On MacConkey agar, lactose fermenters produce what color colonies?

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Study for the NBME Microbiology Test. Utilize flashcards and multiple choice questions, each with explanations. Prepare confidently for your exam!

Multiple Choice

On MacConkey agar, lactose fermenters produce what color colonies?

Explanation:
MacConkey agar differentiates organisms by lactose fermentation using a neutral red pH indicator. When lactose-fermenting bacteria grow, they acidify the medium, lowering the pH and causing the colonies to appear pink to red. Non-lactose fermenters don’t acidify the medium, so their colonies stay colorless or pale. Thus, lactose fermenters produce pink colonies.

MacConkey agar differentiates organisms by lactose fermentation using a neutral red pH indicator. When lactose-fermenting bacteria grow, they acidify the medium, lowering the pH and causing the colonies to appear pink to red. Non-lactose fermenters don’t acidify the medium, so their colonies stay colorless or pale. Thus, lactose fermenters produce pink colonies.

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