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 the 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 upon this description, this medium is ______.

Question

Quizplus · Accepted Answer

EMB agar is both differential, because it allows for the differentiation of organisms based on their lactose fermentation ability (indicated by a color change), and selective, because the presence of methylene blue inhibits the growth of most gram-positive bacteria, thus selecting for gram-negative bacteria.

Eosin-Methylene Blue Agar, or EMB, Is a Commonly Used Bacteriological