title: 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 O157:H7 to identify potential "supershedders." RAJ colonization and fecal excretion prevalences were correlated, and E. coli O157:H7 prevalences and counts were significantly greater for RAJ samples. Based on a comparison of RAJ and fecal ratios of E. coli O157:H7/E. coli counts, the RAJ appears to be preferentially colonized by the O157:H7 serotype. Five supershedders were identified based on persistent colonization with high concentrations of E. coli O157:H7. Cattle copenned with supershedders had significantly greater mean pen E. coli O157:H7 RAJ and fecal prevalences than noncopenned cattle. Cumulative fecal E. coli O157:H7 excretion was also significantly higher for pens housing a supershedder. E. coli O157:H7/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 O157:H7 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 O157:H7 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 O157:H7 can be used to develop preslaughter- and slaughter-level interventions that reduce contamination of the food chain.
authors.affiliation: Field Disease Investigation Unit, College of Veterinary Medicine, Washington State University, Pullman, Washington 99164-6610, USA. r.cobbold@uq.edu.au
authors.forename: Rowland N
authors.initials: RN
authors.lastname: Cobbold
authors.forename: Dale D
authors.initials: DD
authors.lastname: Hancock
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Rice
authors.forename: Janice
authors.initials: J
authors.lastname: Berg
authors.forename: Robert
authors.initials: R
authors.lastname: Stilborn
authors.forename: Carolyn J
authors.initials: CJ
authors.lastname: Hovde
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Besser
mesh_terms: D001003:Anal Canal / Q000382:microbiology*; D000821:Animal Feed; D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000382:microbiology; D015169:Colony Count, Microbial; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D019453:Escherichia coli O157 / Q000145:classification / Q000235:genetics / Q000254:growth & development* / Q000302:isolation & purification; D005243:Feces / Q000382:microbiology*; D015995:Prevalence; D012007:Rectum / Q000382:microbiology*