micro dent lect 1

8/8/2019 Micro Dent Lect 1

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Microbiology and dentistry

Wenyuan Shi

Professor

School of DentistryMicrobiology, Immunology and Molecular Genetics

Tel: 310-825-8356Office: CHS 20-114

E-mail: [email protected]


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Microbial pathogenesis

Bacteria Parasites Viruses Fungi


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The Importance of Studying Bacterial Pathogenesis

A human body has 1 X 1013 eukaryoticcells and 1 X 1014 bacterial cells

Microbial infections are the mostepidemic diseases and the leading causeof death

Diarrhea and enteric bacteria Tuberculosis and Mycobacterium

Ulcer and Helicobacter infection

Urinary tract infection STD

How microbiology is related to dentistry?


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The dirty mouth!

100,000,000,000,000 bacteria/per mouth

>700 bacterial species


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The first microbes observed

Anton Van Leeuwenhoek

(1632-1723) developedthe microscope and wasthe first to discover oralbacterial flora: I didnt

clean my teeth for threedays and then took thematerial that had lodgedin small amounts on the

gums above my frontteeth. I found a fewliving animalcules..


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Microbiology and dentistry

Supragingival plaque

Subgingival plaque

79% of the population infected

Annual dental spending $85 billion

G+

G-


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Dental Caries

Dental Caries is the localized destruction of the hard tissues of the tooth


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What causes dental caries?

Pre-microbiology era

Dental caries is the death (decay) of a tissue

Microbiology period era

Dental caries is a microbe related disease


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W.D. Miller and his "chemico-parasitic" theory

PLAQUEPLAQUEPLAQUE

SUSCEPTIBLEHOST

SUSCEPTIBLESUSCEPTIBLE

HOSTHOST

FERMENTABLE

CARBOHYDRATE

FERMENTABLEFERMENTABLE

CARBOHYDRATECARBOHYDRATE

ACID

PRODUCTION

ACIDACID

PRODUCTIONPRODUCTION

DEMINERALIZATIONDEMINERALIZATIONDEMINERALIZATION


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Plaque is a complex microbial community


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How to identify bacteria within dental plaque?

Culture methods

take saliva or plaque, dilute and plate onappropriate plates, grow to single colonies,identify by microscopic and biochemical methods

16S DNA/RNA based detection use 2 oligo-nucleotide primers universal to ALL

bacteria 16S rDNA, PCR amplification of the total

saliva or plaque DNA pool, clone the PCR productand sequence, phylogenetic analysis using computerdatabase


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The supragingival plaque


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The supragingival plaque


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Supra-gingival plaque species as analyzed by 16s DNA sequencing


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Current knowledge about bacteria in plaque

Both culture and DNA/RNA-based techniquesare used for identification and quantification of

oral microorganisms Overall, there are ~700 species exist in the oral

cavity

~20% of these 700 species have been cultivated

Both Gram-positive and Gram-negative exist

Some archaea are found

Most anaerobic or facultative anaerobic

Who are the bad guys?


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The first isolation of cariogenic bacteria

Clark, 1924

Isolation of cariogenic bacteria from caries lesions

Discovery of Mutans streptococci

***************


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Keyes and Fitzgerald, 1962sRe-isolation of Mutans streptococci:

Streptococcus mutans (human) (samespecies Clark isolated in England in 1924)

Streptococcus sobrinus (human)

Streptococcus rattus (rats)

Streptococcus cricetus

Streptococcus ferus

Streptococcus macacae

Streptococcus downeii


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Quantification of bacteria from healthy and carious sites by DNA analysis


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The cariogenic bacteria bacteriaassociated with dental caries

Actinomyces early colonizers and root caries

A. odontolyticus A. naeslundiigenospecies 2

A. isrealii

A. gerensceriae

Lactobacilli (L. casei) caries progression

Mutans streptococci (S. mutans) caries initiation


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The virulence factors ofcariogenic bacteria

1. Acid production (acidogenicity)

Lower the pH to below 5.5, the critical pH. Drives

the dissolution of calcium phosphate(hydroxyapatite) of the tooth enamel

Inhibit the growth of beneficial bacteria, promote thegrowth of aciduric bacteria.

Further lower the pH, promote progression of thecarious lesion


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Allows the cariogenic bacteria to thrive under acidicconditions while other beneficial bacteria areinhibited. This results in dominance of the plaqueby cariogenic bacteria

2. Acid tolerance (aciduricity)



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Allows the cariogenic bacteria to stick onto the teeth

and form a biofilm

3. Glucan formation

Glucan mediated biofilms are more resistant tomechanical removal

Bacteria in these biofilms are more resistant toantimicrobial treatments



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Carbohydrates (Sucrose)

Cariogenic bacteria such as S. mutans

Glucans/Levans Acids

Dental Caries

Plaque formation Demineralization


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Dental caries is a bacterial infectious disease


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Transmission

Mother Child (vertical transmission) -

true for most oral bacteria Persons in close contact to the

baby

Horizontal transfer (betweenspouses) is rare, only observed insome periodontal pathogens (i.e. P.gingivalis)

The most common vehicle is

saliva


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New problem: everybody has S. mutans!

Fraction

Number of S. mutansin Saliva(104)

1 10 20 50

0

0.27


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Why not every body who has S. mutansdevelopdental caries?

S. mutansis not present in high portions Acid produced is neutralized urea or

ammonia produced by other bacteria in

the plaque

S. mutansis away from the tooth surface

so acid produced is diffused


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The ecologic plaque hypothesisBoth pathogenic and commensal (non-

harmful) bacteria exist in a natural plaque. Atsound site, the pathogenic bacteria may existin low numbers to cause any clinical effect, or

they may exist in higher numbers, but the acidproduced is neutralized by the action of otherbacteria. Disease is a result of a shift in thebalance of the residence microflora driven bya change in the local environment (frequentsugar intake etc).


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The ecological development of

dental caries

Acid producingbacteria

Sugar

Acids

Base producingBacteria: S. sanguis,

S. oralis

Neutral pH

Remineralization

Health

More sugar

Lower pH

Inhibition of beneficial

bacteriaOvergrowth of

cariogenic bacteria

Demineralization

Caries


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Oral bacteria genome projects

Metagenomics of oral cavity

Human genome project


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Complex genetic make-up

Human genome only has 200,000 genes.

Each oral bacterium has 2000-6000 genes,with over 1 million bacterial genes in oral cavity


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The dental plaque is a complex

multispecies biofilm


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Transmission

Mother to Child

Attachment &

Colonization

Pioneer colonizers:S. oralisS. mitis

S. salivarius

S. sanguis

S. anginosus

S. gordonii

Growth of

Pioneer species

Environmental

ModificationpH, Eh

Expose new receptors

Generate new nutrients

MicrobialsuccessionG+, G-

(periodontal pathogens)

Increased species

diversity

Climax

community

Dental plaque formation

an ordered, complex process


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Oral bacteria have the ability to count the population size


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Sm Ss Sm Ss Sm Ss

Competition/coexistence between S. mutans& S. sanguinis

Extensive chemical warfare between bacterial species


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Cariogenic Tooth

Bacteria Decay

Sugars

Xylitol

FluorideAntimicrobial agents


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Future dentistry (minimal invasive)

Diagnosis Treatment/prevention

micro dent lect 1

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