Characterization of surface properties and antimicrobial activity of autochthonous lactic acid bacteria isolated from the reproductive tract of healthy mares.

Equine endometritis, a major cause of subfertility in mares, has a significant economic impact on horse breeding. In the face of rising antimicrobial resistance, the use of beneficial bacteria to prevent this disease is a non-antibiotic alternative which aligns with "One Health" principles. This study characterised vaginal autochthonous lactic acid bacteria (LAB) from healthy mares. Out of the 25 presumptive LAB isolates obtained from 15 clinically healthy thoroughbred mares, 24 were confirmed. Surface properties were assessed (autoaggregation, hydrophobicity, biofilm formation, exopolysaccharide production, adhesion to equine epithelial cells), and their antimicrobial activity tested against 17 potentially pathogenic bacteria from clinical endometritis cases. All the LAB autoaggregated and adhered, with mostly medium to high adhesion percentages. Hydrophobicity was generally low. Biofilm was formed in all tested media, with higher values in the absence of surfactants. Exopolysaccharides were produced by 54 % of the isolates depending on the carbohydrate source. Lastly, 70.8 % inhibited all the bacteria tested, notably Streptococcus zooepidemicus, one of the most prevalent causes of equine endometritis. The 17 isolates with the most promising characterization were identified by MALDI-TOF MS as Pediococcus pentosaceus (6), Enterococcus hirae (6), Enterococcus faecalis (4), and Weissella cibaria (1). Compatibility assays indicated that some of them could be combined in a multi-strain probiotic formulation. This study is among the few to examine in detail the potential probiotic properties of LAB from the equine vaginal niche. The findings hint at the possibility of developing multi-strain probiotics to prevent equine endometritis. Further research is needed into their technological suitability, safety, and in vivo efficacy.