Carbohydrate Fermentation Protocol

Abstract

Carbohydrate fermentation tests aid in determining the ability of microorganisms to ferment a specific carbohydrate. Fermentation patterns can be used to differentiate among bacterial groups or species. Fermentation reactions are detected by the color change of a pH indicator as acid products are formed. A color change only occurs when enough acid products have been produced by fermentation of the carbohydrate to lower the pH to 6.8 or less. Another by-product of fermentation is gas, which may be hydrogen or carbon dioxide. If a Durham tube is added to the fermentation broth, the presence of a gas bubble at the top of the tube is another indication that fermentation of the carbohydrate has taken place. While fermentation tests can be performed on microorganisms other than bacteria, this protocol only addresses fermentation of carbohydrates by bacteria.