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The debate by Professor Quirke (Gut 2001;49:757–60) was an interesting review of the hypothesis of a microbiological aetiology of Crohn’s disease. He indicates that “the hypothesis remains controversial and unproved.”
The point is that proof is never absolute, and indeed the objective of research is to disprove the hypothesis rather than to prove it, the latter being an impossible objective and scientifically flawed. He goes on to mention that “for the infectious disease hypothesis to be proved for any organism, Koch’s postulates need to be fulfilled.” This is not correct. Proof is pragmatic not absolute, and in practice it is the fulfilment of a set of predetermined objectives. Koch’s postulates are but an example of this, the Euclidian principle of quod erat demonstrandum, and an extremely important development of scientific philosophy of the 19th century. Koch himself however recognised the weakness of his postulates in that although he felt that cholera was microbiological in causation, he was unable to apply his postulates to it.
It is important to review Koch’s postulates and they are as follows:
(1) “The specific organism should be shown to be present in all cases of animals suffering from a specific disease but should not be found in healthy animals”
This postulate demands a high level of sensitivity of laboratory methods and the clinicopathological identification of a specific disease—can Crohn’s disease be classified as such? At the time of Koch the important concept of a commensal microbe was not developed.
(2) “The specific microorganism should be isolated from the diseased animal and grown in pure culture on artificial laboratory media”
This demands laboratory methods which have not always been achieved at the …