Phenol Red Sucrose Broth
Phenol Red Sucrose Broth is a liquid medium recommended to differentiate microorganisms based on their ability to ferment sucrose. Proteose Peptone and Beef Extract provide nitrogenous compounds, carbon, vitamins and trace elements to the microorganisms, while Sodium Chloride serves as source of essential electrolytes and maintains the osmotic equilibrium. All members of the Enterobacteriaceae family can use Sucrose as an energy source, and therefore grow well in this medium. Sucrose fermentation produces gases and organic acids, being butyric acid the main constituent. The pH indicator Phenol Red shifts from red to yellow upon accumulation of these products, thus revealing Sucrose fermentation. Additionally, production of butyric acid can be recognized by a pungent, foul odor.