2013 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).
This project has been completed. Cattle are considered a primary reservoir of Shiga-toxin producing Escherichia coli that cause enterohemorrhagic disease (EHEC) in humans and contaminated beef products are considered one vehicle of transmission. However, cattle entering the beef harvest process originate from very different production systems: feedlots, dairies, and beef breeding herds. This study collected feces from 1,042 fed cattle, 1,062 cull dairy cattle and 1,019 cull beef cattle at harvest in five regions of the United States. Results showed that the prevalence of Shiga-toxin (stx) genes in the feces of cattle was statistically different between cull dairy (91%) and cull beef and fed cattle (99%). When additional genetic factors predictive of EHEC were considered, the prevalence of EHEC was statistically different between all 3 groups of cattle (fed = 77.2%, cull dairy = 47.7%, and cull beef = 38.7%). The presence of the top 6 non-O157 EHEC serotypes (O26, O45, O103, O111, O121 and O145) was determined using molecular analysis and physical culture isolation. The most common identified and isolated were EHEC-O26 in 17% of eastern dairy cattle and EHEC-O103 in 32% of northern fed cattle. EHEC-O45 was widely prevalent in about 20% of central fed cattle, eastern fed and cull dairy cattle, and northern fed and cull beef cattle, whereas EHEC-O121 was the least frequent (<1%) but identified in all regions except the north and identified in all cattle types at least once. The results of this study will assist the meat industry, regulators and public health officers by identifying the particular EHEC serogroups that are more commonly associated with the different types of cattle, allowing more targeted and efficient tracking, testing and intervention use.