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Submitted by

Mr.harsh raj

Sec-b

Submitted-to Roll-no-01

Mr.harsh reg.no-1030070007

Acknowledgement

Term paper of cell

biology

on

Submitted to:-

Submitted by:-

Mr. Gagandeep Sumit

kumar

Roll.

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I would like to express my gratitude toall those who gave me

the possibility to complete this term paper on oral microbial

flora .first of all i want to thank the lecturer mr.harsh who tell

me the way to complete the term paperI am also very thankful

to my friends who helped me.

Thank you

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Contents

1.oral microbiology-oral bacteria

3.Dental plague

3.the mouth as a habitat

4.growth and death of oral microorganism

5.metabolism of oral microbial flora

6.the bacterial flora of human

9.normal flora of the oral cavity

10.benefits

11.dental caries and periodontal disease

12.protection

13.dental infection

14.oral microbial ecolgy

15.background

Oral microbiology

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Oral microbiology is the study of themicroorganisms of the oral cavity and the interactions

between the oral microorganisms with each other and with the host. Of particular interest is

the role of oral microorganisms in the two major dental diseases: dental caries and

periodontal disease.

Microbiology began in the mouth: Antony van Leeuwenhoek developed and used the firstmicroscope to examine material collected from teeth, and described motile

animalculesMicrobes include higher and lower organisms, although Oral Microbiology

concerns mainly bacteria, some viruses and few fungi: The mouth harbors a diverse,

abundant and complex microbial community. This highly diverse microflora inhabits the

various surfaces of the normal mouth. Bacteria accumulate on both the hard and soft oral

tissues inbiofilms. Bacterial adhesionis particularly important for oral bacteria.Oral bacteria

have evolved mechanisms to sense their environment and evade or modify the host. Bacteria

occupy the ecological niche provided by both the tooth surface and gingival epithelium.

However, a highly efficient innate host defense system constantly monitors the bacterial

colonization and prevents bacterial invasion of local tissues. A dynamic equilibrium exists

between dental plaquebacteria and the innate host defense system

Oral bacteria

Oral bacteria include streptococci, lactobacilli, staphylococci, corynebacteria, and various

anaerobes in particularbacteroides. The oral cavity of the new-born baby does not contain

bacteria but rapidly becomes colonized with bacteria such as Streptococcus salivarius. With

the appearance of the teeth during the first year colonization by Streptococcus mutans and

Streptococcus sanguis occurs as these organisms colonise the dental surface and gingiva.

Other strains of streptococci adhere strongly to the gums and cheeks but not to the teeth. The

gingival crevice area (supporting structures of the teeth) provides a habitat for a variety ofanaerobic species. Bacteroides and spirochetes colonize the mouth around puberty.[1]

Treponema denticola

The levels of oral spirochetesare elevated in patients withperiodontal diseases. Among this

group, Treponema denticolais the most studied and is considered as one of the mainetiological bacteria of periodontitis. Treponema denticola is a motile and highly proteolytic

bacterium

Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative oral anaerobe strongly associated with chronic

adult periodontitis. The bacterium produces a number of well-characterized virulence factors

and can be manipulated genetically. The availability of the genome sequence is aiding our

understanding of the biology ofP. gingivalis and how it interacts with the environment, other

bacteria and the human host.

Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is considered an oral pathogen due to its virulence

factors, its association with localized aggressive periodontitis in young adolescents, andstudies indicating that it can cause bone loss.[4]

http://en.wikipedia.org/wiki/Microorganismhttp://en.wikipedia.org/wiki/Microorganismhttp://en.wikipedia.org/wiki/Dental_carieshttp://en.wikipedia.org/wiki/Periodontal_diseasehttp://en.wikipedia.org/wiki/Periodontal_diseasehttp://en.wikipedia.org/wiki/Microflorahttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Biofilmhttp://en.wikipedia.org/wiki/Biofilmhttp://en.wikipedia.org/wiki/Adhesionhttp://en.wikipedia.org/wiki/Adhesionhttp://en.wikipedia.org/wiki/Toothhttp://en.wikipedia.org/wiki/Epitheliumhttp://en.wikipedia.org/wiki/Dental_plaquehttp://en.wikipedia.org/wiki/Dental_plaquehttp://en.wikipedia.org/wiki/Anaerobehttp://en.wikipedia.org/wiki/Bacteroideshttp://en.wikipedia.org/wiki/Streptococcus_salivariushttp://en.wikipedia.org/wiki/Streptococcus_mutanshttp://en.wikipedia.org/wiki/Streptococcus_sanguishttp://en.wikipedia.org/wiki/Oral_microbiology#cite_note-AnthonyHRogers-0http://en.wikipedia.org/wiki/Spirocheteshttp://en.wikipedia.org/wiki/Spirocheteshttp://en.wikipedia.org/wiki/Periodontal_diseaseshttp://en.wikipedia.org/wiki/Treponema_denticolahttp://en.wikipedia.org/wiki/Treponema_denticolahttp://en.wikipedia.org/wiki/Porphyromonas_gingivalishttp://en.wikipedia.org/wiki/Aggregatibacter_actinomycetemcomitanshttp://en.wikipedia.org/wiki/Oral_microbiology#cite_note-fine-3http://en.wikipedia.org/wiki/Microorganismhttp://en.wikipedia.org/wiki/Dental_carieshttp://en.wikipedia.org/wiki/Periodontal_diseasehttp://en.wikipedia.org/wiki/Microflorahttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Biofilmhttp://en.wikipedia.org/wiki/Adhesionhttp://en.wikipedia.org/wiki/Toothhttp://en.wikipedia.org/wiki/Epitheliumhttp://en.wikipedia.org/wiki/Dental_plaquehttp://en.wikipedia.org/wiki/Anaerobehttp://en.wikipedia.org/wiki/Bacteroideshttp://en.wikipedia.org/wiki/Streptococcus_salivariushttp://en.wikipedia.org/wiki/Streptococcus_mutanshttp://en.wikipedia.org/wiki/Streptococcus_sanguishttp://en.wikipedia.org/wiki/Oral_microbiology#cite_note-AnthonyHRogers-0http://en.wikipedia.org/wiki/Spirocheteshttp://en.wikipedia.org/wiki/Periodontal_diseaseshttp://en.wikipedia.org/wiki/Treponema_denticolahttp://en.wikipedia.org/wiki/Porphyromonas_gingivalishttp://en.wikipedia.org/wiki/Aggregatibacter_actinomycetemcomitanshttp://en.wikipedia.org/wiki/Oral_microbiology#cite_note-fine-3

