more than twenty other locations in the Baltimore and metro Washington, DC areas on a less regular basis. Samples (100 ml) were filtered and subjected to overnight culture for coliforms using minimal lactose broth, and DNA extracted from the cultures was subjected to PCR for a 500+ bp fragment of the tir gene. When assayed against a panel of n = 46 strains of pathogenic E. coli, these primers amplified DNA from all O157:H7 strains tested (n = 35) as well as from O26:H11, O103:H2, and O26:K60:H11 strains, but not from strains O48:H21, O137:H41, and O139. As of early December, 2002, 267 of 406 samples (65%) were PCR-positive. EPEC constituted from < 0.01 % to as much as 10% of the total E. coli population in the enriched cultures, based on quantitative real time PCR for the lac and tir genes. Samples obtained from streams receiving agricultural runoff were no more likely to test positive than those receiving street runoff, and positives were distributed across a variety of urban land-use types and catchment scales (less than 100 ha. to 17,500 ha). Analysis of tir fragment sequence data from 23 different PCR amplicons indicates that the stream-derived E. coli form two major clades, with strains similar to E. coli O157:H7 segregating in one clade and strains similar to E. coli O26:H11 in the other clade. Our results indicate that EPEC are prevalent in urban and suburban streams and this prevalence is independent of receipt of agricultural runoff.