what are the Koch's postulates and what potential problem does this give? How are the problems modified in the modern era?

Answer 1

Koch's Postulates are a set of rules developed by Robert Koch in the late 1800s that help determine is a specific microorganism causes a specific disease. Robert Koch is considered one of the founders of modern bacteriology, and his research was groundbreaking, at the time. His postulates were:

1. The microorganism must be found in all organisms suffering from the disease, but not in healthy organisms.
2. The microorganism must be isolated from a diseased organism and grown in pure culture.
3. The cultured microorganism should cause disease when introduced into a healthy, susceptible organism.
4. The microorganism must be re-isolated from the experimentally infected host and identified as being identical to the original specific causative agent.

There are several limitations to these rules, that have come out as we've learned more about bacteriology:

1. People can carry organisms and not have symptoms of the disease. 15% of the population are carriers of MRSA (methicillin resistant Staphylococcus aureus) but it doesn't cause disease in the carriers. These patients are asymptomatic and that a violation of postulate 1.
2. In microbiology, we deal with living organism that don't like rules, and are highly specific to the environment they are willing to grow in. Postulate 2 says that the organism needs to grow in pure culture, but if the culture doesn't meet requirements for the organism, it simple won't grow.
3. Postulate 3 requires introduction to a healthy host to confirm that the disease is caused by that organism. Ethically, we can't introduce healthy humans to potential infections, and if introduced to other organism (i.e. mice) there's a chance the organism isn't zoonotic in nature, and won't infect the other organism. That also affects postulate 4
4. Some diseases are also caused by multiple organisms (microbial communities) rather than a single organism. Gum disease, IBD, and chronic infections can be caused by multiple organisms at the same time

Modern microbiology has tried to address these issues in Koch's postulates by using more molecular and ethical adaptions. Using PCR technology, focusing on specific genes versus a whole organism, and gene sequencing have all been introduced to allow pathogen detection without culturing. These allow for faster and more accurate results.