GENETIC STUDIES ON THE MECHANISM OF ACQUIRED STREPTOMYCIN-RESISTANCE IN MICROORGANISMS

Abstract

In studying the effect of SM on the resting cells of bacteria, no evidence was obtained which supports the specific induction of resistance by SM, because neither zero-point mutants nor end-point mutants were induced. Various facts which were thought to be explained only with the mutagenic action of this antibiotic have been shown to be more naturally explained by the spontaneous mutation with selection theory. “Relative selection” due to “relative inhibition” was emphasized in elucidating the emergence of SM-resistance in the wild population.
The experiment on the development of SM-resistance in the minimal medium made it likely that the mutagenic action of SM does not operate but that the spontaneous mutation with selection would be a sole factor.
In relation to the development of SM-resistance, the so-called, SM-resistance was classified into “SM-resistance” and “SM-indifference”, and “SM-resistant” cells were further subdivided into “dysgonic resistant” and “eugonic resistant” cells. “SM-indifference” was considered to be a specific phenomenon for SM, while “SM-resistance” was thought to correspond to the other drug-resistance. The genetic characters of these 3 types of mutants are discussed.
The author is greatly indebted to Prof. Dr. D. Ushiba for his kind sugges tions in conducting this study and for reading the manuscript of this paper.