Micro & Immunology · single question
What bacteria is primarily associated with ROOT SURFACE caries?
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Correct answer: C. Actinomyces viscosus
✓ C) Actinomyces viscosus is most commonly associated with root surface caries.
Root caries organisms: Actinomyces viscosus (and A. naeslundii) are gram-positive rods that preferentially colonize root surfaces (cementum/dentin). They produce acid at lower pH and can degrade the collagen matrix of cementum. S. mutans is also found in root caries but A. viscosus is THE most commonly tested organism specifically for ROOT surface caries. Lactobacillus is associated with lesion PROGRESSION (deeper dentinal caries). P. gingivalis = periodontal pathogen. Fusobacterium = bridging organism in biofilm.
Root caries organisms: Actinomyces viscosus (and A. naeslundii) are gram-positive rods that preferentially colonize root surfaces (cementum/dentin). They produce acid at lower pH and can degrade the collagen matrix of cementum. S. mutans is also found in root caries but A. viscosus is THE most commonly tested organism specifically for ROOT surface caries. Lactobacillus is associated with lesion PROGRESSION (deeper dentinal caries). P. gingivalis = periodontal pathogen. Fusobacterium = bridging organism in biofilm.
- A. ❌ P. gingivalis is a key periodontal pathogen (keystone pathogen) — not associated with caries.
- B. ✅ CORRECT – Actinomyces viscosus is the primary pathogen in root surface caries, thriving in the exposed root environment.
- C. ❌ S. mutans is the primary initiator of CORONAL (enamel) caries — not root surface caries.
- D. ❌ Lactobacillus species are secondary colonizers that drive DENTINAL caries progression — not root surface caries initiation.
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