Koch's postulates

The Henle - Koch's postulates describe the cause -effect relationship between a parasite and the appropriate host, which can be verified experimentally and defined with the help of these postulates. The name of the postulates derived from the work of the anatomist and pathologist Jakob Henle (1809-1885) and the physician and microbiologist Robert Koch ( 1843-1910 ).

Historical derivation

The requirements of the postulates can be traced back to 1840 Henle's work " From the miasms and contagions and the miasmatic contagious diseases " of the year. Here he formulated the conjecture that parasitic microorganisms that cause infections are, but what he could not prove directly. Another source is Edwin Klebs work ' from the 1870s. Klebs formulated the classic three- step of isolating, culturing, inoculation, but without explaining it clearly needed. Robert Koch, who had studied with Henle in Göttingen, has not quoted these postulates in this form in a work. A compilation of certain criteria when an infection was cooking in 1884 in an essay on tuberculosis. Friedrich Loeffler, an employee of cooking, it's the first time in 1884 described the three steps as postulates and was consecutively numbered. In his work on the diphtheria bacillus, he formulated as follows:

" Now, if the Diphtheria is a disease caused by microorganisms, so have to meet those three postulates also with her, the fulfillment of the strict proof of the parasitic nature of any such disease is absolutely necessary:

Koch himself varied its methodology often and never spoke of postulates. But Loeffler's postulates reflect the methodology that both had used in their joint work on tuberculosis. Cook, this also published in 1884, but made the problem and not the solution in the center of his remarks:

" The facts obtained in this way may be able to provide as much evidence already that only the extreme skepticism may raise the objection that the microorganisms found not the cause but an epiphenomenon of the disease were. [ ... ] It is therefore the complete proof that one is not alone content to be stated the coincidence of disease and parasites, but also that these parasites are detected directly as the underlying cause of the disease. This can only be done in such a way that the parasites from the diseased organism completely separated and freed of all products of the disease [ ... ], and that the disease is caused by its peculiar properties of new by introducing the isolated parasite in the healthy organism. "

At the 10th International Medical Congress in Berlin in 1890 Koch spoke " About bacteriological research" and combined to kind of himself and Loeffler:

" If it is now but could be shown:

• First, that the parasite is found in every case of the disease in question, under conditions which correspond to the pathological changes and the clinical course of the disease;

• Secondly, that it appears as random and non-pathogenic parasite with any other disease; and

• Thirdly, that he is capable of completely isolated from the body and often vice breeds sufficiently in pure cultures, again to produce the disease;

Then he could not be more fortuitous accident of the disease, but it could be in any case no other relationship between parasite and disease think more than that the parasite is the cause of the disease. "

Modern form of the postulates

In the "Golden Age of Microbiology", which was followed by discoveries of Louis Pasteur and Koch, Koch's postulates were unrestricted. Many infectious diseases were discovered, developed therapies and vaccines. Today, however, we know that there are pathogens, which can not be fulfill Koch's postulates all. Viruses, for example, can not be cultivated on nutrient media simple, as certain bacteria ( rickettsiae, chlamydiae, treponemes ). Other pathogens affect animals other than humans, so that the third postulate is violated (eg, the causative agent of gonorrhea, Neisseria gonorrhoeae ). Other pathogens are ever became only detectable with modern molecular biological methods. It was therefore necessary to summarize the " postulates " new:

The first postulate concerns the regular, eg microscopic detection of the pathogen in the products of the respective disease. The second postulate deals with the pure cultivation of the pathogen outside of the diseased organism. The third postulate determines the detection of the pathogenic properties of the pure bred pathogen. A now- supplemented fourth postulate formulated also expects nor evidence of immunological host-pathogen relationships to it.

First postulate

The discovery of the natural location of the obligate pathogens corresponds to the first postulate. Each exciter has a specific host spectrum or a specific tissue or organ affinity. Pathogenic characteristics of the pathogen and the sensitivity of the host relate to each other reciprocally. So due one the other and vice versa. The best form of mutual adjustment is the symbiosis, the coexistence of pathogen and host with mutual benefit. For example, people that excrete typhoid bacteria against which their own germs that are highly dangerous for non- immune individuals, immune. Different transfer mechanisms ensure the spread of certain pathogens when the host dies, and with it, the "site" or if the parasites in host defense succumb. Other transmission mechanisms are attached to the continued existence of the site.

In short: The suspected pathogen must always be associated with the disease and may not be detected in healthy animals.

Second postulate

The fulfillment of the second postulate makes special demands on the work of the culture medium for the cultivation conditions. There are the natural environmental conditions of the pathogen simulated and its pathogenic properties are preserved.

In short: The suspected pathogen must be grown in pure culture.

Third postulate

The third postulate is based on the detection of the pathogenic properties of the virus. The features of interest must be quantitatively checked with laboratory methods. The adhesion and penetration of the propagating energy and pathogenicity are properties that the virulence, the number of necessary excitation, and the immunity of the host defenses are dependent. In animal experiments, either the penetrating and proliferation potency of the pathogens and their pathogenicity or or is measured. If there is no pathogenic effects in animal or are the same factors in animals other than humans, so the comparison between the experimental and the infection of humans is doubtful.

In short, a pure culture of the suspected pathogen should trigger the disease in healthy animals.

Supplement: Fourth Postulate

The additional fourth postulate deals with the immunological host-pathogen relationship. Here, the pathogen is defined in terms of the ability to stimulate the system of the white blood cells ( leukocytes) of the host to produce antibodies in accordance with the penetration and proliferation. Antibodies are protein molecules that are formed by de novo synthesis and release into the body fluids against the causative agent or are already available. Due to their specific structure, they are able to produce pathogenic potency of the pathogen, its propagation force or its pathogenicity to reduce after binding to the pathogen or its pathogenic secretions and to neutralize. The presence of such antibody molecules is also an important indication of expiring or expired contacts between the tissues of the host and the pathogen.

In particular, the increase or the reduction of measurable antibody effects in the blood of the host is to provide a clearer, if the pathogens are not difficult to breed or if vaccinations planned and their success will be determined or if the state of preparedness and thus the spread of the pathogen in of the population to be examined.

In short, the organism must be reisolated and be identical to the original pathogen.