Which genus is NOT a lactose fermenter?

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Prepare for the NBME Microbiology Test. Study with flashcards and multiple-choice questions. Each query comes with hints and detailed explanations. Ace your exam!

Multiple Choice

Which genus is NOT a lactose fermenter?

Explanation:
Lactose fermentation is a key way to separate enteric bacteria on lactose-containing media: lactose fermenters acidify the medium and turn colonies pink, while nonfermenters do not and stay colorless. Escherichia is a classic lactose fermenter, so it would show pink colonies. Salmonella, on the other hand, does not ferment lactose, so its colonies remain colorless on such media. This classic distinction makes Salmonella the best answer for a genus that is not a lactose fermenter.

Lactose fermentation is a key way to separate enteric bacteria on lactose-containing media: lactose fermenters acidify the medium and turn colonies pink, while nonfermenters do not and stay colorless. Escherichia is a classic lactose fermenter, so it would show pink colonies. Salmonella, on the other hand, does not ferment lactose, so its colonies remain colorless on such media. This classic distinction makes Salmonella the best answer for a genus that is not a lactose fermenter.

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