Location: Meat Safety & Quality Research
Title: Characterization of Escherichia coli 0157:H7 strains isolated from supershedding cattle Authors
|Ahmed, Rafiq -|
|Chase-Topping, Margo -|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 30, 2013
Publication Date: July 1, 2013
Repository URL: http://handle.nal.usda.gov/10113/57344
Citation: Arthur, T.M., Ahmed, R., Chase-Topping, M., Kalchayanand, N., Schmidt, J.W., Bono, J.L. 2013. Characterization of Escherichia coli 0157:H7 strains isolated from supershedding cattle. Applied and Environmental Microbiology. 79(14):4294-4303. Interpretive Summary: Recent reports have indicated that a small proportion of cattle shedding high levels of the foodborne bacterial pathogen Escherichia coli O157:H7 is the main source for transmission of the pathogen between animals. Cattle excreting very high levels of this bacterium are now referred to as super-shedders. Previous studies have indicated that if super-shedding could be prevented, the bovine-colonization cycle of this 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 strain-specific traits required for super-shedding. Over 5,000 fecal samples were collected from cattle at feedlots or during processing. Super-shedders constituted 2.0% of the bovine population tested. Super-shedder isolates were characterized for several genetic traits. Through a diverse sampling scheme, isolates representing multiple trait combinations were obtained from super-shedding cattle, indicating there is no particular E. coli O157:H7 strain responsible for super-shedding.
Technical Abstract: Previous reports have indicated that a small proportion of cattle shedding high levels of Escherichia coli O157:H7 is the main source for transmission of this organism between animals. Cattle achieving a fecal shedding status of 10**4 CFU of E. coli O157: H7/gram or greater are now referred to as supershedders. The aim of this study was to investigate the contribution of E. coli O157: 7 strain type to supershedding and to determine if supershedding was restricted to a specific set of E. coli O157:H7 strains. Fecal swabs (n=5,086) were collected from cattle at feedlots or during harvest. Supershedders constituted 2.0% of the bovine population tested. Supershedder isolates were characterized by pulsed-field gel electrophoresis (PFGE), phage typing, lineage-specific polymorphism assay (LSPA), Stx-associated bacteriophage insertion (SBI) site determination, and variant analysis of Shiga toxin, tir, and antiterminator Q genes. Isolates representing 52 unique PFGE patterns, 19 phage types, and 12 SBI clusters were obtained from supershedding cattle, indicating that there is no clustering to E. coli O157:H7 genotypes responsible for supershedding. 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 and tir allele, but not for SBI cluster and Q type. We conclude that no exclusive genotype was identified that was common to all supershedder isolates.