|Rivera Betancourt, Mildred|
Submitted to: Journal of Food Protection
Publication Type: Research Notes
Publication Acceptance Date: December 5, 2003
Publication Date: May 20, 2004
Citation: Gallagher, G.A., Arthur, T.M., Rivera Betancourt, M., Nou, X., Shackelford, S.D., Wheeler, T.L., Koohmaraie, M. 2004. Characterization of O157:H7 and other Escherichia coli isolates recovered from cattle hides, feces, and carcasses. Journal of Food Protection. 67(5):993-998. Interpretive Summary: E. coli O157:H7 is a foodborne pathogen of concern to the beef industry, since it has been implicated in illness outbreaks associated with ground beef. The O157 and H7 molecules are used as markers to identify these strains. Toxins and other molecules that are not directly associated with the O157 and H7 markers are required to cause disease. Previously, we recovered a large number of E. coli O157:H7 isolates from samples collected during beef processing. Now we have surveyed these isolates for toxin genes. Most of the time (99.6%), the E. coli O157:H7 isolates carried toxin genes and were therefore capable of causing disease. There was some variation in the types of toxin genes they carried, i.e., genes for toxin type 1, toxin type 2, or both. Problems in identifying E. coli O157:H7 included: (1) rare isolates that were E. coli O157:H7 based on their genes but did not make the O157 or H7 molecule at the time of testing and (2) more common isolates that were able to make the O157 molecule but not the H7 molecule and did have toxin genes or other genes associated with E. coli O157:H7. These results emphasize the difficulty in accurately identifying E. coli 0157:H7 when testing for it.
Technical Abstract: We previously reported the seasonal prevalence of stx+ Escherichia coli O157:H7 in feces and on hides and carcasses of cattle at processing (G. A. Barkocy-Gallagher, T. M. Arthur, M. Rivera-Betancourt, X. Nou, S. D. Shackelford, T. L. Wheeler, and M. Koohmaraie, J. Food Prot., accepted 6-13-03). A total of 1,208 samples were identified as positive. We now report the incidence of: (i) eae-O157, hlyA, stx1, and stx2 in the recovered isolates and (ii) presumptive rough and presumptive nonmotile isolates. Overall, 1,697 recovered isolates were examined that were considered to be O157:H7 strains based on ELISA and/or PCR for rfbE-O157 and fliC-H7. Seven O157:H7 isolates (0.4%) lacked stx genes although they carried eae and hlyA. All but one of the isolates carried both eae and hlyA. Twenty-three of the 25 O157:H7 isolates carrying stx1 and not stx2 were recovered in the summer. More than one-half of the isolates (64% when one isolate per sample was considered) carried both stx1 and stx2. E. coli O157:H7 harboring both stx1 and stx2 were more prevalent on hides in the fall (79% of the fall hide isolates) and winter (84% of the winter hide isolates) than in the spring (53%) and summer (59%). A similar but not statistically significant trend occurred among isolates recovered from pre-evisceration carcasses. Fifteen presumptive rough and 117 presumptive nonmotile stx+ O157:H7 isolates were recovered. Ten of the presumptive rough isolates were recovered in the summer and 95 of the presumptive nonmotile isolates were recovered in the fall. Close to one-half of the false-positive isolates (175 of 363; 48%) were O157+ H7- and lacked eae-O157, hlyA, and stx. These data suggest that in beef processing samples: (i) there are minor seasonal variations in the prevalence of stx genes among E. coli O157:H7 isolates, (ii) presumptive rough and presumptive nonmotile stx+ O157:H7 isolates are present, (iii) E. coli O157:H7 isolates lacking stx genes are rare, and (iv) O157+ H7- isolates lacking stx genes can result in many false-positives.