Last week's post introduced the work of Louis Pasteur, the father of microbiology. It was not long after Pasteur proposed that microorganisms were to blame for food spoilage that someone would make the leap that infection could, too, also be caused by microorganisms. That man (who would become a great scientific rival to Pasteur) came to be known as the founder of modern bacteriology.
Robert Koch, a German physician, sought to identify the causes of diseases using Pasteur’s conjecture that microorganisms were the root of spoilage and infection. By isolating, staining, fixing and photographing bacterial cultures on glass microscope slides, Koch was able to identify the first direct link between organisms and the diseases they cause, in this case, from Bacillus anthracis to anthrax.
Photomicrographs of Bacillus anthracis by Robert Koch
It was his method of cultivating and growing bacteria samples along with his rules for establishing a link between organisms and disease that revolutionized the field.
- The organism must be present in every case of the disease,
- The organisms must be isolated from a host and grown in pure culture,
- Samples of that organisms must cause the same disease when inoculated into healthy laboratory animals, and
- The organism isolated from the inoculated animal and the original host must be the same.
However, these critical postulates would never have been possible without help from a fellow researcher. Koch struggled to find a pure culture medium in which to grow his bacterial samples. He tried potato slices, nutrient broths, and gelatin, each of which presented its own obstacles to an optimal sample, either melting in the heat required for bacteria growth or being consumed by the bacteria. Koch’s lab assistant, Walter Hesse, also struggled in his research due to the lack of a suitable medium. Fanne Hesse, Walter’s wife and a medical illustrator, was aware of the growing problem in the lab. She proposed they use agar-agar, a gelatin-like substance from Indonesia, where it was used to prepare jams and jellies that could withstand the tropical heat. Koch and Hesse tried this new substance, a sugar polymer (repeating chains of molecules) made from algae. It held up well in heat and bacteria could not digest it, forming the perfect, pure culture medium. Agar, as it is known today, is still the primary growth medium in microbiology. And the shallow glass vessel still used for agar and bacterial cultures? The petri dish, invented by Richard Petri, a colleague of Koch and Hesse.
Between Pasteur and Koch, the Golden Age of Microbiology achieved its greatest discoveries. Pathogens were identified, vaccines created, methodologies perfected, and foundations established that support modern research today. Their work would also influence health care and hospital practice, which we will cover in the final post of the series!
Editor's Note: This post was originally published in January 2016 and has been updated for freshness, accuracy and comprehensiveness.