Question

Which of the following associations is INCORRECT regarding selective media?

a. Crystal violet agar: inhibits the growth of gram-negative organisms, used to isolate gram-positive organisms
b. Crystal violet agar: inhibits the growth of gram-positive organisms, used to isolate gram-negative organisms
c. Phenylethyl alcohol agar: inhibits the growth of gram-negative organisms, used to isolate gram-positive organisms
d. NaCl (sodium chloride) agar: inhibits the growth of a non-halophilic organisms, often used to isolate Staphylococcus

Answer 1

The incorrect association among the choices provided is that crystal violet agar inhibits the growth of gram-negative organisms to isolate gram-positive organisms. In contrast, crystal violet actually inhibits gram-positive organisms, favoring gram-negative bacteria.

Step-by-step explanation:

The question is regarding the correctness of associations between selective media and their inhibitory effects. Selective media are designed to support the growth of certain microorganisms while inhibiting others, hence creating a setting that allows for the isolation of specific types of bacteria.

Bile salts and crystal violet work together in selective media to inhibit the growth of most Gram-positive bacteria, thereby creating an environment that favors the growth of Gram-negative organisms, especially from the Enterobacteriaceae family.

Therefore, the incorrect association among the given options is:

• Option a: Crystal violet agar: inhibits the growth of gram-negative organisms, used to isolate gram-positive organisms

This statement is incorrect because crystal violet actually inhibits the growth of gram-positive organisms, favoring the isolation of gram-negative bacteria.