Question

Eosin-methylene blue agar, or EMB, is a commonly used bacteriological medium for growing gram-negative bacteria from complex environments. It contains two dyes, eosin and methylene blue, as well as sugar lactose. Eosin is a pH indicator that changes color when the medium is acidic, while methylene blue inhibits the growth of most gram-positive bacteria. If an organism consumes lactose, acid will be produced, causing the bacterial colonies to change color. Based on this description, this medium is_____________.

Answer 1

Differential and selective

Step-by-step explanation:

A selective media is one used for growth of only selected microorganisms. Since this medium is using methylene blue to inhibit gram-positive bacteria and allowing the growth of gram-negative, then we can cathegorize it as selective. Selective growth media is also used in cell culture to ensure the survival or proliferation of cells with certain properties, such as antibiotic resistance or the ability to synthesize a certain metabolite, so the researchers can study or farm said metabolite or an specific reaction to an antibiotic.

Meanwhile, a differential media, also called indicator media, distinguish one microorganism type from another on the same media. This is done through biochemical characteristics which reacts to specific nutrients or indicators (neutral red, phenol red, eosin y, or methylene blue) added to the medium to visibly indicate the defining characteristics of a microorganism. Since this media is changing colors when the acidic concentration increases, it is a differential media as well.