Because the same pH indicator (phenol red) is also used in these fermentation tubes ... The tube in the center was inoculated with a bilie esculin negative organism and the tube on the left was ...

This weak base raises the pH of the media above 8.4 and the pH indicator, phenol red, turns from yellow to pink. Proteus mirabilis is a rapid hydrolyzer of urea (center tube pictured here). The tube ...