|AHMED, RAFIQ - Public Health Agency Of Canada|
|CHASE-TOPPING, MARGO - University Of Edinburgh|
|Kalchayanand, Norasak - Nor|
|Bono, James - Jim|
Submitted to: American Society for Microbiology General Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/20/2013
Publication Date: 5/20/2013
Citation: Arthur, T.M., Ahmed, R., Chase-Topping, M., Kalchayanand, N., Schmidt, J.W., Bono, J.L. 2013. Characterization of E. coli O157:H7 strains isolated from super-shedding cattle. American Society for Microbiology General Meeting. Poster No. 1707, p 171.
Technical Abstract: Background: Recent reports have indicated that a small sub-population of cattle shedding high levels of Escherichia coli O157:H7 is the main source for transmission of the pathogen between animals. Cattle achieving a fecal shedding status of 104 CFU of E. coli O157:H7/gram are now referred to as super-shedders. Modeling studies have indicated that if super-shedding could be prevented, the bovine-colonization cycle of this foodborne pathogen could be broken, resulting in a dramatically lower prevalence of the organism in cattle environments and a subsequent decrease in the food safety risk of beef products in the human food supply. The work described herein was designed to identify E. coli O157:H7 strain-specific traits required for super-shedding. Materials: Over 5,000 fecal samples were collected from cattle at feedlots or during processing. Super-shedder isolates were characterized by pulsed field gel electrophoresis, phage typing, LSPA6 lineage analysis, Stx-associated bacteriophage insertion (SBI) site determination, as well as variant analysis of Shiga toxin, tir, and antiterminator Q genes. The data were analyzed in a multivariate analysis using nonmetric multidimensional scaling. Results: Super-shedders constituted 2.3% of the bovine population tested. Isolates representing 52 unique PFGE patterns, 18 phage types, and 12 SBI clusters were obtained from super-shedding cattle. When compared to the top 10 genotypes from the PulseNet database, the two largest genotype clusters among the super-shedder isolates matched the two most common human illness PFGE genotypes. The E. coli O157:H7 super-shedder strains were spread among the three LSPA6 lineages approximately equally. In addition, the strains harbored the tirT allele more often (71%) than the tirA allele (29%). Conclusion: The results obtained indicate that there is no clustering to E. coli O157:H7 genotypes responsible for super-shedding. It should be noted that while being isolated directly from cattle, this strain set tended to have higher frequencies of traits associated with human clinical isolates than previously collected bovine isolates with respect to lineage, tir allele, and Q type, but no exclusive genotype was identified that was common to all super-shedder isolates.