What characteristic distinguishes Klebsiella, Enterobacter, and Serratia from other Enterobacteriaceae?

The characteristic that distinguishes Klebsiella, Enterobacter, and Serratia from other members of the Enterobacteriaceae family is that they are invariably positive for the Voges-Proskauer (VP) test. This biochemical test is used to detect the production of acetoin, a fermentation product formed during glucose metabolism. The presence of acetoin leads to a positive result, which can be visually confirmed by the development of a red color in the presence of specific reagents.

In contrast, while some Enterobacteriaceae can be lactose fermenters, not all members of the family possess this characteristic, and thus it cannot be relied upon to distinctly identify these specific genera. Similarly, the non-fermentative nature is not a defining trait of these organisms; the urease test results vary among Enterobacteriaceae, and while some species may produce urease, it does not serve to distinctly differentiate Klebsiella, Enterobacter, and Serratia. Therefore, the VP positive result is a key factor for identifying and distinguishing these particular genera within the broader family of Enterobacteriaceae.