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Oral Cavity Microflora

Q: What protozoan species are part of the normal oral microflora?

The oral microbiota includes the following protozoa: Entamoeba gingivalis — frequently detected in oral pathologies.Trichomonas tenax — a commensal of the oral cavity.

For medical students2 min readUpdated 2026-10-10

Oral microflora is a complex and constantly changing microbiocenosis comprising both permanent and transient microorganism populations. The oral cavity provides ideal conditions for their attachment, reproduction, and the formation of stable biofilms.

DiversityMore than 700 microorganism species identified

ConcentrationGingival pockets contain 100 times more microbes than saliva

Salivary contaminationUp to 1 billion microorganisms per 1 mL

ClassificationDivided into resident (permanent) and transient (temporary)

Environmental Factors and Habitat Conditions

The oral cavity is a favorable ecological niche for bacteria. This is supported by constant humidity, a stable optimal temperature, the presence of nutrients, and a slightly alkaline pH level.

However, microorganisms must adapt to variable conditions. They are influenced by fluctuations in temperature, acidity levels, osmotic pressure, nutrient concentrations, and oxygen partial pressure.

To successfully colonize the oral cavity, bacteria must possess the ability to adhere (attach) to tissues. At the same time, the body constantly eliminates some microbes via mechanical actions (chewing, tongue and lip movements) and the cleansing flow of saliva.

Dynamics of Development (Ontogenesis)

The colonization process of the oral cavity changes throughout a person's life:

Neonatal period. The first bacteria enter from the mother's mouth, air, and food. Streptococci, lactobacilli, and actinomycetes become the "pioneer" colonizers.
Tooth eruption. New niches emerge—gingival sulci. The proportion of primary colonizers decreases, yielding to gram-negative anaerobes.
Puberty. Hormonal changes increase the number of gram-negative anaerobes and spirochetes.
Adult and elderly age. Composition depends on immunity, stress, diet, and salivary flow rate. In elderly individuals, reduced saliva production frequently leads to an overgrowth of Candida albicans fungi, increasing the risk of candidiasis.

Composition and Localization of the Microbiota

Microorganisms are unevenly distributed throughout the oral cavity. They prefer areas poorly washed by saliva: dental plaque, the dorsum of the tongue, interdental spaces, tooth necks, and carious cavities. This is where dental plaque forms—a complex, dynamic microecosystem (biofilm).

Streptococci and lactobacilli are the dominant groups. Based on their ability to survive in oxygen, gram-negative rods are divided into:

Obligate anaerobes: Bacteroides, Porphyromonas, Fusobacterium, Prevotella, and Leptotrichia.
Facultative anaerobes: Haemophilus.

Non-pathogenic spirochetes (Treponema, Leptospira, Borrelia), mycoplasmas, and protozoa are also part of the microflora.

Frequently asked questions

Which streptococcal species dominate the resident microflora of the oral cavity?

The resident oral microflora is dominated by viridans group streptococci. The main representatives of this group include:

Streptococcus salivarius
Streptococcus sanguis
Streptococcus mutans
Streptococcus milleri
Streptococcus mitis

These microorganisms account for about 50% of all oral residents and are consistently detected in all samples.

What protozoan species are part of the normal oral microflora?

The oral microbiota includes the following protozoa:

Entamoeba gingivalis — frequently detected in oral pathologies.
Trichomonas tenax — a commensal of the oral cavity.

What is the physiological and pathogenetic role of lactobacilli in the oral cavity?

The physiological role of lactobacilli involves participating in the initial colonization of the newborn's oral cavity and establishing the microbiocenosis. Their pathogenetic role is linked to the development of dental caries:

Initial colonization: lactobacilli belong to the primary colonizers of a newborn's oral cavity.
Carieogenesis: lactobacilli are leading pathogens of dental caries alongside Streptococcus mutans.

The lactobacillus titer serves as an indicator for assessing caries predisposition. During fermentation, these microorganisms produce organic acids that cause demineralization of hard tooth tissues.

What stages and specific microorganisms are involved in the sequential formation of dental plaque?

Dental plaque forms in several sequential stages with shifting microbial communities:

Initial phase — formation of the acquired pellicle.
Early colonization (Day 1) — adhesion of primary colonizers, which establish anaerobic conditions. Aerobes and facultative anaerobes participate: streptococci (S. gordonii, S. mitis, S. oralis, S. sanguinis), corynebacteria, and actinomycetes.
Intermediate phase (Days 2–4) — decreased number of streptococci, growth of facultative and anaerobic actinomycetes, gram-negative cocci, and rods.
Late colonization (After 1 week) — coaggregation and attachment of other bacterial species, including Porphyromonas gingivalis, Prevotella denticola, Tannerella forsythia, Treponema denticola, Capnocytophaga spp., Actinomyces spp., and Aggregatibacter actinomycetemcomitans; spirochetes appear.

How many species of microbes inhabit the mouth?

Traditional methods detect about 250 species, but modern molecular-genetic studies reveal the presence of more than 700 species, including unculturable forms.

How does microflora change when teeth appear?

When teeth erupt, gingival sulci form. This creates conditions for the proliferation of gram-negative anaerobes, which displace some of the primary colonizers.

Go deeper

Mechanisms of bacterial adhesion to oral tissues
Structure and formation of dental plaque (biofilm)
Principle of selective advantage in microbiocenosis
Impact of carbohydrate diet and smoking on microflora
Peculiarities of microflora during pregnancy
Molecular-genetic methods for microbiome diagnostics