Shiga toxin-producing Escherichia coli (STEC) are major foodborne human pathogens that cause mild to hemorrhagic colitis, which could lead to complications of hemolytic uremic syndrome. Seven serogroups, O26, O45, O103, O111, O121, O145 and O157, account for the majority of the STEC illnesses in the US. Shiga toxins 1 and 2, encoded by stx 1 and stx 2, respectively, and intimin, encoded by eae gene, are major virulence factors. Our objectives were to use culture method to isolate and identify major and minor serogroups of STEC in finisher pig feces. Shiga toxin genes were subtyped to assess public health implications of STEC. Fecal samples (n=598) from finisher pigs, collected from 10 pig flows, were enriched in E. coli broth and tested for stx 1, stx 2, and eae by PCR assay. Samples positive for stx 1 or stx 2 gene were subjected to culture methods, with or without immunomagnetic separation and plating on selective or nonselective media, for isolation and identification of stx- positive serogroups. The culture method yielded a total of 178 strains belonging to 23 serogroups and the three predominant serogroups isolated were O8, O86, and O121. The 178 STEC strains included 26 with stx 1a and 152 strains with stx 2e subtypes. Strains with stx 1a, particularly in association with eae , have the potential to cause severe human infections. All stx 2 strains carried stx 2e, a subtype that causes edema disease in swine, but rarely involved in human infections. A number of strains were also positive for genes that encode for enterotoxins, which are involved in neonatal and postweaning diarrhea in swine. In conclusion, our study showed that healthy finisher pigs harbored and shed a number of serogroups of E. coli carrying virulence genes involved in neonatal diarrhea, postweaning diarrhea, and edema disease, but prevalence of STEC of public health importance was low.
Remfry S, Amachawadi R, Shi X, Bai J, Tokach M, Dritz S, Goodband R, DeRouchey J, Woodworth J, Nagaraja T. Shiga toxin-producing Escherichiacoli in feces of finisher pigs: isolation, identification and public health implications of major and minor serogroups. J Food Prot. 2020 Oct. https://doi.org/10.4315/jfp-20-329