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.