Characterization of E. coli O157:H7 Strains Associated With High Shedding Events

<p>E. coli O157:H7 is an important foodborne pathogen which poses a serious public health concern and financial burden. Cattle are the principal animal reservoir of E. coli O157:H7 and while rumen has been shown to harbor this pathogen on occasion, the rectal-anal junction (RAJ) has been shown to be the predominant colonization site. Once colonized, an animal can shed various amounts of E. coli O157:H7 in the feces. Super-shedders (RAJ colonized at greater than 104 CFU/g) have a significant effect on contamination of the cattle hide and carcass, and are reported to be responsible for increased transmission of E. coli O157:H7 within production environments. Therefore it is critical to identify, minimize or eliminate super-shedders from the cattle population in order to reduce E. coli O157:H7 transmission and beef carcass contamination for enhancing food safety.</p>
<p>Several approaches for reducing E. coli O157:H7 colonization of the cattle gastrointestinal tract (GIT) have been experimentally tested, such as different feeding regiments, feed additives, probiotics, and vaccines. To date, most of these studies have either been inconclusive, or treatments have only modestly affected colonization. More importantly, none of these interventions have tested whether the prevalence of super-shedding is reduced in cattle populations. This is significant, as modeling studies suggest that possibly as high as 96% of E. coli O157:H7 isolates originate from super-shedding animals. It is evident that a more thorough understanding of the factors promoting super-shedding is needed before we can design effective evidence-based methods of reducing transmission of STEC from cattle populations to the food supply. The super-shedding phenomenon can be broken down in to three principle components: (1) phylogenetic lineage of the colonizing O157:H7 strain, (2) the community composition of the microflora of the rectal-anal junction, and (3) the innate and adaptive immune response of the host. This proposal is designed to determine the contribution of strain type in super-shedding.</p>