Discuss simple carbohydrate fermentation tests.

Discuss simple carbohydrate fermentation tests.

Expert Solution

Carbohydrate fermentation test classifies organisms according to their ability to metabolize carbohydrates, in order to obtain energy. Certain microorganisms ferment carbohydrates, producing acid (with or without gas). The acid produced is detected by the color change in the medium, associated with lowering of pH, whereas the production of gas is indicated by the formation of bubbles in the Durham tubes. Phenol Red Carbohydrate broth is used for this purpose. Specific carbohydrates, such as glucose, lactose, sucrose, etc., and a pH indicator (phenol red), which will indicate the production of acid, are added in the medium.

Based on the microrganisms present, and their ability to ferment carbohydrates, different results are obtained-

Positive- The color of the pH indicator changes. For example, Phenol Red is red in color at an alkaline pH, and turns yellow at an acidic pH. Therefore, production of acid as a result of fermentation will be indicated by the development of yellow color (lowering of pH). Production of acid can also be accompanied with production of gases, such as hydrogen and carbon dioxide. This is indicated by the presence or absence of gas bubbles in the durham tubes.

Negative- The medium remains red. This indicates that the bacteria has not fermented the particular carbohydrate present in the media.

gladiator answered 1 year ago

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