Enumeration and strain characterization of fecal Escherichia coli associated with feeding triticale dried distillers grain with solubles in beef cattle diets.

Triticale dried distillers grain with solubles (TDDGS), a major by-product of the bioethanol industry, has potential for utilization in animal feed. This study investigated the changes in generic fecal Escherichia coli strains associated with inclusion of TDDGS in cattle diets. Within this study, a longitudinal experiment (112 days) examined the effect of step-up increasing TDDGS inclusion from control to a final diet containing 30% TDDGS among cattle (n = 4), and a short-term experiment (28 days) compared animals (n = 16) fed control, 20%, 25%, or 30% TDDGS diets. We found that incorporation of either 20%, 25%, or 30% TDDGS did not have any effect on the amount of total E. coli shedding over either the longitudinal (p = 0.06) or the short-term (p = 0. 87) study. In both the experiments, 67% of the total E. coli isolates were found to be resistant to one or more of the 17 antimicrobials tested. Among the resistant isolates, cephalothin was the most prevalent resistance (44% isolates). Over the duration of the study, tet(C) was a commonly detected resistance gene in tetracycline-resistant E. coli. Significant diversity was observed among isolates with 33 and 31 pulsed-field gel electrophoresis patterns clustering into 11 and 10 restriction endonuclease digestion pattern clusters for the longitudinal and short-term studies, respectively. Neither the duration of feeding nor increasing the proportion of TDDGS within the diet affected the diversity of E. coli resistance phenotypes or the clonal relatedness of the observed strains. Individual animals retained similar or closely related strains. Based on this study, inclusion of TDDGS as a protein and fiber source in cattle diets is not associated with increased maintenance, shedding, or proliferation of resistant strains of generic E. coli, which is an important reservoir of antimicrobial resistance among cattle.