Evaluation of cattle for naturally colonized Shiga toxin-producing Escherichia coli requires combinatorial strategies

Authors: Kudva, Indira; OOSTHUYSEN, EBEN - New Mexico State University; Wheeler, Bryan; LOEST, CLINT - New Mexico State University

Submitted to: International Journal of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2021
Publication Date: 4/1/2021
Publication URL: https://handle.nal.usda.gov/10113/7709434
Citation: Kudva, I.T., Oosthuysen, E.R., Wheeler, B.K., Loest, C.A. 2021. Evaluation of cattle for naturally colonized Shiga toxin-producing Escherichia coli requires combinatorial strategies. International Journal of Microbiology. 2021. Article 6673202. https://doi.org/10.1155/2021/6673202.
DOI: https://doi.org/10.1155/2021/6673202

Interpretive Summary: Seven major serotypes of Shiga toxin-producing Escherichia coli (STEC; O157, O26, O45, O103, O111, O145, O121 ) are responsible for 265,000 cases of food-borne illness in the United States each year. Cattle are the primary reservoirs for STEC. In this study, we evaluated cattle in a feedlot in New Mexico for the presence of STEC using a combination of culture, PCR and a cell toxicity assay to evaluate toxin production by the STEC. Of the 59 cattle tested, 19% were positive for viable STEC and the main STEC serotype isolated was O103. There has been an increase in O103 serotype related outbreaks in the US since 2010, involving contaminated venison, ground beef, bison and sprouts which makes our observation epidemiologically relevant. In addition, our results show that while PCR using fecal extracts may be used to screen animals for STEC it does not reflect ongoing colonization of cattle with live STEC whose spread into the food chain is more critical for human infection.

Technical Abstract: Shiga toxin-producing Escherichia coli (STEC) serotypes O157, O26, O103, O111, O121, O145 and O45 are designated as food adulterants by the U.S. Department of Agriculture-Food Safety and Inspection Service. Cattle are the primary reservoir of these human pathogens. In this study, 59 Angus crossbred heifers were tested for the seven STEC serotypes. At the time of fecal sampling the animals were approximately 2 years-old and weighed 1000 to 1200 lbs. The animals were co-mingled and housed in single, soil surface pens. The diet comprised of 37 percent ground alfalfa hay, 25 percent ground Sudan hay and 38 percent ground corn supplemented with trace minerals and rumensin with ad libitum access to water. Standard direct and enrichment fecal culture protocols were used to isolate the seven STEC serotypes. Serological and PCR tests were used to serotype the isolates. Viable non-O157 STEC were isolated from 11/59 (19 percent) animals tested. The predominant non-O157 STEC serotype identified was O103 followed by O26 which was co-isolated with other STEC; interestingly no O157 was isolated from any of the samples tested. Cytopathic effects (CPE) were observed with extracts from 58/59 fecal samples in Vero cell cytotoxicity assays, of which, 95 percent (55/58) were neutralized with anti-Shiga toxin (Stx) 1 and/or anti- Stx2 antisera. Stx-related CPE could be associated with isolation of STEC serotypes O103 and O26, and/or, amplification of toxin genes from feces by PCR suggesting that recent colonization or other STEC serotypes may have contributed to the presence of these toxins. Non-Stx factors may have been the cause for the CPE observed with 5 percent (3/58) fecal extracts that were not neutralized with the anti-Stx antisera. This study highlights a combination of methods needed to isolate viable STEC that pose a greater food safety concern from naturally colonized cattle, compared to non-viable STEC targeted by fecal PCR and cytotoxicity assays.