Which biochemical test is not useful for distinguishing between Enterobacteriaceae and nonfermentative gram-negative bacilli?

The oxidase test is particularly effective in differentiating between groups of bacteria based on the presence of cytochrome c oxidase in the electron transport chain. Enterobacteriaceae are typically oxidase-negative, while many nonfermentative gram-negative bacilli, such as Pseudomonas aeruginosa, are oxidase-positive. However, the oxidase test does not help identify characteristics within the Enterobacteriaceae family itself, as all members share the same oxidase-negative trait.

On the other hand, the motility test, indole test, and catalase test provide valuable distinctions among Enterobacteriaceae species and can also help differentiate them from certain nonfermentative gram-negative bacilli. For example, some Enterobacteriaceae are motile, and this can aid in differentiation from non-motile bacteria. The indole test helps distinguish species like Escherichia coli, which is indole-positive, from others that are indole-negative. The catalase test, while generally positive for both groups, can still confirm aerobic or facultatively anaerobic respiration characteristic of Enterobacteriaceae.

In summary, the oxidase test does not serve as a differentiating tool within the context of Enterobacteriaceae versus