Antimicrobial resistance in horses in Mexico from a One Health perspective

Antimicrobial resistance is one of the main threats to global health in the 21st century, as it decreases the effectiveness of antibiotics in both human and veterinary medicine, with direct implications for public health, food safety and the environment. Furthermore, the WHO and the OIE note that over 70% of emerging infectious diseases in humans are of zoonotic origin, highlighting the role of animals in the transmission of resistant pathogens. In this context, equines are of particular importance due to their close interaction with humans in various activities, which facilitates the cross-species transmission of resistant zoonotic bacteria. However, despite its epidemiological and public health significance, the information available on antimicrobial resistance in horses remains limited in Mexico, even though the country has the world’s second-largest horse population. Against this backdrop, the aim of this study was to identify the bacteria present in horses in central Mexico and to determine their antimicrobial resistance profiles.

To this end, rectal swabs were collected from horses exhibiting clinical signs of enteric disease. The samples were processed using bacterial culture, followed by antimicrobial susceptibility testing against eleven antibiotics commonly used in humans and animals, in accordance with the guidelines established by the CLSI.

This study analysed 30 equine samples, from which various zoonotic enterobacteria were isolated, mainly Escherichia coli, Salmonella spp. and Klebsiella spp. Furthermore, phenotypic profiles revealed high levels of resistance to antimicrobials commonly used in veterinary and human medicine; as, in more than 80% of the isolated strains, susceptibility to antimicrobials was less than 50%, whilst 51% showed resistance to three or more families of antibiotics, classifying them as multidrug-resistant, with β-lactams, tetracyclines and sulphonamides being the least effective against these strains. These findings support the ‘One Health’ approach, which recognises antimicrobial resistance as an interconnected problem affecting human, animal and environmental health.