Effects of age and pasture type on the concentration and prevalence of tetracycline and macrolide resistant Enterococcus species in beef cow-calf production system

Authors: Agga, Getahun; GALLOWAY, HUNTER - Western Kentucky University; NETTHISINGHE, ANNESLY - Western Kentucky University

Submitted to: Frontiers in Antibiotics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2022
Publication Date: 11/3/2022
Citation: Agga, G.E., Galloway, H.O., Netthisinghe, A.M. 2022. Effects of age and pasture type on the concentration and prevalence of tetracycline and macrolide resistant Enterococcus species in beef cow-calf production system. Frontiers in Antibiotics. 1:1052316. https://doi.org/10.3389/frabi.2022.1052316.
DOI: https://doi.org/10.3389/frabi.2022.1052316

Interpretive Summary: Enterococci bacteria are normal inhabitants of the digestive system of humans and animals without causing any diseases. However, when transferred to other body parts such as the heart, urinary tract and the blood circulation, they cause life threatening infections requiring antibiotic treatments. Enterococcal species causing systemic infections are antimicrobial resistant, often multidrug resistant, making it a public health challenge. Enterococci are the second major cause of hospital acquired infections. Moreover, enterococci including antibiotic resistant strains are commonly reported from beef cattle and retail meats, signaling its foodborne route of infection. We investigated enterococci including those resistant to tetracycline and erythromycin antibiotics under cow-calf production system. We also evaluated the potential of wheat grazing to mitigate antibiotic resistant enterococci. Our results indicated that enterococci bacteria including tetracycline and erythromycin resistant strains are widespread in the cow-calf production system. Wheat was shown to reduce tetracycline resistant strains, affected enterococci species distribution and their resistance mechanisms. This finding suggests the need for more studies to further elucidate the potential of wheat grazing to mitigate antimicrobial resistant bacteria in cow-calf production commonly raised on pasture grazing.

Technical Abstract: Enterococci are a normal flora of the gastrointestinal tracts of humans and animals. Enterococci can also cause life threatening nosocomial infections. Antimicrobial resistant Enterococcus species have been reported in feedlot and dairy cattle productions, and in meat and milk products, suggesting enterococci foodborne importance. Cow-calf operations represent a significant segment in beef production system by producing weaned calves. Weaned calves enter the feedlot to be finished for beef; culled cows are also slaughtered for beef, mainly ground beef products. Infection dynamics in the cow-calf operation can contribute to meat contamination. The research assessed the impacts of wheat grazing and age on the burden, species distribution, and antimicrobial resistance of enterococci under cow-calf production system. Two cohorts of Angus breed cow-calf pairs, each with 32 animals, were equally randomized to graze on tall fescue or wheat pasture in 2017 and 2018. Fecal samples were collected weekly during the grazing period and cultured for the isolation and identification of generic-, tetracycline (TETr)-, and erythromycin (ERYr)- resistant enterococci. Generic- and TETr- enterococci were abundant and widespread in the cow-calves, whereas ERYr enterococci occurred in 40% of the fecal samples but at low abundance. Enterococcus faecium and E. faecalis, the two major species commonly reported from human infections, were prevalent in the cow-calf populations. TET- and ERY-resistance were mainly conferred by tet(M) and erm(B), respectively. Wheat grazing reduced the abundance of TETr enterococci, and modified enterococcal species and resistance gene distributions. The potential of wheat grazing to mitigate antimicrobial resistant Enterococcus species in cow-calf production needs to be explored.