Oral Microbial Ecology
 Ecology (from Greek) is the scientific study of
interactions among organisms and their
environment, such as the interactions organisms
have with each other and with their
abiotic environment;
 The ecosystem is composed of microbial
communities living on specific sites surrounded by a
different physical and chemical elements.
 Ecosystems are composed of dynamically
interacting parts including organisms,
the communities they make up, and the non-living
components of their environment;
 Ecosystem processes, such as primary
production, nutrient cycling, and various niche
construction activities, regulate the flux of energy
and matter through an environment.
 Definitions of Hutchinson:
 “The set of biotic and abiotic conditions in which a
species is able to persist and maintain stable
population sizes."
 In ecology, a niche is a term describing the way of
life of a species;
 Each species have a separate, unique niche;
 The ecological niche describes how an organism
responds to the distribution of resources and
competitors (e.g., by growing when resources are
abundant, and when predators, parasites and
pathogens are scarce) and how it in turn alters those
same factors (e.g., limiting access to resources by
other organisms, acting as a food source for
predators and a consumer of prey).
 Termite mounds with
varied heights of
chimneys regulate gas
exchange, temperature
and other environmental
parameters that are
needed to sustain the
internal physiology of the
entire colony.
 Living microorganisms that are so small that they
can be seen only with a microscope and that
maintain a more or less constant presence in a
particular area;
 Includes bacteria, viruses, protozoa, fungi.
Oral microflora
 Oral microflora refers to the community of
microorganisms coexisting in the oral cavity as its
primary habitat;
 These strains of bacteria colonize the various
different surfaces present in the oral cavity, and
communicate between each other through complex
cell signaling processes;
 The body’s own defenses also play a role in
maintaining a balance and ensuring a healthy oral
Normal - resident flora
 In a healthy body, the internal tissues - blood, brain,
muscle, etc., are normally free of microorganisms;
 However, the surface tissues - skin and mucous
membranes, are constantly in contact with
environmental organisms and become readily
colonized by various microbial species;
 The mixture of organisms regularly found at any
anatomical site is referred to as the normal flora
or resident flora, some researchers prefer the
term "indigenous microbiota".
Resident microflora
 Typical microflora of a econiche;
 Microorganisms are separated and grouped
according to the different conditions of life;
 Resident microflora has an important function in
Digestive and nutritional;
Competition with pathogenic microflora.
Transient Microbiota
 Transient microbes are just passing through;
 Although they may attempt to colonize the same
areas of the body as do resident microbiota,
transients are unable to remain in the body for
extended periods of time due to:
Competition from resident microbes;
Elimination by the body’s immune system;
Physical or chemical changes within the body that discourage
the growth of transient microbes.
Opportunistic microbes
 Under normal conditions, resident and transient
microbes cause the host no harm;
 However, if the opportunity arises, some of these
microbes are able to cause disease and become
opportunistic pathogens.
This can happen due to a number of different
 When the immune system isn’t working properly,
normal flora can overpopulate or move into areas of
the body where they do not normally occur;
 When the balance of normal microbes is disrupted,
for example when a person takes broad
spectrum antibiotics, microbes that are normally
crowded out by resident microbes have an
opportunity to take over;
 Disease can result when normal flora are
traumatically introduced to an area of the body that
they do not normally occur in.
Endogenous microflora
 That is microflora already present in the body, but
has previously been inapparent or dormant.
 Bacterial flora is endogenous bacteria, which is
defined as bacteria that naturally reside in a closed
Exogenous microflora
 Exogenous bacteria are microorganisms
introduced to closed biological systems from the
external world;
 They exist in aquatic and terrestrial environments,
as well as the atmosphere;
 Microorganisms in the external environment have
existed on Earth for 3.5 billion years;
 Exogenous bacteria can be either benign or
The origin of Oral Microflora
 The microflora present in our mouths is acquired from
birth, as newborn babies have no bacteria in their
 Over time, the oral cavity becomes colonized by the
strains of bacteria that eventually form the resident
microflora, which establish a permanent population in
the mouth;
 Over time as the individual is further exposed to external
sources of bacteria, the biodiversity of the oral cavity
increases, to a point where stability is reached.
 This is termed the climax community.
The source of microorganisms
 The source of these microorganisms mainly comes from
saliva, although it also includes the food and water
consumed by the individual;
This process takes place within the first few hours of life;
Majority of children obtain their resident microflora
from their mothers, as they often possess identical
strains of bacteria;
This is known as vertical transmission;
Horizontal transmission also takes place as children
interact with their peers, and later in life between
spouses and partners.
