Which bacterial colonies show brick-red fluorescence under ultraviolet (UV) light? (Consider classic oral black-pigmented anaerobes.)

Introduction: Some black-pigmented oral anaerobes demonstrate characteristic fluorescence under UV light, aiding presumptive identification. This question asks for the species known for brick-red fluorescence.

Given Data / Assumptions:

• Nomenclature reflects historical names common in question banks.
• UV fluorescence is observed on blood agar under anaerobic culture.

Concept / Approach: “B. melaninogenicus” (now Prevotella melaninogenica) is classically described as exhibiting brick-red fluorescence. Porphyromonas gingivalis is typically asaccharolytic and pigmented but less consistently brick-red fluorescent in standard descriptions.

Step-by-Step Solution: Recall which black-pigmented anaerobes fluoresce in UV light. Match the canonical example of brick-red fluorescence to B. melaninogenicus. Exclude non-fluorescent or inconsistently fluorescent species.

Verification / Alternative check: Classic lab manuals list P. melaninogenica among species with brick-red fluorescence, supporting its use as a teaching example.

Why Other Options Are Wrong:

• B. gingivalis: Pigmented but not the standard brick-red fluorescent exemplar.
• Bacteroides fragilis: Non-pigmented gut anaerobe; does not show brick-red fluorescence.
• B. levii: Less commonly cited for this specific fluorescence pattern.

Common Pitfalls: Assuming all black-pigmented anaerobes behave identically under UV; fluorescence patterns differ by species.

Final Answer: B. melaninogenicus shows brick-red fluorescence under UV light.