The growth of Mycobacterium tuberculosis and Mycobacterium johnei in a modification of Dubos medium.

The success achieved in growing Mycobacterium tuberculosis in liquid medium (Dubos & Davis, 1946) has aroused interest in the possibility of growing M . johnei in this fluid or similar media, modified to contain the essential growth-promoting substances for these organisms. So far no success has been achieved (Davis & Dubos, 1948; Taylor, 1950). The combination of Tween 80 and bovine albumin fraction V has certain disadvantages which are not completely overcome by modifications introduced by Dubos and his co-workers (Dubos, 1947; Dubos & Middlebrook, 1948; Davis & Dubos, 1948). When added to the rest of the medium, the water soluble lipids selected by Dubos acquire growth-inhibiting properties on standing for several weeks; in consequence, it is necessary to use freshly prepared solutions. In addition, fraction V bovine albumin on incubation with Tween 80 may give rise to toxic substances which are related to the lipase content of the serum (Davis & Dubos, 1948). To some extent this effect can be reduced by heating albumin solution for 30 min. at 56" to destroy most of the lipolytic activity. In the course of experiments to find a substitute for fraction V it was found that Dubos medium without albumin, but enriched with serum treated with ' Liquoid ' (Na polyanethol sulphonate; Roche Products Ltd.) was suitable for the cultivation of the tubercle bacillus and that, with certain modifications, this medium also grew M.johnei. As any new medium incapable of supporting the growth of the tubercle bacillus was unlikely to be of value for M.johnei, all trials were run in parallel with a strain of M . tuberculosis var. bovis which was regarded as an appropriate control test organism.