Formation of the ecosystem
 The development of microbial community comprises
an alternation of populations;
 The process starts with the colonization of the
environment of the first microbial population;
 It fills the new space, modify it and makes it
convenient for resettlement of new microbial
This process continues
 Growing microbial community was enriched with
different species living in complex;
 The process of alternation of populations and
enrichment of the community stops only when no
available niches for colonization of new microbial
Climax community
 The settlement of all econiches occurs relative
stability of the system by the microorganisms –
called climax community;
 The stability of the community is based on the
homeostasis, including compensatory mechanisms
against the effects of various factors.
Bacteria during the life cycle
 Oral colonization begins in the birth canal:
 Populations on the tongue and mucosa;
 Established during infancy - include anaerobes;
 Tooth eruption provides non-shedding surfaces:
 The “window of infectivity” concept;
 Colonization from source sites and caregiver saliva;
 Hormonal shifts - puberty and pregnancy:
 Can alter proportions of Gm- anerobes;
 Complete loss of teeth shifts flora towards infant
Dentures restore supragingival non-shedding sites;
Implants restore supra- and subgingival sites.
Microflora at birth
 At birth, the oral cavity is composed only of the soft
tissues of the lips, cheeks, tongue and palate, which
are kept moist by the secretions of the salivary
 At birth the oral cavity is sterile but rapidly becomes
colonized from the environment, particularly from
the mother in the first feeding.
 Streptococcus salivarius is dominant and may make
up 98% of the total oral flora until the appearance of
the teeth (6 - 9 months in humans).
Periods of formation of the oral ecosystem
 The neonatal period:
 Mostly aerobes;
 Candida albicans - 54%;
 Obtained from the mother and the surrounding area;
 Period before eruption:
 Facultative anaerobes and anaerobes;
 Streptococcus - 90%;
 Actinomyces;
 Candida albicans.
After eruption
 The eruption of the teeth during the first year leads
to colonization by S. mutans and S. sanguis;
 These bacteria require a nondesquamating
(nonepithelial) surface in order to colonize;
 They will persist as long as teeth remain;
 Other strains of streptococci adhere strongly to the
gums and cheeks but not to the teeth.
Period after eruption
 Anaerobes:
 Actinomyces;
 Lactobacillus;
 Veillonella;
 Fusiformis;
 Spirochetes;
 Candida albicans.
Oral surfaces
 The oral cavity contains various different forms of
tissue which have different properties;
 The microflora in the mouth is distributed according
to the different types of surfaces present, which
provide each particular species with its optimal
growing environment;
 Certain breeds of bacteria are dependent on specific
surfaces to adhere to.
Diverse ecological niches in the oral cavity
 The heterogeneity of tissue types in the oral cavity, such
as teeth, tongue and mucosa, means that a variety of sites
are available for colonization by oral microorganisms;
 Each site has unique characteristics and allows those
microorganisms best suited to the environment to
inhabit the site;
 The role of microorganisms in a habitat is referred as an
ecological niche and a number of ecological niches exist
in the oral cavity, including supragingival plaque,
subgingival plaque and tongue coating.
 These ecological niches can be characterized by the
environmental factors and the metabolic characteristics
of the microbial flora occupying these sites.
Mucosal Surfaces:
 These include the palate, cheek and tongue, which have cells
which are constantly replaced due to the normal wear-andtear of the mouth;
 The different mucosal surfaces also have different properties
which contribute to the presence of different types of bacteria:
Areas such as the palate contain keratinized squamous epithelium and
the softer non-keratinized areas such as the cheeks;
The tongue is a unique surface with papillary structures, which provides
ample crevices for a wide variety of different strains of bacteria to reside;
The presence of these crypts allows for bacteria to be protected from the
normal shedding and removal by saliva flow, and hence species not
found elsewhere, such as obligate anaerobes, can be found on the
dorsum of the tongue.
Mucosal reservoir sites
 Smooth exfoliating surfaces:
 How do bacteria keep from being swept away?
 Some oral species can invade epithelial cells:
 Requires communication between bacteria and cells;
 Bacteria “subvert” the cell to take them in:
Take control of the cytoskeleton;
 Can live and grow inside;
Can direct the cell to export them to other cells;
 Multi-species intracellular flora resembles mixed
Oral econiches
 Hard structures – teeth, providing various locations
for colonization:
 Soft structures – mucosa:
 Cheeks, lips, tongue, gingiva, palate;
 Keratinized and nonkeratinized mucosa;
 Epithelium of the gingival sulcus.
