Bordetella bronchiseptica phase variation induced by crystal violet

A method for effective induction of phase variation in Bordetella bronchiseptica by treatment with crystal violet (CV) is presented. When grown in CV-broth, phase I cells dissociated into three serial phases. Appearance of variant cells was observed simultaneously with the beginning of cell multiplication. The maximum effect of CV was obtained at a concentration of 8 micrograms/ml, when the proportion of variants in the population reached 100%. The main factors which affected phase variation were concentration of CV, culture age, and temperature of treatment. The phase variants obtained were phenotypically stable upon serial passages on Bordet-Gengou agar plates. By this treatment, no reversion of phase descendants to former phases was observed.