[Physicochemical characteristics of transfer derepressed pKMR plasmids]

A group of transfer derepressed R factors (pKMR plasmids) was identified with the methods of conjugation and transformation in 2 antibiotic resistant strains of the dysentery bacillus, i. e. Shigella flexneri 3c and Sh. sonnei isolated from patients with acute dysentery. The antibiotic resistance in S. flexneri was controlled by plasmid pKMR 202-2 (Sm Tc Cm Km Su) with a molecular weight of 59 MD and that in Sh. sonnei was controlled by 2 plasmids, i. e. pKMR 203-2 (Ap Sm Tc Cm Km Su) and pKMR 203-3 (Ap Tc Cm Su) with molecular weights of 99 and 65 MD, respectively. When treated with restriction endonuclease BamH 1 plasmids pKMR 203-2 and pKMR 203-3 had each only one fragment with the similar molecular weight (7.7 MD). At the same time plasmid pKMR 202-3 differed from plasmid pKMR 202-2 only by the presence of an additional fragment BamH 1 with a molecular weight of 7.7 MD. The other 6 fragments of both plasmids had similar molecular weight. The data suggest that though plasmids pKMR 202-2 and pKMR 203-3 differ in their phenotypic features, they are closely related and possible belong to the same Inc-group. It was also shown that plasmid pKMR 202-2 segregated on transformation with formation of a nonconjugative plasmid pKMR 202-1 with a molecular weight of 16.6 MD.