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Lactobacillus

SomeLactobacillus species have been associated with dental caries although these bacteria

are normally symbiotic in humans and are found in the gut flora.

Dental plaque

Dental plaque is the material that adheres to the teeth and consists of bacterial cells (mainly

S. mutans and S. sanguis), salivary polymers and bacterial extracellular products. Plaque is a

biofilm on the surfaces of the teeth. This accumulation of microorganisms subjects the teeth

and gingival tissues to high concentrations of bacterial metabolites which results in dental

disease. If not taken care of, via brushing or flossing, the plaque can turn into tartar (its

hardened form)and lead to gingivitis or periodontal disease.

Cell-cell communication

Most of the bacterial species found in the mouth belong to microbial communities, called

biofilms, a feature of which is inter-bacterial communication. Cell-cell contact, is mediated

by specific protein adhesins and often, as in the case of inter-species aggregation, by

complementary polysaccharide receptors. Another method of communication invoves cell-

cell signalling molecules, which are of two classes: those used for intra-species and those

used for inter-species signalling. An example of intra-species communication isquorum

sensing. Oral bacteria have been shown to produce small peptides, such as competence

stimulating peptides, which can help promote single-species biofilm formation. A common

form of inter-species signalling is mediated by 4, 5-dihydroxy-2, 3-pentanedione (DPD) or

Autoinducer-2 (Al-2).

Vaccination against oral infections

Dental caries and periodontitis have an infectious etiology and immunization has been

proposed as a means of controlling them. However, the approaches vary according to the

nature of the bacteria involved and the mechanisms of pathogenesis for these two very

different diseases. In the case of dental caries, proteins involved in colonization of teeth by

Streptococcus mutans can produce antibodies that inhibit thecariogenic process. Periodontal

vaccines are less well developed, but some antigenic targets have been identified. :

The Mouth as a Habitat

Host defences associated with the tooth surfaces:-

http://en.wikipedia.org/wiki/Biofilmhttp://en.wikipedia.org/wiki/Adhesinhttp://en.wikipedia.org/wiki/Quorum_sensinghttp://en.wikipedia.org/wiki/Quorum_sensinghttp://en.wikipedia.org/wiki/Quorum_sensinghttp://en.wikipedia.org/w/index.php?title=Competence_stimulating_peptides&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Competence_stimulating_peptides&action=edit&redlink=1http://en.wikipedia.org/wiki/Autoinducer-2http://en.wikipedia.org/wiki/Streptococcus_mutanshttp://en.wikipedia.org/w/index.php?title=Cariogenic&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Cariogenic&action=edit&redlink=1http://en.wikipedia.org/wiki/Biofilmhttp://en.wikipedia.org/wiki/Adhesinhttp://en.wikipedia.org/wiki/Quorum_sensinghttp://en.wikipedia.org/wiki/Quorum_sensinghttp://en.wikipedia.org/w/index.php?title=Competence_stimulating_peptides&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Competence_stimulating_peptides&action=edit&redlink=1http://en.wikipedia.org/wiki/Autoinducer-2http://en.wikipedia.org/wiki/Streptococcus_mutanshttp://en.wikipedia.org/w/index.php?title=Cariogenic&action=edit&redlink=1

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The host defences associated with oral mucosal surfaces:-

Specific and non-specific host defence factors in the mouth.

Specific Factor Main function Non-specific factor Main function

Intra-epithelial

lymphocytes

Cellular barrier to

bacteria antigens

Saliva flow physical removal of

organisms

Langerhans cell

sIgA

Prevents adhesion &

metabolism

Mucin/agglutinins physical removal of

organisms

IgG, IgA, IgM prevent adhesion, Lysozyme-protease- cell lysis

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opsonise, complement anion system

Complement activates neutrophils,

bactericidal

Lactoferrin iron sequestration

Neutrophils,

macrophages

phagocytosis Apo-lactoferrin Cell killing

Sialoperoxidase system Neutral pH:

hypothiocyanite

Acid pH:

hypocyanous acid

Histatins antibacterial and

antifungal

Growth and Death of Oral Microorganisms

Reproduction and growth of bacteria Measurement of growth Growth curves Environmental factors affecting growth and survival Introduction to sterilisation and disinfection

Growth of a biological system or of a living organism, or part of one, may be defined as anincrease in mass or size (in any direction) accompanied by the synthesis of macromolecules,

leading to the production of a newly organised structure. Measurement of the growth of some

organisms is dictated by the nature of the organism; actinomycetes and fungi exist as

hyphae, which increase in length by extension of the zone behind the hyphal tip. A fungal

colony will increase in diameter with most growth occurring at the margin. Yeasts and some

bacteria reproduce by budding. Growth when applied to bacteria normally refers to an

increase in the number of individual cells and so is a measure of population density, denoting

an increase in number beyond that in the original inoculum. Bacterial growth can be very

rapid (a culture ofEscherichia coli can double in size in 20 minutes in a rich medium) andthis characteristic is especially important in vivo when nutrients may be extremely scarce.

