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INTRODUCTION. INFECTION:DISEASE:ASYMPTOMATIC CARRIAGE:COLONIZAION: (NORMAL FLORA). BACETRAIL PATHOGENESIS. What is virulence?The ability of a bacterium to cause infection.Virulence factors: Two types:Those that promote bacterial colonization and invasion of the host tissue Those that c

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3. BACETRAIL PATHOGENESIS What is virulence? The ability of a bacterium to cause infection. Virulence factors: Two types: Those that promote bacterial colonization and invasion of the host tissue Those that cause damage of the host tissue.

4. Research in the past four decades have accumulated information which led to identification of possible pathogens of human dental caries. Q. How a cause and effect relationship is established between bacterium and the disease? A. Kochs Postulate (1800s).

5. KOCHS POSTULATES The bacterium should be found in people with the disease The bacterium should be isolated from the lesions of infected person Pure culture, inoculated into a susceptible individuals or animals should produce the disease Same bacterium should be re-isolated from intentionally infected animals or humans.

6. LIMITATIONS OF KOCHS POSTULATES Virulence is within the bacterium and is independent of the host Isolation and growth of bacterium is necessary: Yet, some pathogens not yet cultured Nos. 2 & 4: assume that all members of the same species are virulent No. 3: Ethics with human subjects, Yet some pathogens from humans can not cause the same effect in animals.

7. WHAT IS THE ALTERNATIVE? MOLECULAR POSTULTES Gene should be found in the bacterial strain. Disturbing the virulent gene should reduce its virulence. Bacterial virulent gene should be expressed in the animal or human at sometime during the infectious process Abs to gene product should be protective or should elicit protective immunity (cell-mediated).

9. Q. Why Did it Take Long Time for Caries Microbiology? Complex ecology of the oral cavity. 300 400 species are indigenous oral flora. History: Miller (1880): Little knowledge about which bacteria. Clarke (1924): First who associate bacteria with dental caries First to isolate MS from human dental caries First to produce caries in extracted teeth. Orland (1955): Used animals to induce dental caries using MS.

10. DENTAL CARIES MICROBIOLOGY RESEARCH 1960s : germ-free animals 1960s and 70s: importance of glucan (glucanase): Clinical trials using glucan hydrolyase rinses Glucan is plaque enhancer Problem with isolation: Number, media .etc. Specific plaque theory MS identified as an associated bacteria with caries.

11. MUTANS STRPETOCOCCI (MS) TYPES: (Coykendall, 1989) S. anginosus : important in purulent infections S. bovis : found in patients with colon cancer S. mitis : similar to sanguis but doesnt ferment any sugar S. mutans : seven species S. salivarius : in saliva, rare in infections S. sanguis : causes endocarditis S. vestbularis : new species from oral cavity.


14. WHY S. mutans SUCCEED? Three factors: Ability to adhere to other bacteria and tooth surface Ability to rapidly metabolize nutrients (CHO) Ability to tolerate acidic environment.

15. ADHERENCE OF S. mutans Saliva: Lysozyme IgA: (IgA protease), (IgA deficiency) Bacterial proteins: Ag I/II family: Adhere to saliva proteins Adhesin Fimbrial adhesion: Adhere to saliva pellicle glucan binding (GBP)

16. CHO METABOLISM BY S.mutans CHO must be transported across the membrane (Sugars must be phosphorylated): Multiple Sugar Metabolism (MSM) System: Transport via the Phosphoenolpyruvate (PEP): Sugar Phosphotransferase System (PTS):

17. CHO Metabolism PEP + CHO PTS Pyruvate +P-CHO S.mutans enolase: Fluoride inhibits it. S.mutans store polysaccharides .. Why?

18. S. mutans ACID TOLERANCE Through cell membrane, extrusion of protons: Membrane ATPase hydrolyze ATP molecules Hydrolysis of one ATP, results in extrusion of three protons This results in elevation of cytoplasmic pH. When pH decreases, ATPase activity increases 4-folds.

19. COLONIZATION OF S. mutans Based on ability of S. mutans to synthesize insoluble glucan. S. mutans have 3 genes: gtfB encodes GTF-I enzyme: insoluble glucan gtfC encodes GTF-SI enzyme: insoluble glucan gtfD encodes GTF-S enzyme: soluble glucan

20. RESEARCH USING GTFs Purified S.mutans GTFs were used for caries immunization in rodents. (Smith et al., 1979). Implantation of S. mutans defective in IS glucan synthesis into rats resulted in reduced smooth surface caries induction. (Munro et al., 1991).

23. ACQUISITION OF S. mutans Sterile mouth at birth S. sanguis and S. mutans colonize teeth Number of bacteria increases in the presence of: Sucrose Caries Teeth

25. ACQUISITION OF S. mutans Important facts: Difficult to change S. mutans strain(s) High number of S.mutans strains and isolates. One (or more) strain (isolates) is/are present in the mouth.

27. TRANSMISSION OF CARIOGENIC FLORA Mothers to children: DNA technique Method of transmission Spouses: Different bacteria studied Replacement Therapy

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