Metaphylactic antimicrobial effects on occurrences of antimicrobial resistance in Salmonella enterica, Escherichia coli, and Enterococcus spp. measured longitudinally from feedlot arrival to harvest in high-risk beef cattle

Authors: LONG, NATHAN - Texas Tech University; Wells, James - Jim; Berry, Elaine; LEGAKO, J - Texas Tech University; WOERNER, DALE - Texas Tech University; LONERAGAN, GUY - Texas Tech University; Broadway, Paul; Carroll, Jeffery - Jeff Carroll; Sanchez, Nicole; FERNANDO, SAMODHA - University Of Nebraska; BACON, CARLEY - Texas Tech University; HELMUTH, CORY - Texas Tech University; SMOCK, TAYLOR - Texas Tech University; MANAHAN, JEFFERY - Texas Tech University; HOFFMAN, ASHLEY - Texas Tech University; HALES, KRISTIN - Texas Tech University

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2022
Publication Date: 6/29/2022
Citation: Long, N.S., Wells, J.E., Berry, E.D., Legako, J.F., Woerner, D.R., Loneragan, G.H., Broadway, P.R., Carroll, J.A., Sanchez, N.C.B., Fernando, S.C., Bacon, C.M., Helmuth, C.L., Smock, T.M., Manahan, J.L., Hoffman, A.A., Hales, K.E. 2022. Metaphylactic antimicrobial effects on occurrences of antimicrobial resistance in Salmonella enterica, Escherichia coli, and Enterococcus spp. measured longitudinally from feedlot arrival to harvest in high-risk beef cattle. Journal of Applied Microbiology. Article 15691. https://doi.org/10.1111/jam.15691.
DOI: https://doi.org/10.1111/jam.15691

Interpretive Summary: Feedlot cattle that are of a high-risk to develop bovine respiratory disease (BRD) typically receive substantial antibiotic treatments when sick. To reduce the need to treat sick animals they often receive antimicrobials upon arrival to the feedlot. Therefore, BRD high-risk cattle are exposed to a variety of antimicrobials within the first month at the feedlot and little is known about antimicrobial resistant (AMR) bacteria and pathogens in these cattle. Fecal samples were collected over eight months from BRD high-risk cattle that were or were not treated with an antimicrobial at arrival to the feedlot. Treatment with an antimicrobial upon arrival reduced the incidence of cattle developing BRD. Antimicrobial use at arrival also resulted in increased AMR bacteria temporarily, but few differences were observed in AMR bacteria in the feces at harvest. Salmonella is a foodborne pathogen commonly found in cattle feces, and this pathogen was consistently found in the fecal samples. Antimicrobial treatment was not associated with AMR Salmonella in the feces. However, the use of some antimicrobials on cattle at arrival was associated with increased Salmonella over time. Treating all high-risk cattle with an antimicrobial upon arrival at the feedlot reduced incidence of BRD and did not increase incidence of AMR Salmonella.

Technical Abstract: Aims: Our objective was to determine how injectable antimicrobials affected populations of Salmonella enterica, Escherichia coli and Enterococcus spp. in feedlot cattle. Methods and Results: Two arrival date blocks of high-risk crossbred beef cattle (n = 249; mean BW = 244 kg) were randomly assigned one of four antimicrobial treatments administered on day 0: sterile saline control (CON), tulathromycin (TUL), ceftiofur (CEF) or florfenicol (FLR). Faecal samples were collected on days 0, 28, 56, 112, 182 and study end (day 252 for block 1 and day 242 for block 2). Hide swabs and subiliac lymph nodes were collected the day before and the day of harvest. Samples were cultured for antimicrobial-resistant Salmonella, Escherichia coli and Enterococcus spp. The effect of treatment varied by day across all targeted bacterial populations (p <= 0.01) except total E. coli. Total E. coli counts were greatest on days 112, 182 and study end (p <= 0.01). Tulathromycin resulted in greater counts and prevalence of Salmonella from faeces than CON at study end (p <= 0.01). Tulathromycin and CEF yielded greater Salmonella hide prevalence and greater counts of 128ERYR E. coli at study end than CON (p <= 0.01). No faecal Salmonella resistant to tetracyclines or third-generation cephalosporins were detected. Ceftiofur was associated with greater counts of 8ERYR Enterococcus spp. at study end (p <= 0.03). By the day before harvest, antimicrobial use did not increase prevalence or counts for all other bacterial populations compared with CON (p >= 0.13). Conclusions: Antimicrobial resistance (AMR) in feedlot cattle is not caused solely by using a metaphylactic antimicrobial on arrival, but more likely a multitude of environmental and management factors.