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Master of Public Health

Tetracycline- and 3rd generation cephalosporin- resistant, and extended spectrum beta-lactamase producing-E. coli in beef cow-calf production system

AUTHORS

Agga GE , Galloway HO , Netthisinghe AMP , Schmidt JW , Arthur TM , . Journal of food protection. 2022 8 18; ().

ABSTRACT

Cow-calf production plays a significant role in the beef production chain. However, it is not typically monitored for antimicrobial resistance (AMR). We determined the baseline level of bacterial AMR in pre-weaned calves prior to feedlot entry and evaluated wheat grazing and age effects on their occurrence. Two grazing experiments, with 16 cow-calf pairs each, were conducted on tall fescue or wheat. Fecal samples were cultured for the detection of tetracycline (TETr )-, 3rd generation cephalosporin (3GCr )-resistant, and extended spectrum β-lactamase (ESBL) producing E. coli. Isolates were characterized for resistance to other antibiotics and resistance mechanisms. Concentration (P <0.001) and prevalence (P =0.007) of TETr E. coli were significantly higher in the claves (5.1 log10 CFU/g and 93%, respectively) than in the cows (4.4 log10 CFU/g and 80%, respectively). Wheat grazing did not affect TETr E. coli phenotypically however, it significantly (P =0.005) expanded the resistant population carrying tet(A) over tet(B). Fecal prevalence of 3GCr- and ESBL producing-E.coli was 31.3% and 3.4%, respectively with no significant effects of age (P =0.340) or wheat grazing (P =0.597). All 3GCr – and ESBLs producing- E. coli isolates were multidrug resistant. 3GCr were positive for blaCMY-2 (73%) or blaCTX-M (27%) and blaCTX-M-15 was the most prevalent (94%, n=17) among the CTX-M positive isolates. Wheat grazing significantly (P <0.001) expanded 3GCr population carrying blaCTX-M while reducing the blaCMY-2 carrying population. Five of the seven ESBL producing E. coli isolates were positive for blaCTX-M. Our study found age-dependent occurrence of TETr E. coli, and that wheat grazing expanded the resistant population carrying certain resistance mechanisms over others. Cow-calf production is a significant reservoir for antibiotic resistant bacteria of significant public health importance such as 3GCr- and CTX-M type ESBLs producing-E. coli.

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