Prevalence, genomic diversity and emerging antimicrobial resistance of Taylorella asinigenitalis in Grand Noir du Berry breeding donkeys.

Taylorella asinigenitalis is a fastidious Gram-negative bacterium of the equine genital tract, found more commonly in donkeys than horses. Although considered non-pathogenic, it is closely related to Taylorella equigenitalis, the agent of contagious equine metritis, and has been linked to experimental and natural cases of endometritis. The SAFRAN project (French acronym for "Sauvegarde de la fertilité de l'âne", meaning "Preservation of donkey fertility"), launched in 2024 by the French National Research Institute for Agriculture, Food and Environment (INRAE) with support from the Centre-Val de Loire region, aims to improve the reproductive performance in an endangered French donkey species, the Grand Noir du Berry (GNB). While screening for infectious agents was not a primary objective of the SAFRAN project, a complementary study was conducted in the newly-established GNB breeding herd. Between 2024 and 2025, 28 donkeys (six males, 22 females) underwent bacteriological, mycological and molecular testing. T. asinigenitalis was detected and isolated exclusively in males, whereas T. equigenitalis was absent. PCR data suggested lower bacterial loads in semen than penile sites. Several opportunistic microorganisms were also isolated. Despite antiseptic and antibiotic treatments - including local gentamicin, systemic enrofloxacin, and subsequently systemic oxytetracycline - some males remained persistently or intermittently positive. Whole-genome sequencing revealed seven previously undescribed MLST types. Phylogenetic analyses indicated that each male initially carried a distinct strain, but later clustering around ST102 and ST104 suggested horizontal transmission. Enrofloxacin treatment selected quinolone-resistant strains carrying the GyrA S83I mutation. These findings demonstrate that T. asinigenitalis circulates efficiently among male GNB donkeys and can acquire antimicrobial resistance, emphasising the need for targeted surveillance and strict biosecurity while avoiding fluoroquinolones in herd health plans.