oral micro flora - seminar

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.

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.

Ø  The eruption of deciduous teeth provides a different surface for microbial attachment.

Ø  Characterized by the appearance of streptococcus sanguis and mutants.

Ø  With increasing to teeth and changes in the diet the overall properties of organisms in the mouth will change.

Ø  Actinomycetes, lactobacilli and Rothia are tuned regularly.

3. Adolescence

Ø  The greatest increase in number of organisms in the mouth occurs when the permanent teeth erupt.

Ø  These teeth have deep tissues in their surfaces interproximal spaces are much larger in these in deciduous dentition.

Ø  The gingival crevice is deeper than in deciduous teeth and allows for a great increase in anaerobic organisms.

Ø  Bacteroids spp become established in large number as well as leptofrichia spp, fusobacterium spp and spirochetes.

Ø  The lesion of dental caries will create a new involvement for organisms especially streptococci will furnish.

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.

Ø  Carious lesion and unsatisfactory restoration will provide environment for bacteria.

Ø  There is increase in bacteroids spp and spirochetes superfacial plaque contains many streptococci mostly streptococcus mutans, mitior and sanguis.

Ø  Actinomycetes are also regularly isolated.

Ø  Edentulous patients harbour few spirochetes or bacteriods but their carriage of yeasts increases.

Ø  Yeasts are normally found in the dorsum of tongue.

Ø  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.

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 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.

·        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.

Diet as a nutrient source

Ø  Three factors influences the effectiveness of the diet as a microbial nutrient sources.

Ø  These are the 1) Chemical composition of the diet 2) The physical consistency of its components 3) And the frequency of its presentation.

Ø  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.

Ø  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.

Ø  Low molecular weight soluble carbohydrates such as sucrose and lactose are radially metabolized by the oral flora.

Ø  It is this bioavailability of these simple sugars that make them cariogenic.

Ø  In dental decay the consistency of the diet and the frequency of ingestion may be more important than diet composition.

Ø  Both consistency and frequency influence the length of time that food remains in contact with the plaque and thus is available for bacterial use.

Ø  When snacks are inter porsed between meals they augment the time of nutrient availability.

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.

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.

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.

·        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.

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 from the mouth include streptococcus faccalis and bouis.

·        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.

·        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.

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.

·        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 of modern molecular techniques to the study of this microbiology of oral disease should allow rapid progress in their diagnosis, risk assessment and treatment.