Persistence of Escherichia coli O157:H7 in feces from cattle fed diets with or without wet distillers grains with solubles
Feeding wet distillers grains with solubles (WDGS) to cattle can increase prevalence of E. coli O157:H7, but mechanisms for this increase are not fully understood. The objective of these experiments was to examine the persistence of E. coli O157:H7 in feces from cattle fed diets with or without WDGS. In the first study, fresh feces from steers fed 0, 20, 40 or 60% WDGS were collected and combined (6 to 8 animals/composite, n = 8 separate composites/diet treatment). Feces composites (600 g) were inoculated with a 5-strain mixture of streptomycin-resistant E. coli O157:H7, incubated at room temperature, and sampled periodically up to 14 d. Feces samples were diluted and plated to determine E. coli O157:H7 levels. Compared to levels seen with diets containing WDGS, E. coli O157:H7 levels in feces from cattle fed 0% WDGS rapidly decreased (P < 0.05), from 6.28 log10 cfu/g on d 0 to 2.48 log10 cfu/g by d 14. From the same initial levels, E. coli O157:H7 in feces from cattle fed 20, 40, and 60% WDGS were 4.21, 5.59, and 6.13 log10 cfu/g of feces on d 14, respectively. A second study evaluated survival of E. coli O157:H7 in feces from cattle fed 0 and 40% WDGS. Steers were fed in eight pens (75 to 77 per pen; 4 pens/WDGS treatment). Feces were collected from 5 to 6 animals in each pen, both before and after the corn source was switched from high-moisture corn (HMC) to dry-rolled corn (DRC). Feces samples were combined within pen, inoculated, incubated, and analyzed for E. coli O157:H7 as described above, and examined in triplicate at 0, 1, 2, 4, and 7 d. Within corn source, E. coli O157:H7 persisted at higher levels (P < 0.05) in 40% WDGS feces at d 7. For 40% WDGS feces, E. coli O157:H7 persisted at higher levels (P < 0.05) at d 7 in feces when cattle were fed HMC compared to DRC. Greater persistence of E. coli O157:H7 in the feces and environment of cattle fed WDGS may play a role in the increased prevalence of E. coli O157:H7 seen in these animals, by increasing the risk for recolonization of animals. This work further suggests potential dietary approaches for reducing the occurrence and numbers of this pathogen in cattle fed WDGS. USDA is an equal opportunity provider and employer.
Keywords: E. coli O157:H7, distillers grains, cattle