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

What is the state of the fetus in the womb regarding microorganisms?

Normally sterile.

When does microbial colonization of the infant begin?

At birth.

Where do most of the microorganisms that colonize a newborn come from?

Predominantly from the mother.

Do all microorganisms transmitted to the infant successfully establish in the mouth?

No, only a small proportion can establish.

How does mode of delivery affect the infant oral microbiota?

Vaginal delivery leads to microbiota similar to maternal vaginal microbiota; C-section leads to microbiota resembling maternal skin, including many Staphylococcus species.

How does feeding type affect infant oral microbiota?

Breastfed infants have more Lactobacilli (e.g., L. plantarum) than formula-fed infants.

What effect do Lactobacilli have in infants?

They inhibit the growth of Streptococcus mutans and Candida albicans.

What is vertical transmission in oral microbiota?

Transfer of microorganisms from mother to child via saliva.

Which oral bacteria have confirmed vertical transmission from mother to child?

Streptococcus salivarius, Streptococcus mutans, and some other oral species.

Is there significant father-to-infant transmission of mutans streptococci?

Little evidence exists.

Can horizontal transmission occur within families?

Yes, for some periodontal pathogens like Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans.

What are pioneer species in microbial colonization?

The first microorganisms to colonize a new site.

What factors remove microorganisms from the oral cavity physically?

Shedding of epithelial cells (desquamation), chewing, and saliva flow.

What chemical factors limit microbial growth in the mouth?

Nutrient availability, pH, redox potential, and antibacterial properties of saliva.

How do pioneer species facilitate microbial succession?

By modifying the environment — exposing new receptors, changing pH, reducing oxygen, and generating nutrients.

What is allogenic succession?

Changes in microbial communities due to non-microbial factors.

What is autogenic succession?

Community development influenced by microbial activity, e.g., increase of obligate anaerobes after teeth eruption.

How does the oral microbiota change with age?

Composition continues to develop; after tooth eruption, spirochetes and black-pigmented anaerobes increase.

What is microbial homeostasis?

The stable coexistence of oral microbiota with the host in adults.

Are there direct age-related changes to the oral microbiota?

Yes, they have been detected.

What is critical when sampling oral microbiota?

The quality of the original sample.

Which surfaces can be sampled to study oral microbiota?

Oral mucosa, saliva, dental plaque, fissures, and subgingival areas.

What are the common methods for sampling oral mucosa?

Swabbing, direct impression, scraping or scrubbing epithelial cells.

How can saliva be collected?

By expectoration, either unstimulated (resting) or stimulated (chewing or chemical).

What affects microbial counts in saliva?

Whether collection is stimulated or unstimulated; counts expressed as CFUs/mL.

Why is subgingival plaque difficult to sample?

Due to inaccessibility and anaerobic nature.

How should samples be transported for culture-based studies?

As quickly as possible, ideally in transport fluids with reducing agents to maintain low redox potential.

How are bacterial clumps dispersed before plating?

Vortexing with sterile glass beads or mild sonication.

What is a limitation of sonication?

It can selectively damage spirochetes and some Gram-negative bacteria.

How are culture-based microbiota studies performed?

Samples are diluted and spread on agar plates, either general (blood agar) or selective media.

Why is selective media used?

To recover minor components or inhibit growth of dominant species.

Give examples of selective media adjustments for oral bacteria.

Vancomycin inhibits Gram-positive; high sucrose encourages streptococci; low pH favors lactobacilli.

Are colonies on selective media automatically diagnostic?

No, colonial morphology is not definitive.

How long and under what conditions are obligate anaerobes incubated?

7–14 days at 37°C in anaerobic gas mixtures.

What percentage of oral microbiota can be cultured currently?

About 50–70%.

How are bacteria enumerated after culture?

Colony counts are adjusted for dilutions and expressed as CFUs.

What assumptions are made in colony counting?

Each colony comes from one cell, colonies of the same species have identical morphology, and different species have distinct colony morphology.

What microscopy methods are used to study oral microbiota?

Dark-field, phase contrast, electron microscopy, and confocal laser scanning microscopy (CLSM).

Why is confocal microscopy useful?

It provides 3D images of biofilms without extensive processing.

How can bacteria be identified in microscopy?

Using monoclonal/polyclonal antisera, fluorescent tags, or oligonucleotide probes.

What are in situ models in oral microbiology?

Removable devices or surfaces worn in the mouth to study microbial colonization.

Why are in situ models useful?

They allow controlled studies on microbial development and testing interventions like sugar exposure or antimicrobials.

What molecular approaches avoid culture bias?

DNA-based methods such as PCR and sequencing.

Which bacteria dominate the lips?

Facultative anaerobic streptococci, especially Streptococcus vestibularis.

What bacteria can colonize damaged lip mucosa?

Candida albicans, potentially causing angular cheilitis.

Which bacteria are commonly found on the healthy palate?

Streptococci, Actinomyces, Veillonella, Haemophilus, and Gram-negative anaerobes.

Where is Candida albicans more likely on the palate?

When dentures are worn (denture stomatitis).

Which bacteria predominate on the cheeks?

Streptococci.

Which tongue surface has the highest bacterial density?

Dorsum of the tongue.

What is the approximate proportion of streptococci on the tongue?

~40% of cultivable microbiota.

Which organisms are found in low numbers on the tongue?

Lactobacilli, yeasts, fusobacteria, spirochetes, and other motile bacteria.

What is dental plaque?

Microbial biofilm on teeth.

What factors influence biofilm composition?

Local environment, surface type, oxygen levels, and nutrients.

What are supragingival and subgingival plaque?

Plaque above and below the gum margin, respectively.

Which bacteria are major components of plaque?

Gram-positive rods and filaments (mainly Actinomyces) and obligate anaerobes.

Does saliva have its own resident microbiota?

No.

Why not?

Bacteria are constantly removed by swallowing and flow; they originate from other surfaces.

How is saliva microbial profile used clinically?

To assess caries risk based on mutans streptococci and lactobacilli levels.

What interventions can target individuals with high cariogenic bacteria counts?

Oral hygiene, antimicrobial therapy, and dietary counseling.

What is colonization resistance?

The ability of resident microbes to prevent colonization by exogenous pathogens.

How do resident microbes provide colonization resistance?

Attachment to host receptors, competition for nutrients, creating unfavorable conditions, and producing antagonistic substances like hydrogen peroxide and bacteriocins.

What are prebiotics?

Molecules that stimulate the growth of beneficial resident microbes.

Give examples of oral prebiotics.

Non-digestible fibers like inulin or oligofructose.

How does the host tolerate resident microbiota?

Recognizes commensals via pattern recognition receptors (e.g., Toll-like receptors) and avoids damaging inflammation.

How can beneficial oral streptococci aid the host?

Stimulate interferon pathways, promote wound healing, enhance mucin production, and improve epithelial cytoskeleton function.

What role do oral bacteria play in nitrate metabolism?

Convert dietary nitrate (from vegetables) in saliva to nitrite.

Why is nitrite important?

Regulates blood flow, blood pressure, gastric integrity, tissue protection, and has antimicrobial properties.

What can nitrite convert to in the stomach?

Nitric oxide, which has antimicrobial and protective effects.