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1. ORAL MICRO FLORA
Introduction
The mouth harbours many microorganisms is an ecosystem of
considerable complexity, that has not been fully investigated yet and is far
from completely understood.
Recently the mouth was regarded as a single habitant for
microorganisms but it is how realized that the teeth, gingival crevice, tongue,
other mucosal surfaces and saliva all from different habitat or sites when
microorganisms multiply.
Each habitat contains its characteristic population with many different
microbial species.
Bacteria are the most predominant type of microorganisms present in
human oral cavity.
More than 30 genera of bacteria have been detected in human mouth.
25 of which are regular members of the oral flora.
These belong to both aerobic and anaerobic groups of bacteria. Bacteria
present in the oral cavity are both gram +ve and gram –ve. On average 750
million microorganisms are present in each ml of saliva.
1
2. Development of the oral flora
The divided into 4 categories
1. At birth
2. Infancy and early child hood
3. Adolescence
4. Adult hood
1.
Birth: the mouth of the full term foetus is usually sterile although
organisms which are only transient may be aquired from mother and also
from environment. Several streptococcal and staphylococcal species may
be isolated either with colitumns lactobacilli, bacillus spp, neisseria spp
and yeasts.
Streptococcus salivarious is the most common isolate from the mouth
of young babies and together with staphylococcus albus.
Occasionally candida albicans multiply rapidly in the mouth and in low
pH it prevents the normal growth of other commensals and overgrowth of
yeasts produces what is known as oral thrush.
2. Infancy and early child hood
The infants comes into contact with an ever increasing range of
microorganisms and some of these will become established as part of
commensal flora of the individual.
2
3. The eruption of deciduous teeth provides a different surface for
microbial attachment.
Characterized by the appearance of streptococcus sanguis and
mutants.
With increasing to teeth and changes in the diet the overall
properties of organisms in the mouth will change.
Actinomycetes, lactobacilli and Rothia are tuned regularly.
3. Adolescence
The greatest increase in number of organisms in the mouth occurs when
the permanent teeth erupt.
These teeth have deep tissues in their surfaces interproximal spaces are
much larger in these in deciduous dentition.
The gingival crevice is deeper than in deciduous teeth and allows for a
great increase in anaerobic organisms.
Bacteroids spp become established in large number as well as
leptofrichia spp, fusobacterium spp and spirochetes.
The lesion of dental caries will create a new involvement for organisms
especially streptococci will furnish.
3
4. 4. Adult hood
Varying amount of dental plaque may be present and the degree of
chronic periodontal disease will also govern the number and types of
microorganisms found.
Carious lesion and unsatisfactory restoration will provide environment
for bacteria.
There is increase in bacteroids spp and spirochetes superfacial plaque
contains many streptococci mostly streptococcus mutans, mitior and
sanguis.
Actinomycetes are also regularly isolated.
Edentulous patients harbour few spirochetes or bacteriods but their
carriage of yeasts increases.
Yeasts are normally found in the dorsum of tongue.
Denture provide proved environment in which yeasts can multiply.
Benefits of oral microflora
The beneficial aspects of resident microbial flora of oral cavity for the
host includes
1. Supply of certain nutrients.
2. Aid in food digestion and profection against involving and endodontic
pathogens.
4
5. 3. Oral bacteria like intestinal flora produce certain vitamins and cofactors
which are needed by humans. These include vitamin K, biotin and
riboflavin.
4. Production of digestive enzymes such as amylase, lipase and protease.
5. In the presence of resident flora it is difficult for exogenous organisms
to establish themselves and produce disease. Growth of organisms such
as cornybacterium diptheria, streptococcus pyrogens, staphylococcus
aureus has been shown to be inhibitated in vitro by streptococcus
mitior.
6. Helps in maturation of host immune system.
Factors affecting the development of the oral flora
In order to become established in the mouth an organism must
1. Be introduced
2. Be retained
3. Be able to multiply in the conditions present in the mouth
1.
Introduction: From birth wide variety of microorganisms are
introduced into the mouth only certain species are able to become
established in oral cavity.
2.
Retention: Retention of microorganisms is usually continued to a
particular site in mouth.
