Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Effects of a Direct-Fed Microbial and Feedlot Pen Environmental Change on Phenotypic Resistance among Enterococci Isolated from Beef Cattle Feces

Version 1 : Received: 24 November 2021 / Approved: 25 November 2021 / Online: 25 November 2021 (12:49:29 CET)

How to cite: Murray, S.A.; Holbert, A.C.; Norman, K.N.; Lawhon, S.D.; Sawyer, J.E.; Scott, H.M. Effects of a Direct-Fed Microbial and Feedlot Pen Environmental Change on Phenotypic Resistance among Enterococci Isolated from Beef Cattle Feces. Preprints 2021, 2021110474 (doi: 10.20944/preprints202111.0474.v1). Murray, S.A.; Holbert, A.C.; Norman, K.N.; Lawhon, S.D.; Sawyer, J.E.; Scott, H.M. Effects of a Direct-Fed Microbial and Feedlot Pen Environmental Change on Phenotypic Resistance among Enterococci Isolated from Beef Cattle Feces. Preprints 2021, 2021110474 (doi: 10.20944/preprints202111.0474.v1).

Abstract

In two sequential replicates (n=90 and n=96 feedlot finisher cattle, respectively) we measured the impact of an Enterococcus faecium-based probiotic (DFM) and an altered feedlot pen environment on antimicrobial resistance among fecal enterococci in cattle fed (or, not fed) the macrolide tylosin. Diluted fecal samples were spiral-plated on plain and antibiotic-supplemented m-Enterococcus agar. In the first replicate, tylosin significantly (p<0.05) increased the relative quantity of erythromycin-resistant enterococci. This effect was diminished in cattle fed the DFM in conjunction with tylosin. A similar observed effect was not statistically significant (P > 0.05) in the second replicate. Isolates were speciated and resistance phenotypes were obtained for E. faecium and E. hirae. E. faecium isolates were whole-genome sequenced, which yielded sequence types (ST), resistance genes and phylogeny. Samples of the DFM were sequenced and found to contain E. faecium ST296, which was not present on Day 0 of either replicate. This DFM sequence type was found in fecal samples after Day 0, the majority of which were isolated from cattle in one of the DFM-fed pens. Increased prevalence of ST296 occurred with a concomitant decrease in ST240; of importance, the latter typically harbored both ermB and tet(M) genes.

Keywords

probiotic; Enterococcus faecium; antimicrobial resistance; environmental change

Subject

LIFE SCIENCES, Microbiology

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