PREVALENCE AND CHARACTERIZATION OF NON-O157 SHIGA TOXIN-PRODUCING ESCHERICHIA COLI ON CARCASSES IN COMMERCIAL BEEF CATTLE PROCESSING PLANTS

Authors: Arthur, Terrance; Gallagher, Genevieve; Rivera Betancourt, Mildred; Koohmaraie, Mohammad

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2002
Publication Date: 10/20/2002
Citation: Arthur, T.M., Gallagher, G.A., Rivera Betancourt, M., Koohmaraie, M. 2002. Prevalence and characterization of non-O157 Shiga toxin-producing Escherichia coli on carcasses in commercial beef cattle processing plants. Applied and Environmental Microbiology. 68(10):4847-4852.

Interpretive Summary: E. coli O157:H7 is one of the major bacterial pathogens associated with foodborne diseases. These bacteria are thought to cause human disease by their toxins called Shiga toxins. Although many foods have been associated with E. coli O157:H7 outbreaks, undercooked ground beef is the major source of these outbreaks. E. coli O157:H7 is only one of over 200 E. coli capable of causing human disease. E. coli O157:H7 and non-O157 E. coli are collectively referred to as Shiga toxin-producing E. coli (STEC). STEC are frequently found on the hides and in the feces of cattle. During the slaughter process, these bacteria can be transferred to the beef carcass and thus enter the food supply. In the summer months of the year STECs are most prevalent. In the summer of 1999, we sampled carcasses at four commercial beef plants to determine the prevalence of E. coli O157:H7 on beef during processing. This paper contains information obtained from the same samples but analyzed for non-O157 prevalence. Twenty- eight of the thirty lots of cattle included were positive for non-O157 STEC. Approximately half of the samples taken prior to carcass evisceration produced a non-O157 STEC isolate, whereas non-O157 STEC isolates were recovered from less than 10% of the samples taken after carcass processing. Pathogenic E. coli is far more common than previously thought. These results indicate that the current interventions used by beef processors are very effective in reducing the incidence of STEC, but as evidenced by frequent outbreaks, more needs to be done to manage the problem.

Technical Abstract: Beef carcass sponge samples collected from July to August, 1999, at four large processing plants were surveyed for presence of non-O157 Shiga toxin-producing Escherichia coli (STEC). Enriched samples were processed by colony hybridization and probed for stx1 and stx2. Twenty-eight of the 30 single-source lots (93%) surveyed included at least one sample containing non-O157 STEC. Of 334 preevisceration samples, 180 (54%) produced a non-O157 STEC isolate. Non-O157 STEC isolates were also recovered from 27 (8%) of 326 postprocessing samples. Altogether, 361 non-O157 STEC isolates, comprising 41 different O serogroups, were recovered. Sixteen (5%) preevisceration samples produced multiple isolates of different O serogroups. In two such samples, all three isolates were of different serogroups. O serogroups that previously have been associated with human disease accounted for 171 (47%) of 361 isolates. Forty isolates (11%) carried a combination of virulence factor genes (EHEC-hlyA, eae, and at least one stx gene) frequently associated with STEC strains causing severe human disease. However, only 12 (3%) of 361 isolates had this combination of virulence factors and were of an O serogroup previously associated with human disease. Combining previously reported data on O157 positive samples (Elder, Keen, Siragusa, Barkocy-Gallagher, Koohmaraie, and Laegreid, 2000, Proc. Natl. Acad. Sci. USA 97:2999-3003) with this data regarding non-O157 positive samples results in a total STEC prevalence of 72% and 10% in preevisceration and postprocessing beef carcass samples, respectively. Finally, these results indicate that current interventions used by the beef processing industry are highly effective, resulting in a seven-fold reduction in STEC prevalence.