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Robert Koch's Germ Theory:All subjects must present with the same symptoms | Causative organism must be isolated in pure culture | When inoculated into a 2nd host, it must produce the same symptoms | Identical pure culture must be obtained from second host |
Modification of Koch’s postulates for oral opportunistic infections:
> Should be present in sufficient numbers to cause disease
> Should have access to the affected tissues
> Should be in an environment that permits its survival and multiplication
> Inhibitory organisms should be absent or not affect it
> The host must be susceptible Difficulties:Koch's Postulate in Oral Infections:> No overt pathogen - mostly mixed infections | > More than 700 identified oral species | > Not all members of biofilm community are cultivable | > Presence may be as a result rather than cause of disease | > Sites don't appear to be actively progressing at all times | > Different sites in mouth may break down as a result of different species | > Strains of putative pathogens may vary in virulence | > Some strains may harbour bateriophages or plasmids that confer virulence properties |
Non-specific Plaque HypothesisOvergrowth of indigenous microbiota | Same organisms observed in health and disease | Shifts in microbial proportions rather than specific pathogens | Any plaque biofilm can cause disease |
Problems with NSPH:
- Focus is on quantitative changes only
- Disease in animals not the same as in humans
- Impractical to compare virulence in different host species
- Doesn't explain why individuals with: 1) longstanding plaque don't develop disease and 2) minimal plaque have lower resistance to disease Specific Plaque HypothesisMore sophisticated studies demonstrated: | > Improved cultural and sampling methods | > Composition of plaque biofilm differs both inter-orally and intra-orally | > Increase at a sight of infection | > Decrease in health or following treatment | > Qualitative changes in plaque biofilm |
| | Exogenous Theory:Exogenous pathogens and not endogenous microbiota caused disease | Fails to explain: > Mode of transmission | |
> Acquisition | |
> Means of colonization | |
> Effect of treatment on indigenous species |
Contraindications:
- Over simplification
- Overlaps often occurred (Negated SPH and NSPH)
- Eradication of exogenous pathogens (Incorporated both SPH and NSPH) Ecological Plaque Hypothesis:Opportunistic endogenous infection | Ecological shift from predominatly G+ cocci to G- rods/cocci-bacilli | Any bacterial species may be pathogenic | Ecological changes in environment dictate virulence mechanisms | Disease prevented by elimination or interruption of ecological succession |
Role of Biofilms in Infection:Most common: | 1. Dental caries (supragingival plaque) | 2. Periodontal disease (subgingival plaque) |
Dental Caries Theories1) Tooth worm: 5000BC, 1803 - Diagrams and 1825- Case histories | 2) Humoral Theory: Blood, phlegm, black bile, yellow bile - Imbalance= disease | 3) Chemical Theory: Fermentation of food remains | 4) Parasitic Theory: Decomposition resulting from action of organisms in the mouth |
| | Millers (1882) Chemo-parasitic Theory:2 stage process: | i) decalcification of enamel resulting in destruction of dentin | ii) dissolution of softened residue of enamel and dentin |
Dietary carbohydrates -> convert into acid -> calcium and phosphate diffuse out of enamel -> a caries lesion Proteolytic Theory (Gotliebb 1946)Invasion of enamel by m/o's -> proteolytic activity -> alteration of pH -> resulting in liquidification of organic matrix of enamel -> inorganic salts dissolved by acidogenic bacteria |
The proteolytic-chelation TheorySchutz and Martin (1955) | Simultaneous attack on organic and inorganic compounds of tooth |
Kaeratinolytic bacteria attack enamel ->
Breakdown of protein and other organic components of enamel (keratin) ->
Formation of complexes with calcium from plaque which chelates with mineral component of the tooth ->
Increased solubility, decalcification of enamel ay neutral or alkaline pH Current Concepts in Caries Etiology
Keyes Triad & Newbeun's Tetrad
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