On MacConkey agar, pink colonies indicate which metabolic property?

On MacConkey agar, pink colonies indicate which metabolic property?

• A. Lactose fermentation positive
• B. Lactose fermentation negative
• C. Sulfide production
• D. Motility

Answer: (A)

Pink colonies on MacConkey agar indicate lactose fermentation with acid production. The medium uses lactose and the pH indicator neutral red, which turns pink when the environment becomes acidic. Fermenters like many Enterobacteriaceae lower the pH as they metabolize lactose, producing pink colonies, while non-fermenters do not acidify the medium and appear colorless or pale. Sulfide production and motility aren’t determined by this pink color on MacConkey.

Pink colonies on MacConkey agar indicate lactose fermentation with acid production. The medium uses lactose and the pH indicator neutral red, which turns pink when the environment becomes acidic. Fermenters like many Enterobacteriaceae lower the pH as they metabolize lactose, producing pink colonies, while non-fermenters do not acidify the medium and appear colorless or pale. Sulfide production and motility aren’t determined by this pink color on MacConkey.