Enterococcus asini sp. nov. isolated from the caecum of donkeys (Equus asinus)

Researchers isolated 16 bacterial strains from the caecum of donkeys and identified them as members of the genus Enterococcus based on phenotypic and molecular analysis. The isolates were Gram-positive, non-motile cocci that grew as pairs or short chains. Biochemical testing and 16S rRNA gene sequencing revealed these strains were distinct from all known Enterococcus species. The isolates showed 97.4% sequence similarity to E. avium, E. faecium, and E. pseudoavium but could be differentiated by specific characteristics: they failed to grow in 6.5% NaCl, did not produce acid from mannitol, sorbitol, sorbose, sucrose, raffinose, ribose, and tagatose, produced acid from D-xylose, utilized pyruvate, and tested negative for arginine dihydrolase. The DNA G-C content was 39.4 mol%, consistent with other enterococci. Phylogenetic analysis confirmed the strains formed a distinct lineage within Enterococcus. The authors propose these donkey caecal isolates represent a new species, Enterococcus asini sp. nov., with strain AS2T designated as the type strain and deposited as DSM 11492T.

Key findings

• Sixteen isolates from donkey caecum represent a novel Enterococcus species, E. asini sp. nov., distinct from all previously known Enterococcus species
• E. asini differs from related species by inability to grow in 6.5% NaCl and negative reactions for acid production from multiple substrates including mannitol and raffinose
• 16S rRNA sequencing shows highest sequence similarity (97.4%) to E. avium, E. faecium, and E. pseudoavium, but phylogenetic analysis places E. asini in a distinct lineage
• The species demonstrates a unique phenotypic profile including acid production from D-xylose and pyruvate utilization combined with arginine dihydrolase negativity