ACID RESISTANCE STATUS OF ESCHERICHIA COLI O157 IN BOVINE FECES AS SHED FROM NATURALLY CONTAMINATED CATTLE

Authors: Berry, Elaine; Gallagher, Genevieve

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 3/11/2002
Publication Date: 7/24/2002
Citation: Berry, E.D., Gallagher, G.A. 2002. Acid resistance status of Escherichia coli O157 in bovine feces as shed from naturally contaminated cattle [abstract]. Journal of Animal Science. 80(Suppl. 1):150.

Interpretive Summary:

Technical Abstract: Exposure to low pH and acids in the bovine gastrointestinal (GI) tract may result in the induced acid resistance of E. coli O157. Because bovine feces are a source of carcass contamination, and acid tolerance of bacteria can affect the efficacy of decontamination procedures, the acid resistance of this organism as shed from cattle was determined. The objectives of this study were to examine the capacity of naturally-occurring E. coli O157 shed in bovine feces to survive exposure to low pH and to assess the relative acid resistance status of E. coli O157 as shed from cattle. Fecal grab samples and freshly-dropped feces were collected randomly from cattle in the MARC feedlot from August through October in 2000 and 2001. Initial numbers of E. coli O157 and numbers following exposure to pH 2.5 for 6 h were determined in fecal slurries, using a most probable number-immunomagnetic separation procedure. Isolates were confirmed as E. coli O157 and genotyped by pulsed-field gel electrophoresis. Fifteen positive fecal samples containing at least four distinct genotypes were analyzed. Initial populations ranged from 0.99 to 4.86 log10 CFU/g, and log reductions following acid challenge ranged from 0.68 to 3.21 log10 CFU/g. For each unique isolate, acid resistance was determined in vitro for cells both in mid-log and stationary phases of growth, cultured with and without glucose (acid-adapted [AA] and nonacid-adapted [NA], respectively), by exposing the cells to the same acid challenge as the fecal slurries. Stationary phase cells were resistant to the acid challenge; generally, reductions of AA cells were <0.20 log10 CFU/g and NA cells were <0.60 log10 CFU/g. Log reductions of all mid-log phase cells were >4.00 log10 CFU/g and many populations were reduced below detectable levels. Comparison of the in vivo and in vitro acid resistance data indicates that residence in the bovine GI tract does not result in the development of extreme acid resistance of E. coli O157.