Koch’sPostulates - A set of rules for proving that amicroorganism causes a parti
ID: 2974 • Letter: K
Question
Koch’sPostulates - A set of rules for proving that amicroorganism causes a particular disease.Koch’s Postulates: 1. Themicroorganism must be present in every case of the disease butabsent from health organisms. (Koch developeda staining technique to examine human tissue. M.tuberculosis cells could be identified in diseasedtissue). 2. The suspectedmicroorganisms must be isolated and grown in a pureculture. (Koch grew M.tuberculosis in pure culture on coagulated bloodserum). 3. The same disease mustresult when the isolated microorganism is inoculated into a healthyhost. (Koch injected cells fromthe pure culture of M. tuberculosis into guineapigs. The guinea pigs subsequently died oftuberculosis). 4. The same microorganismmust be isolated again from the diseased host. (Koch isolated M.tuberculosis from the dead guinea pigs and was able to againculture the microbe in pure culture on coagulated bloodserum). Question: If several people got sickafter eating cheese from a particular grocery store, describe howyou would demonstrate which microorganism had caused theproblem. Koch’sPostulates - A set of rules for proving that amicroorganism causes a particular disease.
Koch’s Postulates: 1. Themicroorganism must be present in every case of the disease butabsent from health organisms. (Koch developeda staining technique to examine human tissue. M.tuberculosis cells could be identified in diseasedtissue). 2. The suspectedmicroorganisms must be isolated and grown in a pureculture. (Koch grew M.tuberculosis in pure culture on coagulated bloodserum). 3. The same disease mustresult when the isolated microorganism is inoculated into a healthyhost. (Koch injected cells fromthe pure culture of M. tuberculosis into guineapigs. The guinea pigs subsequently died oftuberculosis). 4. The same microorganismmust be isolated again from the diseased host. (Koch isolated M.tuberculosis from the dead guinea pigs and was able to againculture the microbe in pure culture on coagulated bloodserum). Question: If several people got sickafter eating cheese from a particular grocery store, describe howyou would demonstrate which microorganism had caused theproblem.
Explanation / Answer
If all you've learned so far is Koch's Postulates, and the questionis just testing your understanding of them, your answer wouldprobably go something like this: 1. Determine which microorganisms were present in the cheese. 2. Determine which, if any, of the microorganisms present in thecheese are likely present in the individuals who fell ill. You can try to do this using culture of blood, tissue, etc, but alot of microorganisms don't culture well (this is one, of many,reasons why Koch's postulates aren't strictly applied thesedays). You could do an ELISA or Western Blot, looking for animmune response to the pathogens at issue (especially IgM, sincethat usually indicates recent infection). You can tryPCR. 3. If you find an organism present in all individuals who were ill,you could run the same tests on a group of healthy controls to makesure that the organism is not also found in them (note, however,that even if some healthy people also have this microorganism, thisdoesn't mean that it isn't the cause of disease. With manyillnesses, there are plenty of people who are "silently infected" -they have the organism on their body, but they don't havesymptoms). 4. If you want to follow Koch's postulates here, you would then tryto isolate the organism, culture it, innoculate it into a healthyrodent or primate (once you know what the organism is, it will beeasier to pick a suitable animal model, if one exists). Thenwait to see if the animal shows similar symptoms to the human (evenif it doesn't, this doesn't rule out the possibility that theorganism caused the disease. Many diseases arespecies-specific). Epidemiological studies can also be very useful in cases where itis difficult to apply Koch's postulates. You could also start with feeding the cheese to laboratory animals,seeing if they get sick, then trying to isolate the pathogencausing their disease, then seeing if the sick humans have the samepathogens.
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