Mucosa of the gingiva, palate, cheek, floor of the
 Streptococcus:
 S. oralis, S. sanguis;
 Neisseria;
 Haemophilus;
 Veillonella.
Surface of the tongue
 Streptococcus salivarius, S. mitis;
 Veillonella spp.;
 Peptostreptococcus spp.
 Gram + rods - Actinomyces spp.;
 Gram - rods - Bacteroides spp.;
 Obligate anaerobes black - rods and spirochetes
associated with periodontal diseases.
Dental econiches
 Supragingival plaque:
 On approximal surfaces;
 On occlusal surfaces - fissures, pits and grooves;
 Cervical;
Gram positive MO;
 Facultative anaerobes:
 Streptococcus;
 Actinomyces;
 Gram negative:
 Veillonella, Haemophilus, Bacteroides
Subgingival plaque
 From healthy gingival sulcus isolate:
 Gram negative rods:
 Porphyromonas gingivalis;
 Porphyromonas endodontalis;
 Prevotella malaninogenica;
 Prevotella intermedia;
 Prevotella loesheii;
 Prevotella denticola.
Subgingival tooth surfaces
 Narrow crevice between gingival epithelium and
Low oxygen tension
favorable for Gm- anaerobes;
Major site for interaction between
bacteria and host tissues;
Species mix varies between each side and the
center- distinct microenvironments.
Microorganisms in saliva
 Depend on the microorganisms of all ecological
 Microbial composition of saliva is the most similar to
the tongue.
Oral fluids
 Oral surfaces washes of two liquids:
 Saliva;
 Gingival fluid;
 They are the basis for maintaining oral ecosystem:
 Provide water;
 Nutrients;
 Adhesion;
 Antimicrobial factors.
Pathogenicity of microflora
 Microflora usually is non-pathogenic and form an
integral part of the host;
 The presence of friendly resident microorganisms on
oral surfaces contributes to the body’s defense
against foreign pathogens, which are generally
transient and can give rise to harmful infections.
 This is known as colonization resistance;
Function of Microflora
 Colonization resistance is firstly achieved through
the saturation of oral surfaces with preexisting
resident bacteria, which reduces the available sites
left for the attachment of exogenous organisms;
 Essential nutrients derived from the saliva and
various proteins in the oral cavity are also more
effectively utilized by the resident microflora, which
inhibits infections via competition for resources;
Resident microflora modified the conditions of the
 It maintains unfavorable conditions for invading
 Producing substances such as hydrogen peroxide
that actively inhibits pathogen growth;
 As a result, the harmony between the oral microflora
and the body’s natural defenses acts as an effective
deterrent to infections, and thus maintains the
health of the host.
Variations in Microflora
 Everyone has microflora, but it varies between
people depending on the condition of their oral
 Not all individuals would have the same microflora
 Not all bacteria are ubiquitous in all individuals.
Gingival crevicular fluid:
 At the gingival margin, serum flows from the inside
the gingiva into the mouth;
 The flow of this fluid removes foreign microbes
which do not adhere to these surfaces;
 For the resident population, the flow of crevicular
fluid provides these organisms with a source of
 They have specialised enzymes which can break
down these proteins to provide them with the
nutrients necessary for growth.
Teeth and artificial hard surfaces:
 Microbes can accumulate on teeth;
 This generally forms a dense layer of bioflim known
as dental plaque;
 Fissures and deep grooves in the teeth provide ideal
conditions for the formation and build-up of dental
 Most of the bacteria found in dental plaque is absent
in individuals without teeth, such as babies.
The role of saliva in the maintenance of a
healthy oral environment
 By acting as a buffer, saliva maintains the pH of the
mouth, ensuring the optimal growth of the resident
 Most of the microbes present in the mouth utilize the
glycoproteins and proteins in the saliva as their main
source of nutrition;
 Proteins and glycoproteins of saliva are responsible for
the formation of the pellicle, a film on the surface of the
tooth enamel where the microorganisms of the
microflora can adhere to.
Salivary flow
 It is responsible for the removal of non-endogenous bacteria
which is unable to adhere to specific sites in the mouth;
Saliva acts a collector of these cells and facilitates their
Areas which receive markedly less saliva flow, such as deep
gingival crevices, proximal spaces and occlusal fissures, tend
to have significantly higher levels of bacterial buildup;
Saliva is carrying bacteria - the main source of microbial
transmission between individuals;
Saliva also circulates bacteria within the oral cavity, resulting
in re-colonization of oral surfaces where the microflora might
be removed via mechanical forces such as cleaning.
