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a postulate formulated in 1890s still used by scientific community as guidelines for
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establishing that microbes causes specific diseases and that is coach's postulate hi friends
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at the end of the discussion you will be able to understand the contributions of robert coach
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what are the four coach postulate exceptions with example if you are new to this channel
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please consider subscribing this channel. First let us understand the experiment of coach and how
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he formulated the porcelain from his experiment. He developed a staining technique to examine human
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tissue. He was working on tuberculosis, the causative organism mycobacterium tuberculosis. He could identify mycobacterium tuberculosis cells in deceased tissue. This is a deceased animal and
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from the tissues, he could identify the suspected pathogen that is mycobacterium tuberculosis
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So in the case of healthy animal, that particular causative organism is absent. And he observed
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the cells under the microscope and found out this suspected pathogen or mycobacterium tuberculosis
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So from this experiment, he formulated his first postulate. The microorganism must be present in
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every case of the disease but absent from healthy organisms. As you see in the
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diseased animal the suspected pathogen or microorganism is present in the tissues whereas in healthy animal the microorganism the causative
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microorganism is absent. But there are some exceptions. Polio, AIDS and cholera
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can be carried asymptomatically without any symptoms that violates the first principle. So he did his work on cholera and found out that there are many
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asymptomatic carriers. So he even considered modifying or relaxing this first post lead because of his discovery in studies with cholera. So in the case
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of some diseases the patient may be asymptomatic but the disease-cousing organism may be present Then he grew this mycobacterium tuberculosis in pure culture on coagulated blood serum He isolated the pathogen Then he made a pure culture that is only with that unique or disease microorganism
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So this culture is from the cells or tissues of the deceased animal
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And from this he formulated that the second postulate, the suspected microorganisms must be isolated and grown in a pure culture
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But now we know that with the advancement of microbiology, now we know many pathogens that
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cannot be cultured in an artificial medium like Trepanema that causes syphilis then Mycobacterium
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leprae that causes leprosy. This cannot be cultured in an artificial medium. Riketsia and
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chlamydia both these requires a host or a cell to multiply then the classical examples now we have
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many subcellular disease causing particles like viruses prions etc prions are proteinaceous
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infectious particles that cannot be cultured a disease may be caused by many causative organism
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so we may not be getting a pure culture in the case of diarrhea meningitis etc is caused by many
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microorganisms like bacteria, fungus, etc. So we may not be getting a pure culture
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a single microorganism as a causative agent of a particular disease. Then some microorganisms
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can cause many diseases at different sites within an individual or a deceased animal
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Like Streptococcus pyogenes can cause sore throat but also cause scarlet fever and bone
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inflammation. Even in the case of mycobacterium tuberculosis it can cause infections in lungs
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bone, skin etc. Then he injected cells from the pure culture of mycobacterium tuberculosis
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in guinea pigs and found out that these pigs died of tuberculosis. So he injected this pure
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culture in guinea pigs and found out that the guinea pigs got a disease and died. From this he
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formulated the third postulate the same disease must result when the isolated microorganism is inoculated into a healthy host but there are some exceptions He himself proved that both tuberculosis and cholera when injected into
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organisms not all organisms exposed get the infectious agents or acquire the infection
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Now we know that depending on the immune response or the health of the individual
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the infected microorganism may not cause disease in all healthy hosts. Then another problem is
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in the case of human limited diseases like AIDS caused by HIV virus so without a suitable non-human
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host a researcher cannot evaluate this posulate 3 as we cannot deliberately infect a pathogen
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into humans to test whether it is causing infection or not and this presents an obvious
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ethical concern. So in the case of human limited diseases we cannot assess based
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on this posulate tree. Then Koch isolated mycobacterium tuberculosis from the dead guinea pigs and was able to again culture the microbe in pure culture on
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coagulated blood serum. So he isolated cells and tissues from this diseased animal that is injected with causative organism and found out that in
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the tissues. The suspected pathogen micro bacterium tuberculosis is there and he then
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further cultured made a pure culture out of these cells or tissues
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From this he formulated that the same microorganism must be isolated again
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from the deceased host. The exceptions are many infections by microbes considered as the underlying cause of the disease are absent from the lesions
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that ultimately develop. If a microbe is causing a disease, at the beginning the presence of that
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microbe may be there but at a later stage when a symptom like lesions develop that microbe may not
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be present. This is a case with streptococcus infection considered as an underlying cause of
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rheumatic fever or we cannot detect the presence of the streptococcus once volvular and endocrinal lesions of rheumatic fever appears At a later stage this disease organism may not be present in the deceased host The same is the case with
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HPV, human papilloma virus, considered as an underlying cause of nearly all cases of
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scammar's carcinoma or cancer of uterine cervix. But after many years, we cannot detect the presence
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of papilloma virus or we cannot recover virus from the patients. These all suggest that
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the same microorganism or the causative microorganism sometimes we cannot isolate it
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from the deceased host at a later time. So these are all exceptions of Coats postulate
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Now we have a postulate which is called as molecular Coats postulate. Based on this
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cos posulate incorporating the advancement in the field of microbiology, genomics, genetics and
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molecular biology to assess the relationship between microorganism and a disease at a molecular
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level. So we'll be discussing that molecular cos posulate in the next video. Now let us discuss
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the contributions of Robert Koch. As we said earlier, a posulate that is formulated in 1890s
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still considered as a gold standard to assess our microorganisms. A specific microorganism
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is responsible for causing a disease. Still widely accepted or widely useful in majority
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of the cases. As we discussed there are some exceptions. He was working on bacillus anthracis
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He discovered the anthrax life cycle then also tuberculosis, a mycobacterium tuberculosis
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causative organism of TB for his contribution in the field of tuberculosis and causative organism
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He was awarded with Nobel Prize in the year 1905. In the next video, we'll be discussing
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the modified version of coxposlate, that is molecular coxposlate. Hope you understand
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the four coxposlate and its exceptions. If you find this video useful, please consider
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subscribing this channel. Take care. Stay blessed. Thank you so much for your support. You are with
