The cross resistance of intermediate resistant mutants to streptomycin (SM) and kanamycin (KM) was studied genetically by several investigators. The present author attempted to observe the cross resistance of one-step highly SM resistant mutants and SM dependent mutants against KM, and to analyze the genetics of the cross resistance using SM dependent mutants. Strains used were Escherichia coli, strain B/r and its mutants. Phage P 1 was used for transduction technique.
One-step highly SM resistant mutants showed the slightly increased resistance to KM, but SM dependent mutants showed various resistant levels, increased or decreased, to KM.
From the results of reciprocal transduction between SM dependent mutants and original strain, it was clearly shown that a resistance level to KM was controlled by SM dependent mutation itself or by a closely linked mutation not separable from SM dependent mutation through transduction.
The analysis of non-dependent (suppressor) mutants derived from SM dependent mutants indicated that resistance level to KM was also controlled by the suppressor mutation.