Evolution of In Vitro Antimicrobial Susceptibility of Equine Clinical Isolates in France between 2016 and 2019

SIMPLE SUMMARY: The emergence and the spread of antimicrobial drug resistant bacteria around the world is a major public health issue. In fact, the transmission of these bacteria from animals to humans has been already observed. In this context, the close relationships between horses and humans may contribute to cross-infection. Our objective in this study was to describe the antimicrobial susceptibility profiles of major equine pathogens over a 4-year period (2016–2019). For this purpose, more than 7800 bacterial isolates collected from horses in France with different types of infection were phenotypically analysed for their antimicrobial susceptibility. An increase in the resistance of Staphylococcus aureus and Enterobacter spp. was observed, especially between 2016 and 2019, with the percentage of multi-drug resistant strains rising from 24.5% to 37.4%, and from 26.3% to 51.7%, respectively. Our results point to the need to support veterinary antimicrobial stewardship to encourage the proper use of antibiotics. ABSTRACT: The present study described the evolution of antimicrobial resistance in equine pathogens isolated from 2016 to 2019. A collection of 7806 bacterial isolates were analysed for their in vitro antimicrobial susceptibility using the disk diffusion method. The most frequently isolated pathogens were group C Streptococci (27.0%), Escherichia coli (18.0%), Staphylococcus aureus (6.2%), Pseudomonas aeruginosa (3.4%), Klebsiella pneumoniae (2.3%) and Enterobacter spp. (2.1%). The majority of these pathogens were isolated from the genital tract (45.1%, n = 3522). With the implementation of two French national plans (named ECOANTIBIO 1 and 2) in 2012–2016 and 2017–2021, respectively, and a reduction in animal exposure to veterinary antibiotics, our study showed decreases in the resistance of group C Streptococci, Klebsiella pneumoniae and Escherichia coli against five classes, four classes and one class of antimicrobials tested, respectively. However, Staphylococcus aureus, Escherichia coli and Enterobacter spp. presented an increased resistance against all the tested classes, excepted for two fifths of E. coli. Moreover, the percentages of multi-drug resistant strains of Staphylococcus aureus and Enterobacter spp. also increased from 24.5% to 37.4% and from 26.3% to 51.7%, respectively. The data reported here are relevant to equine practitioners and will help to improve knowledge related to antimicrobial resistance in common equine pathogens.