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

• A. Naglertest
• B. SPS sensitivity test
• C. Cytotoxin assay
• D. Fluorescence test

Answer: (D)

The key idea is that Prevotella melaninogenica can be presumptively identified by its pigment-related property visible in culture. This organism produces porphyrin compounds that fluoresce under ultraviolet light, giving an unmistakable orange fluorescence. That rapid, simple fluorescence test leverages this specific trait to distinguish Prevotella melaninogenica from many other anaerobes in the sample.

The other tests don’t fit this organism’s typical profile. The Nagler test detects lecithinase activity, which is a toxin-related test for Clostridium species, not for Prevotella. The SPS sensitivity test serves to differentiate certain Gram-positive cocci and is not used for identifying anaerobic Gram-negative rods like Prevotella. The cytotoxin assay detects toxin production by other pathogens (such as C. difficile) and isn’t relevant for this organism either. Thus, the fluorescence test is the most appropriate presumptive identification method here because it directly exploits a distinctive pigment-related trait of Prevotella melaninogenica.