Question

What are Koch's postulates and what are they used for? Give an example of a modern exception to each postulate.  

Answer 1

Four criteria by Robert Koch to identify the causative agent of a particular disease, these include:

1. the microorganism or other pathogen must be present in all cases of the disease
2. 
   
3. the pathogen can be isolated from the diseased host and grown in pure culture
4. 
   
5. the pathogen from the pure culture must cause the disease when inoculated into a healthy, susceptible laboratory animal
6. 
   
7. the pathogen must be reisolated from the new host and shown to be the same as the originally inoculated pathogen

Exceptions

1 .Some microbes are obligate intracellular parasites (like chlamydia or viruses) and are very challenging, or even impossible, to grow on artificial media.

2. Some diseases, such as tetanus, have variable signs and symptoms between patients.

3. Some diseases, such as pneumonia & nephritis, may be caused by a variety of microbes.

4. Certain pathogens, such as HIV, cause disease in humans only -- it is unethical to purposefully infect a human.

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