A cervical mucosal abscess grew an anaerobic gram-negative bacillus that was inhibited by bile, produced a black pigment, and was negative for indole production but positive for glucose, sucrose, and lactose fermentation. This isolate would most likely be which species?

A cervical mucosal abscess grew an anaerobic gram-negative bacillus that was inhibited by bile, produced a black pigment, and was negative for indole production but positive for glucose, sucrose, and lactose fermentation. This isolate would most likely be which species?

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

Answer: (D)

The main point is recognizing a pigmented, anaerobic Gram-negative bacillus from mucosal infections and using pigment plus sugar fermentation patterns to identify Prevotella species. The black pigment points to Prevotella, and among those, Prevotella melaninogenica is characteristically inhibited by bile, indole negative, and capable of fermenting glucose, sucrose, and lactose. This combination of traits fits Prevotella melaninogenica and distinguishes it from Bacteroides fragilis (which is bile-resistant and nonpigmented), Porphyromonas gingivalis (pigmented but not a strong carbohydrate fermenter), and Campylobacter ureolyticus (not an anaerobic gram-negative bacillus and not pigmented). Thus, the isolate is Prevotella melaninogenica.

The main point is recognizing a pigmented, anaerobic Gram-negative bacillus from mucosal infections and using pigment plus sugar fermentation patterns to identify Prevotella species. The black pigment points to Prevotella, and among those, Prevotella melaninogenica is characteristically inhibited by bile, indole negative, and capable of fermenting glucose, sucrose, and lactose. This combination of traits fits Prevotella melaninogenica and distinguishes it from Bacteroides fragilis (which is bile-resistant and nonpigmented), Porphyromonas gingivalis (pigmented but not a strong carbohydrate fermenter), and Campylobacter ureolyticus (not an anaerobic gram-negative bacillus and not pigmented). Thus, the isolate is Prevotella melaninogenica.