Which organism matches the profile NLF; VP positive; Motile; A/A?

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Multiple Choice

Which organism matches the profile NLF; VP positive; Motile; A/A?

Interpreting a bacterial profile often means combining several tests to narrow down the genus. Here, you’re looking at lactose fermentation status (non-lactose fermenter), a positive Voges-Proskauer (acetoin) result, motility, and a sugar-fermentation pattern in a carbohydrate test that can show acid production in both the slant and the butt (A/A). Non-lactose fermentation rules out the usual lactose fermenters like many Enterobacteriaceae that appear pink on MacConkey. Among the non-lactose fermenters, the Voges-Proskauer test helps separate organisms that funnel pyruvate to acetoin from those that don’t. A positive VP result points toward genera such as Klebsiella, Enterobacter, and Serratia. However, Klebsiella is non-motile, and Enterobacter, while motile, is typically a lactose fermenter, which conflicts with the non-lactose profile. That leaves Serratia as the match: motile and VP positive. The A/A result in the carbohydrate test (often visible in a glucose-containing medium that also includes a disaccharide) indicates the organism can produce acid in both the slant and the butt, which corresponds to fermenting multiple sugars or a strong metabolite flux that drives acid production throughout the medium. Serratia can show this pattern, supporting its identification with the given profile. So, a non-lactose fermenter that is motile and VP positive, with an A/A pattern on carbohydrate testing, best fits Serratia marcescens.

Interpreting a bacterial profile often means combining several tests to narrow down the genus. Here, you’re looking at lactose fermentation status (non-lactose fermenter), a positive Voges-Proskauer (acetoin) result, motility, and a sugar-fermentation pattern in a carbohydrate test that can show acid production in both the slant and the butt (A/A).

Non-lactose fermentation rules out the usual lactose fermenters like many Enterobacteriaceae that appear pink on MacConkey. Among the non-lactose fermenters, the Voges-Proskauer test helps separate organisms that funnel pyruvate to acetoin from those that don’t. A positive VP result points toward genera such as Klebsiella, Enterobacter, and Serratia. However, Klebsiella is non-motile, and Enterobacter, while motile, is typically a lactose fermenter, which conflicts with the non-lactose profile. That leaves Serratia as the match: motile and VP positive.

The A/A result in the carbohydrate test (often visible in a glucose-containing medium that also includes a disaccharide) indicates the organism can produce acid in both the slant and the butt, which corresponds to fermenting multiple sugars or a strong metabolite flux that drives acid production throughout the medium. Serratia can show this pattern, supporting its identification with the given profile.

So, a non-lactose fermenter that is motile and VP positive, with an A/A pattern on carbohydrate testing, best fits Serratia marcescens.

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