Factors covering these are
i)
Adherence: Some bacteria have the ability to adhere to soft
tissues. Streptococcus salivarius can adhere to the mucosa of dorsum of
tongue. Other in particular streptococcus mutans, mitior and sanguis to
5
6. enamel as the result of production of extracellular polysaccharide.
Some oral actinomycetes adhere through a hyaluronic acid mediated
mechanism.
ii)
Protected sites: Dental plaque will provide a protected
environment for bacteria. The largest protected site is gingival crevice
where species such as melaniogenicus and sphirochetes can survive.
iii)
Detachment forces: salivary flow the movement of tongue.
Abrasive action of diet serve to remove bacteria.
3.
Multiplication: To become established as a measure of the oral flora
an organism must be able to multiply in the particular site in which it can
be retained.
The factors govern this are
i)
Availability of substrates in order to grow bacteria must be
able to metabolic the availability substrates which come in diet. Increased
carbohydrates in diet probably has the greatest effects in increasing the
number of oral bacteria especially streptococci.
ii)
pH: the metabolism of microorganisms is often dependent on
pH and bacteria inhibit by low pH may not survive in the acid conditions
of dental plaque or under the base of denture.
6
7. • Bacteroids melaninagericus and veillanella spp are inherent if
pH below 5.5.
• Lactobacillus spp and candida albicans can tolerate very low pH
values.
iii)
Oxidation or reduction of surrounding: The oxidation
reduction potentional of the site is often crucial in determining the nature
of the flora in that site.
•
Anaerobic
organisms
such
as
bacteroids
fusobacteria,
spirochetes actinomyctes will only multiply in reduced surroundings.
•
Low oxidation reduction potential can only be achieved radily in
the gingival crevice and in the deeper layer of dental plaque.
iv)
Microbial Interactions: The complexity of communities of
microorganisms is the result of a mucosa of microbial interactions.
•
Some of these are nutritional such as provision of para amino
benzoic acid by streptococcus sanguis for streptococcus mutans in
reduced conditions.
•
Provision of vitamin K for bacteroids melanegenious which in
turn produce format for cariopylobacteria sputorum.
pH: members of the oral flora grow best in vitro at about 70.
• However, the plaque pH can drop to below 5.0 during eating this
low pH could select for aciduric organisms.
• When the pH was dropped to 5.0 only strep mutans and L. Casei
were capable of growth.
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8. Diet as a nutrient source
Three factors influences the effectiveness of the diet as a
microbial nutrient sources.
These are the 1) Chemical composition of the diet 2) The
physical consistency of its components 3) And the frequency of its
presentation.
The macromolecular nutrients such as starches, proteins and
lipids are normally not available to the oral flora because their transit
time through the oral cavity is too short for then to be degraded to
usuable nutrients.
It physical consistency of the food that contain them permits
retention such as fibrous food between the teeth or sticky foods in
tissures pits and contact points then some utilization of starches and
proteins could occur.
Low molecular weight soluble carbohydrates such as sucrose
and lactose are radially metabolized by the oral flora.
It is this bioavailability of these simple sugars that make them
cariogenic.
In dental decay the consistency of the diet and the frequency of
ingestion may be more important than diet composition.
Both consistency and frequency influence the length of time that
food remains in contact with the plaque and thus is available for bacterial
use.
When snacks are inter porsed between meals they augment the
time of nutrient availability.
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9. The consistency of food also influences the plaque flora liquid foods
such as fruit juices and tonics are usually swallowed quickly and for this
reason they are not readily available to oral flora.
Thus for those subjects who eat between meals, sugar could be defected
in their salivas during most of the day. This meant that some microbial
fermentation was ongoing in the plaque the most of the day.
The pH at plaque enamel interface probably was below pH 5.5 this is
the critical pH for enamel demineralization.
Saliva as a nutrient source
Saliva is hameostatic fluid that buffers the plaque, saliva can provide
nutrients to flora it contains about 1% solids, which include glycoproteins
inorganic salts, aminoacids, glucose.
Gingival crevice fluid
Gingival crevice contain serum transudate that contains tissue and
serum proteins as well as free amino acid, vitamins, glucose.
Shed cells
The epithelial surfaces of oral cavity shedding their surface cells, also
phagocytic cells enter the oral cavity.