Measurement of Growth

Growth may be estimated as an increase in the number of bacteria, cell mass, or any cellular

constituent. When measuring populations counting methods can be divided into two broadgroups: total counts, including both living and dead bacteria, and viable counts in which

only cells able to grow in the conditions provided are counted. Both types of procedures are

used commonly to enumerate and evaluate oral bacteria. Total counts give much higher

numbers of organisms in plaque, not only because dead cells are counted, but also because

many of the organisms in plaque cannot yet be cultivated in the lab (eg many oral

spirochaetes, which can be seen by microscopy and their nucleic acids can be detected, are

non-cultivable).

Environmental Factors Influencing Growth

Microorganisms in their natural environments and in the laboratory are subjected to a widevariety of environmental influences, which combine to determine whether growth can occur

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and the rate at which it can occur. Organisms which are best adapted to the environment will

grow best and will consequently be selected from a mixed population. For example, as

organisms in subgingival plaque grow and the periodontal pocket deepens, conditions

become increasingly anaerobic so the bacteria which come to predominate in periodontal

pockets do not require oxygen for metabolism.

Temperature: Temperature primarily affects the enzymes of a microorganism: a rise in

temperature increases enzyme activity and allows a faster growth rate, until key enzymes are

denatured. The temperatures at which these events occur vary widely amongst microbes,

which all have characteristic maximum, minimum and optimum temperatures for growth.

Organisms which inhabit the human body as commensals and/or pathogens are mesophiles,

and grow most rapidly within the range 20C to 45C, with growth optima between 35C and

40C.

pH: Most bacteria have an optimum pH for growth in the range 6.5 - 7.5 with limits

somewhere between 5 and 9. Acidophilic bacteria can grow at a low pH, and such organisms

are very important in Oral Microbiology as the causative agents of caries: lactobacilli andmutans streptococci produce acid as end products of metabolism of dietary sugars, and are

able to survive and grow in the acidic conditions created (aciduric). The organisms found in

periodontal disease are usually not aciduric as they tend to rely for growth on protein/peptide

breakdown and this produces slighlty alkaline end products.

Oxygen: Bacteria vary widely in their requirements for oxygen, ranging from obligate

aerobes through facultative anaerobes and microaerophiles to obligate anaerobes. Because

oxygen and its derivatives are toxic and can lethally damage certain cellular components,

aerobic and facultative organisms have evolved protective enzyme systems: superoxide

dismutase (SOD) eliminates superoxide radicals and hydrogen peroxide can be removed by

catalase and peroxidase enzymes. In general, anaerobes lack protective mechanisms.

Aerobic bacteria use oxygen as the terminal electron acceptor in respiration, and obligate

aerobes have an absolute requirement for oxygen to grow.

Microaerophilic (eg. Campylobacterspp.) organisms require a low concentration of oxygenfor growth, and are sensitive to atmospheric concentrations.

Facultative anaerobes, such as streptococci andNeisseria, use oxygen but also grow in its

absence although growth is usually slower without oxygen.

An obligately anaerobic organism is one whose energy generating and synthetic pathways do

not require molecular oxygen, and which demonstrates a high degree of adverse sensitivity to

oxygen. Because of their extreme sensitivity, obligate anaerobes must be cultivated in the

absence of atmospheric oxygen and a low redox potential (Eh) must be maintained in the

growth medium (Eh is a measure of the tendency of a solution to give up or receive

electrons). These conditions can be acheived using specialised techniques, such as incubation

in anaerobic jars or cabinets. These cultivation techniques, and anaerobic sampling methods,

are essential in Oral Microbiology when examining samples from, for example, periodontal

pockets or abscesses which contain high numbers of obligately anaerobic bacteria.

Control of microorganisms

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Control of the growth and spread of microorganisms is acheived in three main ways (apart

from by developments in sanitation, water purification etc.).

Chemotherapy: most successful antimicrobial agents are antibacterial, with target sites in the

cell wall, the bacterial ribosome, nucleic acid synthetic pathways or the cell membrane. They

may be bactericidal (kill bacteria) or bacteriostatic (inhibit growth, thereby limiting numbersof infecting organisms to levels which the host defences can control). There are far fewer

antifungal drugs available; because fungi are eukaryotic, there are fewer target sites within

fungal cells which differ sufficiently from host cells to ensure non-toxicity of the antifungal

agent. Similarly, development of antiviral drugs is difficult because interference with viruses

is often impossible without damage to host cells.

Immunisation: vaccines have been of enormous importance in controlling, and in some

cases (eg. smallpox) eradicating, significant diseases. In Oral Microbiology the diseases to be

controlled are often caused by too many different organisms to make vaccination a realistic

option, but much work has been done on a vaccine based on Streptococcus mutans to control

dental caries.

Sterilisation and disinfection: excluding sources of infection from equipment, dressings,

medicines, water supplies etc. is of paramount importance in infection control within

hospitals/clinics/practices.

