Robert Koch is widely known for his work with anthrax, discovering the causative agent of the fatal disease to be Bacillus anthracis. Koch discovered the formation in anthrax bacteria of spores that could remain dormant under specific conditions. However, under optimal conditions, the spores were activated and caused disease. To determine this causative agent, he dry-fixed bacterial cultures onto glass slides, used dyes to stain the cultures, and observed them through a microscope. Koch’s work with anthrax is notable in that he was the first to link a specific microorganism with a specific disease, rejecting the idea of spontaneous generation and supporting the germ theory of disease.
Koch's Four Postulates
Koch accepted a position as government advisor with the Imperial Department of Health in 1880. During his time as government advisor, he published a report in which he stated the importance of pure cultures in isolating disease-causing organisms and explained the necessary steps to obtain these cultures, methods which are summarized in Koch’s four postulates. Koch’s discovery of the causative agent of anthrax led to the formation of a generic set of postulates which can be used in the determination of the cause of any infectious disease. These postulates, which not only outlined a method for linking cause and effect of an infectious disease but also established the significance of laboratory culture of infectious agents, are listed here:
The organism must always be present, in every case of the disease.
The organism must be isolated from a host containing the disease and grown in pure culture.
Samples of the organism taken from pure culture must cause the same disease when inoculated into a healthy, susceptible animal in the laboratory.
The organism must be isolated from the inoculated animal and must be identified as the same original organism first isolated from the originally diseased host.
Isolating pure culture on solid media
Koch began conducting research on microorganisms in a laboratory connected to his patient examination room. Koch’s early research in this laboratory proved to yield one of his major contributions to the field of microbiology, as it was there that he developed the technique of growing bacteria. Koch's second postulate calls for the isolation and growth of a selected pathogen in pure laboratory culture. In an attempt to grow bacteria, Koch began to use solid nutrients such as potato slices. Through these initial experiments, Koch observed individual colonies of identical, pure cells. Coming to the conclusion that potato slices were not suitable media for all organisms, Koch later began to use nutrient solutions with gelatin. However, he soon realized that gelatin, like potato slices, was not the optimal medium for bacterial growth, as it did not remain solid at 37˚C, the ideal temperature for growth of most human pathogens. As suggested to him by Walther and Angelina Hesse, Koch began to utilize agar to grow and isolate pure cultures, as this polysaccharide remains solid at 37˚C, is not degraded by most bacteria, and results in a transparent medium.
Cholera
Koch next turned his attention to cholera, and began to conduct research in Egypt in the hopes of isolating the causative agent of the disease. However, he was not able to complete the task before the epidemic in Egypt ended, and subsequently traveled to India to continue with the study. In India, Koch was indeed able to determine the causative agent of cholera, isolating Vibrio cholera. The bacterium had originally been isolated in 1854 by Italian anatomist Filippo Pacini, but its exact nature and his results were not widely known.
Tuberculosis
During his time as the government advisor with the Imperial Department of Health in Berlin in the 1880s, Robert Koch became interested in tuberculosis research. At the time, it was widely believed that tuberculosis was an inherited disease. However, Koch was convinced that the disease was caused by a bacterium and was infectious, and tested his four postulates using guinea pigs. Through these experiments, he found that his experiments with tuberculosis satisfied all four of his postulates. In 1882, he published his findings on tuberculosis, in which he reported the causative agent of the disease to be the slow-growing Mycobacterium tuberculosis (known as 'tubercle bacillus' back then). His work with this disease won Koch the Nobel Prize in Physiology and Medicine in 1905. Additionally, Koch's research on tuberculosis, along with his studies on tropical diseases, won him the Prussian Order Pour le Merite in 1906 and the Robert Koch medal, established to honor the greatest living physicians, in 1908.
