Rectoanal junction colonization of feedlot cattle by Escherichia coli O157:H7 and its association with supershedders and excretion dynamics.

ABSTRACT

Feedlot cattle were observed for fecal excretion of and rectoanal junction (RAJ) colonization with Escherichia coli O157H7 to identify potential "supershedders." RAJ colonization and fecal excretion prevalences were correlated, and E. coli O157H7 prevalences and counts were significantly greater for RAJ samples. Based on a comparison of RAJ and fecal ratios of E. coli O157H7/E. coli counts, the RAJ appears to be preferentially colonized by the O157H7 serotype. Five supershedders were identified based on persistent colonization with high concentrations of E. coli O157H7. Cattle copenned with supershedders had significantly greater mean pen E. coli O157H7 RAJ and fecal prevalences than noncopenned cattle. Cumulative fecal E. coli O157H7 excretion was also significantly higher for pens housing a supershedder. E. coli O157H7/E. coli count ratios were higher for supershedders than for other cattle, indicating greater proportional colonization. Pulsed-field gel electrophoresis analysis demonstrated that isolates from supershedders and copenned cattle were highly related. Cattle that remained negative for E. coli O157H7 throughout sampling were five times more likely to have been in a pen that did not house a supershedder. The data from this study support an association between levels of fecal excretion of E. coli O157H7 and RAJ colonization in pens of feedlot cattle and suggest that the presence of supershedders influences group-level excretion parameters. An improved understanding of individual and population transmission dynamics of E. coli O157H7 can be used to develop preslaughter- and slaughter-level interventions that reduce contamination of the food chain.