Sterilisation means the process of killing or removing all viable organisms. Sterilisation may

be acheived by:

heat- moist heat, more often used than dry heat, is used within autoclaves where saturatedsteam under pressure ensures sufficient killing and penetration of heat into materials to be

sterilised. The usual sterilisation cycle of 121C for 15 minutes is sufficient to kill all

vegetative bacterial cells and the heat resistant endospores of clostridia andBacillus spp.

irradiation - gamma irradiation is used to sterilise needles, syringes, gloves, vaccines and

heat-sensitive items and equipment. Free radicals are produced by the irradiation and these

attack target sites such as DNA.

chemical agents - the gases, ethylene oxide and formaldehyde, are alkylating agents which

damage proteins and nucleic acids. Many chemical agents are capable of disinfecting but few

are capable of rendering articles sterile.

filtration - passing fluids through nitrocellulose membranes with pore sizes of 0.6 or 0.22mm

removes microbial cells as well as particles and pyrogens. Filtration may also be used to

isolate very small numbers of organisms from large volumes of fluid, for example when

looking for pathogens in water supplies.

Disinfection is a process which kills most, but not all, viable organisms. It may employ a

chemical agent which kills pathogens, but does not kill viruses or endospores, or a physical

process such as boilong water to reduce the viable microbial load. Antiseptics, a particular

group of disinfectants, reduce the number of organisms on the skin.

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Pasteurisation eliminates pathogens and reduce the total numbers of viable microbes, but

does not affect endospores. The original regime of 62C for 30 min has been replaced by the

Flash method of about 71C for 15 seconds to pasteurise many bulk fluids.

Metabolism of Oral Microorganisms

Oral microorganisms derive nutrients from saliva and GCF. Additionally, exogenous

substrates are provided intermittently in the diet. Thus, there is an enormous diversity in

substrates available and in the metabolic activities of the organisms which colonise the

mouth.

Carbohydrate metabolism (figure) has received much attention because of its role in caries

production. End products of such fermentation in the mouth are varied e.g., Streptococcus

mutans produces only lactic acid from sugars, some lactobacilli produce lactic acid and

ethanol, whereas yeasts convert glucose to ethanol and CO2. The substrates used are also

very varied and many of the anaerobes seen in the mouth are able to utilise amino acids as

substrates for fermentation; therefore, periodontal organisms are predominantly proteolytic.

The Bacterial Flora of Humans

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The Normal Flora

In a healthy animal, the internal tissues, e.g. blood, brain, muscle, etc., are normally free of

microorganisms. However, the surface tissues, i.e., 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 referredto as the normal flora, except by researchers in the field who prefer the term " indigenous

microbiota". The normal flora of humans consists of a few eucaryotic fungi and protists, but

bacteria are the most numerous and obvious microbial components of the normal flora.

Figure 1. Gram stain of a species ofMicrococcus, commonly isolated from the skin and nasal

membranes of humans.

The predominant bacterial flora of humans are shown in Table 1. This table lists

only a fraction of the total bacterial species that occur as normal flora ofhumans. A recent experiment that used 16S RNA probes to survey the diversity

of bacteria in dental plaque revealed that only one percent of the total species

found have ever been cultivated. Similar observations have been made with the

intestinal flora. Also, this table does not indicate the relative number or

concentration of bacteria at a particular site. . (1) The staphylococci and

corynebacteria occur at every site listed. Staphylococcus epidermidis is highly

adapted to the diverse environments of its human host. S. aureus is a potential

pathogen. It is a leading cause of bacterial disease in humans. It can be

transmitted from the nasal membranes of an asymptomatic carrier to a

susceptible host.

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S. epidermidis. Scanning EM. CDC.

(3)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 in the United States.

Streptococcus mutans. Gram stain. CDC

(5)Streptococcus pneumoniae is present in the upper respiratory tract of about half the population. If itinvades the lower respiratory tract it can cause pneumonia. Streptococcus pneumoniae causes 95 percent

of all bacterial pneumonia.

Streptococcus pneumoniae. Direct fluorescent antibody stain. CDC.

(6)Streptococcus pyogenes refers to the Group A, Beta-hemolytic streptococci. Streptococci cause

tonsillitis (strep throat), pneumonia, endocarditis. Some streptococcal diseases can lead to rheumatic

fever or nephritis which can damage the heart and kidney.

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Streptococcus pyogenes. Gram stain.

(7)Neisseria and other Gram-negative cocci are frequent inhabitants of the upper respiratory

tract, mainly the pharynx.Neisseria meningitidis, an important cause of bacterial meningitis, can

colonize as well, until the host can develop active immunity against the pathogen.

Neisseria meningitidis. Gram stain.

Lactobacilli in the oral cavity probably contribute to acid formation that leads to dental caries.

Lactobacillus acidophilus colonizes the vaginal epithelium during child-bearing years and

establishes the low pH that inhibits the growth of pathogens.

Lactobacillus species and a vaginal squaemous epithelial cell. CDC

Normal Flora of the Oral Cavity The presence of nutrients, epithelial debris, and secretions

makes the mouth a favourable habitat for a great variety of bacteria. Oral bacteria include

streptococci, lactobacilli, staphylococci and corynebacteria, with a great number of

anaerobes, especially bacteroides.The mouth presents a succession of different ecologicalsituations with age, and this corresponds with changes in the composition of the normal floras

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birth, the oral cavity is composed solely of the soft tissues of the lips, cheeks, tongue and

palate, which are kept moist by the secretions of the salivary glands. 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 oralflora until the appearance of the teeth (6 - 9 months in humans). The eruption of the teeth

during the first year leads to colonization by S. mutans and S. sanguis. These bacteria requirea nondesquamating (no epithelial) 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. The creation of the gingival crevice area (supporting structures of the teeth)

increases the habitat for the variety of anaerobic species found. The complexity of the oral

flora continues to increase with time, and bacteroides and spirochetes colonize around

puberty.

