The pleiotropic effect of spontaneous single-step variant production in Mycobacterium intracellulare.

A strain of M. intracellulare, AT 13786, derived from human sputum, gave rise to transparent and opaque colony forms which were cloned and investigated. From the results the conclusion was drawn that the opaque form was a mutant of the transparent type and possessed alterations in the cell envelope which were responsible for enhanced permeability. The opaque form was more susceptible to a number of antibiotics; it grew faster in standard medium, and was not dependent on tween for dextrose utilization. Tween enhanced the antibiotic susceptibility of the opaque form more than that of the transparent. The avirulent opaque colony form of the pathogenic strain serotype Boone also revealed a loss of tween dependence for dextrose utilization. The significance of the overall change has been discussed with respect to the question of virulence.