Ace the 2026 Clinical Lab Science Bacteriology Exam – Unleash Your Inner Science Superstar!

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.