Which gram-negative bacilli produce black pigment and brick red fluorescence when exposed to an ultraviolet light source?

The correct answer is that Porphyromonas spp. and Prevotella spp. are known for producing black pigment and exhibiting brick red fluorescence under ultraviolet light. These characteristics are significant in distinguishing these bacteria in microbiological studies.

Porphyromonas and Prevotella, both members of the Bacteroidetes phylum, are commonly found in the oral cavity and are often associated with periodontal diseases. The black pigment they produce is primarily due to the presence of heme, which can be utilized by these organisms under anaerobic conditions, leading to pigmentation observable on specific media. The brick red fluorescence is a useful diagnostic feature in clinical microbiology, helping to identify these species rapidly in laboratory settings.

Understanding these traits is crucial for microbiologists in diagnosing infections and assessing the microbial flora of various environments, particularly in periodontal studies. The other mentioned groups, such as Fusobacterium and Actinomyces, do not share these specific fluorescence and pigmentation characteristics and are thus not the focus of this question.