Koch's postulates

Koch's postulates

Koch's postulates are four criteria designed to establish a causal relationship between a causative microbe and a disease. The postulates were formulated by Robert Koch and Friedrich Loeffler in 1884 and refined and published by Koch in 1890. Koch applied the postulates to establish the etiology of anthrax and tuberculosis, but they have been generalized to other diseases.

The postulates

Koch's postulates are:
# The microorganism must be found in abundance in all organisms suffering from the disease, but not in healthy organisms.
# The microorganism must be isolated from a diseased organism and grown in pure culture.
# The cultured microorganism should cause disease when introduced into a healthy organism.
# The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

However, Koch abandoned the second part of the first postulate altogether when he discovered asymptomatic carriers of cholera [cite journal |author=Koch Robert |title=Über den augenblicklichen Stand der bakteriologischen Choleradiagnose |language=German
journal=Zeitschrift für Hygiene und Infectionskrankheiten |year=1893 |volume=14 |pages=319-333
] and, later, of typhoid fever. Asymptomatic carriers are now known to be a common feature of many infectious diseases, especially viruses such as polio, herpes simplex, HIV and hepatitis C. As a specific example, all doctors and virologists agree that poliovirus causes paralysis in just a few infected subjects, and the success of the polio vaccine in preventing disease supports the conviction that the poliovirus is the causative agent.

The third postulate specifies "should", not "must", because as Koch himself proved in regard to both tuberculosis and cholera, [cite book |author= Koch Robert |year=1884 |title=Mitt Kaiser Gesundh |chapter=2 |pages=1-88 ] not all organisms exposed to an infectious agent will acquire the infection. Noninfection may be due to: chance or to the host's immune system successfully repulsing the invading pathogen; acquired immunity, as from previous exposure or vaccination; or genetic immunity, as with the resistance to malaria conferred by possessing at least one sickle cell allele.


Koch's postulates were developed in the 19th century as general guidelines to identify pathogens that could be isolated with the techniques of the day. [cite journal | author = Walker L, Levine H, Jucker M | title = Koch's postulates and infectious proteins. | journal = Acta Neuropathol (Berl) | volume = 112 | issue = 1 | pages = 1–4 | year = 2006 | pmid = 16703338 | doi = 10.1007/s00401-006-0072-x] Even in Koch's time, it was recognized that some infectious agents were clearly responsible for disease even though they did not fulfill all of the postulates. [Koch R. (1884) "Mitt Kaiser Gesundh" 2, 1-88; Koch R. (1893) "J. Hyg. Inf." 14, 319-333] Attempts to rigidly apply Koch's postulates to the diagnosis of viral diseases in the late 19th century, at a time when viruses could not be seen or isolated in culture, may have impeded the early development of the field of virology. [Brock TD (1999) Robert Koch: a life in medicine and bacteriology. American Society of Microbiology Press, Washington] [Evans AS (1976) Causation and disease: the Henle-Koch postulates revisited. Yale J Biol Med 49:175–195] Currently, a number of infectious agents are accepted as the cause of disease despite their not fulfilling all of Koch's postulates. [cite journal | author = Jacomo V, Kelly P, Raoult D | title = Natural history of Bartonella infections (an exception to Koch's postulate). | journal = Clin Diagn Lab Immunol | volume = 9 | issue = 1 | pages = 8–18 | year = 2002 | pmid = 11777823 | doi = 10.1128/CDLI.9.1.8-18.2002] Therefore, while Koch's postulates retain historical importance and continue to inform the approach to microbiologic diagnosis, fulfillment of all four postulates is not required to demonstrate causality.

Koch's postulates have also influenced scientists who examine microbial pathogenesis from a molecular point of view. In the 1980s, a molecular version of Koch's postulates was developed to guide the identification of microbial genes encoding virulence factors. [Falkow S (1988). "Molecular Koch's postulates applied to microbial pathogenicity." "Rev Infect Dis" 10(Suppl 2):S274-S276.]


Further reading


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Koch's postulates — In 1890 the German physician and bacteriologist Robert Koch set out his celebrated criteria for judging whether a given bacteria is the cause of a given disease. Koch s criteria brought some much needed scientific clarity to what was then a very… …   Medical dictionary

  • koch's postulates — noun plural also koch s laws Usage: usually capitalized K : a statement of the steps required to establish a microorganism as the cause of a disease: (1) it must be found in all cases of the disease; (2) it must be isolated from the host and… …   Useful english dictionary

  • Koch&’s postulates — The criteria, first advanced by Robert Koch, by which the causative agent of a disease can be unambiguously identified. For an organism to be accepted as the causative agent it must be (i) present in all cases, (ii) isolatable in pure culture,… …   Dictionary of molecular biology

  • Koch's postulates — (koks pos tu leīts) A set of rules for proving that a microorganism causes a particular disease …   Dictionary of microbiology

  • Molecular Koch's postulates — are a set of experimental criteria that must be satisfied to show that a gene found in a pathogenic microorganism encodes a product that contributes to the disease caused by the pathogen. Genes that satisfy molecular Koch s postulates are often… …   Wikipedia

  • Koch (surname) — Koch (pronounced in German, although it is often pronounced differently in other countries) is a German surname meaning cook and may refer to: * Bill Koch (skier), cross country skier * Billy Koch, Major league baseball relief pitcher * Bobby… …   Wikipedia

  • Koch — may refer to: * Koch (surname), people with this surname * Koch (boat), a type of Arctic boat * Koch (language), a language spoken in India and Bangladesh * Koch method of learning Morse Code * Koch snowflake or star, and Koch curve * Koch s… …   Wikipedia

  • Koch's bacillus — kōks , käch əz or Koch bacillus kōk , käch n a bacillus of the genus Mycobacterium (M. tuberculosis) that causes human tuberculosis Koch kȯk (Heinrich Hermann) Robert (1843 1910) German bacteriologist. Koch is usually hailed as the founder of… …   Medical dictionary

  • Postulates, Koch's — In 1890 the German physician and bacteriologist Robert Koch set out his celebrated criteria for judging whether a given bacteria is the cause of a given disease. Koch s criteria brought some much needed scientific clarity to what was then a very… …   Medical dictionary

  • Koch , (Heinrich Hermann) Robert — (1843–1910) German bacteriologist Born the son of a mining official in Klausthal, Germany, Koch studied medicine at the University of Göttingen where he was a pupil of Jacob Henle. After graduating in 1866 and serving in the Franco–Prussian War,… …   Scientists