Actinomycosis of dogs caused by Actinomyces hordeovulneris

Actinomyces hordeovulneris was isolated from the lesions of chronic pyogranulomatous pleuritis and pericarditis of one of three dogs showing similar symptoms. The parietal pleura and the pericardium were thickened and covered with fine short threads of angiofibroblastic tissue. About 500-1000 ml of reddish purulent exudate in the thorax of all three dogs contained large numbers of rice-grain-sized, soft, yellowish-white granules ("sulphur granules"). These granules had a central core of branching filaments of gram-positive bacteria embedded in thick granulation tissue. The parietal pleura, the mediastinal pleura and the pericardium were infiltrated mainly with neutrophils, and to a lesser extent with lymphocytes and plasma cells. A small number of eosinophils and giant cells was also observed. Large numbers of pyogranulomas embedded in the granulation tissue were composed of a core of necrotized granulation tissue, mixed with clusters of gram-positive branching bacteria, surrounded by an area of intact and degenerating neutrophils and lymphocytes. Bacteria were detected in the lesions by Brown-Brenn staining and were isolated from one of the affected animals. The isolated bacteria were identified as A. hordeovulneris. This was the first isolation of A. hordeovulneris in Hungary.