Prior to inoculation with E. coli O157:H7 strains, cattle did not contain ruminal or fecal E. coli populations capable of growth on agar containing concentrations of antibiotics used to differentiate each inoculated E. coli O157:H7 strain (data not shown). Following inoculation with E. coli O157:H7 strains (12 h), populations of each strain of E. coli O157:H7 ranged from 105 to 107 cfu/g of feces and 105 to 106 cfu/mL of ruminal fluid (Figures 2a and b). Populations of E. coli O157:H7 remained stable in ruminal fluid and feces until chlorate treatment commenced (at 0 h). Fecal populations of all three inoculated strains of E. coli O157:H7 in control cattle remained constant (106 cfu/mL) throughout the study, but chlorate treatment reduced fecal populations (P 3) was returned to the cattle after a 24-h withdrawal period, cattle drank copiously; water intake between controls and chlorate-treated groups were not different (43.8 L vs 44.9 L per day per animal). Water intake diluted ruminal contents and caused a decrease (P
Throughout the gastrointestinal tract, chlorate treatment reduced total coliform, E. coli, and E. coli O157:H7 populations (Figures 3a and b). Total coliforms and generic E. coli were reduced approximately 100-fold in the rumen (P
Total culturable anaerobic bacterial populations of the rumen, cecum, and colon were not affected by chlorate treatment (Figure 4). Chlorate treatment did not significantly affect gastrointestinal pH (Figure 5). The fermentation profile throughout the gastrointestinal tract was not significantly affected by chlorate treatment, as indicated by total VFA concentration and the acetate:propionate ratio (Figures 6a and b). Hide swabs from the ventral midline and hock contained 2 cfu/ cm2 of each E. coli O157:H7 strain (data not shown). Because E. coli O157:H7 populations were so low, chlorate treatment did not affect populations of O157:H7 strains, coliforms, or generic E. coli recovered from hide swabs of the ventral midline or the hock.
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