PC agar is a selective media for isolation of B. cepacia. What is the purpose of the polymixin B and ticarcillin in the media?
a. They provide nutrients to enrich the growth of B. cepacia.
b. They cause color change in the media from yellow to pink.
c. They inhibit growth of gram-positive and other gram-negative organisms.
d. They stabilize the media to support growth if prolonged incubation is needed.
C
PC agar is a selective and differential media designed to enrich the growth of B. cepacia from respiratory specimens from CF patients. PC agar contains crystal violet, bile salts, polymyxin B, and ticarcillin to inhibit gram-positive and rapid-growing, gram-negative organisms. Inorganic and organic components, including pyruvate and phenol red, also are added. B. cepacia breaks down the pyruvate, creating an alkaline pH and resulting in a color change of the pH indicator (phenol red) from yellow to pink.
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