Author
|
Submitted to: Meeting Abstract
Publication Type: Abstract Only Publication Acceptance Date: 2/9/2012 Publication Date: 7/20/2012 Citation: Arthur, T.M. 2012. Characterization of E. coli O157:H7 strains associated with super-shedding cattle [abstract]. 2012 Beef Industry Safety Summit. Abstract No. 1. Interpretive Summary: Technical Abstract: Category: Preharvest pathogen reduction Objective: Cattle are the principal animal reservoir of E. coli O157:H7 and while the 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 and reduce the number of super-shedders in the cattle population in order to reduce E.coli O157:H7 transmission and beef carcass contamination. Several approaches for reducing E. coli O157:H7 colonization of the cattle gastrointestinal tract (GIT) have been experimentally tested, such as different feeding regimens, 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 into 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 project was designed to determine the contribution of E. coli O157:H7 strain type to development of super-shedding. Experimental process: Collected ˜ 4,500 swab samples from recto-anal junction of cattle in feedlots and at slaughter. All samples were processed for enumeration of E. coli O157:H7. Up to twenty E. coli O157:H7 strains from super-shedder samples (>100,000 CFU/swab) were characterized for genotype and phenotype. Analyses included phage typing, curli production, PFGE, stx typing, lineage determination, and comparative genomic fingerprinting. Key results: Super-shedder prevalence ranged from 0 to 4.5% between lots of commercial cattle at harvest. The overall average of super-shedders was 2%. Among the 103 super-shedder strains collected, no common genotype or phenotype was identified. How this information can be applied to industry: Based on these results, E. coli O157:H7 strain type has no influence on the achievement of super-shedding levels. Thus, strain type will no longer be a variable in super-shedder modeling and research efforts should be focused on the other potential determinants of super-shedding. Figure 1. PFGE and Phage typing for a subset of super-shedder strains. (Figure 1 also submitted). |
