Which bacterial species requires xylene extraction and Ehrlich's reagent for the indole test?

The correct answer is Flavobacterium, primarily due to its biochemical characteristics that necessitate certain tests for identification, such as the indole test. In the context of the indole test, Flavobacterium species possess the ability to produce indole from tryptophan, but their cell wall structure can inhibit typical testing methods, particularly when using common substrates.

The use of xylene extraction in preparing the culture helps in isolating and concentrating the indole produced by the bacteria. Xylene is a non-polar solvent that can facilitate the extraction of indole from the bacterial cells effectively. Following this extraction, Ehrlich's reagent is applied; it reacts with indole to produce a colored complex, indicating a positive result. This need for both xylene extraction and Ehrlich's reagent sets Flavobacterium apart from other species like Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae, which either do not require such a specific method for indole testing or have differing biochemical pathways that do not make use of this sequence.

Therefore, recognizing the unique requirements of Flavobacterium for indole testing is essential for accurately identifying and differentiating it from other bacterial species.