Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2002
Publication Date: 1/1/2003
Citation: Jenkins, M., Hartel, P.G., Olexa, T.J., Stuedemann, J.A. 2003. Putative temporal variability of Escherichia coli ribotypes from yearling steers. Journal of Environmental Quality.
Interpretive Summary: The concern for maintaining watersheds with a minimum of fecal contamination as measured by the concentrations of fecal bacteria in surface waters has lead to various methods of identifying the host origin of standard indicator fecal organisms such as Escherichia coli and the Enterococci. If the host origin of fecal pollution can be identified, measures to attenuate or eliminate the source can be taken. Several genetic methods have been developed for identifying host origins of fecal bacteria, techniques referred to as 'microbial source tracking.' To identify microbes found in the environment, these techniques require the development of a data base profiling previously identified microbes. Profiling of E. coli is a source tracking technique that shows promise of being effective. The usefulness of these databases may, however, be affected by the genetic variability of the microbes. We investigated variability of E. coli from cattle. Results of this study indicated the presence of some key resident E. coli, but the majority of the E. coli were transient indicating substantial turnover. A host origin database including this variability may require constant updating unless both resident and transient genetic types are demonstrated to be distinct from other animal hosts.
Technical Abstract: Escherichia coli is a ubiquitous component of the intestinal microflora of warm blooded animals, and is used as a standard indicator organism of fecal pollution of surface waters. Ribotype profiling of E. coli is one of several genotypic methods that have been developed to determine host origin of fecal bacteria, and may be used to identify point and non-point sources of fecal contamination. Like other genotypic methods of source tracking, ribotyping relies on a host origin data base to identify environmental isolates. Little is known, however, about the temporal variability of ribotype profiles, and how temporal variability may affect the usefulness of a database. To determine the extent of temporal variability of Escherichia coli ribotypes, 451 E. coli were isolated from fecal samples taken from two herds of steers at four sampling times from October 1999 to July 2000. At each sampling time, fecal samples were taken from 6 steers. The first set of samples were taken from a herd at the end of the grazing season. The second through fourth set of samples were taken from a herd at the beginning, middle, and end of the grazing season on the same experimental fields. At a similarity index of 90%, 240 ribotypes were identified from a total of 451 E. coli isolates that were typed. Twenty ribotypes were shared across sampling times and between steers, and were considered putative resident ribotypes. Resident ribotypes comprised 32.6% of the total isolates. The majority of the ribotypes were transient and unique to each sampling time. These data indicate a substantial turnover of E. coli clones over the span of weeks between sampling, and a clonal diversity of 0.972, which may affect the utility of a host origin database.