This study was designed to determine the antibiotic resistance patterns of Enterococcus sp. isolated from feedlot cattle supplemented with a novel direct-fed microbial (DFM) Lactobacillus salivarius (L28) in replacement of tylosin in finishing diets of feedlot steers.
Antibiotics have been used widely in veterinary and human health for more than 50 years (Dibner and Richards, 2005). The broad use of antibiotics in animal agriculture, specifically for growth promotion, has increased concerns that it could contribute to the increased prevalence of antimicrobial-resistant (AMR) bacteria. Using antibiotics over time can potentially result in significant pools of resistance genes among bacteria, including foodborne pathogens (Noyes et al., 2016). Therefore, further investigation of appropriate alternatives to the sub-therapeutic dosages of antibiotics in feedlot operations is necessary. Alternatives such as direct-fed microbials may be an effective solution. The use of DFM for ruminants has shown to enhance milk production in dairy cows, and for beef cattle, improve feed efficiency and increase average daily gain (Krehbiel et al., 2010). Research from Peterson et al. (2006) has also shown a reduction in fecal shedding of Escherichia coli O157:H7 in feedlot cattle with supplementation of a DFM.