Oral microbiome

Oral Microbiome - Mouth's Microbial Menagerie

• Definition: A dynamic community of commensal microbes (bacteria, fungi, viruses) in the oral cavity, vital for homeostasis.
• Key Phyla: Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria.
• Dominant Genera: Streptococcus, Veillonella, Prevotella, Fusobacterium.

⭐ Streptococcus mutans metabolizes sucrose to lactic acid, which demineralizes enamel, leading to dental caries. This biofilm formation is known as plaque.

Key Species - The Usual Suspects

⭐ The "Red Complex" (P. gingivalis, T. forsythia, T. denticola) is a group of bacteria strongly associated with severe forms of periodontal disease.

Dental Plaque - Biofilm Builders' Brigade

• Dental plaque is a classic example of a biofilm, a structured community of bacteria that adheres to tooth surfaces.
• Its development is a multi-stage process involving specific bacterial species in a predictable sequence.

• Primary Colonizers: Aerobic bacteria like S. sanguinis attach to the pellicle.

  ⭐ Streptococcus mutans metabolizes sucrose into dextrans (glucans), which forms the scaffolding of plaque, enabling other bacteria to adhere.

• Secondary Colonizers: Fusobacterium nucleatum acts as a crucial bridging organism, co-aggregating with both early and late colonizers.
• Mature Biofilm: Creates an anaerobic niche, promoting the growth of pathogenic, gram-negative anaerobes (Porphyromonas gingivalis, Tannerella forsythia).

Clinical Correlations - When Good Microbes Go Bad

• Dental Caries: Caused by acidogenic bacteria, primarily Streptococcus mutans. They ferment dietary sugars (especially sucrose) into lactic acid, which demineralizes tooth enamel.

  • $Sucrose \xrightarrow{S. mutans} Lactic;Acid + Glucans/Fructans;(Biofilm)$

• Gingivitis & Periodontitis: Results from dysbiosis-a shift to Gram-negative, anaerobic bacteria (e.g., Porphyromonas gingivalis, Tannerella forsythia) below the gumline. The host's inflammatory response to these pathogens causes progressive destruction of gingival tissue and alveolar bone.

• Systemic Disease Links:
  • Infective Endocarditis: Transient bacteremia, often after dental procedures, can allow Streptococcus viridans to colonize damaged heart valves.
  • Aspiration Pneumonia: Aspiration of oral anaerobes can cause lung abscesses.

⭐ High-Yield: The viridans group streptococci produce dextrans from sucrose, which helps them adhere to fibrin-platelet aggregates on previously damaged heart valves, a critical step in causing Subacute Bacterial Endocarditis (SBE).

High‑Yield Points - ⚡ Biggest Takeaways

• Viridans streptococci are the most abundant organisms, primarily α-hemolytic.
• Streptococcus mutans is the main cause of dental caries by synthesizing dextrans from sucrose.
• S. sanguinis is a major component of dental plaque and a cause of subacute bacterial endocarditis after dental work.
• Actinomyces israelii is associated with actinomycosis, forming characteristic sulfur granules.
• Porphyromonas gingivalis is a key pathogen in chronic periodontitis.
• Oral flora form biofilms (plaque), protecting them from host defenses and antimicrobials.