EMB Agar Preferentially Selects for the Growth of ________ Bacteria

Question

EMB agar preferentially selects for the growth of ________ bacteria.
A) gram-positive
B) gram-negative
C) gram-variable
D) both gram-positive and gram-negative

Accepted Answer

EMB (Eosin Methylene Blue) agar preferentially selects for the growth of gram-negative bacteria, especially those that ferment lactose. The agar contains eosin and methylene blue dyes, which inhibit the growth of gram-positive bacteria and allow the growth of gram-negative bacteria. It also contains lactose as a carbohydrate source, which is fermented by lactose-fermenting gram-negative bacteria, resulting in the production of acid and gas that turns the colonies dark purple or black.