Question

Which of the following examples indicates an agar that is selective, but NOT differential?

Choose one:
A. Phenylethyl alcohol agar that restricts or reduces the growth of Gram-negative bacteria
B. MacConkey agar containing bile salts to inhibit growth of certain organisms and dye that indicates lactose fermentation
C. nutrient agar that allows growth of most organisms
D. blood agar that changes color on the basis of whether an organism can lyse red blood cells

Answer 1

Phenylethyl alcohol agar is an example of a selective agar that is not differential.

Step-by-step explanation:

In this case, the correct option would be A. Phenylethyl alcohol agar that restricts or reduces the growth of Gram-negative bacteria.

Selective media selectively inhibit the growth of certain types of bacteria, while allowing others to grow. In the case of phenylethyl alcohol agar, it restricts or reduces the growth of Gram-negative bacteria. However, it does not have any components that allow for differentiation between different types of bacteria, so it is not differential.

MacConkey agar would be an example of a medium that is both selective and differential because it inhibits the growth of certain organisms (Gram-positive bacteria) with bile salts and crystal violet, while also indicating lactose fermentation through the use of a dye.