FSBEI HE Astrakhan SMU MOH Russia
Department of Microbiology and Virology
LECTURE №7
Microbiocenosis of the oral
cavity. Factors of
symbiosis. Formation of
microbial associations.
Resident microbiota of
oral cavity: main
representatives, their role
in opportunistic infections
development
The author: Assistant Abdrahmanova R.O.
Microbiology and Virology Department of ASMU
In the oral cavity, there are favorable physicochemical
conditions for the living of various microbes:
1. The constant presence of nutrients (food debris, saliva
glycoproteins).
2. Optimum temperature
3. Constant humidity
4. Weakly alkaline reaction
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There are several biotopes in the oral cavity
Biotope (from Ancient Greek βίος (bios) 'life' + τόπος
(topos) 'place')
Biotopes in the oral cavity are
specific habitats of
microorganisms, each being
characterized by different
physicochemical factors and
thus supporting the growth of a
specific microbial community.
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Microbiocenosis (from Greek: bios - life, koinos - general), or
microbiota (microflora) - a set of microbial species in one
biotope.
The microbiota of the oral cavity depends on endogenous (age,
health) and exogenous (diet, living conditions) factors.
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The quantitative composition of the microbiota of the oral
cavity
The formed biocenosis is characterized by constancy of species
9,5%
0,5%
The resident flora
The facultative flora
The transient flora
90,0%
There are two fractions of the resident (autochthonous) flora:
The 1st fraction of this group is obligate + The 2nd fraction is
facultative
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The main positive functions of obligate
microbiota
The providing colonization resistance: it prevents the
colonization of the mucosa by pathogenic and conditionally
pathogenic microbes
Activation of the immune system: it stimulates the development
of lymphoid tissue and the synthesis lysozyme, cytokines,
immunoglobulins, interferons
Suppression of translocation of microbes into the internal
environment of the body
Synthesis of vitamins, amino acids and other biologically active
substances
Salivary secretion stimulation
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Biofilm formation
In vivo, bacteria form biofilms - an organized community of
resident bacteria
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The structure of the microbial biofilm of the tooth
Biofilm on the teeth
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The microbial biofilms on the
surface of the tongue
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Between different species of microbes in a microbial community and
between the microbes and the host organism there are various forms of
mutual influence (biotic factors)
A biotic factor could be defined as «the influence upon the environment of
organisms owing to the presence and activities of other organisms, as distinct
from a physical, abiotic, environmental factor»
The main forms of biotic factors
Antibiosis
Symbiosis
According the nature of the relationship
Mutualism
Competition
Antagonism
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Commensalism
Parasitism
Symbiosis factors are phenotypic properties of a microbial
cell, allowing it to interact with cells of other microbes and
with a microorganism.
Symbiosis factors of microbes with the host organism:
•adhesion and colonization factors - surface structures of bacteria
•invasion factors - pathogenicity enzymes
•toxins
Symbiosis of microbial symbiosis with other microbes:
•adhesion factors - surface structures of bacteria
•metabolic features
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The stimulating effect of symbionts:
Streptococci decompose carbohydrates to acid that is used by Veillonella
as an energy source
Streptococci reduce pH creating conditions for the multiplication of
lactobacilli
Yeast-like fungi synthesize vitamins that stimulate the growth of
lactobacilli
The members of Corynebacterium genus reduce the concentration of O2
creating conditions for the reproduction of anaerobes
The members of Corynebacterium genus synthesize vitamin K that
stimulates the growth of bacteroids
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The inhibitory effect of antagonists:
Streptococci form lactic acid, hydrogen peroxide,
bacteriocins that inhibit the growth of the members of
Corynebacterium genus and Fusobacterium genus
Acid-forming bacteria (acidogens) reduce pH of the
environment to inhibit the growth of proteolytic bacteria
Resident microbiota is a natural antagonist of pathogenic
microorganisms
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The formation of microbial associations
Interactions of microbes with each other in one biotope form
a stable associations (communities).
Adhesion using surface structures (pilli, teichoic acid). The
ability to attach to a particular surface depends on the nature
of adhesins: Streptococcus salivarius attaches to the
epithelium of the smooth mucosa and to the surface of the
tongue; other types of streptococci attach to other bacteria
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Streptococcus mutans is involved in the
formation of biofilms on the surface of the teeth,
coaggregating and forming such as "corn cob"
structures
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Eubiosis is definde as "state of
having a healthy population of
bacteria naturally occurring in a
body site
Dysbiosis is an inbalance in the
structural and/or functional
configuration of the microbiota,
leading to a disruption of hostmicroorganism homeostasis
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The main biotopes of the oral cavity
an oral mucosa
the ducts of the salivary glands
the gingival crevicular fluid
the gingival sulcus
the saliva
a dental plaque
The microbial composition of the each biotope is
affected by the physicochemical characteristics of
the environment:
pH
a viscosity
a temperature
the presence of O2
the presence of food debris, etc.
