Botryomycosis (also known as granular bacteriosis and bacterial pseudomycosis) is an uncommon chronic granulomatous bacterial infection characterized by fungus-like granules in suppurative foci. The granules measure 1-3 mm and are yellow-white, resembling actinomycosis.

Two-thirds of patients have skin involvement. Lesions develop slowly over weeks and months. These patients usually have no systemic symptoms, although local pain and pruritus may occur. A visceral form (usually involving the lungs but sometimes disseminating to the kidneys, liver, or nodes) may rarely occur. Visceral forms may be primary or may occur as a result of cutaneous extension.

Approximately 40% of cases of botryomycosis are due to Staphylococcus aureus, with Pseudomonas spp. causing another 20% of cases. Other reported causative bacteria include Proteus, Moraxella, Serratia, Escherichia coli, Corynebacteria, and streptococci.

Disease is reported worldwide. A history of local injury is common. Patients with low T-cell counts are predisposed to developing botryomycosis, as are patients with alcoholic liver disease, diabetes, human immunodeficiency virus (HIV), cystic fibrosis, hyper-IgE syndrome, and those on chronic corticosteroids. It rarely occurs in healthy individuals. The pathogenesis most likely represents an interaction between bacterial load, the organism's virulence, and the host's immunity.

Botryomycosis may be confused with cellulitis. Immunosuppression and the finding of lesions discharging a granular, purulent drainage should prompt consideration of this diagnosis.