Which tests best distinguish Enterobacter aerogenes from Edwardsiella tarda?

The correct choice is identified because it highlights specific biochemical tests that effectively differentiate Enterobacter aerogenes from Edwardsiella tarda, primarily focusing on fermentation and metabolic capabilities.

Hydrogen sulfide (H2S) production is a key characteristic that can help distinguish between these two organisms as Edwardsiella tarda is known to produce H2S while Enterobacter aerogenes typically does not. Sucrose fermentation is another important test; Enterobacter aerogenes is capable of fermenting sucrose, which distinguishes it from Edwardsiella tarda that generally does not ferment this sugar. The indole test adds further differentiation, as Enterobacter aerogenes is typically indole negative, whereas Edwardsiella tarda is indole positive.

The combination of these tests provides a clear and distinctive profile for the identification of each organism, underscoring how they metabolize different substrates and produce or do not produce certain by-products, thus allowing for accurate differentiation in a laboratory setting.