Abstract: Objectives: The aims of this study were to isolate and identify non-O157 Escherichia coli strains from bovine fecal and beef samples and to detect the virulence genes of the isolates, in order to understand the contamination status of non-O157 E. coli. Methods: After selective enrichment of beef and fecal samples by the USDA method with slight modifications, multiplex PCR was used as a prescreening method to determine the O-groups (O157, O121, O111, O103 and O26). The enriched positive sample was streaked for isolation and purification on chromogenic rainbow agar, and tested for the O-groups. The flagellar antigens were identified by PCR-restriction fragment length polymorphism (PCR-RFLP) and the positive isolates were further verified by means of serum agglutination test. The virulence genes (stx1, stx2, eae, and hly) of the positive isolates were detected by PCR. Results: A total of 153 fecal samples and 49 beef samples were collected. Overall, 40 samples were tested positive for one O-group, and the detection rate in feces was higher than that in beef, 19.3% of which were tested positive for non-O157, and 0.50% positive for O157. After purification, 30 positive isolates were identified. O26 was detected most frequently, accounting for 73.3% of the total isolates, followed by O26, O121, O103, and O157, accounted for 73.3%, 16.7%, 6.7% and 3.3%, respectively. The results of virulence gene analysis showed that two strains of O26:H11 were isolated from beef, one being positive for stx1 and hly and the other being positive for hly. One strain of O26:H11 harboring the hly gene was obtained from feces. Therefore, 10.0% of the 30 strains were positive for virulence genes, and 3.4% were non-O157 STEC. Conclusion: The contamination rate of non-O157 E. coli, especially O26:H11, in feces and beef was significantly higher than that of O157. Shiga toxin-producing E. coli was even detected in the beef samples, which suggested that there is a potential risk of non-O157 E. coli contamination in the retail beef market. The detection and monitoring of non-O157 E. coli should be strengthened in China.

Key words: non-O157 E. coli, feces, beef, contamination status, virulence genes