Tetracycline-resistant, third-generation cephalosporin–resistant, and extended-spectrum b-lactamase–producing Escherichia coli in a beef cow-calf production system

Authors: Agga, Getahun; GALLOWAY, HUNTER - Western Kentucky University; NETTHISINGHE, ANNESLEY - Western Kentucky University; Schmidt, John; Arthur, Terrance

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2022
Publication Date: 8/18/2022
Citation: Agga, G.E., Galloway, H.O., Netthisinghe, A.M., Schmidt, J.W., Arthur, T.M. 2022. Tetracycline-resistant, third-generation cephalosporin–resistant, and extended-spectrum b-lactamase–producing Escherichia coli in a beef cow-calf production system. Journal of Food Protection. 85(11):1522-1530. https://doi.org/10.4315/JFP-22-178.
DOI: https://doi.org/10.4315/JFP-22-178

Interpretive Summary: Cow calf operation is the first step in beef production system. It provides calves that go to feedlots and finished for meat. Cows when culled from the breeding herd are also used for ground beef production. Antibiotic resistant bacteria can multiply within the cow calf operation and pass to the calves. When calves carrying resistant bacteria enter the feedlot, the bacteria will further propagate with the potential to result in beef contamination during slaughtering process. Therefore, it is essential to understand the burden of antibiotic resistant bacteria under cow calf production system. However, beef cow calf production is not often studied for antimicrobial resistance. Under cow calf production system, animals are raised on pasture and spend most of their time outdoors. Although animal density is low and infection pressure is less, antibiotics are sparingly used to treat sick animals. Wheat is often used as cover crop, and animal grazing was thought to increase crop yield and improves animal performance. We evaluated wheat grazing as a potential strategy to reduce antibiotic resistance in beef cow calf production system. Results indicated that the level of tetracycline resistant bacteria is higher in the calves than in the cows. Both cows and calves carried bacteria resistant to antibiotics that are critically important for the treatment of human infection. Wheat grazing did not have any impact on the phenotypically observed resistance. However, it affected the fraction of the resistant bacterial population by modifying the distribution of the genetic mechanisms for resistance. In conclusion, cow calf production can be a reservoir for bacteria resistant to antibiotics of critical importance for public health. Pre-harvest food safety measures that also target the cow calf production will have the greatest benefit in ensuring the safety of beef.

Technical Abstract: Cow-calf production plays a significant role in the beef production chain. However, bacteria in these systems are not typically monitored for antimicrobial resistance (AMR). We determined the baseline level of AMR in fecal bacteria collected from preweaned calves prior to feedlot entry and evaluated the effects of type of graze and age on AMR occurrence. Two grazing experiments (16 cow-calf pairs each) were conducted on tall fescue or wheat. Fecal samples were cultured for the detection of tetracycline-resistant (TETr), third-generation cephalosporin–resistant (3GCr), and extended-spectrum b-lactamase (ESBL)–producing Escherichia coli. Isolates were characterized for resistance to other antibiotics and resistance mechanisms. Concentrations (P , 0.001) and prevalence (P ¼ 0.007) of TETr E. coli isolates were significantly higher in the calves (5.1 log CFU/g and 93%, respectively) than in the cows (4.4 log CFU/g and 80%, respectively). Wheat grazing did not affect TETr isolates phenotypically; however, it significantly expanded (P¼0.005) the resistant population carrying tet(A) over that carrying tet(B). Fecal prevalence of 3GCr and ESBL-producing isolates was 31.3 and 3.4%, respectively, with no significant effects of age (P ¼ 0.340) or wheat grazing (P ¼ 0.597). All 3GCr and ESBL-producing isolates were multidrug resistant (resistant to at least three antimicrobial classes). 3GCr isolates were positive for blaCMY-2 (73%) or blaCTX-M (27%), and blaCTX-M-15 was the most prevalent gene (94%, n¼17) among the CTX-M–positive isolates. Wheat grazing significantly expanded (P , 0.001) the 3GCr population carrying blaCTX-M and reduced the population carrying blaCMY-2. Five of the seven ESBL-producing isolates were positive for blaCTX-M. Our study revealed age-dependent occurrence of TETr E. coli and that wheat grazing expanded the resistant population carrying certain resistance genes. Cow-calf production is a significant reservoir for antibiotic-resistant bacteria of significant public health importance such as 3GCr and CTX-M ESBL-producing E. coli.