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

Overview

• This study investigated the presence, genetic diversity, and antibiotic resistance of the bacterium Taylorella asinigenitalis in a breeding population of Grand Noir du Berry (GNB) donkeys in France.
• Researchers found that T. asinigenitalis is prevalent in male donkeys, can spread between animals, and may develop resistance to certain antibiotics, highlighting concerns for breeding herd health management.

Background and Study Context

• Organism of interest: Taylorella asinigenitalis is a Gram-negative bacterium commonly found in the genital tract of equines, especially donkeys.
• Related species: It is closely related to Taylorella equigenitalis, which causes contagious equine metritis, a significant reproductive disease in horses.
• Pathogenicity: While T. asinigenitalis is generally considered non-pathogenic, it has been linked to uterine infections (endometritis) in natural and experimental settings.
• Project context: The SAFRAN project, initiated by INRAE in 2024, aims to preserve fertility and improve reproductive outcomes in the endangered French donkey breed Grand Noir du Berry.
• Complementary study: Although identifying infectious agents was not a primary goal, a supplementary investigation was performed in the newly established GNB breeding herd to monitor microbial presence.

Methodology

• Sampling: Between 2024 and 2025, 28 GNB donkeys (6 males and 22 females) were sampled for bacteriological, mycological, and molecular testing.
• Testing sites: Semen and penile samples were examined for the presence of T. asinigenitalis using culture and PCR methods.
• Additional microbial assessments: Opportunistic microorganisms were also identified from the samples.
• Antibiotic treatments: Donkeys testing positive were treated with antiseptics and several antibiotics: local gentamicin, systemic enrofloxacin, followed by systemic oxytetracycline.
• Genome sequencing: Whole-genome sequencing and multilocus sequence typing (MLST) were conducted to characterize bacterial strains and their genetic diversity.
• Phylogenetic analyses: Determined relationships among strains to infer transmission patterns.
• Resistance screening: Detection of mutations conferring antibiotic resistance was performed, focusing on known quinolone resistance markers.

Key Findings

• Exclusive detection in males: T. asinigenitalis was isolated only in male donkeys, with no detection of T. equigenitalis in any sampled animal.
• Bacterial loads: PCR results suggested that bacterial loads were lower in semen compared to penile sites.
• Persistence despite treatment: Some males remained intermittently or persistently positive for T. asinigenitalis despite undergoing rigorous antiseptic and multiple antibiotic treatments.
• Genomic diversity: Seven novel MLST types of T. asinigenitalis were discovered, expanding known genetic diversity within this species.
• Transmission insights: Initially, each male carried a distinct bacterial strain, but later data indicated clustering around specific sequence types (ST102 and ST104), suggesting horizontal transmission among males.
• Antimicrobial resistance: Treatment with enrofloxacin, a fluoroquinolone antibiotic, selected for quinolone-resistant T. asinigenitalis strains harboring a GyrA S83I mutation—an established marker for fluoroquinolone resistance.

Implications and Recommendations

• Infection dynamics: T. asinigenitalis can circulate efficiently among breeding male donkeys, indicating the importance of monitoring this bacterium in reproductive health programs.
• Resistance development: The emergence of antibiotic-resistant strains due to certain treatments underscores the risk of resistance selection when using fluoroquinolones in managing this infection.
• Biosecurity measures: Strict surveillance and infection control protocols are necessary to limit spread and persistence of T. asinigenitalis in donkey breeding populations.
• Antibiotic stewardship: Given the demonstrated resistance, avoidance of fluoroquinolones like enrofloxacin in treatment regimens for T. asinigenitalis should be considered to reduce resistance pressure.
• Conservation impact: Maintaining the health and reproductive viability of the endangered Grand Noir du Berry donkey breed requires careful integrated approaches combining microbiological monitoring, targeted treatment, and biosecurity.