Hey everybody, Dr. O here. This video we are going we’re going to cover Koch’s Postulates, so they are named after um uh Robert Koch, one of the most important historical figures figures in Microbiology. We covered him way back in the beginning with the with the Microbiology history lesson stuff. So uh he is really famous for a couple of things, these postulates but also how he is kind of he's kind of given credit to be the father of creating aseptic laboratory techniques. And you will see why he had to in order for his postulates to work. So um he would of first used these postulate to prove that the uh causative agent of Anthrax was the bacteria known at Bacillus anthracis. So but we can use it in quite a few cases but I really want to focus in on why we can’t use it as well. So Koch’s postulates are a way to try to prove that organism a causes disease y. Whatever So you will see here at the top that a uh first thing is that an organism that causes a disease should be absent from healthy org animals. So you see here the the healthy rodent uh is the has the is the organism is absent so that is like kind of rule number one. And then rule two to actually run through his postulates you take a diseased animal or organism and you you take samples and you remove the organism that you think is the causative agent of the disease. So number one the suspected causative agent must be absent from all healthy organisms but present in all diseased organisms and that is very important. Now number two you take that and you isolate it and grow it in pure culture. So number two the causative agent must be isolated from the diseased organism and grown in po pure culture. So you take it out and you and you isolate it so that it’s the only organism around. If you take just a sample from a diseased animal and put it in a healthy animal and it gets sick or dies. All you know is one of the organisms that you that you transmitted or some compound was what caused it. So so isolating pure culture is very important. He took this very seriously, he would of done rounds and rounds of isolating pure culture maybe six eight different rounds of isolating pure cultures before he put them in the next animal. So step three uh the cultured agent must cause the same disease when inoculated into healthy susceptible organism. So he took that organism that he isolated pure culture and gave it to another animal and it got the same disease or died the same way if it led to death. Then the last step in Koch’s postulates the same causative agent must then be reisolated from the second animal and and obviously be the same organism. So this is how you are able to prove that a certain organism is the causative agent of a certain disease and this is very important and this was a huge deal back when Robert Koch came up with these postulates and actually did it. Right he proved the causative agent of several diseases. But I want to talk about the ways this wont work. So number one you keep seeing this term pure isolating, pure culture. Some organisms cant be grown in pure culture. So there there are some organisms we can not culture. We are learning a lot about that now, when you analyze samples genetically, you realize there might be four six ten twenty times more organisms there than what you can actually grow on a petri dish somewhere. Uh one good example would be like uh Mycobacterium leprae, they have to grow in the fat pads of rodents or like armadillos to get it to grow because there isn’t an easy way to grow it in a laboratory and some organisms just can not be grown. So if you cant isolate an organism in pure culture then then you really cant use these postulates. That’s number one reason it wont work. Number two if multiple organisms cause the same disease your gonna your gonna have a problem here. So think about the cold or really lots of different things um yes you can prove that one organism is a causative agent of of of of a certain disease but you cant say that its the causative agent if there are multiple organisms that can cause the same disease. And then the last reason this wont work very well or when it wont work is if one organism can lead to multiple diseases. So you could take lets say this this first um lab rat here died lets say they have streptococcus pneumonia and they died of pneumonia. So you extract it you isolate the organism you grow it in pure culture and give it to another rodent and it it dies of sepsis and you give it to a third rodent and it dies of meningitis. See how one organism could cause multiple diseases. So those so Koch’s postulates very important they were especially important important back in the early history of microbiology but you will see that those are the three reasons that it doesn’t always work. Alright so that is Koch’s postulates and the exceptions to those rules. I hope it helps have a wonderful day. Be blessed