Epidemiology and Antimicrobial Resistance of Salmonella Isolated from Racehorses and Horsemen in Northeastern Thailand

Salmonella is one of the major causes of foodborne diseases in humans. These bacteria can colonize within the gastrointestinal tracts of both humans and animals, and there have been reports of incidences of Salmonella in horses. This study aimed to investigate the prevalence, serotypes, and antimicrobial resistance of Salmonella isolates from racehorses and horsemen, as well as to explore the possible transmission between horses and humans. Fecal samples from racehorses (247 samples) and horsemen (33 samples) were collected from horse farms located in 3 provinces of upper Northeastern Thailand between March and August 2019. Salmonella was isolated and identified. Broth microdilution was used to determine the minimal inhibitory concentrations (MICs) of the antimicrobial agents for antimicrobial. Salmonella isolates were detected in 4.86% (12/247) of racehorses and 3.03% (1/33) of horsemen. The most commonly found serotypes in the isolates obtained from the racehorses were Abony (25%) and Iganda (16.67%). Only the Tumodi II serotype was found in one horseman. Salmonella isolates collected from the racehorses had been the most resistant to streptomycin (66.67%), while the isolate from a horsemen had been resistant to ampicillin, streptomycin, oxytetracycline, and to tetracycline. Although Salmonella transmission between racehorses and horsemen was not found to be obviously present in this study, the appropriate use of antimicrobials and hygienic procedures are still necessary in order to prevent antimicrobial resistance and the transmission of drug-resistant Salmonella between horses and humans.