Escherichia coli O157 in the rectoanal mucosal region of cattle.

The rectoanal junction mucosal region is the site of colonization of Escherichia coli O157 in cattle. Our objective was to determine the genetic relatedness of E. coli O157 in the mucosa of the rectoanal junction to isolates from colon contents and feces. Colon contents and rectums were collected from cattle at harvest. Rectums were opened and feces were sampled with a cotton swab. The mucosa of the rectum was cleansed free of visible feces with water and saline. The region, 2 to 5 cm proximal to the rectoanal junction, was swabbed with a foam-tipped applicator and then incisions were made in this region and the submucosa was swabbed with an applicator. Isolation and identification of E. coli O157 was performed in accordance with well-documented methods. Prevalence of E. coli O157 in the colon contents, feces, rectal mucosa, and rectal submucosa was 21%, 29%, 54%, and 34%, respectively. Pulsed-field gel electrophoresis was used to compare clonal similarity among isolates from different sampling regions. Sixty-seven cattle had E. coli O157 isolated from the rectal mucosa swab and feces of which 82% were clonally similar (dice similarity >95%) within animal. Escherichia coli O157 isolates from feces and colon contents were similar in 76% of cattle, but E. coli O157 isolates from the rectoanal mucosal swab and colon contents were only similar in 61.4% of cattle. Our results suggest that E. coli O157 in the feces may be from two sources, colonized in the rectoanal mucosa or transient in the gastrointestinal tract.