Characterization of Escherichia coli harboring colibactin genes (clb) isolated from beef production and processing systems

Certain strains of Escherichia coli possess and express the toxin colibactin (Clb) which induces host mutations identical to the signature mutations of colorectal cancer (CRC) that lead to tumorigenic lesions. Since cattle are a known reservoir of several Enterobacteriaceae including E. coli, this study screened for clb amongst E. coli isolated from colons of cattle-at-harvest (entering beef processing facility; n = 1430), across the beef processing continuum (feedlot to finished subprimal beef; n = 232), and in ground beef (n = 1074). Results demonstrated that clb⁺ E. coli were present in cattle and beef. Prevalence of clb⁺ E. coli from colonic contents of cattle and ground beef was 18.3% and 5.5%, respectively. clb⁺ E. coli were found susceptible to commonly used meat processing interventions. Whole genome sequencing of 54 bovine and beef clb⁺ isolates showed clb occurred in diverse genetic backgrounds, most frequently in phylogroup B1 (70.4%), MLST 1079 (42.6%), and serogroup O49 (40.7%).