Abstract
The streptomycin-resistance of M. tuberculosis var. hominis has been studied from genetic aspect, and the following conclusions have been obtained.
The streptomycin-susceptibility of this organism is concerned with three genotypes, sensitivity, lower resistance, and higher resistance. The genotype, for lower resistance consists of multiple factors and produces such mutants as giving various sizes of colonies on the medium containing lower streptomycin concentrations but only small colonies on the medium containing higher drug concentrations. The genotype for higher resistance probably consists of a single gene and produces such mutants as giving large colonies even on the medium containing higher drug concentrations. Mutation to these two genotypes for streptomycin-resistance occurs independently. The system of genetic control for streptomycin-resistance in M. tuberculosis var. hominis appears to be similar to that in Escherichia coli in spite of the difference of bacterial species.
Fluctuation of phenotype in the existence of the same genotype exists also in bacteria.