The normal bacterial flora of the oral cavity
 Benefit from the host who provides nutrients and
 Occupy available colonization sites which makes it more
difficult for other microorganisms to become established;
 Contribute to host nutrition through the synthesis of
vitamins, and they contribute to immunity by inducing
low levels of circulating and secretory antibodies that
may cross react with pathogens;
 Exert microbial antagonism against exogenous species
by production of inhibitory substances such as fatty
acids, peroxides and bacteriocins.
The oral flora are the usual cause of various oral
 Abscesses, dental caries, gingivitis, and periodontal
 If oral bacteria can gain entrance into deeper tissues,
they may cause abscesses of alveolar bone, lung, brain, or
the extremities;
 Such infections usually contain mixtures of bacteria
with Bacteroides melaninogenicus often playing a
dominant role;
 If oral streptococci are introduced into wounds created
by dental manipulation or treatment, they may adhere to
heart valves and initiate subacute bacterial endocarditis.
• Commensal: An organism living in/on an organism of another
species without injuring the host;
 Parasite: An organism living in/on and at the expense of another
organism (the host). Equivalent to a pathogen;
 Opportunistic Pathogen: A commensal organism that can cause
disease in certain circumstances ;
 Symbiosis: The mutually beneficial association between two
organisms ;
 Aerobic Organism: requiring oxygen for growth and replication;
 Anaerobe: Organism that grows and replicates in the absence of
oxygen; not necessarily killed by oxygen;
 Strict anaerobe: Anaerobe killed by oxygen;
 Facultative anaerobe: Organism capable of growth and
replication in the presence or absence of oxygen;
Various streptococci in a biofilm in the
oral cavity.
Members of Human Resident oral microflora
 Gram-
Aerobes, facultative
S. anginosus
P. anaerobius
S. cricetus
P. micros
S. gordonii
S. mitis
S. mutans
S. oralis
S. rattus
S. sanguinus
S. sorbinus
S. vestibularis
Stomatococcus – S.
Important Oral Bacteria
 1. Gram Positive organisms:
• Rods (bacilli), cocci or irregular shape (pleomorphic);
• Oxygen tolerance varies from aerobes to strict anaerobes;
• Most are fermentative;
• Cell wall has thick peptidoglycan layer (penicillin has effect by
interfering production of this layer).
 Isolated from all sights of the mouth;
 Large proportion of resident microflora;
 Majority α-haemolytic.
Strep mutans:
 Associated with caries;
 Associated with bacterial endocarditis.
Streptococcus mutans.
 Streptococcus
mutans is the primary
bacterium involved in
plaque formation and
initiation of dental
 Viewed as an
opportunistic infection,
dental disease is one of
the most prevalent and
costly infectious
Strep salivarius:
 Colonise mucosal surfaces especially the tongue.
Strep angiosus:
 Isolated dental plaque & mucosal surfaces;
 Seen in maxillofacial infections, brain, liver etc.
Strep mitis:
 Opportunistic pathogens e.g. endocarditis.
Dental plaque
Scanning electron micrograph
illustrating the diversity of
microbes in plaque
Three important genera:
 Actinomyces, facultative anaerobe;
• Lactobacillus, produce lactic acid, facultative
anaerobe, role in dentine caries rather than enamel
• Streptococcus facultative anaerobic cocci, produce
lactic acid some implicated in caries.
Lactobacillus species
 Lactobacilli in the
oral cavity probably
contribute to acid
formation that leads
to dental caries.
Important of Streptococci in the oral
and their properties
Growth on Prohard
duction of
Production of
Cariogenic Endocarditis
S mutans
S sanguis
S mitior
S milleri
S salivarius
Distribution of Streptococci in the oral
S. mitior
S. salivarius
Biofilm formation
Biofilms usually occur when one bacterial species attaches
specifically or non specifically to a surface, and then secretes
carbohydrate slime (exopolymer) that imbeds the bacteria
and attracts other microbes to the biofilm for protection or
nutritional advantages.
 The classic biofilm that involves components of the
normal flora of the oral cavity is the formation of
dental plaque on the teeth;
 Plaque is a naturally-constructed biofilm, in which
the consortia of bacteria may reach a thickness of
300-500 cells on the surfaces of the teeth;
 These accumulations subject the teeth and gingival
tissues to high concentrations of bacterial
metabolites, which result in dental disease.
