Studies on the Virulence of Atypical Acid-Fast Bacilli: On the fate of viable bacilli and the pathological changes in organs of mice intravenously infected with various types of atypical acid-fast bacilli

In the present paper it was attempted to make the comparative studies on the virulence of atypical acid-fast bacilli isolated in U. S. A. and Japan and various types of mycobacteria. At the different periods after the intravenous infection of these strains, three mice of each group were sacrificed. The fate of viable bacilli in organs was determined by culture and the pathological changes were histologically examined. The results obtained were summarized as follows.(1) Photochromogenic strains isolated in U. S. A. had high virulence for mice, showing almost the same grade of bacterial multiplication and pathological changes in organs of mice as those infected with human type (H2), bovine type (Ravenel) and avian type (Kirchberg) tubercle bacilli. (2) Mice infected with nonphotochromogenic and scotochromogenic strains and rapid growers showed a steady decrease in microbial population and slight pathological changes in organs. Therefore, the virulence of these strains was considered to be very low for mice. (3) A nonphotochromogenic strain, which had special affinity to the kidney of mice. This strain was isolated freshly from sputum of a patient. (4) The principal pathological changes of mice infected with atypical acid-fast bacilli was the granulom, consisting mainly of the proliferation of epithelioid cells and quite resembling to those of tuberculous lesions produced by tubercle bacilli.