Location: Meat Safety & Quality ResearchTitle: Effects of in-feed Chlortetracycline prophylaxis in beef cattle on antimicrobial resistance genes
Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2018
Publication Date: 11/13/2018
Citation: Miller, E.W., Vikram, A., Agga, G.E., Arthur, T.M., Schmidt, J.W. 2018. Effects of in-feed Chlortetracycline prophylaxis in beef cattle on antimicrobial resistance genes. Foodborne Pathogens and Disease. 15(1):689-697. https://doi.org/10.1089/fpd.2018.2475.
Interpretive Summary: The Food and Drug Administration has recently implemented significant restrictions on use of antimicrobials for growth enhancement in food animals. However, concern remains about the impact of in-feed antimicrobials on antimicrobial resistance. Chlortetracycline is an antimicrobial commonly fed to calves for five days shortly after entry into feedlots to prevent bovine respiratory disease. We evaluated the impact of a 5-day in-feed chlortetracycline regimen on the levels of 10 antimicrobial resistance genes and found no differences between the Chlortetracycline and Control groups at any time from 5 to 117 days after treatment. We conclude that a single 5-day in-feed of chlortetracycline administration to beef cattle does not appreciably impact antimicrobial resistance levels.
Technical Abstract: Approximately 20% of U.S. beef cattle receive prophylactic in-feed administration of chlortetracycline (CTC) to reduce bovine respiratory disease (BRD) incidence during the transition into feedlots. To determine the impact of prophylaxis on selected antimicrobial resistance genes (ARGs), 300 beef cattle were placed into 10 pens (30 head/pen). Five “CTC group” pens received in-feed CTC (10'mg/lb of body weight/d) from the fifth to ninth day after feedlot arrival, whereas the five “Control group” pens received no CTC. Fecal swabs and pen surface materials were collected for metagenomic DNA isolation on five sample occasions: arrival at the feedlot, 5 d posttreatment (dpt), and 27, 75, and 117 dpt. For each sample occasion, fecal samples and pen surface material samples were pooled by pen. Quantitative polymerase chain reaction was used to determine the abundances of 10 ARGs. Due to low detection percentages (%D) and quantification percentages (%Q), the abundances of five ARGs were not analyzed: aac(6')-Ie-aph(2'') (%D'='43%, %Q'='4%), blaCMY-2 (%D'='41%, %Q'='0%), blaCTX-M (%D'='0%, %Q'='0%), blaKPC-2 (%D'='21%, %Q'='16%), and mecA (%D'='4%, %Q'='0%). The %D and %Q for the ARGs aadA1, erm(B), tet(A), tet(B), and tet(M) were =98% and =90%, respectively. The abundances of aadA1, erm(B), tet(A), tet(B), and tet(M) resistance genes did not differ (p'>'0.05) between the CTC and control groups at any sampling time for feces or pen surface material. Although only 10 ARGs were examined in this study, the results suggest that a single 5-d in-feed CTC prophylaxis of beef cattle to prevent BRD has a negligible impact on the abundances of ARGs.