Which test is most appropriate for the presumptive identification of Prevotella melaninogenica?

• A. Sodium polyanethole sulfonate (SPS) sensitivity test
• B. Nagler test
• C. Cytotoxin assay
• D. Fluorescence test

Answer: (D)

Presumptive identification of Prevotella melaninogenica hinges on pigment-related properties and how the organism appears under UV light. This anaerobe forms dark, pigmented colonies, and it also produces porphyrin compounds that fluoresce under long‑wave ultraviolet light. Observing this characteristic fluorescence provides a rapid, distinctive clue that helps separate Prevotella melaninogenica from nonpigmented anaerobes, guiding further confirmatory testing.

The other tests don’t align with what identifies Prevotella melaninogenica. Tests focused on toxin production or cytotoxic effects, such as those used for certain Clostridium species, or assays like the SPS sensitivity test, don’t provide information relevant to this organism’s presumptive ID. The fluorescence observation specifically leverages the pigment-related and fluorescence traits that are characteristic of Prevotella melaninogenica, making it the best choice for a quick, presumptive identification.