Among the following anaerobic Gram-negative rods, which species is classified as moderately saccharolytic? (Consider classic oral anaerobe taxonomy and carbohydrate fermentation profiles.)

Introduction:
Oral anaerobes historically classified within “Bacteroides” were later reallocated into Prevotella (saccharolytic) and Porphyromonas (asaccharolytic). This question assesses recognition of carbohydrate fermentation traits used in classic identification.

Given Data / Assumptions:

• Species names reflect older nomenclature used in many exam banks.
• “Moderately saccharolytic” indicates fermentation of sugars with pigment production in some species.
• We compare relative saccharolysis among listed taxa.

Concept / Approach:
Prevotella (formerly Bacteroides melaninogenicus complex) are saccharolytic to moderately saccharolytic, whereas Porphyromonas (e.g., “B. gingivalis”) are asaccharolytic, preferring peptides. Bacteroides fragilis is strongly saccharolytic but is primarily an intestinal commensal rather than a classic oral black-pigmented anaerobe.

Step-by-Step Solution:
Map old names to modern groups: “B. melaninogenicus” → Prevotella melaninogenica (saccharolytic). Recognize Porphyromonas gingivalis (“B. gingivalis”) as asaccharolytic. Differentiate B. fragilis (gut-associated) from oral pigmented species. Between the listed oral species, the classic “moderately saccharolytic” label aligns with B. melaninogenicus.

Verification / Alternative check:
Textbook oral microbiology tables consistently place melaninogenicus/Prevotella among saccharolytic black-pigmented anaerobes and Porphyromonas among asaccharolytic organisms.

Why Other Options Are Wrong:

• Bacteroides fragilis: Saccharolytic but not the classic moderately saccharolytic oral pigmented species targeted here.
• B. gingivalis: Asaccharolytic; peptide-dependent metabolism.
• B. levii: Taxonomically aligned with Prevotella/Porphyromonas history; not the standard exemplar asked in classic MCQs.

Common Pitfalls:
Assuming all black-pigmented anaerobes share identical carbohydrate use; Porphyromonas and Prevotella differ.

Final Answer:
B. melaninogenicus is recognized as moderately saccharolytic.