Prevalence of non-O157 STEC in live animals and at various steps during harvest

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

Submitted to: American Meat Science Association Conference Reciprocal Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/29/2002
Publication Date: 6/16/2002
Citation: Arthur, T.M., Gallagher, G.A., Rivera-Betancourt, M., Koohmaraie, M. 2002. Prevalance of non-0157 STEC in live animals and at various steps during harvest. Proceedings of 55th American Meat Science Association Reciprocal Meat Conference. p.21-27.

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 cause 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). In the summer months of the year STEC are most prevalent. 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. It is believed that some non-O157 STEC are unable to cause disease even though they can produce the Shiga toxin. There is no way to determine which non-O157 STEC can and cannot cause disease at this time, although work is ongoing to find traits used by these organisms that allow them to cause disease. Few studies have looked at non-O157 STEC contamination on beef carcasses. This paper summarizes the results obtained from such studies. A study done in the United States found that 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. Studies from France and Hong Kong showed similar numbers of carcasses were contaminated with STEC after 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: Shiga toxin-producing Escherichia coli (STEC) have been implicated as the causative agents in several human diseases ranging from mild diarrhea to very severe and life threatening conditions such as hemolytic uremic syndrome (HUS). The STEC strain most frequently associated with clinical disease in the U.S. is serotype O157:H7. However, several other serotypes (O26, O103, O111, O113, and O121) are commonly associated with severe disease outbreaks and in some countries are isolated from clinical cases more often than O157. At the present time, several clinical laboratories in the U.S. only screen for E. coli O157, leaving non-O157 STEC-associated diseases underreported. Cattle are considered the primary reservoir for both O157 and non-O157 STEC. Over 200 STEC serotypes have been isolated from cattle. Several human infections have been linked to STEC present in undercooked ground beef. STEC contamination in ground beef is presumably due to contamination of the carcass at the time of processing. It is believed that not all non-O157 STEC are capable of causing disease. However, there is not sufficient data to identify those STEC that can and cannot cause disease. Attempts to associate human disease with various types of STEC based on the possession of certain virulence factors have been made. At this time, strains carrying the combination of virulence factors (Shiga toxin, intimin, and EHEC hemolysin) seem to be the most virulent. When sampling beef carcasses for non-O157 STEC after antimicrobial interventions had been used, studies from the U.S, France and Hong Kong have shown approximately the same prevalence levels (8%-13%). The U.S. study provided the only report of carcass contamination levels before antimicrobial interventions were applied. Of 334 preevisceration samples, 180 (54%) produced a non-O157 STEC isolate. This study and others show that the majority of bovine-related STEC usually harbor stx1 as opposed to stx2 and rarely carry the accessory virulence factors intimin and EHEC-hemolysin. However, STEC strains having the same serotypes and virulence factor profiles as strains causing human disease can be found in the bovine-related STEC population.