Ultrastructure of rabbit lung intravenously infected with Mycobacterium simiae "Weiszfeiler" no 52

M. simiae "Weiszfeiler" strain No. 52 belongs to the second Runyon Group of Atypical Mycobacteria characterized by rough, eugonic, yellow-orange pellicle grown on Sauton medium incubated for 14 days at 37 degrees C. A suspension containing 10 mg/ml (equalling 5 times 10-7 viable units) injected intraveneously into rabbits provokes profound changes in the ultrastructure of the pulmonary tissue, manifested in activation of macrophages and pathologic alteration of pneumocytes. In histologic sections stained according to the Ziehl-Neelsen technique and examined in a light-microscope cytoplasmic acid-fast, highly dispersed granules are found in macrophages, resembling in morphological appearance the cellular phospholipids in sarcoid granuloma. Abundant production of interalveolar and interseptal fibrotic collagen tissue was observed in rabbits infected with M. Simiae a rather striking phenomenon in fresh experimental mycobacterial infection in the rabbit. The strain in question should therefore be considered not as Saprophyte but as a Mycobacterium Species with attenuated virulence, closely related to Prissic and Masson's M. scrophulaceum.