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A Common Practice of Widespread Antimicrobial Use in Horse Production Promotes Multi-Drug Resistance
S Álvarez-Narváez1, L J Berghaus1, E R A Morris2
1Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, Ga, USA.
Abstract:
The practice of prophylactic administration of a macrolide antimicrobial with rifampin (MaR) to apparently healthy foals with pulmonary lesions identified by thoracic ultrasonography (i.e., subclinically pneumonic foals) is common in the United States. The practice has been associated epidemiologically with emergence of R. equi resistant to MaR. Here, we report direct evidence of multi-drug resistance among foals treated with MaR. In silico and in vitro analysis of the fecal microbiome and resistome of 38 subclinically pneumonic foals treated with either MaR (n = 19) or gallium maltolate (GaM; n = 19) and 19 untreated controls was performed. Treatment with MaR, but not GaM, significantly decreased fecal microbiota abundance and diversity, and expanded the abundance and diversity of antimicrobial resistance genes in feces. Soil plots experimentally infected with Rhodococcus equi (R. equi) and treated with MaR selected for MaR-resistant R. equi, whereas MaR-susceptible R. equi out-competed resistant isolates in GaM-treated or untreated plots. Our results indicate that MaR use promotes multi-drug resistance in R. equi and commensals that are shed into their environment where they can persist and potentially infect or colonize horses and other animals.
Insights
Prophylactic macrolide antimicrobial with rifampin (MaR) use in foals promotes antimicrobial resistance in Rhodococcus equi and other bacteria. This resistance can spread to the environment, potentially infecting other animals.
Area of Science:
- Veterinary Medicine
- Microbiology
- Antimicrobial Resistance
Background:
- Prophylactic macrolide antimicrobial with rifampin (MaR) is commonly used in foals with subclinical pneumonia in the US.
- This practice has been linked to the emergence of MaR-resistant Rhodococcus equi.
- Direct evidence of multi-drug resistance in foals treated with MaR is reported.
Purpose of the Study:
- To investigate the impact of MaR treatment on the fecal microbiome and resistome of subclinically pneumonic foals.
- To compare the effects of MaR with gallium maltolate (GaM) and untreated controls.
- To assess the selection of MaR-resistant R. equi in an experimental setting.
Main Methods:
- In silico and in vitro analysis of fecal microbiome and resistome.
- Treatment of 38 subclinically pneumonic foals with MaR (n=19), GaM (n=19), or no treatment (n=19).
- Experimental infection of soil plots with R. equi and treatment with MaR, GaM, or no treatment.
Main Results:
- MaR treatment significantly reduced fecal microbial diversity and increased antimicrobial resistance genes.
- GaM treatment did not significantly alter the fecal microbiome or resistome.
- MaR selected for MaR-resistant R. equi in soil, while susceptible strains predominated in GaM-treated or untreated soil.
Conclusions:
- MaR use in foals drives the development of multi-drug resistance in R. equi and commensal bacteria.
- These resistant bacteria are shed into the environment, posing a risk for infection in other animals.
- Alternative treatments like GaM may mitigate the development of antimicrobial resistance.
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