Oral microbiology — dental caries etiology: Which bacteria are most strongly implicated in initiating dental caries in humans based on plaque ecology and acidogenic potential?

Introduction / Context:
Dental caries is a multifactorial disease driven by microbial metabolism of dietary carbohydrates, acid production, and demineralization of enamel and dentin. Certain streptococci are classically associated with caries initiation, particularly in fissures and smooth surfaces.

Given Data / Assumptions:

• Streptococcus mutans (mutans group) is highly acidogenic and aciduric.
• Streptococcus sanguis (now S. sanguinis) participates in plaque development and can contribute to caries ecology.
• Streptococcus pyogenes is a group A streptococcus associated with pharyngitis and skin infections, not caries.

Concept / Approach:

Caries initiation correlates with organisms that adhere to enamel, synthesize extracellular glucans from sucrose (via glucosyltransferases), and maintain metabolism at low pH. S. mutans is the prime initiator; S. sanguis contributes to plaque and early colonization that can support cariogenic communities.

Step-by-Step Solution:

Verification / Alternative check:

Experimental models show S. mutans produces lactic acid and thrives at pH < 5.5, promoting demineralization; epidemiologic studies correlate S. mutans/S. sanguinis ratios with caries risk.

Why Other Options Are Wrong:

Choosing only S. mutans ignores contributions from other plaque streptococci.

Choosing only S. sanguis omits the principal cariogenic species.

S. pyogenes is unrelated to caries pathogenesis.

Common Pitfalls:

Assuming one pathogen is solely responsible. Caries reflects a dysbiotic biofilm where multiple species interact under dietary sugar pressure.

Final Answer:

Both (a) and (b)