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1. The surface of the mucous membrane of oral
cavity
Biotope features:
•Big area
•Smooth and ridged mucosa
•Absence of O2 in the sublingual space
The investigation of microbiota is carried out by
a) a microscopic method with preparation impression smear
on glass,
b) a bacteriological method by inoculation of impression
smear on agar blocks
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2. The ducts of the salivary glands
The saliva in the ducts is almost sterile. The
composition of it includes:
Lysozyme
Secretory IgA
The specific and nonspecific factors of
resistances
Saliva is taken with a cannulation
•In the oral cavity, the saliva microbiota is the
same as in the oral mucosa: Streptococcus
salivarius, etc.
•Amount of bacterial cells in 1 ml = 10 mln - 100
mln.
•The study of microbiota is carried out by the
bacteriological method.FSBEI HE Astrakhan SMU MOH Russia
3. Oral fluid
Oral fluid = saliva (as a base) +
gingival crevicular fluid (transudate
from the blood secreted in the gingival
groove).
In the oral fluid are microbes from
the mucosa, from the gingival sulcus,
from the dental plaque.
Total amount of bacteria in saliva
varies in the range from 40-50 million
to more than 5 billion per 1 ml, for
about 750 million an average.
Investigated by the bacteriological
method.
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5. Dental plaque
The place of the largest accumulation of microbes both
in quantity (biomass) and in species diversity.
The microbial composition varies in plaque depending
on the location - on the surface of the tooth, at the root of
the tooth, in the interdental spaces.
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Resident microbiota of oral cavity:
main representatives, their role in
opportunistic infections
development
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The main groups of representatives of the resident
microbiota of the oral cavity:
Gram positive
Aerobes and
Gram negative
Aerobes and
Strict anaerobes
facultative anaerobes
Strict anaerobes
facultative anaerobes
Streptococci
Peptococci
Neisseria
Veillonella
Staphylococci
Peptostreptococcus
Bacteroides
Lactobacilli
Bifidobacteria
Porhyromonas
Corynebacterium
Clostridia
Prevotella
Fusobacteium
Leptotrichia
Anaerobes prevail over aerobes in a ratio of 15: 1
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The predominant bacteria in the oral cavity
The members of Streptococcus genus and
Peptostreptococcus genus - more than 50%
Veillonella genus members- less than 25%
Diphtheroids (Corynebacterium genus members and related
bacteria: actinomycetes, eubacteria, bifidobacteriapropionibacteria) - less than 25%
25%
25%
50%
Streptococcus
Peptostreptococcus
Veillonella
Diphtheroids
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The criteria are used to divide the representatives of the
autochthonous microflora into groups:
The Gram stain procedure distinguishes between Gram
positive and Gram negative groups
The morphological type of bacteria: spherical, rod-shaped,
spiral, filamentous
The type of cellular breathing: aerobes, facultative or strict
anaerobes
The biological properties:
•acidophilic properties - an ability to produce various acids
and shift the acid - base balance to the acid side
•proteolytic properties - an ability to produce enzymes that
decompose proteins, destroy microorganism tissues
The etiological role: cariogenic, periodontopathogenic
pathogens of purulent-inflammatory processes.
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Streptococci:
Streptococcus mutans, S. salivarius,
S. sanguis, S. mitis, S. milleRi,
S. intermedius
Cocci are arranged in chains
Gram positive
Aerobes and anaerobes (S. intermedius)
Acidogens, decompose carbohydrates to acid, reduce pH
Cause the inflammatory diseases of the maxillofacial
region : pulpitis, periodontitis, osteomyelitis, abscesses and
phlegmon. S. mutans and S. sanguis are the main etiological
factor of dental caries; S. millegi is the etiological factor of
stomatitis and gingivitis
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Pathogenic properties of streptococci
Most are alpha-hemolytic and non-hemolytic
microorganisms except S. milleri
S. intermedius - periodontopathogenic species
S. sanguis may cause bacteremia, septic endocarditis during
dental interventions
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Habitats for streptococci (biotopes)
Depends on different adhesive activity of
microorganisms:
S. mutans and S. sanguis adhere to enamel and
dominate tooth plaque
S. salivarius dominate the back of the tongue and saliva
S. mitis, S.milleri, S. sanguis are highly adhesive to
mucosal epithelium
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Peptostreptococcus
Peptostreptococcus anaerobius
Cocci are arranged in pairs or short chains
Gram positive
Strict anaerobes
Proteolytic properties - decompose proteins with formation
hydrogen sulfide and mercaptan.
