MUTAGENIC EFFECT OF MITOMYCIN C ON MYCOBACTERIUM AND ITS COMBINED EFFECT WITH ULTRAVIOLET IRRADIATION

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1. Mitomycin C acted as a mutagen only when it acted bactericidally. It acted on mycobacteria bactericidally only when cells were in their actively growing state. It was almost ineffective in causing loss of viability and mutations when cells were in the resting state. Mitomycin C never exhibited its mutagenic action under the bacteriostatic conditions. When Mycobacterium "Jucho" was incubated statically in a phosphate buffer solution, containing 1μg of mitomycin C per ml, for 24 hours neither loss of viability nor increase of mutations occurred. However, when the organism was incubated under ashaking condition in the Sauton medium containing the same concentration of the antibiotic for 5 hours, a significant increase in mutation frequency and a loss of viability were observed.
2. The combined effect of mitomycin C with ultraviolet irradiation as a mutation, was slightly antagonistic. The mutation frequency actually observed with the combined use of mitomycin C and ultraviolet irradiation was much less than that calculated from a supposition of an individual action of both mutagens, although it was higher than the mutation frequency obtained when a single mutagen was used.
3. Mitomycin C acted bacteriostatically at very low concentrations, and it inhibited the growth of M. tuberculosis H37Rv and M. Jucho at concentrationsof 0.32μg/ml and 0.04μg/ml, respectively.