These memamalian cells can be lysed by the hypotonicity of saliva and
their contents are than available for microbial nutrients.
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10. Bacteria
The bacteria them selves can provide nutrients for each other. Lactic
acid producing bacteria such as streptococcus and lactate utilizing species such
as veillonella alkalescens.
The Normal Microbial Flora of Different Sites of the Mouth
Lips: On the lips there is a transition from skin to oral mucosa and is also
changes in the bacterial population. Staphylococcus albus with large number
of streptococci typical of the mouth. If the commisures are moistened by saliva
an angular chilitis may develop from which candida albicans staphylococcus
aurius and streptococcus pyrogens are isolated.
Cheek: Predominant cheek bacterium is streptococcus mitior with
streptococcus sanguis and salivaries yeasts may be isolated from the cheeks.
Palate: Hard palate supports a streptococcus flora haemophili are found
regularly and lactobacilli are common.
• Few anaerobes found in exposed mucosal surface.
• Yeasts and lactobacilli will increase dramatically in some
denture wearers.
The soft palate will harbour respiratory tract bacteria such as
hemophillus, comebacterium, Neisseria.
10
11. Tongue: The keratinized dorsal surface of the tongue is an ideal site for the
retention of microorganisms streptococcus salivarious is the predominant
organisms.
• Streptococcus mitior and Hemophillus spp are also common.
• Dorsum of the tongue is frequently colonized by small number
of candida albicans.
Gingival crevice
The bacterial population of the gingival crevice is perhaps the most
numerous of any site in the mouth.
•
The gingival crevice is relatively well protected from the forces
that dislodge bacteria and the cervicular fluid transudate provides a rich
nutrients for some fastidious organisms.
•
Facultative Gram +ve cocci: Anaerobic gram tye cocci are
recovered from gingival crevice.
Teeth: All erupted teeth have microorganisms attached usually in the deposits
termed dental plaque.
•
These bacterias are depositioned in the occlusal tissues and in
enamel defects and in interproximal spaces, close to gingival margin.
•
Oral streptococci gram +ve rods and some gram –ve anaerobic
are always present.
Gingival: Salivary samples can be used in detecting caries of candida albicans
or beta hemolytic streptococci.
11
12. • Veillonella spp, streptococcus oralis, streph salivarius, strept, mutans,
strept sangins are isolated from saliva.
Denture and other intra oral appliances
Yeasts and lactobacilli will multiply on any mucosal surfaces protected
from the flow of saliva.
• Candida albicans can be cultured in large numbers from the fitting
surfaces of acrylic dentures.
The Principle Microorganisms of the Mouth
Some organisms described below are present in all mouths in large
number.
Grame +ve cocci
Streptococci
The oral streptococci comprise a group of bacteria that are either non
hemolytic or produce various hemolytic patterns.
For many years they were termed streptococcus viridans but it has been
realized that this group consists at least five distinct species. Streptococcus
sanguis, mitior, mutans, salivarius and mitieri.
These are known as the viridans streptococci they dominate the oral
flora in early life. They represent about half of bacteria on the tongue other
mucosal surfaces and saliva.
12
13. They occupy about 30% of the flora of dental plaque and gingival
crevice.
Streptococcus Sarguis: It is a common constituent of dental plaque
because it adheres readily to the tooth surface through the production of
extracellular gluean.
Strephicoccus mitior: is also a common constituent of dental plaque and
some strains produce extracellular glucan.
Streptococcus mutans: Is the bacterium widely regarded as causing the
initial carious lesion on a tooth.
• Several serotypes like types ‘c’ and ‘d’ are most commonly implicated
in dental caries.
• These polymers from dietary sucrose including mutan and glucan.
• These polymers can attach firmly to the tooth and the bacteria attach to
the polymers.
• Streptococcus salivarius: Is mostly found attached to epithelial surfaces
particularly the dorsum of the tongue.
• It produces fraction from dietary sucrose.
• When
grown
on
sucrose
containing
agar
the
colonies
are
characteristically mucoid.
• Other
aerobic
streptococci
isolated
streptococcus faccalis and bouis.
