Rhodococcus equi Carrying Resistance Genes in the Environment of Horse-Breeding

Antimicrobial Residue Accumulation Contributes to Higher Levels of Rhodococcus equi Carrying Resistance Genes in the Environment of Horse-Breeding Farms

Vet Sci. 2024 Feb 17;11(2):92. doi: 10.3390/vetsci11020092.

Authors
Courtney Higgins 1 , Noah D Cohen 2 , Nathan Slovis 3 , Melissa Boersma 4 , Pankaj P Gaonkar 1 , Daniel R Golden 1 , Laura Huber 1
Affiliations

1 Pathobiology Department, College of Veterinary Medicine, Auburn University, Auburn, AL 36832, USA.
2 Large Animal Clinical Sciences, School of Veterinary Medicine and Biomedical Sciences, Texas A&M, College Station, TX 77843, USA.
3 Hagyard Equine Medical Institute, Lexington, KY 40511, USA.
4 College of Sciences and Mathematics, Auburn University, Auburn, AL 36849, USA.

PMID: 38393110
DOI: 10.3390/vetsci11020092

Abstract

Antimicrobial residues excreted in the environment following antimicrobial treatment enhance resistant microbial communities in the environment and have long-term effects on the selection and maintenance of antimicrobial resistance genes (AMRGs). In this study, we focused on understanding the impact of antimicrobial use on antimicrobial residue pollution and antimicrobial resistance (AMR) in the environment of horse-breeding farms. Rhodococcus equi is an ideal microbe to study these associations because it lives naturally in the soil, exchanges AMRGs with other bacteria in the environment, and can cause disease in animals and humans. The environment is the main source of R. equi infections in foals; therefore, higher levels of multidrug-resistant (MDR) R. equi in the environment contribute to clinical infections with MDR R. equi. We found that macrolide residues in the environment of horse-breeding farms and the use of thoracic ultrasonographic screening (TUS) for early detection of subclinically affected foals with R. equi infections were strongly associated with the presence of R. equi carrying AMRGs in the soil. Our findings indicate that the use of TUS contributed to historically higher antimicrobial use in foals, leading to the accumulation of antimicrobial residues in the environment and enhancing MDR R. equi.

Keywords: Rhodococcus equi; antimicrobial pollution; antimicrobial resistance selection and maintenance; antimicrobial-resistant bacterial population dynamics.