Attachment of enterohemorrhagic Escherichia coli to the surface of beef and a culture medium

This study was undertaken to evaluate the role of curli in the attachment of Enterohemorrhagic Escherichia coli (EHEC) to the surface of beef and a culture medium. Beef from an eye round roast and beef salami was sliced and cut into 3-mm thick, 4.6-cm diameter circles. The beef was exposed for different lengths of time to six EHEC cultures: the curli-expressing and noncurli-expressing variants of Escherichia coli 5-11 (O157:H7) and E. coli 7-52 (O103:1-12) as well as a wild-type curli-expressing strain E. coli 7-57 (111:H-) and a noncurli-expressing strain E. coli 5-9 (O157:1-17). The beef slices were rinsed following the exposure, and the EHEC cells that attached to the surfaces of the beef were enumerated. Two replications of each experiment were performed and the data generated was analysed statistically based on a 95% confidence level. In separate experiments, the EHEC cultures were grown on Luria-Bertani no salt agar at 28 degrees C for 72 h and the ease of removing the attached EHEC cells from the surface of the agar was evaluated. The results indicated that the curli-expressing cells had a firmer association with, and was more difficult to remove from, the surface of the agar in comparison to the noncurli-expressing cells. Cells of certain curli-expressing strains/variants of EHEC attached more efficiently under appropriate conditions, to the beef surface than did the cells of noncurli-expressing strains/variants. The differences in attachment by curliated and noncurliated cells were, however, minor. The study revealed the difficulties of studying EHEC attachment on biotic surfaces such as beef, suggesting that a better methodology is needed for more accurate evaluation of EHEC association with their contact surfaces. (c) 2005 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.