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
1. MICROBIOLOGY OF DENTAL CARIES
2. INTRODUCTION INFECTION:
COLONIZAION: ( NORMAL FLORA)
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. Koch’s Postulate (1800s).
5. KOCH’S 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 KOCH’S 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.
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 doesn’t 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.
12. STREPTOCOCCUS MUTANS
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:
IgA: (IgA protease), (IgA deficiency)
Ag I/II family: Adhere to saliva proteins
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:
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:
Method of transmission
Different bacteria studied