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Robert Koch (1843 – 1910) was a German physician and scientist who won the Nobel Prize for his microbiological work on tuberculosis. He also established many foundational techniques for microbiology, some of which are still used today. In this lesson, learn more about this innovative scientist.

Robert Koch and his Life’s Work

In the late 19th century, tuberculosis killed nearly a third of all middle-aged adults in Europe. A statistic that large is hard to comprehend; just imagine that one out of every three adults you know all got sick with the same illness today. Surely, several scientists would work hard to find a cure.

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In his time, finding a cure for the scourge of tuberculosis was Robert Koch’s life mission.Despite making tremendous progress in the disease’s identification and potential treatment, even receiving the Nobel Prize in medicine for this work, Koch never fully realized his dream of finding a cure. However, in the process of this ultimately unsuccessful quest, his creativity and tenacity resulted in techniques and methodologies that greatly influenced the entire field of microbiology, some of which persist more than a century later.

Koch’s Early Life and Career Preparation

Robert Koch’s parents were poor miners, who were startled when he showed them that he had taught himself to read at age 5. This precociousness heralded his Nobel Prize-winning career in microbiology. He received his medical degree in 1866 and spent the next decade as a physician in various hospital and government research posts.

During this time, Koch did not have a particularly noteworthy research facility. In 1876, he published a major study that identified the causative agent of anthrax, which gained him wide acclaim. Several years later, he was appointed as an advisor to the German Imperial Health Bureau, a position of great esteem, and from which he did much of his famous tuberculosis work.

Identifying the Cause of Tuberculosis

Today, we are pretty clear what causes most illnesses.

Back in Koch’s time, such knowledge was not as common. One of his first major findings was the identification of Mycobacterium tuberculosis, the bacterium that causes this incredibly deadly disease.Koch deliberately infected guinea pigs with material from one of three tuberculosis-infected animals: apes, cattle and humans. Each of the guinea pigs became afflicted with the same illness – tuberculosis – and the bacterium that Koch isolated from each guinea pig was identical, regardless of the animal source of the infection.

Koch’s Postulates

One of the most influential methods that Koch championed was the proposal that a disease’s causative agent could be identified with a high degree of certainty if four conditions were met (listed below).

Prior to the widespread adoption of these postulates, scientists working on diseases that killed millions could spend years researching microbes that were not ultimately responsible for the disease. His four postulates were:

  1. The microbe should cause disease in all organisms in which it is abundantly present, but should not be abundantly present in organisms not infected by the disease.
  2. The suspected microbe should be isolated in pure form and grown in culture.

  3. Re-introducing the culture-grown suspected microbe should induce disease in a previously uninfected organism.
  4. The suspected microbe should be re-isolated from the test organism (from Postulate #3), grown in culture, and identical to the originally isolated microbe (from Postulate #2).

Limitations of Koch’s Postulates

While there were many areas in which his postulates provided helpful guidance for disease pathologists, the requirement of isolating the microbe in culture was limiting in some instances, particularly in the study of virus-induced illnesses, since scientists did not yet have modern virus-isolation procedures. The requirement that the microbe cause illness in all organisms in which it is abundantly present was limiting as well. For example, many instances of food poisoning, both short- and long-term, are caused by a bloom of bacteria that normally exist abundantly in the digestive tract of healthy individuals (and in fact are necessary for good health). Today, a modified version of Koch’s postulates has been updated to incorporate the gene-based study of microbes and illnesses.

Koch’s Other Major Contributions

Though he is best known for his postulates and the tuberculosis work that earned him the Nobel Prize in 1905, Koch made many other contributions to the field of microbiology. They include:

  • Techniques for growing bacteria on a plate
  • Techniques for fixing bacteria onto a slide for study under a microscope
  • Descriptions and discoveries of several other diseases’ causative agents, including those microbes causing anthrax (Bacillus anthracis), cholera (Vibrio cholerae), and wound Staph infections (Staphylococcus sp.).

Ironically (since it went against the postulates for which he is so well-known), he also observed that healthy individuals could carry a disease-causing pathogen in abundance.

Summary of Koch’s Work

Few figures have contributed as prominently to any field as Robert Koch did to microbiology. His work hugely influenced several other Nobel Prize-winning scientists, in a time when the world of the microscopic unseen was just beginning to become seen. His work and contributions have undoubtedly saved tens of millions of lives.

While he was best known for his work on tuberculosis, he worked on other diseases as well, in the process articulating and formalizing microbiology techniques, some of which are still practiced over a century later.


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