Prevalence and distribution of Escherichia coli O157 among finishing beef cattle supplemented with Lactobacillus-based direct-fed microbials

Escherichia coli O157 has emerged as a prominent food-borne pathogen that is associated with cattle and consumption of beef products. The objectives of this research were: (1) to quantify the prevalence of E. coli O157 in feces and on hides of finishing beef cattle fed a standard diet and those fed diets supplemented with Lactobacillus acidophilus-based direct-fed microbials (DFM); and (2) to describe the dynamics of within-pen prevalence of fecal shedding of E. coli O157 among finishing beef cattle supplemented with the DFM. The DFM used in supplemented diets included various combinations and concentrations of two strains of Lactobacillus acidophilus (NP 51 and NP 45) and Propionibacterium freudenreichii. Overall, cattle receiving a 1 x 109 CFU/steer daily of NP 51 throughout the feeding period were 57% less likely to be shedding a detectable level of E. coli O157 in their feces compared with those receiving the control diet. When each pen sampling was considered an independent observational unit, zero or one out of five steers were found to be shedding E. coli O157 in 84% of within-pen prevalence observations. Fecal shedding of E. coli O157 was not associated with hide contamination on either the pen or individual animal level. The decrease in the overall prevalence of fecal shedding of E. coli O157 among cattle receiving a high-level dose of NP 51 was a function of a decrease in both the number of animals per pen that were positive and the number of pens with at least one positive animal. Supplementing cattle with Lactobacillus acidophilus strain NP 51 may be an efficacious intervention strategy to control E. coli O157 in the pre-harvest environment.