Saccharolytic properties are poorly expressed
Participate in the development of caries, pulpitis,
periodontitis, abscesses
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Staphylococci
Staphylococcus epidermidis
Cocci are arranged in grapelike clusters
Gram positive
Aerobes
Do not reduce pH
They are conditionally pathogenic microbes representatives of facultative microflora, they can cause
stomatitis, pharyngitis and other inflammatory diseases of
the oral cavity
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Veillonella
Veillonella parvula
Gram-negative
Anaerobes
Small cocci, arranged singly, in pairs or small clusters
They ferment numerous organic acid (lactate, pyruvate,
acetate and others) with forming C02 and H20 end products,
leading to acid content neutralization and pH rise and thus
protecting against caries.
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Lactobacilli
Lactobacillus casei, L. salivarius,
L. acidophilus
have polymorphic morphology: can be a rod-shaped,
spherical, filamentous form
Gram positive
belong to microaerophiles by type of cellular breathing
generate ample quantities of lactic acid upon carbohydrate
fermentation that actively stimulates caries progression.
produce vitamin К that is used as potent growth factor by
many oral bacteria (bacteroides).
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Diphtheroids
Genus: Corynebacterium (C. pseudodiphtheriticum)
Actinomyces (A. israelii, A. viscosus, A.odontolyticus)
Bifidobacterium (B.dentium, B.bifidum)
rod-shaped with thickened ends or branching
Gram (+)
strict or facultative anaerobes
biological properties vary
Corynebacteria reduce the redox potential, create
anaerobic conditions; stimulate the growth of bacteroids due
to the synthesis of vitamin K; take part in a development of
periodontal disease
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Actinomycetes
Gram stained smear of
actinomycetes culture
Scanning electron microscopy of
Actinomyces israelii
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Actinomycetes
Actinomyces (A.israelii, A.viscosus, A. odontolyticus)
filamentous branching cells, there may also be rod-shaped
or have the shape of the Y or V letters
Gram (+)
The genus includes anaerobic and aerobic species
Acidogenic - form lactic, acetic, formic, succinic acids;
have weak proteolytic activity
are typical microbial constituents of dental plaque and
dental stone
are commonly isolated from ducts of salivary glands,
gingival pockets, and carious cavities
cause abscesses and systemic actinomycosis.
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Bacteroides
Genus: Bacteroides (B.fragilis),
Prevotella (P.melaninogenica)
Fusobacterium (F. necrophorum)
polymorphic rod-shaped bacteria
Gram (-)
strict anaerobes
have proteolytic properties, upon decomposition of amino
acids cause halitosis
participate in the development of gingivitis, periodontitis,
moderate and deep caries, pulpitis
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Leptotrichia
Leptotrichia buccalis
rod-shaped bacteria up to 15 m long, arranged in pairs
Gram (-)
Anaerobes
Acidogenic - ferment glucose to lactic acid, which leads
to a decrease in pH to 4.5
participate in the development of periodontal disease
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Spirochetes
Treponema (T. macrodentium,
T.denticola, T.orale, t.vincentii)
Borrelia (B.buccalis)
spiral bacteria is rare, less than 1.8% of cases
Gram (-)
anaerobes
live in dental pockets, on the cheek mucosa
have proteolytic activity, and also have a small
saccharolytic activity
participate in the development of periodontitis (while their
number increases to 40%).
Treponema vincentii together with prevotellas and
fusobacteria causes acute necrotizing ulcerative gingivitis (or
ANUG) with sudden onset.
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Age-related changes in the microbiota of
the oral cavity
During the first months of life - aerobes and facultative
anaerobes predominate
During teething - strict anaerobes appear and quickly
multiply
During puberty, the microbiota is similar to the microbiota
of the adult
In old age, with tooth loss and wearing prosthesis, candidal
prosthetic stomatitis may develop, random microbes from the
respiratory tract, gastrointestinal tract: Escherichia,
enterococci, pneumococci
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Thank you for the attention !
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