Microbes appear in every
corner of human life, and
microbes affect every aspect
of human life. The human
oral cavity contains a number
of different habitats. Synergy
and interaction of variable
oral microorganisms help
human body against invasion
of undesirable stimulation
outside. However, imbalance
of microbial flora contributes
to oral diseases and systemic
diseases. Oral microbiomes
play an important role in the
human microbial community
and human health.
The oral cavity is a border area between the environment and the human organism, a gateway for food, an outpost of the
immune system and above all a multilayered habitat inhabited by countless microorganisms.
The mouth is continually exposed to organisms from the external environment ,beginning with the passage through the
In time a ecological balance is reached that serves to establish a resident microbial flora that remains fairly stable
Microorganisms in mouth were first described by Anton von Leeuwenhoek in 1683.
Louis Pasteur – Father of Microbiology
Antony Van Leeuwenhook in 16th century identified bacteria and its shapes
– rods , cocci and spiral forms .
Willoughby D. Miller proposed that carbohydrate from food were broken
down by oral bacteria and the resulting acids caused dissolution of the
Pierre Fauchard in 1745 described tartar and plaque .
J.K. Clark in 1942 identified coccus from carious lesion and named as
The discovery of microbes dates back to the 1700 y.
Historically, Antonie van Leeuwenhoek peered and
examined dental plaque sampled from himself and others
through his microscope. His sense of awe and his early
appreciation of the diversity our microbial partners were
evident. He named the microbes “Dierken”, meaning
small lively objects.
The human oral cavity contains a number of different
habitats, including the teeth, gingival sulcus, tongue, hard
and soft palates, and tonsils, and acts the tube which
connect the outside and the digestive tract and respiratory
tract of human body, which provides the appropriate
space for the colonization of microorganisms. The
microorganisms found in the human oral cavity have
been referred to as the oral microflora, oral microbiota,
or oral microbiome.
• 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.
•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 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 environment.
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
Microorganisms are separated and grouped
according to the different conditions of life;
Resident microflora has an important function
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.
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 conditions:
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.
That is microflora already present in the
body, but has previously been inapparent or
Bacterial flora is endogenous bacteria, which
is defined as bacteria that naturally reside in a
Exogenous bacteria are microorganisms introduced to closed biological
systems from the external world;
They exist in aquatic and terrestrial environments, as well as the
Microorganisms in the external environment have existed on Earth for
3.5 billion years;
Exogenous bacteria can be either benign or pathogenic.
The origin of Oral Microflora
The microflora present in our mouths is acquired from birth, as newborn
babies have no bacteria in their mouths;
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.
• 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:
Candida albicans - 54%;
Obtained from the mother and the surrounding area;
Period before eruption:
Facultative anaerobes and anaerobes;
Streptococcus - 90%;
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.
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
Not all bacteria are ubiquitous in all individuals.
• 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
• 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;
Important Oral Bacteria
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).
Streptococci: Isolated from all sights of the mouth;
Large proportion of resident microflora;
Strep mutans: Associated with caries;
Associated with bacterial endocarditis.
Streptococcus mutans is the primary bacterium involved in plaque formation
and initiation of dental caries;
Viewed as an opportunistic infection, dental disease is one of the most
prevalent and costly infectious diseases
Colonise mucosal surfaces especially the tongue.
Strep angiosus: Isolated dental plaque & mucosal surfaces;
Seen in maxillofacial infections, brain, liver etc.
Actinomyces, facultative anaerobe;
• Lactobacillus, produce lactic acid, facultative anaerobe, role
in dentine caries rather than enamel caries;
• Streptococcus facultative anaerobic cocci, produce lactic acid
some implicated in caries.
Lactobacilli in the oral cavity probably contribute to acid
formation that leads to dental caries.
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 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.
Oral flora changes with age. Time during a lifetime
MAJOR COMPONENTS & CHANGES IN ORAL FLORA
Oral cavity sterile. Soon colonised by facultative and aerobic organisms; esp S. salivarius
Flora becomes more complex & includes anaerobic orgs eg. Veillonella sp. & Fusobacteria
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
Reappearance of bacteria able to grow on hard surfaces.
Regulation of oral microbiota on systematic
•Oral microbiota is related to oral and
systematic diseases. Oral microbiota is
altered during oral and whole body diseases.
Thus, oral microbiota will be a new target
for treating oral diseases and improving the
body’s physical state.