A retrospective analysis of bacterial pathogens in wounds in an equine hospital (2017–2022)

Summary Background Bacterial infections are a major cause of morbidity in horses, particularly in soft tissue wounds (STW) and surgical site infections (SSI). Rising antimicrobial resistance poses challenges for timely treatment. Knowledge of common pathogens and their resistance patterns is therefore essential. Objectives This study aimed to characterise bacterial pathogens isolated from STW and SSI at an equine hospital between 2017 and 2022 and to compare prevalent pathogens and their antimicrobial resistance profiles in these groups. Study Design Retrospective observational study. Methods Samples for culture of bacteria from equine wounds submitted to the Section of Veterinary Bacteriology and the Equine Hospital at the University of Zurich between 2017 and 2022 were retrospectively analysed. Wounds were classified as STW or SSI. Antimicrobial susceptibility testing using VITEK® 2 provided minimal inhibitory concentrations which were interpreted using horse‐specific breakpoints where available and otherwise human‐specific breakpoints. Resistance rates of common pathogens, phenotypic methicillin resistance in staphylococci and ESBL production in Escherichia (E.) coli were compared between groups. Results A total of 472 bacterial isolates from 242 samples were included (54% SSI, 46% STW). The most prevalent pathogens were E. coli, Staphylococcus (S.) aureus and Streptococcus (St.) equi ssp. zooepidemicus . E. coli predominated in SSI, while St. equi ssp. zooepidemicus was most prevalent in STW. S. aureus isolates from SSI showed significantly higher resistance to gentamicin, tetracycline and trimethoprim/sulfamethoxazole, as well as higher rates of phenotypic methicillin resistance, than STW isolates. Main Limitations Limitations included the retrospective nature, incomplete susceptibility data, limited equine‐specific clinical breakpoints and inclusion of only hospitalised horses, many pre‐treated with antibiotics. Conclusions Escherichia coli , S. aureus and St. equi ssp. zooepidemicus were the predominant equine wound pathogens, irrespective of wound type. High resistance rates in surgical site infections, especially in S. aureus , highlight the importance of culture and susceptibility testing, especially in these sites.