Oral Microbiome

Oral Microbiome Overview - Mouth's Tiny Tenants

• Definition: Diverse, dynamic microbial community (bacteria, fungi, viruses, archaea) inhabiting the oral cavity.
• Composition: Primarily bacteria; over 700 species identified. Dominant phyla: Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria, Fusobacteria.
• Biofilms: Microbes form structured communities (dental plaque) on teeth and mucosal surfaces.
• Eubiosis (Health): Contributes to homeostasis, initial digestion, pathogen defense.
• Dysbiosis (Disease): Imbalance leads to caries, periodontal diseases, and can influence systemic health.

⭐ Streptococcus mutans is a key cariogenic bacterium, producing acid from dietary sugars, leading to enamel demineralization.

Key Oral Microbes & Niches - Microbial Hotspots

• Supragingival Plaque (Enamel):
  • Early (aerobic/facultative): S. sanguinis, S. gordonii, A. naeslundii.
  • Caries: S. mutans (acidogenic/aciduric), Lactobacillus spp.
  • Other: Veillonella spp. (lactate utilizer).
• Subgingival Plaque (Crevice/Pocket): Anaerobic.
  • Key bridging species: Fusobacterium nucleatum.
  • Periodontitis:
    • Red Complex: P. gingivalis, T. forsythia, T. denticola (major periodontopathogens).
    • Aggregatibacter actinomycetemcomitans (LAP, leukotoxin).
• Tongue Dorsum:
  • VSC production (halitosis): Solobacterium moorei, Atopobium parvulum.
• Buccal Mucosa:
  • Streptococcus salivarius (BLIS producer).
• Saliva:
  • Transient microbes, host defense (sIgA, lysozyme).
• Fungi:
  • Candida albicans (thrush, denture stomatitis).
• Viruses:
  • HSV (latency), EBV (hairy leukoplakia), HPV (warts, cancer risk).

⭐ Streptococcus mutans, a key cariogen, uses sucrose for adherent glucans (biofilm) & lactic acid, causing enamel demineralization.

Dental Plaque & Biofilms - Sticky Situations

• Dental Plaque: Resilient, organized microbial biofilm. Bacteria in self-produced Extracellular Polysaccharide (EPS) matrix, adhering to tooth surfaces.
• Composition: Bacteria (Streptococci, Actinomyces), salivary glycoproteins, food debris, EPS (glucans, fructans for matrix).
• Key Bacteria & Roles:
  • Early colonizers: S. sanguinis, S. mitis, A. naeslundii.
  • Bridging: F. nucleatum.
  • Caries: S. mutans (acid/EPS), Lactobacillus spp. (aciduric).
  • Periodontal: Red complex (📌 PG Took Tooth: P. gingivalis, T. forsythia, T. denticola).
• Significance: Etiology of caries (demineralization), gingivitis, periodontitis (destruction), calculus formation.

⭐ S. mutans is a keystone pathogen in caries; it metabolizes sucrose using glucosyltransferases (GTFs) to produce sticky, insoluble glucans (EPS). These glucans are vital for strong bacterial adhesion, biofilm matrix integrity, and high cariogenic potential.

Oral Dysbiosis & Diseases - When Bugs Go Bad

Oral dysbiosis: Microbial imbalance (↑pathogens, ↓commensals) → disease.

• Dental Caries:
  • Bugs: S. mutans (initiator, acidogenic/aciduric), Lactobacillus spp. (progression).
  • Path: Sugars → Lactic acid → Enamel demineralization (pH <5.5).
• Periodontal Diseases:
  • Shift: Predominantly Gram(+) aerobes/facultative → Gram(-) strict anaerobes.
  • 📌 Red Complex: P.T.T. (P. gingivalis, T. forsythia, T. denticola).
  • Gingivitis (reversible inflammation) → Periodontitis (irreversible bone loss).
• Oral Candidiasis:
  • Candida albicans overgrowth.
  • Risks: Immunosuppression, antibiotics, xerostomia, dentures.
• Halitosis:
  • Anaerobes (e.g. P. gingivalis) → Volatile Sulfur Compounds (VSCs).

⭐ P. gingivalis is a keystone pathogen in chronic periodontitis, dysregulating host immunity even at low abundance.

Dysbiosis Triggers: High sugar diet, poor oral hygiene, smoking, systemic diseases (e.g., diabetes), xerostomic medications.

High‑Yield Points - ⚡ Biggest Takeaways

• Oral cavity: diverse microbial community, second most complex after gut.
• Streptococcus mutans: key cariogenic bacterium, produces acid from sugars, causing caries.
• Red complex (P. gingivalis, T. forsythia, T. denticola): strongly associated with periodontitis.
• Biofilm (dental plaque): essential for microbial colonization and oral disease pathogenesis.
• Saliva: crucial for oral homeostasis, providing nutrients, buffering, and antimicrobial factors.
• Oral dysbiosis: linked to dental caries, periodontal disease, and various systemic conditions.