Location: Meat Safety & Quality ResearchTitle: Effect of in-feed Chlortetracycline prophylaxis in beef cattle on levels of 10 antimicrobial resistance genes
Submitted to: American Society for Microbiology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 1/27/2017
Publication Date: 3/22/2017
Citation: Miller, E.W., Agga, G.E., Vikram, A., Arthur, T.M., Schmidt, J.W. 2017. Effect of in-feed Chlortetracycline prophylaxis in beef cattle on levels of 10 antimicrobial resistance genes. [Abstract]. American Society for Microbiology Meeting. p.43, no.13.
Technical Abstract: Background: The majority of antimicrobial products used in food-animal production are administered in-feed to control or prevent disease. These uses are controversial since it has been argued that they have contributed to increased occurrence of antimicrobial resistance (AMR). Beef cattle are susceptible to bovine respiratory disease (BRD) during weaning and transition into feedlots. In-feed administration of chlortetracycline (CTC) for 5 days is an option for the prevention and control of BRD. The goal of this research was to determine if this CTC administration effects the fecal and pen surface occurrences of 10 antimicrobial resistance genes (ARGs): tetracyclines (tetA, tetB, tetM), aminoglycosides (aac(6')-Ie-aph(2"), aadA1), macrolides (ermB), and beta-lactams (blaCMY, blaCTX-M, blaKPC-2, mecA). Methods: Three hundred weaned calves were randomly assigned to two groups. The CTC treatment group consisted of 150 calves housed in 5 pens (30 head/pen), while the control group consisted of 150 calves housed in 5 pens (30 head/pen). The CTC treatment group received medicated feed (Aureomycin, a chlortetracycline complex) equivalent to 10 mg/lb of body weight/day. Samples were obtained on five occasions: feedlot arrival, 5 days post CTC treatment (dpt), 27 dpt, 75 dpt, and 117 dpt. On each sample occasion, fecal swabs were obtained from all animals and four samples of surface material were obtained from each pen. For each sample type and occasion samples were pooled by pen and genomic DNA was isolated resulting in 50 pen surface samples and 50 fecal swab samples. Endpoint and quantitative PCR were utilized to examine the abundance of specific resistance genes normalized to 16S rRNA gene abundance. Results: tetM and ermB abundances were higher for the CTC treatment group at 5 dpt, but did not differ between groups at 27 dpt, 75 dpt, and 117 dpt. Both tetA and tetB showed an increased abundance at later time points; however, there was no divergence between the CTC treatment group and the control group. The abundances of the remaining ARGs did not differ between treatment groups nor changed over time. Conclusions: These results suggest that the AMR impacts of a 5 day in-feed CTC administration are minimal and transient.