Mycobacterium fortuitum pneumonia in a cat and the role of lipid in the pathogenesis of atypical mycobacterial infections.

Mycobacterium fortuitum is a saprophytic, fast-growing, nontuberculous, and nonlepromatous mycobacterium that can cause infections in animals and humans. In dogs and cats, it is one of the most common agents of ulcerative dermatitides and panniculitides caused by atypical mycobacteria. In humans, it is frequently found in lipoid pneumonias or contaminated surgical sites. We report a cat with granulomatous pneumonia caused by M fortuitum resembling lipoid pneumonia in humans. The similarity between the histopathology of the lung and skin lesions caused by this organism in dogs and cats is emphasized. We discuss the role of lipids in the pathogenesis of mycobacterioses and suggest an association between atypical mycobacteria and lipid-rich environments. We conclude that M fortuitum should be included as a differential in cases of lipid-rich pneumonias that do not respond to common antibiotics.