Gram-negative bacteria
Aerobes, facultative
anaerobes, microaerophils
 Cocci
 Neisseria
N. flavescens
 N. mucosa
 N. sicca
 N. subflava
B. catarrhalis
 Veillonella
 V. atypica
 V. dispar
 V. parvula
2. Gram Negative organisms
 Many Gram-negative bacteria found in the mouth,
especially in established/subgingival plaque;
 Cocci, rods, filamantous rods, spindle shaped or spiral
 Range of oxygen tolerance but most important strict or
facultative anaerobes;
 Some fermentative, produce acids which other organisms
use acids as an energy source, others produce enzymes
which break down tissue;
Most important Gram negative bacteria:
Porphyromonas: P. gingivalis major periodontal pathogen;
 Prevotella: P. intermedia a periodontal pathogen;
Fusobacterium: F. nucleatum periodontal pathogen;
 Actinobacillus/Aggregatibacter: A.actinomycetemcomitans associated with
aggressive periodontitis;
 Treponema: group important in acute periodontal conditions i.e ANUG;
 Neisseria;
 Veillonella.
A. naeslundii
A. odontolyticus
A. viscosus
A. israelii
A. meyeri
Actinomyces and various proteolytic
bacteria are commonly found in human
carious dentin and cementum, which
suggests that they are secondary invaders
that contribute to the progression of the
 Short pleomorphic rods with branching;
 Major proportion of plaque;
 Increase in gingivitis;
 Associated with root caries.
Microbial habitats
 Lips, cheek, palate
•Biomass limited by
•Some surfaces have
specialised host cell
 Tongue
•Highly papillated surface ;
•Acts as a reservoir for
obligate anaerobes .
Teeth and Gingival crevice
 Teeth
 Gingival crevice /Pocket
 Non-shedding surface
enabling large masses of
microbes to accumulate
(dental plaque biofilm);
 Teeth have distinct
surfaces for microbial
colonisation (Smooth
surfaces, pits & fissures
etc) will support distinct
micro flora due to their
biological properties;
 Health - aerobic, disease
- anaerobic.
Cheeks, lips, palate
-Saliva is major influence;
-Microflora has small
-Sterptococcus spp.
-Some periodontal
pathogens persist by
invading buccal cells
- Non-shredding surfaces;
-Stagnant sites – food
impaction possible;
-Diverse microflora –site
-Many obligate anerobes;
-Influenced by saliva and
Actinomyces, Veillonella,
Fusobacterium, Prevotella,
Treponema, unculturable
High papillated surface;
Some anaerobic sites;
Diverse microflora;
Facultative and obligate anerobes;
Streptococcus, Actinomyces, Rothia, Nisseria, some Gr- anaerobes.
The tongue
 A shedding
 Structure includes
crypts and
 Favorable for Gm-
crevice plaque
Factors Affecting Growth of
Microorganisms in the oral cavity
1. Temperature;
2. REDOX Potential / Anaerobiosis;
3. pH;
4. Nutrients (endogenous & exogenous (diet);
5. Host Defences (Innate & Acquired immunity);
6. Host genetics (changes in immune response etc);
7. Antimicrobial agents & inhibitors.
 Relatively constant - 34˚-36 ˚;
 Life allows a large number of microorganisms;
 The temperature is variable on the teeth and
 When eating microorganisms colonized there are
exposed to extreme temperatures;
 No evidence of metabolic disorders in
microorganisms to these short periods.
pH, or hydrogen ion concentration
 Affects their metabolism;
 In the mouth pH varies between 6.7 and 7.3;
 It is maintained by saliva through:
salivary flow;
buffer systems;
 In an acid medium in the eco niches are developed:
Str. mutans;
 In the gingival sulcus pH is alkaline -7.5 - 8.5;
 In the gingival fluid pH is 7,5 - 7,9 . It develops
periodonto-pathogenic microorganisms.
Redox potential and anaerobiosis
 Under the action of the enzymes some of the components
are subjected to oxidation, and others to reduction;
These processes depend on the oxygen and are redox
In a predominance of reduction processes have a
negative redox potential and develop anaerobic
With positive redox potential are buccal and palatal
mucosa and the back part of the tongue;
With negative redox potential are approximal surfaces,
fissures and gingival sulcus.
 Desquamated epithelial cells;
 Gingival fluid;
 Saliva;
 Residues from host`s food;
 Products of metabolism of other microbial species.
Host factors
 Host defense mechanisms;
 Hormonal changes;
 Stress;
 Genetic factors.
Relationships with the host
 Host defenses in the mouth:
 Epithelial cells:
Barrier function;
 Innate immunity - sensors (Toll-like receptors);
 Inflammatory mediators, antimicrobial peptides;
Salivary antimicrobial factors - DENT 5302;
Mucosal antibodies (secretory IgA);
Cell-mediated immunity (T-cells);
 In most cases, host defenses tolerate oral bacteria
 The predominant relationships are commensal.
