Experimental evaluation of tylosin use for the prevention of liver abscesses in beef cattle on bacterial resistance to critically important antibiotics for human use

Authors: Agga, Getahun; GALLOWAY, HUNTER - Western Kentucky University

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: 3/3/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Although tylosin, a veterinary only macrolide used to prevent liver abscess in feedlot cattle, was shown to select for macrolide resistant Gram-positive bacteria, its influence on Gram-negative foodborne bacteria is unknown. The purpose is to evaluate the effect of continuous in-feed tylosin use on the concentration and prevalence of tetracycline resistant (TETr)-, 3rd generation cephalosporin resistant (3GCr)-, and extended spectrum beta-lactamase producing (ESBLs)-E. coli in feedlot cattle. A cohort of weaned calves with 10 animals/group were randomized to receive tylosin supplemented mineral (Tylosin group) or nonsupplemented mineral (Control group). Fecal samples were collected approximately monthly for the entire feeding period of one year. Pen surface and feed samples were also collected. Samples were cultured on antibiotic supplemented media. Enumeration and binary outcomes were analyzed by multilevel mixed effects linear regression or logistic regression, respectively using treatment and days on feed (DOF) as factors. Tylosin did not significantly affect total and TETr E. coli concentrations or the prevalence of 3GCr- and ESBLs-E. coli in the cattle feces, feed and pen-surface samples. However, fecal total and TETr E. coli concentrations and the prevalence of 3GCr- and ESBLs-E. coli increased over time during the feedlot cycle. 3GCr and ESBLs-E. coli were not detected from the feed samples; they were detected from the pen-surface samples with no significant tylosin effect. In-feed tylosin was used to prevent liver abscess in feedlot cattle, although known to select for antimicrobial resistant Gram-positive bacteria such as enterococci, it did not select for antimicrobial resistant Gram-negatives including ESBLs-producing Enterobacteriaceae, considered as a serious public health threat by the U.S. CDC. However, the study indicated that feedlot cattle production setting gradually increases the levels of E. coli resistant to the critically and/or important antibiotics for public health, indicating an increased risk of their dissemination beyond the beef cattle production setting.