| Escherichia coli
The American Academy of Microbiology has noted that “there is a critical need to identify the ways pathogens enter the farm environment, how they persist and spread in the environments, what dosage of organisms cause disease in humans, and whether on-farm acquisition of these pathogens leads to increased risks of foodborne disease in humans.” Currently, however, there is little routine pathogen surveillance in livestock prior to slaughter, and the ecology and epidemiology of these organisms in the agriculture environment is largely a black box. What is known is that the pathogen makeup of a given farm environment is determined by a complex interplay of factors, including animal density, the use of contaminated livestock feed or water, climate, unsanitary handling of water and wastes, contact between infected and uninfected animals, and an animal’s own microflora. While pathogens are ubiquitous in the agricultural environment and can never be completely eliminated, they can be understood and the burden of those most troublesome to humans can be reduced.
Escherichia coli is a bacterium which frequently causes food poisoning in humans due to consumption of contaminated meat. One serotype of this bacterium, O157:H7, is estimated to cause 73,000 cases of illness per year in the United States. Disease can range from watery and bloody diarrhea to the life-threatening hemolytic uremic syndrome. One virulence factor involved in the development of disease is the Shiga toxin, encoded by the phage-carried stx gene. Strains of E. coli which carry this toxin are referred to as Stx-producing E. coli (STEC). This can be found in two forms: Stx1 and Stx2. Severe disease has most often been linked to the presence of Stx2. Altogether, STEC cause an estimated 110,000 illnesses and 90 deaths annually.
Though severe disease has been most often associated with STEC serotype O157:H7, many other serotypes have been shown to carry the gene as well. In a recent study of STEC isolated from humans, cattle, sheep, and food in Spain, 581 out of 722 (81%) STEC isolates were from serotypes other than O157:H7. A summary of the literature shows that at least 250 non-O157 STEC serotypes have been reported, and more than 100 of them have been associated with human illness. Most commonly found in the United States to date have been serotypes O26, O111, O103, O121, O45, and O145. Several recent human cases involving non-O157 E. coli isolates have been recently confirmed by the University Hygienic Laboratory, but it is not known whether the serotypes of these isolates correlate with the serotypes of STEC isolates commonly found in the agricultural environment in Iowa. Our current research seeks to address this question. |
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