Host defense mechanisms
 Removing the microorganisms through stimulation of
salivary flow;
 Specific protection:
SIg A;
 Nonspecific protection:
Antimicrobial factors:
 Lactoferrin;
 Salivary peroxidase;
 Histatine-rich peptides;
 Cistatin;
 Leukocytes;
 Complement.
Removing of the microorganisms
 The majority of microorganisms in the mouth is
removed by washing action of saliva;
 Salivary flow is stimulated by muscle activity of lips
and tongue.
Specific protection - Secretory IgA system
 SIgA-antibodies reduce microbial adhesion to
enamel epithelium and through:
Neutralizing enzymes microorganisms;
Neutralize toxins and viruses;
Synergy with other antibacterial agents such as lysozyme,
lactoferrin, peroxidase and mucin;
 Protects the mucosa of penetration of antigens;
 Helps complement activation.
 Provides a protective coating of enamel and mucosa;
 Catches microorganisms and antigens like in a trap;
 Limits microorganisms penetration into tissues;
 Eliminates microorganisms with continuous
updating of mucin layer combined with washing
action of saliva flow;
 As part of peliculla protects teeth from
IgG, (IgA,
Flow rate;
Lysozyme-proteaseanion system;
Salivary peroxidase
Flora of normal, healthy dentate
% (approx)
Gram positive Diptheroids
Gram negative anaerobic rods
Staphylococci & Micrococci
Other bacteria, fungi,
protozoa & viruses
Difference between mature supra &
sub-gingival plaque
Supra gingival
Sub gingival
Grams stain
Gram + or -ve
Mainly Gram –ve
Cocci, branching
rods, filaments &
Mainly rods &
Energy Metabolism
Facultative, some
Mainly anaerobic
Energy source
Mainly ferment
Many proteolytic
Caries & gingivitis
Gingivitis &
Oral flora changes with age
Time during a
Oral cavity sterile. Soon colonised by facultative and
aerobic organisms; esp S. salivarius
6 months
Flora becomes more complex & includes anaerobic
orgs eg. Veillonella sp. & Fusobacteria
Tooth eruption
Increase in complexity. S sanguis, S mutans and A
viscosus appear. New habitats include hard surfaces
and gingival crevice.
Child to adult
Various anaerobes frequently found inc. Members
of the Bacteroidaceae. Spirochaetes isolated more
Loss of teeth
Disappearance of S mutan, S sanguis, spirochaetes
and many anaerobes
Dentures etc
Reappearance of bacteria able to grow on hard
Oral ecological zones
 Mostly the same species present, but proportions
 High biomass sites:
Non-shedding surfaces:
Supragingival tooth surfaces;
 Subgingival tooth surfaces;
Shedding surface:
The tongue;
 Low biomass (reservoir) sites;
 Shedding oral mucosal surfaces:
Buccal, palate, external gingiva, floor of mouth;
 Saliva as a transitional zone.
Ecological succession
 1° colonizers (Gram+)
 Streptococci bind pellicle
proteins from saliva DENT 5302;
 2° colonizers (Gram-)
 Bridge species - F.
 Bind other bacteria
 3° colonizers (Gram-)
 Porphyromonas gingivalis
Biofilm on tooth surfaces
- The “natural habitat” of most oral bacteria;
- A structured multi-species community;
- Bacteria embedded in matrix with water channels;
- Attachment - growth - ecological succession – maturation.-
Adherence and microcolonies
 Biofilms are initiated by
bacterial adherence to a
 Isolated cells bind
receptors on surface;
 Replication (growth) is
required to form singlespecies microcolonies;
 Growth requires “quorum
In vitro biofilm by Streptococcus sanguinis
SEM by Tracy Grossman
Salivary transport
 Quorum sensing tells
bacteria when to grow, and
when it’s time to go;
 Bacteria at the outer
surface of mature biofilms
are signaled to detach and
become planktonic;
 The goal is to find a new
 Different genes are active
in planktonic and biofilm
˚Saliva is the transport medium for planktonic oral bacteria:
-They don’t grow unless they encounter another surface;
˚Exfoliated epithelial cells in saliva can also transport bacteria;
-A protected environment.
Interspecies collaboration - O2
Streptococcus cristatus:
Facultative species:
Can live w/ or w/o O2;
Uses up O2 when available;
 Fusobacterium nucleatum:
 Robust anaerobe;
 Binding strep improves
survival when O2 is present;
 Porphyromonas gingivalis:
 Sensitive anaerobe;
 Coaggregation essential to
survival when O2 is present.
