Title: Waterborne Dissemination of Escherichia coli O157:H7
Dr. Charles W. Kaspar
University of Wisconsin
Madison, WI
Organization: Washington State University
FDA Grant FD-U-001616-02 (September 1998 - September 2000)
Background:
Escherichia coli O157:H7 is epidemiologically the most significant member of the enterohemorrhagic E. coli. Each year in the United States, E. coli O157:H7 is estimated to cause between 7,000 and 20,000 cases, 150 to 300 deaths, at a cost of $230 - $600 million in medical and productivity costs. Despite advances in detection methodologies and our understanding of the virulence, comparatively little is known about the dissemination of E. coli O157:H7 between farms and cattle. An understanding of the dissemination and persistence of E. coli O157:H7 among cattle is particularly important when considering that ground beef is the primary food associated with outbreaks involving this human pathogen. The long-term goals of these studies were to further define the on-farm ecology of E. coli O157:H7 in order to understand and ultimately control the dissemination of this important foodborne pathogen in cattle. The specific objectives of this project were to: (1) replace a large-volume (i.e. 500 gallon) water tank with a small volume (i.e., 30 gallon) high-turnover water trough and determine if the shedding of serotype O157:H7 strains in weaned heifers is influenced, (2) incorporate high-turnover water troughs into a second pen housing older heifers and determine if the shedding of E. coli O157:H7 is impacted, (3) determine the herd prevalence of E. coli O157:H7 following installation of high-turnover water troughs, and (4) conduct molecular subtyping of O157:H7 isolates to determine the homogeneity of the isolates in order to assess whether there was a common source or if new strains were introduced into the herd both before and after installation of the high-turnover water troughs. This project was designed to potentially provide valuable information on waterborne transmission in cattle of this important human pathogen and provide a potential point for on-farm control.
The four specific aims of the research in this grant proposal included:
1. Determine the effect of replacement of a large volume water tank with a small volume high turnover on the shedding of E. coli O157:H7 in weaned heifers.
Results: The prevalence of E coli O157:H7 could be reduced in weaned calves by eliminating water tanks as a source or vehicle for transmission of the pathogen.
2. Determine the effect of changing tank type on prevalence of the pathogen in older heifers.
Results: The prevalence of E. coli in these animals was not affected by changing the water tank. This result is most likely explained by the fact that the new tank was installed in a location that allowed fecal contamination of the water.
3. Determine the herd prevalence of E. coli O157:H7 after replacement of the water tanks.
Results: The whole herd prevalence remained at 2%. This shedding rate was consistent with previous prevalence data for this herd. The data suggested that the replacement heifers being introduced into the milking herd were the source of the organism.
4. Conduct molecular subtyping of isolates recovered throughout the survey to identify their source.
Results: The PFGE profiles suggested that the strains isolated on the farm were highly related and in is most probable that the strains shed by the milking cows came from the replacement heifers.
Overall Conclusions
These finding are in agreement with the failure of the new water tanks to decrease the prevalence of E. coli O157:H7. These data confirm the importance of water as an important vehicle of E. coli O157:H7 dissemination in cattle and indicate that the type of water delivery device may be an on-farm control point for this important human pathogen.
Further reading:
Faith, N.G., J.A. Shere, et.al., 1996. Prevalence and Clonal Nature of Escherichia coli O157:H7 on Dairy Farms in Wisconsin. Appl. Environ. Microbiol. 62:1519-1525.
Shere, J.A., K.J. Bartlett, and C.W. Kaspar. 1998. Longitudinal Study of Escherichia coli O157:H7 Dissemination on Four Dairy Farms in Wisconsin. Appl. Environ. Microbiol. 64:1390-1399.
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