Various streptococci in a biofilm in the oral cavity.

The normal bacterial flora of the oral cavity clearly benefit from their host who provides

nutrients and habitat. There may be benefits, as well, to the host. The normal flora occupyavailable colonization sites which makes it more difficult for other microorganisms

(nonindigenous species) to become established. Also, the oral flora 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. Finally, the

oral bacteria exert microbial antagonism against nonindigenous species by production of

inhibitory substances such as fatty acids, peroxides and bacteriocins.On the other hand, the

oral flora are the usual cause of various oral diseases in humans, including abscesses, dental

caries, gingivitis, and periodontal disease. 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 withBacteroides melaninogenicus often

playing a dominant role. If oral streptococci are introduced into wounds created by dental

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manipulation or treatment, they may adhere to heart valves and initiate subacute bacterial

endocarditis

Beneficial Effects of the Normal Flora

The effects of the normal flora are inferred by microbiologists from experimentalcomparisons between "germ-free" animals (which are not colonized by any

microbes) and conventional animals (which are colonized with a typical normal

flora). Briefly, some of the characteristics of a germ-free animals that are

thought to be due to lack of exposure to a normal flora are:

1. vitamin deficiencies, especially vitamin K and vitamin B12

2. increased susceptibility to infectious disease

3. poorly developed immune system, especially in the gastrointestinal tract

4. lack of "natural antibody" or natural immunity to bacterial infection

Because these conditions in germ-free mice and hamsters do not occur in

conventional animals, or are alleviated by introduction of a bacterial flora (at the

appropriate time of development), it is tempting to conclude that the human

normal flora make similar contributions to human nutrition, health and

development. The overall beneficial effects of microbes are summarized below.

1. The normal flora synthesize and excrete vitamins in excess of their own

needs, which can be absorbed as nutrients by their host. For example, in

humans, enteric bacteria secrete Vitamin K and Vitamin B12, and lactic acid

bacteria produce certain B-vitamins. Germ-free animals may be deficient inVitamin K to the extent that it is necessary to supplement their diets.

2. The normal flora prevent colonization by pathogensby competing for

attachment sites or for essential nutrients. This is thought to be their most

important beneficial effect, which has been demonstrated in the oral cavity, the

intestine, the skin, and the vaginal epithelium. In some experiments, germ-free

animals can be infected by 10 Salmonella bacteria, while the infectious dose for

conventional animals is near 106 cells.

3. The normal flora may antagonize other bacteria through the production

of substances which inhibit or kill nonindigenous species. The intestinal bacteria

produce a variety of substances ranging from relatively nonspecific fatty acidsand peroxides to highly specific bacteriocins, which inhibit or kill other bacteria.

4. The normal flora stimulate the development of certain tissues, i.e., the

caecum and certain lymphatic tissues (Peyer's patches) in the GI tract. The

caecum of germ-free animals is enlarged, thin-walled, and fluid-filled, compared

to that organ in conventional animals. Also, based on the ability to undergo

immunological stimulation, the intestinal lymphatic tissues of germ-free animals

are poorly-developed compared to conventional animals.

5. The normal flora stimulate the production of natural antibodies. Since

the normal flora behave as antigens in an animal, they induce an immunological

response, in particular, an antibody-mediated immune (AMI) response. Lowlevels of antibodies produced against components of the normal flora are known

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to cross react with certain related pathogens, and thereby prevent infection or

invasion. Antibodies produced against antigenic components of the normal flora

are sometimes referred to as "natural" antibodies, and such antibodies are

lacking in germ-free animals.

Harmful Effects of the Normal Flora

Harmful effects of the normal flora, some of which are observed in studies with

germ-free animals, can be put in the following categories. All but the last two are

fairly insignificant.

1. Bacterial synergism between a member of the normal flora and a potential

pathogen. This means that one organism is helping another to grow or survive.

There are examples of a member of the normal flora supplying a vitamin or some

other growth factor that a pathogen needs in order to grow. This is called cross-

feeding between microbes. Another example of synergism occurs during

treatment of"staph-protected infections" when a penicillin-resistantstaphylococcus that is a component of the normal flora shares its drug resistance

with pathogens that are otherwise susceptible to the drug.

2. Competition for nutrients Bacteria in the gastrointestinal tract may get to

some of our utilizable nutrients before we are able to absorb them. Germ-free

animals grow more rapidly and efficiently than germ-free animals. The

explanation and absurd rationale for incorporating antibiotics into the food of

swine, cows and poultry is that they grow faster (and thereby get to market

earlier).

3 Induction of a low grade toxemiaMinute amounts of bacterial toxins (e.g.endotoxin) may be found in the circulation. Of course, it is these small amounts

of bacterial antigen that stimulate the formation of natural antibodies.

4. The normal flora may be agents of disease. Members of the normal flora

may cause endogenous disease if they reach a site or tissue where they

cannot be restricted or tolerated by the host defences. Many of the normal flora

are potential pathogens, and if they gain access to a compromised tissue from

which they can invade, disease may result.

