The malonate test is most useful in differentiating which members of the Enterobacteriaceae?

The malonate test is primarily used to differentiate members of the Enterobacteriaceae based on their ability to utilize malonate as a sole carbon source. In particular, this test is highly effective in identifying certain Salmonella subgroups, including subgroup 2 and 3, which were previously classified under the genus Arizona.

These Salmonella subgroups can utilize malonate, leading to a positive result in the malonate test, distinguishing them from other closely related genera that are unable to utilize malonate. This ability is significant in clinical microbiology for the identification and characterization of enteric pathogens.

While the other genera listed can also be differentiated using various biochemical tests, they do not specifically relate to the malonate test as closely as the Salmonella subgroups do, making the selection of this answer particularly relevant for understanding the biochemical characteristics used in classifying Enterobacteriaceae.