Antoine Bechamp: microzymas ("little bodies") are fundamental building blocks of life;
can assume different forms
- in a healthy body, microzymas repair and nourish cells
- in a diseased body (i.e. acidic pH), microzymas morph to destructive bacteria, viruses
etc.
- disease is caused by poor environment/diet; can be prevented/treated by improved
air quality and nutrition
*** "germs" are the result of host disease, not the cause
Germ theory of disease
*** diseases are caused by living microorganisms
- Louis Pasteur: process of fermentation, food spoilage ("pasteurization"), and
silkworm disease were caused by the growth of microorganisms; "father of germ
theory disease"
- Friedrich Henle
Dr. Robert Koche
- improved pure-culture isolation and staining methods; animal models of disease
,MCB 4203 - Pathogenic Microbiology
- best known for his discovery of Mycobacterium tuberculosis
Koch's 1st Postulate
1) the microorganism should be found in all cases of the disease in question, and its
distribution in the body should be in accordance with the lesions observed.
-isolated from a dead animal
Koch's 2nd Postulate
2) the microorganism should be grown in pure culture in vitro (or outside the body of
the host) for several generations and identified
Koch's 3rd Postulate
When such a pure culture is inoculated into susceptible animal species, the typical
disease must result
Koch's 4th Postulate
4) the microorganisms must again be isolated from the lesions of such experimentally
produced disease in pure culture and identified
Is postulate 1 applicable to all disease-causing animals?
,MCB 4203 - Pathogenic Microbiology
- some pathogens colonize many people ('carrier-state'), but only cause disease in
some (ex. Helicobacter pylori & Staphylococcus aureus)
- microbes as a risk factor for disease, rather than a cause (ex. Chlamydophila
pneumoniae)
Can all disease- causing bacteria be isolated in pure culture? (postulate 2)
- there are many pathogens that are difficult or impossible to culture in vitro
- not all diseases are caused by a single species of bacteria (ex. polymicrobial or
microbiota shift disease)
-instead use molecular techniques (PCR & immunohistochemistry) to identify
pathogens in diseased tissue
PCR polymerase chain reaction
1) DNA sample is heated
2) DNA strands separate
3) Primers bind
4) Primers extended
DNA is isolated from infected tissue (mixture of host and bacterial DNA) - PCR is
performed 1) agarose-gel electrophoresis 2) quantitative real-time PCR 3) detection of
product
**must include positive and negative controls
-positive control: bacterial DNA isolated from pure culture
, MCB 4203 - Pathogenic Microbiology
-negative control: DNA from healthy uninfected tissue
Immunohistochemistry
- labeled antibodies or DNA probes (specific for the bacteria) are used to detect the
presence of bacteria in tissue samples
- +ve detection signal should be observed in diseased tissue but not healthy tissue
Demonstrating the ability of isolated bacterium to cause disease in humans or animals
(postulate 3)
- can be difficult to satisfy this postulate for many pathogens
- a "human model" of infection is usually not allowed
- a "good" animal model may not be available (ex. H. pylori)
Can the disease causing bacterium be re-isolated from intentionally infected animals?
(postulate 4)
- assuming postulates 1-3 have been met, postulate 4 demonstrates that the disease
lesions of the intentionally-infected host contain the microbe
Is a 5th postulate needed?
- "information about the microbe should enable scientists to design effective
therapeutic or preventative measure for eliminating the disease"
- may provide more convincing evidence if other postulates are not "conclusive"
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