Phenol Red-China blue as an indicator in fermentation tests of bacterial cultures

Abstract

A special medium for the differentiation of members of the typhoid-coli group of bacteria was devised by me1 in 1916; it contained decolorized china blue as an indicator. The use of this stain in combination with malachite green had been recommended in 1911 by Bitter2 in a special medium for the isolation of typhoid bacilli from stools. Harding and Ostenberg8 employed decolorized soluble a stain related to china blue, as an indicator for acid formation in broth cultures. Bronfenbrenner4 recommended the use of a combination of china blue and rosolic acid as an indicator for both acid and alkali in fluid mediums for fermentation tests of growing bacterial cultures. He did not decolorize the china blue before adding it to the medium; but if the medium was sufficiently alkaline, the china blue was decolorized during the sterilization. Bronfenbrenner, Davis, and Morishima5 described the action of this indicator in milk mediums. The fact that rosolic acid is insoluble in water appeared to me to be a disadvantage.