Cystine promotes the formation of cystine-dependent dwarf colonies. Bromothymol blue is the indicator used in the agar, it changes to yellow in case of acid production during fermentation of lactose or changes to deep blue in case of alkalinization.
Cystine encourages the formation of cystine-dependent dwarf colonies. Methylthymol blue is the indicator used in the agar; it turns yellow if acid production occurs during lactose fermentation or deep blue if alkalinization happens.