A microbiologist plated a bacterium on a specific medium. After incubation, she noted that the previously yellow medium was now hot pink and there were numerous bacterial colonies growing on the medium. What type of medium did the microbiologist use in this example?

A) selective

B) general purpose

C) nonsynthetic

D) differential

A differential medium

Explanation:

Bacteria require nutrients for growth, and in order to culture (grow) them and study their characteristics, different types of media are used.

A selective media is used to grow a particular group of organism while suppressing another. So a selective media usually has an inhibitory agent, which will inhibit the growth of the undesired group. An antibiotic can be added to a medium to make it selective.

A general purpose medium as the name implies can be used to grow any group of bacteria. It has no inhibitory agent and indicator that differentiates between organisms. An example of general purpose media is nutrient agar.

A non-synthetic media is made from natural ingredients.

A differential media differentiates between groups of organisms. Example of differential media is MacConkey agar and Mannitol Salt agar. On MacConkey agar, lactose fermenting bacteria turn pink while non-lactose fermenting bacteria are colorless.

On Mannitol Salt agar, mannitol fermenting bacteria turn yellow while non-mannitol fermenting bacteria are colorless. Mannitol Salt agar is also a selective medium. It has a high salt concentration which inhibits certain organisms.