Heinrich Hermann Robert Koch


Heinrich Hermann Robert Koch
(1843 - 1910)


German physician, one of the founders of the science of bacteriology, who discovered the tubercle bacillus (1882) and the cholera bacillus (1883). He won the Nobel Prize for Physiology or Medicine in 1905.

Early training
Koch attended the University of Gottingen, where he studied medicine, graduating in 1866. He then became a physician in various provincial towns. After serving briefly as a field surgeon during the Franco-Prussian War of 1870-71, he became district surgeon in Wollstein, in what was then Germany, where he built a small laboratory. Equipped with a microscope, a microtome (an instrument for cutting thin slices of tissue), and a homemade incubator, he began his study of algae, switching later to pathogenic organisms.
One of Koch's teachers at Gottingen had been the anatomist and histologist Friedrich Gustav Jacob Henle, who, in 1840, published the theory that infectious diseases were caused by living microscopic organisms. In 1850 the French parasitologist Casimir-Joseph Davaine, who was among the first to observe organisms in the blood of persons suffering certain diseases, reported the transmission of anthrax by the inoculation of healthy sheep with the blood of animals dying of the disease and the finding of microscopic rod-shaped bodies in the blood of the dead sheep. Inspired by the work of the French microbiologist Louis Pasteur, Davaine in 1863 showed that it was highly probable that, because the sheep did not become diseased in the absence of these rodlike bodies, anthrax was due to the presence of such organisms in the blood. The natural history of the disease was, nevertheless, far from complete.


Anthrax research
It was at this point that Koch began. He cultivated the anthrax organisms in suitable media on microscope slides, demonstrated their growth into long filaments, and discovered the formation within them of oval, translucent bodies--dormant spores. Koch found that the dried spores could remain viable for years, even under exposed conditions. This finding explained the recurrence of the disease in pastures long unused for grazing, for the dormant spores could, under the right conditions, develop into the rod-shaped bacilli that cause anthrax. The anthrax life cycle, which Koch had discovered, was announced and illustrated at Breslau in 1876, on the invitation of Ferdinand Cohn, an eminent botanist. Julius Cohnheim, a famous pathologist, was deeply impressed by Koch's presentation. "It leaves nothing more to be proved," he said. "I regard it as the greatest discovery ever made with bacteria and I believe that this is not the last time that this young Robert Koch will surprise and shame us by the brilliance of his investigations." Cohn, whose discovery of spores was published earlier in 1876, was also very much impressed and generously helped to prepare the engraving for Koch's epochal paper, which he also published. One of Cohn's pupils, Joseph Schroeter, found that chromogenic (colour-forming) bacteria would grow on such solid substrates as potato, coagulated egg white, meat, and bread and that these colonies were capable of forming new colonies of the same colour, consisting of organisms of the same type. This was the starting point of Koch's pure-culture techniques, which he worked out a few years later. That a disease organism might be cultured outside the body was a concept introduced by Louis Pasteur, but the pure-culture techniques for doing so were perfected by Koch, whose precise and ingenious experiments demonstrated the complete life cycle of an important organism. The anthrax work afforded for the first time convincing proof of the definite causal relation of a particular bacillus to a particular disease.
In 1877 Koch published an important paper on the investigation, preservation, and photographing of bacteria. His work was illustrated by superb photomicrographs. In this paper he described his method of preparing thin layers of bacteria on glass slides and fixing them by gentle heat. Koch also invented the apparatus and the procedure for the very useful hanging-drop technique, whereby microorganisms could be cultured in a drop of nutrient solution on the underside of a glass slide. In 1878 Koch summarized his experiments on the etiology of wound infection. By inoculating animals with material from various sources, he produced six types of infection, each due to a specific microorganism. He then transferred these infections by inoculation through several kinds of animals, reproducing the original six types. In this study, he also observed differences in pathogenicity for different species of hosts and demonstrated that the animal body is an excellent apparatus for the cultivation of bacteria.


Discovery of tubercle bacillus
Koch, now recognized as a scientific investigator of the first rank, obtained a position in Berlin in the German Health Office, where he set up a laboratory in bacteriology. With his collaborators, he devised new research methods. To obtain a pure culture outside the body, Koch mixed the organisms in melted gelatin; then, after solidification of the gelatin and growth of the organisms, portions of pure colonies were placed into separate tubes of broth or other media. Koch also concentrated his efforts on the study of tuberculosis, with the aim of isolating its cause. Although it was known that tuberculosis was due to an infective agent, the organism had not yet been isolated and identified. By modifying the method of staining, the bacillus was discovered and its presence established in preparations of tuberculous material. A fresh difficulty arose when, for some time, it proved impossible to grow the organism in pure culture. But, eventually, Koch succeeded in isolating the organism on a succession of media. Its etiologic role was now established. On March 24, 1882, Koch announced before the Physiological Society of Berlin that he had isolated and grown the tubercle bacillus, which he believed to be the cause of all forms of tuberculosis.
Meanwhile, Koch's work was interrupted by the appearance of cholera in Egypt and the danger of its transmission to Europe. As member of a German government commission, Koch went to Egypt to investigate the disease; although he soon had reason to suspect a particular comma-shaped bacillus as the specific cause of cholera, he was frustrated by the cessation of the epidemic. Nevertheless, he discovered the cause of amebic dysentery and the bacilli of two varieties of Egyptian conjunctivitis. Proceeding to India, where cholera is endemic, he completed his task, discovering the cholera organism and its transmission via drinking water, food, and clothing.

Resuming his studies of tuberculosis, Koch investigated what effect an injection of dead bacilli would have on a person who subsequently received a dose of living ones; he concluded that the local reaction produced might prove the means by which the disease could not only be diagnosed but, in the early stages, perhaps even cured. In his studies, he used as the active agent a sterile liquid produced from cultures of the bacillus. But this liquid (tuberculin, 1890) proved disappointing as a curative agent, and, consequently, its importance as a means of detecting a present or past tubercular state was not immediately recognized.

Additional work on tuberculosis came later in Koch's career, but, after the seeming debacle of tuberculin, he was occupied (1891-99) with a great variety of investigations into diseases of humans and animals--studies of leprosy, rinderpest, bubonic plague, surra, Texas fever, and malaria. The spread of malaria was still a mystery; Koch had nearly satisfied himself that it was transmitted by mosquitoes when the British bacteriologist Ronald Ross published his findings pointing to the same conclusion.

In 1901 Koch reported work done on the pathogenicity of the human tubercle bacillus for domestic animals. He believed that infection of human beings by bovine tuberculosis is so rare that it is not necessary to take any measures against it. This conclusion was rejected by commissions of inquiry in Europe and America in an extensive and important work that was stimulated by Koch's theory, even though it proved to be partly wrong. But, in most cases, the successful measures of prophylaxis were those firmly laid down by Koch.

 

BIBLIOGRAPHY.
Thomas D. Brock, Robert Koch: A Life in Medicine and Bacteriology (1988).



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