Which anaerobic gram-negative bacillus shows brick-red fluorescence under UV light and can produce a black pigment?

Which anaerobic gram-negative bacillus shows brick-red fluorescence under UV light and can produce a black pigment?

• A. Bacteroides fragilis group
• B. Bacteroides ureolyticus
• C. Porphyromonas gingivalis
• D. Prevotella melaninogenica

Answer: (D)

Some anaerobic gram-negative rods make porphyrin pigments that glow under UV light, and many of them also form dark pigmented colonies. Prevotella melaninogenica is a classic example: it produces a black pigment on blood-containing media and, when examined under long-wave UV light, shows a brick-red fluorescence due to these porphyrin pigments. This combination of dark pigment and brick-red fluorescence is a distinctive clue for Prevotella melaninogenica, helping to separate it from other anaerobic Bacteroides/Prevotella species that may not fluoresce as strongly or may not produce the same pigment.

Some anaerobic gram-negative rods make porphyrin pigments that glow under UV light, and many of them also form dark pigmented colonies. Prevotella melaninogenica is a classic example: it produces a black pigment on blood-containing media and, when examined under long-wave UV light, shows a brick-red fluorescence due to these porphyrin pigments. This combination of dark pigment and brick-red fluorescence is a distinctive clue for Prevotella melaninogenica, helping to separate it from other anaerobic Bacteroides/Prevotella species that may not fluoresce as strongly or may not produce the same pigment.