Effects of Tylosin, a Direct-Fed Microbial and Feedlot Pen Environment on Phenotypic Resistance among Enterococci Isolated from Beef Cattle Feces.

Sarah A Murray,Jason E Sawyer,Harvey M Scott,Sara D Lawhon,Ashlyn C Holbert,Keri N Norman

doi:10.3390/antibiotics11010106

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, indicating a macrolide susceptible probiotic may help mitigate resistance. 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. Susceptible strains of bacteria fed as DFM may prove useful for mitigating the selective effects of antibiotic use; however, the longer-term sustainability of such an approach remains unclear.

Highlights

While the use of antibiotics for growth promotion was banned in the United States in 2016, they are still widely used for the prevention, control, and treatment of disease.Antibiotics, including tylosin and chlortetracycline, are used in feed for the prevention and control of liver abscesses in cattle
Antibiotics 2022, 11, 106 increase in prevalence of ST296 occurred in tandem with a decrease in ST240, the dominant sequence type associated with resistance genes tet(M) and ermB [25]. By studying both the independent and interactive combined effects of an Enterococcus faecium-based direct-fed microbial, tylosin and pen environmental change on phenotypic resistance in enterococci, we report their effects on the following objectives: (1) log10 overall and resistant Enterococcus CFU, (2) trends in resistance to a wide array of antibiotics, and
Of the 558 fecal samples, 270 samples were collected from Trial Replicate 1 and 288 fecal samples were collected from Trial Replicate 2

Summary

Introduction

While the use of antibiotics for growth promotion was banned in the United States in 2016, they are still widely used for the prevention, control, and treatment of disease. Antibiotics, including tylosin and chlortetracycline, are used in feed for the prevention and control of liver abscesses in cattle. Grain-rich diets are widely accepted as the main cause of ruminal acidosis, rumenitis, and subsequent liver abscess formation [1,2]. It has been suggested that these two organisms initiate a synergistic reaction in causing the formation of liver abscesses [3]. Certain Salmonella enterica serotypes such as Lubbock have been isolated during anaerobic culture from a liver abscess [1,4]

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Discussion

Conclusion