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United States Department of Agriculture

Agricultural Research Service


Location: Molecular Characterization of Foodborne Pathogens

Title: Assessment of enhanced surveillance for non-O157 STEC in beef in the USA

item Fratamico, Pina

Submitted to: Safefood VTEC Knowledge Network E-Newsletter
Publication Type: Popular Publication
Publication Acceptance Date: May 16, 2013
Publication Date: N/A

Technical Abstract: The USDA Food Safety and Inspection Service (FSIS) classified E. coli O157:H7 as an adulterant in raw ground beef and began a verification testing program for this pathogen in 1994 in response to a large outbreak associated with undercooked ground beef. It has become evident that non-O157 Shiga toxin-producing E. coli (STEC), particularly STEC serogroups O26, O45, O103, O111, O121, and O145 cause illnesses similar to those caused by E. coli O157:H7. These STEC serogroups, possibly with the exception of O45 are a common cause of illness in other countries, as well. Cattle are a major reservoir for STEC in the U.S.; however, as in other countries, sheep, goats, and swine, as well as domestic and wild animals are carriers of STEC. Outbreaks due to non-O157 STEC, including O26 and O111 have been associated with beef, although produce and other foods, as well as animal contact have also been linked to outbreaks (Table 1- Outbreaks that occurred from 2013-1992 shown in descending order). FoodNet surveillance data for culture-confirmed non-O157 infections from 2000 to 2010 showed that STEC serogroups O26, O45, O103, O111, O121, and O145 accounted for 83% of the isolates for which the O-group was identified (Gould et al., 2013), and these have been referred to as the “top six” non-O157 STEC. By 2010, the number of non-O157 STEC infections was similar to those caused by O157:H7. Similar to O157:H7, non-O157 STEC can be found as contaminants in beef, can cause severe illness, may not be destroyed by ordinary cooking, can cause illness even at low dose, and can spread by person-to-person contact. Therefore, in the U.S., the top six non-O157 STEC were declared as adulterants in beef trim, and FSIS verification testing for these pathogens began on June 4, 2012 in domestic and imported beef manufacturing trimmings. Establishments were also required to reassess their HACCP systems in response to non-O157 STEC positive test results. Expanding the regulatory testing program to other beef products is also being considered. The method used by the FSIS for non-O157 STEC testing can be found at Development of methods for detection of non-O157 STEC in beef and other foods has been a challenge, since they comprise a heterogeneous group of pathogens with differences in their virulence gene profiles and growth characteristics. Furthermore, since non-O157 STEC generally ferment sorbitol and are ß-glucuronidase positive, it is difficult to distinguish these pathogens from non-pathogenic E. coli on selective and differential agars that are currently available. The FSIS method includes multiplex PCR screening for the Shiga toxin (stx) gene(s) and for the locus of enterocyte effacement (LEE)-encoded eae (intimin protein) gene since most strains implicated in hemorrhagic colitis and hemolytic uremic syndrome carry eae. However, LEE-negative STEC, including serogroups O91, O113, and O104 can cause serious illness and outbreaks, and thus vigilant monitoring for emerging non-O157 STEC serogroups is critical. One additional concern is the false positive rate obtained from PCR screening for stx and eae since the target genes may not be found in a single cell, but each may come from different strains in the sample. Research in a number of laboratories throughout the world is focused on identifying additional STEC virulence markers associated with strains that cause severe disease and development of improved isolation methods. Since verification testing for the top six non-O157 STEC began only less than a year ago, the true impact of surveillance for these pathogens in beef by the FSIS is currently unknown. From January 1 to May 5, 2013, there were 1,034 raw ground beef component (RGBC) samples analyzed for non-O157 STEC from federal plants and 200 samples from imports ( The samples from federal plants consisted of 651 trim verification samples, 115 follow-up to raw ground beef positive at supplier samples, and 268 follow up to RGBC positive samples. There were 7/651 (1.08%) trim verification positive samples. Two samples were positive for STEC O26, four for O103, and one for O145. There were 2/268 (0.75%) samples positive for STEC O103 with follow-up to RGBC positive sample testing. For E. coli O157:H7, 1/682 (0.15%) of the trim verification samples were positive, while there were 2/291 (0.69%) and 1/209 (0.48%) follow up to RGBC positive and verification/follow-up samples positive, respectively. Testing results for veal and mixed source (beef and veal) samples are also available at the above FSIS website. From June 4, 2012 to December 31, 2012, 2119 RGBC samples from federal plants and 249 import samples were tested, and results are available at Gould, L.H., Mody, R.K., Ong, K.L., Clogher, P., Cronquist, A.B., Graman, K.N. et al. 2013. Increased recognition of non-O157 Shiga toxin-producing Escherichia coli infections in the United States during 2000-2010: epidemiologic features and comparison with E. coli O157 infections. Foodborne Pathog. Dis. 10:1-8.

Last Modified: 4/23/2014
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