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Association between antimicrobial treatment of subclinical pneumonia in foals and selection of macrolide- and rifampicin-resistant Rhodococcus equi strains at horse-breeding farms in central Kentucky.
Abstract: To compare soil concentrations of macrolide- and rifampicin-resistant strains (MRRE) on horse-breeding farms that used thoracic ultrasonographic screening (TUS) to identify foals with subclinical pneumonia combined with subsequent administration of macrolides and rifampin to affected foals (TUS farms) versus soil concentrations on farms that did not (non-TUS farms), determine whether the combined use of TUS and antimicrobial treatment of subclinically affected foals was associated with soil concentration of MRRE, and assess whether there were temporal effects on soil concentrations of MRRE during the foaling season. Methods: 720 soil samples and 20 completed questionnaires from 20 horse-breeding farms (10 TUS farms and 10 non-TUS farms) in central Kentucky. Methods: A questionnaire was used to gather information from participating farms about their 2019 foaling season. Soil samples were collected during January, March, May, and July 2019 for bacterial culture and antimicrobial susceptibility testing to identify any isolates of MRRE. Results were compared for TUS farms versus non-TUS farms. Linear mixed-effects modeling was used to evaluate for potential associations between the soil concentration of MRRE and the use of TUS. Results: Overall, the sum of the mean soil concentrations of MRRE was significantly higher for TUS farms (8.85 log-transformed CFUs/g) versus non-TUS farms (7.37 log-transformed CFUs/g). Conclusions: Our findings indicated that farms that use TUS to identify foals with subclinical pneumonia for antimicrobial treatment select for antimicrobial-resistant strains. Because prognosis is worse for foals infected with resistant versus nonresistant strains of , prudent use of antimicrobials to treat foals with subclinical pulmonary lesions attributed to is recommended.
Publication Date: 2021-03-09 PubMed ID: 33683955DOI: 10.2460/javma.258.6.648Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
Summary
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This research investigates the impact of antimicrobial treatment for subclinical pneumonia in foals on the selection of drug-resistant strains of Rhodococcus equi bacteria at horse-breeding farms in central Kentucky. The results suggest that farms using a specific pneumonia detection method and subsequent drug treatment have higher concentrations of drug-resistant bacteria in their soil.
Objective and Methodology
The main aim of the study was to evaluate the concentration of macrolide- and rifampicin-resistant Rhodococcus equi strains (MRRE) in soil on farms following different strategies. The researchers compared:
- Farms following a thoracic ultrasonographic screening (TUS) approach to identify foals with subclinical pneumonia, followed by macrolide and rifampin treatment (TUS farms)
- Farms not using this approach (non-TUS farms).
The study sought to determine if the combined use of TUS and antimicrobial treatment was linked to soil concentration of MRRE and if the soil concentration of MRRE changed during the foaling season.
A total of 720 soil samples were collected during January, March, May, and July 2019, from 20 horse-breeding farms (10 TUS farms and 10 non-TUS farms). The farmers also filled out questionnaires regarding their 2019 foaling season. The soil samples were cultured and tested for antibacterial resistance to identify MRRE strains.
Key Findings
The study revealed that the mean soil concentrations of MRRE were significantly higher at TUS farms (8.85 log-transformed CFUs/g) compared to non-TUS farms (7.37 log-transformed CFUs/g). This shows a link between the utilization of TUS and subsequent antimicrobial treatment, and an increase in drug-resistant bacteria in the soil of the farms.
Conclusion and Recommendations
The study concludes that horse-breeding farms using TUS to identify foals with subclinical pneumonia for antimicrobial treatment tend to favor the selection of antimicrobial-resistant Rhodococcus equi strains. This is concerning as foals infected with resistant strains have a worse prognosis compared to those infected with nonresistant strains. The authors, therefore, recommend the prudent use of therapeutic antimicrobials for treating foals with subclinical pulmonary lesions related to Rhodococcus equi infection.
Cite This Article
APA
Huber L, Giguère S, Hart KA, Slovis NM, Greiter ME, Dailey CA, Cohen ND.
(2021).
Association between antimicrobial treatment of subclinical pneumonia in foals and selection of macrolide- and rifampicin-resistant Rhodococcus equi strains at horse-breeding farms in central Kentucky.
J Am Vet Med Assoc, 258(6), 648-653.
https://doi.org/10.2460/javma.258.6.648 Publication
Researcher Affiliations
MeSH Terms
- Actinomycetales Infections / drug therapy
- Actinomycetales Infections / veterinary
- Animals
- Farms
- Horse Diseases / drug therapy
- Horses
- Kentucky / epidemiology
- Macrolides / therapeutic use
- Rhodococcus
- Rhodococcus equi
- Rifampin / therapeutic use
Citations
This article has been cited 5 times.- Cohen ND, Flores-Ahlschewde P, Gonzales GM, Kahn SK, da Silveira BP, Bray JM, King EE, Blair CC, Bordin AI. Fecal concentration of Rhodococcus equi determined by quantitative polymerase chain reaction of rectal swab samples to differentiate foals with pneumonia from healthy foals. J Vet Intern Med 2022 May;36(3):1146-1151.
- Song Y, Xu X, Huang Z, Xiao Y, Yu K, Jiang M, Yin S, Zheng M, Meng H, Han Y, Wang Y, Wang D, Wei Q. Genomic Characteristics Revealed Plasmid-Mediated Pathogenicity and Ubiquitous Rifamycin Resistance of Rhodococcus equi. Front Cell Infect Microbiol 2022;12:807610.
- Álvarez-Narváez S, Huber L, Giguère S, Hart KA, Berghaus RD, Sanchez S, Cohen ND. Epidemiology and Molecular Basis of Multidrug Resistance in Rhodococcus equi. Microbiol Mol Biol Rev 2021 May 19;85(2).
- Hardefeldt L, Thomas K, Page S, Norris J, Browning G, El Hage C, Stewart A, Gilkerson J, Muscatello G, Verwilghen D, van Galen G, Bauquier J, Cuming R, Reynolds B, Whittaker C, Wilkes E, Clulow J, Burden C, Begg L. Antimicrobial prescribing guidelines for horses in Australia. Aust Vet J 2025 Dec;103(12):781-889.
- Higgins C, Cohen ND, Slovis N, Boersma M, Gaonkar PP, Golden DR, Huber L. 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).
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