The ultrastructure of mycobacterium marinum granuloma in man

3 biopsies of 3-5 week-old nodular lesions in 2 patients with so-called swimming-pool (aquarium-) granuloma have been examined by electron microscopy. The cytohistological spectrum simultaneously comprises acute exudative as well as chronic proliferative phenomena. Epithelioid cells and collagen producing fibroblasts are already conspicious in 3 week-old granuloma. According to the cytological composition the Mycobacterium marinum granuloma represents a high-turnover granuloma with immunogenic origin. It is comparable to mycobacterial diseases in the presence of well developed cell mediated immunity (Lupus vulgaris, tuberculoid leprosy). Degrading mycobacteria have been rarely detected in phagocytes and are compared with viable bacilli in macrophages of experimentally infected mice. Curved and annular parallel membranes ("worm-like structures") in the cytoplasm of transformed macrophages and in fibroblasts presumably originate from the membranes of endoplasmic reticulum. Cord-like structures with transverse bands (periodicity 170-180 A) in the lumen of RER of some fibroblasts are interpreted as intracellularly aggregated collagen precursors.