Location: Meat Safety and QualityTitle: In-feed tylosin phosphate administration to feedlot cattle minimally affects antimicrobial resistance
Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2019
Publication Date: 1/23/2020
Citation: Schmidt, J.W., Vikram, A., Miller, E., Jones, S., Arthur, T.M. 2020. In-feed tylosin phosphate administration to feedlot cattle minimally affects antimicrobial resistance. Journal of Food Protection. 83(2):350-364. https://doi.org/10.4315/0362-028X.JFP-19-342.
Interpretive Summary: The antibiotic tylosin phosphate (trade name Tylan) is approved by the United States Food and Drug Administration to be included in cattle feed to improve liver health. Tylosin use in cattle feed has not been linked to any specific pathogen causing an antibiotic resistant human infection, however, concerns persist that tylosin use may increase human exposure to antimicrobial resistance. This study compared the presence and levels of antibiotic resistant bacteria and antibiotic resistance genes in cattle and their environment with and without a tylosin feed treatment. A few small increases in resistance for tylosin treated cattle were found but these differences were smaller than the natural variation in resistance seen across the seven-month sampling period, regardless of treatment. Furthermore, most of the measures of resistance were not different between control and tylosin treatment. Thus, we conclude that tylosin inclusion in cattle feed likely has little or no impact on antimicrobial resistance associated with human health.
Technical Abstract: The macrolide class antimicrobial tylosin (trade name Tylan) is approved by the U.S. Food and Drug Administration for continuous inclusion in feed for liver abscess prevention. To address concerns that this antimicrobial application may threaten human health, a population of feedlot steers was split into a control treatment (n = 42) and a tylosin treatment (n = 42). Feed rations were identical except for the inclusion of tylosin at 60 to 90 mg per head per day. Fecal swab (n = 335), pen surface material (n = 256), feed (n = 56), and water trough (n = 32) samples were obtained over four sample occasions: November (1 day before the start of tylosin inclusion in feed), January (80 days of tylosin in feed), April (167 days), and June (253 days). These samples were cultured for Escherichia coli, tetracycline-resistant E. coli, third-generation cephalosporin-resistant E. coli, Enterococcus, tetracycline-resistant Enterococcus, and erythromycin-resistant Enterococcus. Metagenomic DNA was isolated from each June fecal swab and pen surface material sample. Metagenomic DNA samples were pooled by pen for 14 fecal and 14 pen surface material samples. Quantitative PCR was employed to assess the abundances of the following 10 antimicrobial resistance genes: aac(6')-Ie-aph(2")-Ia, aadA1, blaCMY-2, blaCTX-M, blaKPC-2, erm(B), mecA, tet(A), tet(B), and tet(M). Nasal swab samples (n = 335) were obtained from each steer during each sample period and cultured for the presence of Staphylococcus aureus and methicillin-resistant S. aureus. Of these measurements, only January and June mean fecal swab erythromycin-resistant Enterococcus colony counts for tylosin-treated cattle were significantly higher (P <= 0.05) than the range of mean values for control treatments. These results suggest that in-feed tylosin through the end of finishing has a narrow and minimal antimicrobial resistance impact.