Studies on Transformations of Hemophilus influenzae : III. The genotypes and phenotypic patterns of three streptomycin-resistant mutants

A general method of determining the nature of the genotypes in mutants of transformable bacteria with similar phenotypes is discussed. The method is used to identify the genotypic patterns of three mutants of Hemophilus influenzae which are resistant to different levels of streptomycin. A mutant resistant to 700 µg per ml of the antibiotic was found to be made up of two unlinked, independent loci—presumably on different molecules of transforming DNA. These loci, when in separate cells, render them resistant to maximum levels of 10 and 100 µg per ml streptomycin respectively and are therefore designated as Sm(10) and Sm(100). When they enter the same cell they produce a resistance up to 700 µg per ml streptomycin, so the cells are noted as Sm(700). This multiplicative action is more easily visualized as due to two independent processes of combating the antibiotic which enhance each other rather than two identical processes.