STREPTOMYCIN-DEPENDENT TUBERCLE BACILLI: A SIMPLE METHOD FOR ISOLATION

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Abstract
Mycobacterium tuberculosis, strain H37Rv, was grown in a liquid sorbitan monooleate albumin medium. Streptomycin was then added to a final concn. of 100 [mu]g. per ml. of medium. One ml. of the culture containing 280 million cells was used to inoculate each of 50 plates containing 100 ug. of streptomycin per ml. of solid oleic acid albumin medium. The plates were incubated and examined after 30, 51 and 70 days. Colonies were counted and tested for susceptibility to streptomycin. Of 96 colonies found growing, 81 were streptomycin-resistant, 12 were streptomycin-dependent, and 3 showed increased growth in the presence of the drug. A similar expt. using M. ranae resulted in 40 colonies, of which 27 were resistant, and 13 were dependent. In contrast to streptomycin-dependent M. ranae, some strains of M. tuberculosis are strictly dependent, whereas others exhibit only growth enhancement. Also, a higher incidence of streptomycin-resistant variants was found in the streptomycin-dependent populations of M. tuberculosis. These studies make it possible to isolate streptomycin-dependent M. tuberculosis. from strains not previously exposed to the drug.