Identification of Actinomyces denticolens as a cause of a soft tissue abscess in a horse.

Abstract

CASE REPORT: A 6-year-old Arabian mare had a 4-week history of a subcutaneous mass (15 × 15 cm) at the base of the neck, cranial and distal to the prescapular lymph node on the right side. The mass was solid and painful on deep palpation. Ultrasonographic examination showed a soft-tissue abscess. Purulent aspirate was submitted for bacterial culture, which showed a moderate growth of an Actinomyces species. 16S rRNA gene sequencing was performed for definitive identification. Gene sequencing demonstrated close nucleotide homology with A. denticolens. Prolonged therapeutic management resulted in resolution of the abscess with a small scar. CONCLUSIONS: Speciation of actinomycetes is not a routine diagnostic procedure and 16S rRNA gene sequencing to identify A. denticolens as a cause of soft-tissue abscessation in horses in Australia has not been previously described. Practitioners should include this bacterial species in their differential diagnosis, particularly if abscesses do not respond to drainage and lavage alone.