5. Transfer to susceptible hosts Some pathogens of humans that are

members of the normal flora may also rely on their host for transfer to other

individuals where they can produce disease. This includes the pathogens thatcolonize the upper respiratory tract such as Neisseria meningitidis,

Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus,

and potential pathogens such as E. coli, Salmonella or Clostridium in the

gastrointestinal tract.

Dental Caries, Gingivitis and Periodontal DiseaseThe most frequent and economically-important condition in humans resulting

from interactions with our normal flora is probably dental caries. Dental plaque,

dental caries, gingivitis and periodontal disease result from actions initiated and

carried out by the normal bacterial flora.

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Dental plaque, which is material adhering to the teeth, consists of bacterial

cells (60-70% the volume of the plaque), salivary polymers, and bacterial

extracellular products. 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.

The dominant bacterial species in dental plaque are Streptococcus sanguis and

Streptococcus mutans, both of which are considered responsible for plaque. .

Plaque formation is initiated by a weak attachment of the streptococcal cells to salivary

glycoproteins forming a pellicle on the surface of the teeth. This is followed by a stronger

attachment by means of extracellular sticky polymers of glucose (glucans) which are

synthesized by the bacteria from dietary sugars (principally sucrose). An enzyme on the cell

surface ofStreptococcus mutans, glycosyl transferase, is involved in initial attachment of the

bacterial cells to the tooth surface and in the conversion of sucrose to dextran polymers

(glucans) which form plaque.

Dental plaque, scanning electron micrograph illustrating the diversity of

microbes in plaque.

Dental Caries is the destruction of the enamel, dentin or cementum of teeth

due to bacterial activities. Caries are initiated by direct demineralization of the

enamel of teeth due to lactic acid and other organic acids which accumulate in

dental plaque. Lactic acid bacteria in the plaque produce lactic acid from the

fermentation of sugars and other carbohydrates in the diet of the host.

Streptococcus mutans and Streptococcus sanguis are most consistently been

associated with the initiation of dental caries, but other lactic acid bacteria are

probably involved as well. These organisms normally colonize the occlusal

fissures and contact points between the teeth, and this correlates with the

incidence of decay on these surfaces.

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Cross section of a tooth illustrating the various structural regions susceptible to colonization or attack by

microbes.

Streptococcus mutans in particular has a number of physiological and biochemical properties

which implicate it in the initiation of dental caries.

1. It is a regular component of the normal oral flora of humans which occurs in

relatively large numbers. It readily colonizes tooth surfaces: salivary components

(mucins, which are glycoproteins) form a thin film on the tooth called the enamel

pellicle. The adsorbed mucins are thought to serve as molecular receptors for

ligands on the bacterial cell surface.

2. It contains a cell-bound protein, glycosyl transferase, that serves an adhesin

for attachment to the tooth, and as an enzyme that polymerizes dietary sugars

into glucans that leads to the formation of plaque.

3. It produces lactic acid from the utilization of dietary carbohydrate which

demineralizes tooth enamel. S. mutans produces more lactic acid and is more

acid-tolerant than most other streptococci. 4. It stores polysaccharides made

from dietary sugars which can be utilized as reserve carbon and energy sources

for production of lactic acid. The extracellular glucans formed by S. mutans are,

in fact, bacterial capsular polysaccharides that function as carbohydrate

reserves. The organisms can also form intracellular polysaccharides from sugars

which are stored in cells and then metabolized to lactic acid.

Streptococcus mutans appears to be important in the initiation of dental caries

because its activities lead to colonization of the tooth surfaces, plaque formation,

and localized demineralization of tooth enamel. It is not however, the only cause

of dental decay. After initial weakening of the enamel, various oral bacteria gain

access to interior regions of the tooth. Lactobacilli,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 lesions.

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Actinomyces israelii

Periodontal Diseases are bacterial infections that affect the supporting structures of the teeth

(gingiva, cementum, periodontal membrane and alveolar bone). The most common form,gingivitis, is an inflammatory condition of the gums. It is associated with accumulations of

bacterial plaque in the area. Increased populations ofActinomyces have been found, and they

have been suggested as the cause. Diseases that are confined to the gum usually do not lead to

loss of teeth, but there are other more serious forms of periodontal disease that affect

periodontal membrane and alveolar bone resulting in tooth loss. Bacteria in these lesions are

very complex populations consisting of Gram-positive organisms (includingActinomyces andstreptococci) and Gram-negative organisms (including spirochetes andBacteroides).

Themechanisms of tissue destruction in periodontal disease are not clearly defined but

hydrolytic enzymes, endotoxins, and other toxic bacterial metabolites seem to be

involved.The microbial flora of the oral cavity are rich and extremely diverse. This reflects

the abundant nutrients and moisture, and hospitable temperature, and the availability of

surfaces on which bacterial populations can develop. The presence of a myriad of

microorganismsis a natural part of proper oral health. However, an imbalance in the

microbial flora can lead to the production of acidic compounds by some microorganisms that

can damage the teeth and gums. Damage to the teeth is referred to a dental caries.Microbes

can adhere to surfaces throughout the oral cavity. These include the tongue, epithelial cells

lining the roof of the mouth and the cheeks, and the hard enamel of the teeth. In particular,

the microbial communities that exist on the surface of the teeth are known as dental plaque.

The adherent communities also represent a biofilm. Oral biofilms develop over time into

exceedingly complex communities. Hundreds of species ofbacteria have been identified in

such biofilms.Development of the adherent populations of microorganisms in the oral cavitybegins with the association and irreversible adhesion of certain bacteria to the tooth surface.

