Antimicrobial resistance at two United States cull cow processing establishments

Authors: Schmidt, John; VIKRAM, AMIT - Intralytix, Inc; Arthur, Terrance; BELK, KEITH - (NCE, CECR)networks Of Centres Of Exellence Of Canada, Centres Of Excellence For Commercilization A; MORLEY, PAUL - Texas A&M University; Weinroth, Margaret - Maggie; Wheeler, Tommy

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2020
Publication Date: 12/1/2020
Citation: Schmidt, J.W., Vikram, A., Arthur, T.M., Belk, K.E., Morley, P.S., Weinroth, M.D., Wheeler, T.L. 2020. Antimicrobial resistance at two United States cull cow processing establishments. Journal of Food Protection. 83(12):2216-2228. https://doi.org/10.4315/JFP-20-201.
DOI: https://doi.org/10.4315/JFP-20-201

Interpretive Summary: Culled cows that supply cattle feeding operations with calves and culled dairy cows contribute about 18% of the cattle harvested in the U.S. each year. While published studies have demonstrated that antibiotic use has minimal effect on antibiotic resistance in fed cattle little data exists regarding cows. To address this data gap, carcass samples and feces were obtained from culled beef cows (conventional beef), culled dairy cows (conventional dairy), and culled organic dairy cows produced without using antibiotics (organic dairy) from two beef harvest and processing plants. At one plant, meat trimmings for ground beef also were sampled. Results indicate a few antibiotic resistance levels were higher in feces from conventional cows compared to organic cows. However, sample day had similar impacts on antibiotic resistance levels indicating that antibiotic use had only marginal impacts on antibiotic resistance levels. The impact of these marginally higher levels on human exposures to antibiotic resistance through beef is likely small since production without using antibiotics did not affect the levels of any measured antimicrobial resistance on beef products.

Technical Abstract: Culled beef cows (cows that have reached the end of their productive life span in cow-calf operations) and culled dairy cows represent approximately 18% of the cattle harvested in the United States annually, but data on antimicrobial resistance (AMR) in these cull cattle are extremely limited. To address this data gap, colon contents were obtained from 180 culled conventional beef cows, 179 culled conventional dairy cows, and 176 culled organic dairy cows (produced without using antimicrobials). Sponge samples were also collected from 181 conventional beef, 173 conventional dairy, and 180 organic dairy cow carcasses. These samples were obtained on 6 days (3 days each at two beef harvest and processing establishments). At one establishment, 30 samples of beef manufacturing trimmings from conventional cows and 30 trim samples from organic dairy cows were acquired. All 1,129 samples were cultured for Escherichia coli, tetracycline-resistant (TETr) E. coli, third-generation cephalosporin-resistant (3GCr) E. coli, Salmonella, and 3GCrSalmonella. Metagenomic DNA was isolated from 535 colon content samples, and quantitative PCR assays were performed 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). For colon contents, only TETrE. coli (P < 0.01), 3GCrE. coli (P < 0.01), and erm(B) (P = 0.03) levels were higher in conventional than in organic cows. Sampling day also significantly affected (P < 0.01) these levels. Production system did not affect the levels of any measured AMR on carcasses or trim. The human health impact of the few significant AMR differences could not be determined due to the lack of standards for normal, background, safe, or basal values. Study results provide key heretofore unavailable data that may inform quantitative microbial risk assessments to address these gaps.