Periodontitis Microbiology — MFDS Part 1 MCQ
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Correct answer: D — Porphyromonas gingivalis
Porphyromonas gingivalis is a Gram-negative anaerobic organism recognised as a keystone pathogen in periodontitis. Its virulence factors, including gingipain proteases, impair host defence and promote a dysbiotic subgingival microbial community and destructive inflammation. Streptococcus mutans is principally associated with dental caries, while Streptococcus salivarius is predominantly an oral commensal. Candida albicans is an opportunistic fungus associated mainly with oral candidosis, and Staphylococcus aureus is not recognised as a canonical keystone periodontal pathogen. Therefore, A is the single best answer.
Reference: Curtis MA, Garnett JA, Darveau RP. The Keystone-Pathogen Hypothesis Updated: The Role of Porphyromonas gingivalis in Periodontitis. Journal of Periodontal Research. 2025. https://pubmed.ncbi.nlm.nih.gov/41174353/