Which test would be used for presumptive identification of Prevotella melaninogenica?

• A. SPS sensitivity test
• B. Nagler test
• C. Fluorescence test
• D. Esculin hydrolysis

Answer: (C)

Prevotella melaninogenica is a pigmented anaerobic Gram-negative rod, and its hallmark in the lab is the porphyrin-based fluorescence it produces when exposed to long‑wave UV light. The fluorescence test specifically detects this pigment-related property, giving a quick presumptive indication that the isolate is Prevotella melaninogenica. The other tests aren’t used for this organism: the SPS sensitivity test is about susceptibility to sodium polyanethol sulfonate and isn’t a diagnostic marker for Prevotella, the Nagler test detects lecithinase activity (used with Clostridium species), and esculin hydrolysis distinguishes other groups like Enterococcus. So the fluorescence response best matches Prevotella melaninogenica’s characteristic pigment production.