Actinomyces sp. detected by next-generation sequencing in paraffin-embedded, formalin-fixed tissues of a dog with severe panophthalmitis and periocular cellulitis.

A 9-mo-old, castrated male Saint Bernard dog was presented for evaluation of periorbital swelling, severe uveitis, and secondary glaucoma. Concurrently, chest radiographs had evidence of pneumonia. Enucleation was performed after failure of aggressive medical management. Histopathology of the globe confirmed severe necrosuppurative panophthalmitis and periocular cellulitis with myriad intra- and extracellular bacteria forming long filamentous chains. The bacteria were gram-positive and GMS-positive but acid-fast-negative. Next-generation sequencing (NGS) was performed on formalin-fixed, paraffin-embedded (FFPE) tissue from the eye. We identified a bacterium in the Actinomycetaceae family with a 100% BLAST match, suggestive of the previously described Actinomyces catuli strain (CCUG 41709). Clinical improvement followed enucleation and continued medical management, leading to reduction of the periocular swelling and resolution of the lung disease. Uveitis is common in dogs and is the most common cause of glaucoma. In many cases of bacterial uveitis, the exact bacterial organisms remain unknown if culture is not performed before fixation. Actinomyces sp. should be considered in patients with severe endophthalmitis or panophthalmitis, especially with evidence of systemic disease. NGS on FFPE samples may be a useful tool for identifying infectious organisms, especially in cases in which culture is not an option.