2012 Annual Report
1a.Objectives (from AD-416):
Characterization of carriage rates and types of non-O157 Shiga toxin-producing E. coli (STEC) in cattle from different production systems at harvest and determine if regional variations in non-O157 STEC serogroups exist.
1b.Approach (from AD-416):
Sample collections will be made at numerous beef processing plants located across the United States in order to generate an extensive set of samples from the most relevant commercial sources. Targeted locations include California, Wisconsin, Nebraska, Texas, and Pennsylvania. Samples will consist of feces collected from colons during processing in order to have samples that reflect the production environment from which the animal originated. Processing plants that harvest fed cattle and cull cows and bulls from dairy and beef sources will be visited for sample collection. Feces will be screened before and after enrichment for the presence of STEC using a semi-quantitative molecular amplifiation method that detects the presence of Shiga toxin genes. This will not only identify cattle that carry STEC but also identifying those that carry higher loads and provide an estimate of the level of STEC that is shed. Samples found positive for STEC will be subjected to culture isolation for the Top-6 serotypes as well as all other STEC serotypes. All STEC isolates will be serotyped and characterized for genes that are known to contribute to increased virulence. These genes are Shiga toxin 1 (stx1); Shiga toxin 2 (stx2); intimin (eae); EHEC hemolysin (ehx); non-locus of enterocyte effacement effector (nle) products: nleB, nleC, nleF and nleG-2; subA (the prototype Subtilase cytotoxin); chuA, (an outer membrane heme uptake protein); irp2, (an iron repressible protein carried in a high-pathogenicity island); saa (associated with pathogenic STEC adherence); and other type III secreted effectors of EHEC (espK, and Ibe).
Although E. coli O157:H7 is currently the most widely recognized STEC, more than 100 other non-O157 Shiga toxin producing E. coli (STEC) serotypes have been implicated in cases of human diseases. Non-O157 STEC causes approximately 31,000 illnesses per year and these illnesses may probably be underestimated. The serotypes O26, O45, O103, O111, O121 and O145 have been increasingly isolated from clinical cases and outbreaks as well as from meat animals and environmental sources. These bacteria are presumed to have a ruminant host, however, some STEC serotypes appear to be more frequently found than others, and the effects of production system (e.g. feedlot, dairy, beef herd) may play an unrecognized role in their prevalence in beef trim and ground beef. The identification of bovine production systems populated by specific STEC serogroups, as well as the identification of any regional variations in serogroup prevalence can be exploited to assist the beef industry with managing the risk from these STEC. The experimental plan of these studies will test the hypotheses that cattle originating from different production systems will, at harvest, have different prevalences of STEC, and that the STEC they are colonized by will be unique to that production system, but no regionality of STEC or STEC serotypes will be observed. The project is currently in progress with planned sample collections and analysis scheduled to begin in order to have data collected by March of 2013.