Components of the host oral cavity, such as proteins and glycoproteins from the saliva, also

adhere. This early coating is referred to as the conditioning film. The conditioning film alters

the chemistry of the tooth surface, encouraging the adhesion of other microbial species. Over

time, as the biofilm thickens, gradients develop within the biofilm. For example, oxygen may

be relatively plentiful at the outer extremity of the biofilm, with the core of the biofilm being

essentially oxygen-free. Such environmental alterations promote the development of different

types of bacteria in different regions of the biofilm.

This changing pattern represents what is termed bacterial succession. Examples of some

bacteria that are typically present as primary colonizers include Streptococcus,Actinomyces,Neisseria, and Veillonella. Examples of secondary colonizers includeFusobacterium

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nucleatum,Prevotella intermedia, and Capnocytophaga species. With further time, another

group of bacteria can become associated with the adherent community. Examples of these

bacteria include Campylobacter rectus,Eikenella corrodens,Actinobacillusactinomycetemcomitans , and the oral spirochetes of the genus Treponema.

Under normal circumstances, the microbial flora in the oral cavity reaches equilibrium, wherethe chemical by-products of growth of some microbes are utilized by other microbes for their

growth. Furthermore, the metabolic activities of some bacteria can use up oxygen, creating

conditions that are favorable for the growth of those bacteria that require oxygen-free

conditions.This equilibrium can break down. An example is when the diet is high in sugars

that can be readily used by bacteria. ThepH in the adherent community is lowered, which

selects for the predominance of acid-loving bacteria, principally Streptococcus mutans and

Lactobacillus species. These species can produce acidic products. The resulting condition istermed dental caries. Dental caries is the second most common of all maladies in humans,

next only to the common cold. It is the most important cause of tooth loss in people under 10

years of age.Dental caries typically proceeds in stages. Discoloration and loosening of the

hard enamel covering of the tooth precedes the formation of a microscopic hole in theenamel. The hole subsequently widens and damage to the interior of the tooth usually results.

If damage occurs to the core of the tooth, a region containing what is termed pulp, and the

roots anchoring the tooth to the jaw, the tooth is usually beyond saving. Removal of the tooth

is necessary to prevent accumulation of bacterial products that could pose further adverse

health effects.Dental caries can be lessened or even prevented by coating the surface of the

tooth with a protective sealant. This is usually done as soon as a child acquires the second set

of teeth. Another strategy to thwart the development of dental caries is the inclusion of a

chemical called fluoride in drinking water. Evidence supports the use of fluoride to lessen the

predominance of acid-producing bacteria in the oral cavity. Finally, good oral hygieneis of

paramount importance in dental heath. Regular brushing of the teeth and the avoidance of

excessive quantities of sugary foods are very prudent steps to maintaining the beneficial

equilibrium microbial equilibrium in the oral cavity.

There are estimated to be circa 100,000,000,000,000 cells in the human body, of

which only 10% are of human origin. The remaining 90% comprise the commensal

microbial flora. Different anatomical sites are associated with their own

characteristic flora.

Some microbes that come into contact with the body are ill-equipped to exploit the

ecological niche in which they land. These are easily removed and they make up the

transient flora of a site.

Other microbes have evolved to adhere to and grow in a particular location. Oncethese become established they comprise the resident flora at a given site. The mouth is the portal of entry of food. This also provides access to a

wide array of microbes, the majority of which become part of thetransient oral flora.

Protection of the oral cavity

Saliva provides a washing mechanism thatwill help to remove microbes from the mouth.We swallow 30 times per hour, on average

It has been estimated that saliva contains

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1,000,000,000 bacteria per ml.

Saliva also contains digestive enzymes anda number of specifically antimicrobialcompounds. These include secretory IgA,

lysozyme and lactoferrin. Saliva thus helpsto prevent colonisation with potentiallypathogenic bacteria.

Measures designed to improve oral hygienealso remove microbes from the mouth. Thecommensal flora of the mouth is profoundlyinfluenced by diet.

Despite these observations and practices, themouth provides a number ofdistinctecologicalsites and carries a diverse and

rich commensal flora.

The presence of the oral commensal floraprovides protection from overgrowth bypathogens including Streptococcuspyogenes, Streptococcus pneumoniae andCandida albicans.

Dental infection and the oral commensal flora

The commensal oral flora plays a significantrole in dental infections. It is also in aconstant and dynamic flux. This is partly inresponse to the intake of food and alsoinfluenced by oral hygiene measures includingbrushing of teeth and flossing.

The hard surfaces of the teeth and thegingival crevices are the sites ofaccumulation ofdental plaque. This isa complex structure comprisingmicrobes, microbial products, food

particles, host secretions and hostcells.

Plaque is continually altering incomposition in response to micro-environmental changes. It differs inresponse to its location in the mouthand in response to the length of timethat it has been established.

On the surface of a tooth,

Streptococcus mutans is the firstimportant coloniser; particularly in

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people with a high sucrose diet. Thisbacterium can metabolise sucrose toproduce extracellular polysaccharide(glucans) that enable the bacterial cellsto stick onto the surface of the tooth.

Metabolism of the sucrose byStreptococcus mutans also leads to theformation of large quantities oflacticacid. In turn this provides the low pHenvironment that favours colonisation bylactobacilli.

Next in the microbial succession are theactinomycetes. These are filamentousbacteria that provide a web of cellsthat can provide a niche for the

colonisation ofanaerobic bacteria,including those belonging to generasuch as Bacteroides,Capnocytophaga, Veillonella as wellas spirochaetes and fusobacteria. Anarray of poorly-characterised bacteriacan also be found in plaque, which maycontain up to 100,000,000,000 bacteriaper gram wet weight.

