STUDIES ON THE COLONY MUTATION OF VIBRIO COMMA AND EL TOR VIBRIO ON DIFFERENTIAL PLATING MEDIA CONTAINING BILE SALTS

Abstract

Small mutant colonies of Vibrio comma and El Tor Vibrio, which were isolated in 1958-1963, were found on the differential plating media containing bile salts, besides the R or rugose type colonies reported by Balteanu and others. Mutant colonies were found most frequently on the Mac Conkey's medium than on the desoxycholate medium, but not on the TCBS medium. The Balteanus rugose and R type colonies did not appear on these media.The mutation rates of strains, subcultured on heart infusion agar slant every week, were relatively higher than frozen dried stock cultures of the same strains. The mutation rates seemed to be affected by the concentration of desoxycholate in the media. Rugose I type colonies appeared about 80% to all colonies on the desoxycholate agar plate without desoxycholate, but decreased with the raise of its concentration, and did not appear on the media containing above 0.07% of desoxycholate. Rugose II and III type colonies appeared very rarely on the media containing above 0.1% of Na. desoxycholate, small I type colonies were found some 40% to all colonies. Small II type colonies were most frequently produced at 0.04% of desoxycholate.Some of the small II type colonies were more exacting in nutrition than other colonies of the parent strains. They could hardly grow on heart infusion agar or peptone water, and all sugar-fermentations and hemolysin production became negative. These mutants showed the decrease in the resistance to alkaline and bile salts. These characters were fixed and did not change by serial transfers.Other mutant strains scarcely showed any changes in biological characters, and these strains did not seem true mutant strains, because back mutation took place in about 70% of the growing cells.