13
from
the
mouth
include
14. • Isolation of beta hemolytic streptococci is possible from the posterior
soft palate and the tonsillar region.
• Micrococcus mucilaginous is a regular isolate from the dorsum of
tongue.
Grame –ve cocci
Neisseria and Branilanella
Number of grame –ve diplococci are found in the mouth.
• Neisseria magnitudes may be isolated from the throat.
• The remaining Gram –ve diplococci belong to the genus Branhamella
mostly Branhamella catarrhalis these are isolated from dental plaque as
well as from most mucosal surfaces.
Veillonella
This group of gram –ve anaerobic cocci consists two species.
Veillonella parvula and alkalescens.
• They found principally in dental plaque and are the earliest anaerobic to
colonize the mouth.
Gram +ve rods and filaments
There are numerous genera of gram +ve rods and filaments represents
in the mouth mostly found in dental plaque. They are
Lactobacillus
These organisms appear as early colonizers of the mouth and remain as
or a commensally.
14
15. • Two species are commonly found in the mouth, lactobacillus casei and
acidophilus.
Corynebacterium
Member of this genus are found in almost all sites of the body where
there is a commensal flora.
In the U.K. isolations of toxigenic and on toxigenic corybacterium dipth
theroid from the throat and soft palate are isolated.
Bacillus: These sporing gram +ve rods are occasionally isolate from the
mouth but are regarded as transient bacteria.
Actinomyces: Actinomyces are generally isolated from the mouth.
• They are generally found in dental plaque.
• The oral species are mostly facultative anaerobes with only
actinomyces Israeli regarded as a true anaerobe.
• Actinomyces odontolyticus was first isolated from carious dentin and it
may be partly responsible for the progression of the lesion.
• Actinomyces viscous and naeslundii are found in dental plaque.
Eubacterium: Organisms of this genus colonize dental plaque and much of
the digestive tract.
• Eubacterium alactolyticum and saburram are the dominant oral species.
• They are non sporing anaerobic rods.
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16. Propionibacterium: They are anaerobic diptheroids.
• They are characterized by the production of propionic acid from the
breakdown of carbonhydrates.
• They are isolated predominantly from dental plaque.
Gram –ve rods and filaments
Haemophilus: In saliva the predominant species are Haemophillus influenzae
and para influenzae but in dental plaque Haemophillus sings is mostly
commonly isolated.
Fusobacterium: are gram –ve strietly anaerobic filamentous bacteria whose
filaments generally have pointed ends.
• Initially two species were recognized in the mouth. Fusobacterium
nuckleatum and polymorphus and they are isolated from plaque.
Actinobacillus: Actinobacillus actinomycetemitans is found as a commensal
in the gingival crevice.
Spirochetes
These strictly anaerobic organisms are isolated from the deeper parts of
the gingival crevice.
• Spirochetes being dependent for growth on the lowest oxidation
reduction potential of any oral bacteria.
• Two gluer are present in the mouth Borrelia and Trepohema.
16
17. • Oral spirochetes are narrow halically coiled with pointed ends. They are
motile and stain gram –ve but are difficult to see unless stained by a
silver impregnation method.
The larger and less tightly coiled spirochetes seen in oral specimens are
termed Borrelia vincenti and Borrelia buccate.
Yeasts about 30% of the adult population carry yeasts as part of their
normal flora.
• These are usually situated on the hard palate, dorsum of tongue and in
the upper buccal sulens.
Denture wearers may have an increased carriage rate of yeasts.
The most common yeast isolated from the mouth is candida albicans
but candida tropicalis krusei have also been isolated.
Mycoplasm: Two mycoplasms mycoplasma orale and solivaries are found in
the mouth usually in the gingival crevice and also in dental plaque.
Protozoa: Two protozoons Entamoeba gingivalis and trichomonas tenax are
regularly isolated from the mouth particularly from gingival crevice.
Conclusion
The microbial flora of mouth is highly complex containing a wide
variety of bacterial species the most common type of oral disease, dental caries
and periodontal disease are both related to dental plaque and seen to occur in
the normal balance between the microorganisms and lost is altered application
17
18. of modern molecular techniques to the study of this microbiology of oral
disease should allow rapid progress in their diagnosis, risk assessment and
treatment.
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