Prevalence of Extended-Spectrum-Beta-Lactamase Enterobacteriaceae in the environment of the equine clinic

Antimicrobial resistance (AMR) is a growing concern in both human and veterinary medicine, with extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae posing a particular challenge in clinical settings. Equine hospitals, where antimicrobial use is frequent, may serve as reservoirs for resistant bacteria, contributing to their persistence and dissemination. This study aimed to investigate the prevalence of ESBL-producing Enterobacteriaceae in an equine hospital environment, assess their persistence over time, and identify potential sources of contamination. Environmental samples (n=120) were collected from 40 horse stalls at three time points: upon arrival (T1), after 48 hours (T2), and at discharge or 72 hours after arrival (T3). Additional samples were obtained from empty stalls before new admissions and from stable equipment (e.g., shovels). Bacterial isolates were identified by MALDI-ToF and screened for ESBL production and resistance to additional antibiotics by Vitek 2, and statistical analyses (Fisher’s exact test) were performed to determine significant differences in contamination patterns over time. ESBL-producing bacteria were detected in 22.5% of environmental samples at T1 and T2, with a non-statistically significant increase to 35% at T3. Contamination patterns varied between stall surfaces, with porous materials such as rubber mats and wooden grilles showing higher ESBL-E prevalence. Notably, 8 out 14 tested stable tools carried ESBL-producing bacteria, indicating their role as potential transmission vectors. Pseudomonas spp. was frequently found in stalls where horses had been housed but was absent from tools and empty boxes, suggesting an association with organic material rather than persistent environmental contamination. This study highlights the persistence and transmission of ESBL-producing Enterobacteriaceae in an equine hospital setting. The findings emphasize the role of stable equipment, porous surfaces, and horse-associated shedding in sustaining bacterial contamination. While no carbapenem resistance was detected, high rates of multi drug resistance were found 45 suggesting that continued monitoring and targeted disinfection strategies are essential to mitigate AMR spread. Future studies should focus on genomic tracking of bacterial strains and evaluating intervention-based cleaning protocols to enhance biosecurity in equine clinics.