Oral Microbial Ecology and the Role of Salivary

Immunoglobulin A *

In the oral cavity, indigenous bacteria are often associated with two major oral diseases,

caries and periodontal diseases.These diseases seem to appear following an inbalance in the

oralresident microbiota, leading to the emergence of potentially pathogenicbacteria. To

define the process involved in caries and periodontaldiseases, it is necessary to understand

the ecology of the oralcavity and to identify the factors responsible for the transition of the

oral microbiota from a commensal to a pathogenic relationship

with the host. The regulatoryforces influencing the oral ecosystemcan be divided into three major categories: host related,

microberelated, and external factors. Among host factors, secretory immunoglobulinA

(SIgA) constitutes the main specific immune defense mechanismin saliva and may play an

important role in the homeostasis ofthe oral microbiota. Naturally occurring SIgA antibodies

thatare reactive against a variety of indigenous bacteria are detectablein saliva. These

antibodies may control the oral microbiota byreducing the adherence of bacteria to the oral

mucosa and teeth.It is thought that protection against bacterial etiologic agents of caries and

periodontal diseases could be conferred by the inductionof SIgA antibodies via the

stimulation of the mucosal immune system.However, elucidation of the role of the SIgA

immune system incontrolling the oral indigenous microbiota is a prerequisite forthe

development of effective vaccines against these diseases.

The role of SIgA antibodies in theacquisition and the regulationof the indigenous microbiota is still controversial. Our review

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discusses the importance of SIgA among the multiple factors thatcontrol the oral microbiota.

It describes the oral ecosystems,the principal factors that may control the oral microbiota, a

basic knowledge of the secretory immune system, the biologicalfunctions of SIgA, and,

finally, experiments related to the roleof SIgA in oral microbial ecology.

The oral microbial flora contains over 500 different microbial species thatoften interact as a means to compete for limited space and nutritionalresources. Streptococcus mutans, a major caries-causing pathogen, is aspecies which tends to interact competitively with other species in theoral cavity, largely due to its ability to generate copious quantities ofthetoxic metabolite, lactic acid. However, during a recent clinical study, we discovered anovel oral streptococcal species, Streptococcus oligofermentans, whose abundanceappeared to be inversely correlated with that of S. mutans within dental plaquesamples and thus suggested a possible antagonistic relationship with S. mutans. Inthis study, we used a defined in vitro interspecies interaction assay to confirm that S.oligofermentans was indeed able toinhibit the growth of S. mutans. Interestingly, this

inhibitory effect was relatively specific to S. mutans and was actually enhanced bythe presence of lactic acid. Biochemical analyses revealed that S. oligofermentansinhibited the growth of S. mutans via the production of hydrogen peroxide with lacticacid as the substrate. Further genetic and molecular analysis led to the discovery ofthe lactate oxidase (lox) gene of S. oligofermentans as responsible for this biologicalactivity. Consequently, the lox mutant of S. oligofermentans also showeddramatically reduced inhibitory effects against S. mutans and also exhibited greatlyimpaired growth in the presence of the lactate produced by S. mutans. These dataindicate that S. oligofermentans possesses the capacity to convert its competitor'smain 'weapon' (lactic acid) into an inhibitory chemical (H2O2) in order to gain a

competitive growth advantage. This fascinating ability may be an example of acounteroffensive strategy used during chemical warfare within the oral microbialcommunity.

BACKGROUND

The oral cavity is comprised of many surfaces, each coated with a plethora of bacteria, the

proverbial bacterial biofilm (see figure below). Based on both culture and culture-

independent molecular methods using sequence analysis of 16S rRNA genes, we and others

have identified most of the predominant bacterial species in the oral cavity. Collectively

speaking, there are about 550 oral bacterial species, of which about 60% have not yet beencultivated in vitro. These "uncultivables" are often termed phylotypes.

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In order to make definitive bacterial associations with oral health and disease states, the

microbial profiles of large numbers of clinical samples must be determined. 16S rRNA-based

DNA probes have been designed and validated. We have developed the Human Oral Microbe

Identification Microarray, orHOMIM, in order to examine complex oral microbial diversity

in a single hybridization. This high throughput technology will allow the simultaneous

detection about 300 bacterial species, including the "uncultivables".

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Recently, it has been recognized that oral infection, especially periodontitis, may affect thecourse and pathogenesis ofa number of systemic diseases, such as cardiovascular disease,

bacterial pneumonia, diabetes mellitus, and low birth weight. The purpose of this review is to

evaluate the current status oforal infections, especially periodontitis, as a causal factorfor

systemic diseases. Three mechanisms or pathways linking oralinfections to secondary

systemic effects have been proposed: (i)metastatic spread of infection from the oral cavity as

a resultof transient bacteremia, (ii) metastatic injury from the effectsof circulating oral

microbial toxins, and (iii) metastatic inflammation caused by immunological injury induced

by oral microorganisms.Periodontitis as a major oral infection may affect the host's

susceptibility to systemic disease in three ways: by shared riskfactors; subgingival biofilms

acting as reservoirs of gram-negativebacteria; and the periodontium acting as a reservoir of

inflammatory

mediators. Proposed evidence and mechanisms of the above odontogenicsystemic diseases aregiven.

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Bibliography

It has been made with the help of following

1.microbiology written by pelzar

2.a text book of microbiology

3.microbial ecology

4.oral microbiology

5.google search

6.yahoo search

7.ask.com search

8.wikipedia