Robert Koch

Robert Koch (11 December 1843 - 27 May 1910) was a celebrated German physician and pioneering microbiologist. As the founder of modern bacteriology, he is known for his role in identifying the specific causative agents of tuberculosis, cholera, and anthrax and for giving experimental support for the concept of infectious disease.

Robert Koch was the man who, building on the work of Pasteur and Lister, set bacteriology on its way to being a modern science. He discovered the causative organisms of anthrax, septicemia, tuberculosis and cholera. He was christened Heinrich Herrmann Robert but dropped the first two names.

Koch’s Postulates

The first direct demonstration of the role of bacteria in causing disease came from the study of anthrax by the German physician Robert Koch (1843–1910).

Koch used the criteria proposed by his former teacher Jacob Henle (1809–1885) to establish the relationship between Bacillus anthracis and anthrax; he published his findings in 1876.

Koch injected healthy mice with material from diseased animals, and the mice became ill. After transferring anthrax by inoculation through a series of 20 mice, he incubated a piece of spleen containing the anthrax bacillus in beef serum. The bacilli grew, reproduced, and produced endospores. When the isolated bacilli or their spores were injected into healthy mice, anthrax developed. His criteria for proving the causal relationship between a microorganism and a specific disease are known as Koch’s postulates.

Koch’s proof that B. anthracis caused anthrax was independently confirmed by Pasteur and his co-workers. They discovered that after burial of dead animals, anthrax spores survived and were brought to the surface by earth-worms. Healthy animals then ingested the spores and became ill. After completing his anthrax studies, Koch fully outlined his postulates in his work on the cause of tuberculosis. In 1884 he reported that this disease was caused by the rod-shaped bacterium Mycobacterium tuberculosis, and he was awarded the Nobel Prize in Physiology or Medicine in 1905 for his work.

Koch’s postulates were quickly adopted by others and used to connect many diseases to their causative agent. However, their use is at times not feasible. For instance, organisms such as Mycobacterium leprae, the causative agent of leprosy, cannot be isolated in pure culture.

Koch’s Postulates

1. The microorganism must be present in every case of the disease but absent from healthy organisms.

2. The suspected microorganisms must be isolated and grown in a pure culture.

3. The same disease must result when the isolated microorganism is inoculated into a healthy host.

4. The same microorganism must be isolated again from the diseased host.

Koch’s Experimentation

1. Koch developed a staining technique to examine human tissue. M. tuberculosis cells could be identified in diseased tissue.

2. Koch grew M. tuberculosis in pure culture on coagulated blood serum.

3. Koch injected cells from the pure culture of M. tuberculosis into guinea pigs. The guinea pigs subsequently died of tuberculosis.

4. Koch isolated M. tuberculosis from the dead guinea pigs and was able to again culture the microbe in pure culture on coagulated blood serum.

Limitations of Koch’s Postulates:

• The particular bacteria (such as the one that causes leprosy) cannot be “grown in pure culture” in the laboratory.

• There is no animal model of infection with that particular bacteria.

Harmless bacteria may cause disease if:

• It has acquired extra virulence factors making it pathogenic.

• It gains access to deep tissues via trauma, surgery, an IV line, etc.

• It infects an immunocompromised patient.

• Not all people infected by a bacteria may develop a disease-subclinical infection is usually more common than clinically obvious infection.

Despite such limitations, Koch’s postulates are still a useful benchmark in judging whether there is a cause-and-effect relationship between a bacteria (or any other type of microorganism) and clinical disease.