Genomic diversity of Taylorella equigenitalis introduced into the United States from 1978 to 2012.
Authors: Hicks Jessica, Stuber Tod, Lantz Kristina, Erdman Matthew, Robbe-Austerman Suelee, Huang Xiaoqiu
Journal: PloS one
Summary
# Editorial Summary: Genomic Diversity of *Taylorella equigenitalis* Introductions into the USA Contagious equine metritis (CEM), caused by the bacterium *Taylorella equigenitalis*, remains a significant disease concern globally despite the United States maintaining official disease-free status; however, sporadic outbreaks linked to imported horses have occurred periodically, prompting investigation into the strain diversity circulating in the country. Researchers sequenced five isolates of *T. equigenitalis* recovered from separate introductions into the USA using both short and long-read sequencing technologies, then compared these high-quality genomes against archived diagnostic samples and published sequences to map genetic variation and identify virulence-associated regions. Genome sizes varied by up to 100,000 base pairs (averaging 1.68 megabases), with four major regions of difference ranging from 15,000 to 45,000 base pairs containing functionally distinct genes: hypothetical proteins, CRISPR elements, haemagglutinin proteins involved in adhesion, and type IV secretion system components—mechanisms typically associated with pathogenicity and host interaction. Notably, *T. equigenitalis* displayed greater genetic diversity than the entire *Mycobacterium tuberculosis* complex, and evidence of streptomycin resistance was detected, highlighting the potential for antimicrobial resistance emergence in CEM isolates. For equine professionals involved in breeding, import protocols, and disease surveillance, these findings underscore the importance of genomic tracking for future CEM introductions and suggest that strain diversity may influence virulence or treatment responsiveness, warranting consideration in diagnostic and management strategies.
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Practical Takeaways
- •Contagious equine metritis remains a disease risk in the US through horse importation; understanding the genetic diversity of introductions supports diagnostic and quarantine protocols
- •The significant genomic diversity among T. equigenitalis strains suggests variable virulence potential and antibiotic resistance profiles may exist in field isolates—treatment protocols should account for this heterogeneity
- •Genomic surveillance of imported horses and diagnostic isolates can track the origin and relatedness of introductions, aiding disease control efforts
Key Findings
- •Five T. equigenitalis isolates introduced to the USA varied in genome size by up to 100,000 base pairs, averaging 1.68 megabases
- •Four main regions of difference (15,000-45,000 bp each) were identified containing CRISPR, hemagglutinin proteins, type IV secretion systems, and hypothetical proteins
- •T. equigenitalis demonstrated greater genetic diversity than the entirety of Mycobacterium tuberculosis complex despite being a bacterial pathogen with limited recombination
- •Streptomycin resistance mechanisms and multiple virulence factors were identified across the isolate collection