Inter-species competition
 Many oral species
produce substances that
can kill closely related
 Overlay experiment:
 Streptococcus sobrinus
 Spotted with wild-type
Streptococcus mutans
strain producing
mutacins I and IV
Inter-species communication
 Streptococci ferment CHO;
 Excrete lactic acid;
 Veillonella use lactate made
by Strep for nutrition;
 They are biofilm buddies.
Strep can make amylase;
Starch-digesting enzyme;
Enhances lactate excretion;
Veillonella send a chemical
signal to activate
transcription of Strep
amylase gene;
 Bacteria sense other species.
Collaborative invasion
 Tissue culture
 F. nucleatum invades
epithelial cells;
 S. cristatus does not
invade cells;
 After coaggregation, S.
cristatus is carried inside
by F. nucleatum.
Criteria for colonization
 Major milestone allowing resistance of the
microorganisms against washing action of the
 Provides from adhesins of the microbial surface and
receptors on oral surfaces.
microbial adhesins
 Constructed of:
 Polysaccharides;
 Lipoteichoic acid;
 Glycosyltransferase;
 Carbohydrate-binding proteins;
 They are located in the cell wall in the form of:
 Fimbriae;
 Fibrils;
 Capsules.
Receptors on the oral structures
salivary components
bacterial components
 Mucin;
 Glycosyltransferase;
 Glycoproteins;
 Glucans.
 Amylase;
 Lysozyme;
 IgA, IgG;
 Proline-rich proteins.
 Adherence mechanisms of oral bacteria are essential
to bacterial colonization of the oral cavity;
 In their absence, bacteria become part of the
salivary flow and are swallowed;
 Consequently, oral bacteria have evolved several
mechanisms to fulfill this role.
 The first organisms to attach are the primary (early)
colonizers and primary colonization is mediated
through specific or non-specific physio-chemical
interactions with components of an adsorbed,
organic conditioning film;
Mechanism of adhesion
 Nonspecific chemical and physical interactions:
 Example: Lipoteichoic acid at the microbial surface interacts
with the negative charged components of the host by Ca, H
ions or hydrophobic coatings;
 Then act strong stereo-chemically interactions;
 Microorganisms can adhere to the surface of the
already colonized microorganisms – coaggregation.
Inter-bacterial coaggregation
 Streptococcus cristatus coaggregating with F. nucleatum
- adhesins interacting with receptors;
 Coaggregation is important in ecological succession;
 Fusobacterium nucleatum is considered a bridge species
because it is a promiscuous coaggregator.
Mechanism of the coaggregation
 Coaggregation interactions are believed to
contribute to the development of biofilms by two
The first route is by single cells in suspension specifically
recognizing and adhering to genetically distinct cells in the
developing biofilm;
The second route is by the prior coaggregation in suspension
of secondary colonizers followed by the subsequent adhesion
of this coaggregate to the developing biofilm;
 In both cases, bacterial cells in suspension
(planktonic cells) specifically adhere to cells in the
biofilm in a process known as coadhesion.
Ecological significance of bacterial coaggregation
 Specific coaggregation processes are likely to have
an important ecological role as an integral process in
the development and maintenance of mixed-species
biofilm communities;
 Allows adhesion of the microorganisms, who are not
able to direct adhesion;
 Strengthens bacterial attachment;
 Increases the stability of the plaque matrix.
Bacterial attachment to a surface can be divided
into several distinct phases
 Primary and reversible adhesion;
 Secondary and irreversible adhesion;
 Biofilm formation.
Adhesion is dependent on:
 A contact:
 Start of interaction;
 A dose:
 There is a certain amount of micro-organisms;
 Frequency of exposure:
 Partial colonization;
 Adsorption:
 By electrostatic forces to the surface of pellicle;
 With specific receptors on the cell surfaces;
 With fibrillere coupling end.
 Adaptation;
 Growth;
 Reproduction;
 Accumulation.
Ecological relationships
 Independence
 Life free from influences, management or control of other
 Favorable relationships – commensal;
 One type of benefit, but others did not suffer;
 Pathological.
Microbial relationships
 There are a complex of relationships between
different microbial species:
Antagonistic microbial interactions;
 Relationship between two species living together
without affecting each other - neither favorable nor
 Relationships between the two microbial species
living together, wherein both are mutually favored,
leading to enhancement of the effects of each of
Example of synergy
 Various microorganisms may cooperate to use
substances which are not able to metabolise
P. gingivalis and F. Nucleatum are unite to hydrolyze casein.
 Relationship of two microbial species living
together, yielding inhibition of their function, and
less effect on the independent operation of each one
of them.
