Conversion of Rough to Smooth Forms of Certain Dysentery Bacilli by Repeated Transfers in Dextrose Broth.

Abstract

In our study of the factors influencing change in colony form it was found that repeated transfers in dextrose broth were quite effective in causing reversion of R to S forms of Bact. dysenteriae, Sonne. A typical experiment is shown in the accompanying table.

In this and in similar experiments with different R isolations of other strains, irregularity in the rate of reversion to the S form was always seen. In some cases S colonies appeared early in the series of dextrose broth transfers and soon entirely replaced the R forms, while in other instances only a few S forms resulted even after a number of transplants. Also, intermediate and other variant colony forms were more rarely encountered here than in the course of the S to R change.

In a number of instances cultures which had undergone the S to R change in broth or peptone solutions and then the R to S reversion in dextrose broth were subjected to comparison with the original or parent S culture of the same strain. The newly converted S forms produced the same uniform turbidity in nutrient broth and similar fermentation results in dextrose, lactose and sucrose broths, and they were agglutinated by immune S serum apparently in as high dilution as was the parent S culture. In 0.85% salt solution, however, the recently derived S forms showed some tendency to spontaneous agglutination, while the original S culture showed no such tendency.