Distribution, Development, and Benefits of the Oral Microbiota (Condensed Version)

When does microbial colonization of the infant begin?

At birth.

Where do most early oral microbes come from?

Predominantly from the mother.

How does delivery method affect infant oral microbiota?

Vaginal → resembles vaginal microbiota; C-section → resembles skin microbiota.

How does breastfeeding affect oral microbiota?

Increases Lactobacilli, which inhibit S. mutans and C. albicans.

What is vertical transmission?

Mother-to-child transfer via saliva.

Which periodontal pathogens can be transmitted horizontally in families?

Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans.

What are pioneer species?

First colonizers of a site.

How do pioneer species aid succession?

Modify environment, expose new attachment sites, change pH, reduce oxygen, produce nutrients.

What is allogenic succession?

Changes due to non-microbial factors.

What is autogenic succession?

Changes due to microbial activity.

How does oral microbiota change after tooth eruption?

Increase of spirochetes and black-pigmented anaerobes.

What is microbial homeostasis?

Stable coexistence of microbiota and host in adults.

Which surfaces can be sampled for oral microbiota?

Mucosa, saliva, plaque, fissures, subgingival sites.

How is saliva collected?

Unstimulated or stimulated expectoration; CFUs/mL measured.

Why is subgingival plaque difficult to sample?

Inaccessible and anaerobic.

How should samples be transported?

Quickly in reducing transport fluids; disperse clumps before plating.

How are culture-based microbiota studies done?

Dilute, plate on general or selective media, incubate under appropriate conditions.

What proportion of oral microbiota can currently be cultured?

50–70%.

How is microbial enumeration done?

Count colonies, adjust for dilutions, expressed as CFUs.

Which microscopy methods are used?

Dark-field, phase contrast, confocal laser scanning.

Why use confocal microscopy?

3D structure of biofilms without destroying architecture.

What are in situ models?

Removable devices in the mouth to study microbial colonization.

Why are molecular methods important?

Detect unculturable species and avoid culture bias.

Which bacteria dominate the lips?

Facultative streptococci (S. vestibularis).

Which bacteria colonize cheeks?

Streptococci.

Which tongue surface has the highest diversity?

Dorsum of the tongue; ~40% streptococci.

Which organisms are found in low numbers on the tongue?

Lactobacilli, yeasts, fusobacteria, spirochetes.

What is dental plaque?

Biofilm on teeth.

What bacteria dominate plaque?

Gram-positive rods (Actinomyces) and obligate anaerobes.

Difference between supragingival and subgingival plaque?

Above vs below gum margin.

Does saliva have its own resident microbiota?

No; bacteria come from surfaces like tongue.

How is saliva used clinically?

Caries risk indicator (mutans streptococci, lactobacilli).

What is colonization resistance?

Resident microbes prevent pathogen colonization.

How do microbes provide colonization resistance?

Attach to host, compete for nutrients, create unfavorable conditions, produce inhibitory substances.

What are prebiotics?

Compounds stimulating beneficial microbes (e.g., inulin, oligofructose).

How does the host tolerate commensals?

Pattern recognition receptors detect microbes, avoiding harmful inflammation.

Benefits of oral streptococci to host?

Stimulate interferons, promote healing, enhance mucin, improve epithelial cytoskeleton.

Role of oral bacteria in nitrate metabolism?

Reduce nitrate in saliva to nitrite.

Why is nitrite important?

Regulates blood pressure, blood flow, gastric integrity, antimicrobial defense.

What can nitrite convert to in the stomach?

Nitric oxide, with antimicrobial and protective effects.