Mechanisms of microbial antagonism
 Competition for adhesion receptors;
 Competition for nutrients;
 Production of inhibitory substances:
 Organic fatty acids;
 Hydrogen peroxide:
 Dairy complex;
 Antibiotics;
 Enzymes;
 Bacteriocins.
An example of microbial antagonism
 S. mutans and Lactobacillus produce lactic acid;
 It is caused an acidic environment;
 It inhibits the growth of S.sanguis and S. oralis, and
gram negative microorganisms;
 Separation bacteriocins inhibit gram positive
Host – microorganisms relationships
 Symbiosis;
 Comensal;
 Mutualism;
 Parasitism.
 Symbiotic relationships include those associations in
which one organism lives on another, or where one
partner lives inside the other .
 Commensalism describes a relationship between two
living organisms where one benefits and the other is
not significantly harmed or helped;
 Commensal relationships may involve one organism
using another for transportation or for housing ,
or it may also involve one organism using
something another created, after its death.
 Mutualism is any relationship between individuals of
different species where both individuals benefit;
 During mutualistic symbioses, the host cell lacks some of
the nutrients, which are provided by the endosymbiont;
 As a result, the host favors endosymbiont's growth
processes within itself by producing some specialized
 These cells affect the genetic composition of the host in
order to regulate the increasing population of the
endosymbionts and ensuring that these genetic changes
are passed onto the offspring via vertical transmission.
Mutualistic relationship
 Coaggregating cells can possess a combined
metabolic advantage over single cells;
 Mutualistic relationship that allowed each to grow
where neither grew alone;
 Example: coaggregating partnership of S. oralis and
Actinomyces naeslundii formed a nutritionally
beneficial, mutualistic relationship that allowed each
to grow where neither grew alone.
 A parasitic relationship is one in which one member
of the association benefits while the other is harmed;
 This is also known as antagonistic or antipathetic
Influence of external factors
 Diets;
 Oral hygiene and antimicrobial agents;
 Drugs and diseases.
 Food high in carbohydrates increases the
development of Str. mutans and Lactobacillus;
 A diet high in protein inhibits the development of
oral Hygiene
 Good oral hygiene:
 Facultative aerobes;
 Acidogenious microorganisms;
 Neglected oral hygiene:
 Anaerobes;
 Proteolytic microorganisms.
Antimicrobial agents
 Fluorides have depressing effect on microbial p-
 Reducing sugar transport;
 Reduce their glycolytic activity;
 Suppress the acid tolerance of gram +
Drugs and diseases
 Patients with reduced salivation have reduced
capacity to remove sugars, reduced buffering
capacity and reduced protection;
 Antibiotics suppress the resident microflora, leading
to over-development of antibiotic resistant species Candida and allow colonization of exogenous
pathogens such as Enterobacteriaceae.
Beneficial effect of the microflora on the body
 Prevention of exogenous and endogenous infections;
 Stimulating an immune response;
 Renewal and healing of the epithelium;
 Delivery of certain biological factors to the host.
Adverse effects
 Source of endogenous infection;
 Change the local environment to physiological
conditions facilitating exogenous microbial
 Create hypersensitivity in macroorganism to
microbial agents.
Protective mechanisms in the
Protective mechanisms in the mouth
 1. Protection of enamel;
 2. Protection of the oral mucosa;
 3. Protection of the oral physiological fluid;
 4. Protective mechanisms of microbial life.
Enamel Protection
 Protects underlying tooth structure and tissue;
 Provides the physiological mineralization;
 Opportunity for remineralization.
Protection of the oral mucosa
 Protection of the epithelium
 by keranitization
 cell exfoliation
 Renewal and regeneration
 intercellular connections
 Relationship between cell layers
 Langerhans cells
 receptors
Protection of other layers of the mucousa
 Basement membrane:
 Lamina Propria:
Connective tissue cells;
 Blood element;s
 Collagen fibers;
 Matrix;
 Receptors;
 Innervation.
Protection of the physiological content - saliva
 Mechanical washing;
 Salivary anti-caries activity;
 Buffer systems;
 Immunoglobulins;
 Enzymes.
Protective mechanisms of gingival fluid
 Microphages;
 Macrophages;
 Immunoglobulins;
 Urea;
 ALP;
 Lysozyme;
 Lactoferrin;
 Epithelial timoactive factor.
Protective mechanisms of microorganisms
 Prevention of exogenous and endogenous infections;
 Renewal and healing of the epithelium;
 Stimulating an immune response;
 Development of oral tolerance;
 Delivery of certain biological factors to the host.

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