Consider a culture medium on which only gram-positive organisms such as Staphylococcus aureus colonies can grow due to an elevated NaCl level. A yellow halo surrounds the growth, indicating the bacterium fermented a sugar in the medium, decreasing the pH as a result and changing the color of a pH indicator chemical. This type of medium would be referred to as a(n)
A) selective and differential medium.
B) differential medium.
C) selective medium.
D) enrichment culture.
E) differential and enrichment culture.

Question

Quizplus · Accepted Answer

This medium is selective because it allows only gram-positive organisms to grow due to the high NaCl concentration. It is also differential because it distinguishes organisms based on their ability to ferment a sugar, indicated by the color change around the colonies.

Consider a Culture Medium on Which Only Gram-Positive Organisms Such