THE MICROBIAL MENACE

PASTEUR AND KOCH - BACTERIOLOGY -
GERM THEORY OF DISEASE

In the field of observation, chance favors only those who are prepared... .
-Louis Pasteur, 1854

Though Leeuwenhoek's microscope made it possible to see bacteria, bacteriology did not emerge as a science until almost two centuries later. Viruses, almost all of which are smaller than the smallest bacteria, were suspected as a cause of disease in the 19th century and even named (virus being a name for "poison"), but were not specifically seen until well into the 20th century with the advent of electron microscopy.

Louis Pasteur came to his formulation of the germ theory of disease through his studies of fermentation for the French wine industry and through subsequent studies of silkworm diseases for the silk industry. His investigation of fermentation focused on the role of living organisms. These discoveries helped Pasteur formulate his "germ theory of disease" and led directly to the development of a process in which heat is used to kill bacteria. The process, known as pasteurization, is still used. Pasteur also developed a vaccine for rabies.

Robert Koch confirmed Pasteur's germ theory and took it several steps further. His investigations began with a study of Bacillus anthracis, which causes a disease affecting cattle. He cultured the anthrax bacillus and later used the same techniques in tracking and culturing the organism responsible for tuberculosis. Koch won a Nobel Prize for his work on tuberculosis, but is perhaps better remembered for his formulation of four basic principles or postulates of bacteriology.

Left: Joseph Meister came to Pasteur after being bitten by a rabid dog. Pasteur treated him with a rabies vaccine, an unorthodox use of vaccines in that infection had probably already occurred. However, the treatment apparently succeeded. The rabies virus would not be identified for another half a century.
Right: Vaccine as a treatment.

KOCH'S POSTULATES

The organism must be present in every case of the disease The organism must not be present in any other disease as an agent not responsible for disease The organism must be capable of being isolated After growth in pure culture, the organism must be able to produce the disease

Koch's postulates, formalized in 1882: Koch's postulates ushered in a sustained era of pathogen research and identification. In their day, these postulates were enormously helpful to epidemiologists helping to formalize standards by which new pathogens could be identified. Koch's postulates are still taught to medical students, but modern medical science is starting to pass them up. Most of the pathogens that can be identified by Koch's postulates are believed to have been identified, and interest is turning to diseases with multiple causes or factors and to infectious agents that cannot be cultured.

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