Question

lab 6: selective and differential media objectives

Answer 1

Selective media is the one which is used to a specific group of bacterial cells. In this type of media, one type of bacterial cells are selected Over The Other type of bacterial cells. For example, mannitol agar salt is a media which is used to differentiate between gram positive and Gram Negative cell. It is toxic to gram-negative cells and therefore they cannot grow on it. Only Gram Positive cells will grow.

A differential media is the one which is used to differentiate between closely related bacterial species. Differentiation is done on the basis of Colony morphology or their ability to use the nutrient media which is done on the basis of biochemistry of microbes. For example, blood Agar which uses the ability of bacteria cell to lyse the red blood cells to form colonies (hemolyses). This medium is used to differentiate between various species of staphylococcus which use blood Agar differently.

To identify a microbes in microbiology experiment, we first used preliminary test like gram staining or endospore staining or acid fast staining. Then we use confirmatory test to identify the bacterial species. In the confirmation, first we use selective media and then we use differential medium.

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