MacConkey agar and eosin- methylene blue (EMB) agar are __________ media.

Question

Quizplus · Accepted Answer

MacConkey agar and eosin-methylene blue (EMB) agar are both selective and differential media. They are selective because they contain components that inhibit the growth of certain types of bacteria while allowing the growth of others. For example, MacConkey agar is selective for Gram-negative bacteria by incorporating crystal violet and bile salts into the medium, which inhibit the growth of Gram-positive bacteria. EMB agar is selective for Gram-negative bacteria as well, but uses eosin and methylene blue to inhibit the growth of most Gram-positive bacteria.

They are also differential because they contain indicators that allow for the visual differentiation of different groups of bacteria based on their metabolic activity or other characteristics. For example, MacConkey agar contains lactose and a pH indicator that allow for the differentiation of lactose fermenters from non-fermenters, with the former producing pink or red colonies and the latter producing colorless colonies. EMB agar also contains lactose and a pH indicator, as well as eosin and methylene blue dyes that allow for the differentiation of strong lactose fermenters, weak lactose fermenters, and non-lactose fermenters based on colony color and morphology.

MacConkey Agar and Eosin- Methylene Blue (EMB) Agar Are __________