Robert Koch

Dr Robert Koch was a pivotal figure in the golden age of microbiology. It was the German bacteriologist who discovered the bacteria that causes anthrax, septicaemia, tuberculosis and cholera, and his methods enabled others to identify many more important pathogens. Thanks to his contributions to the field, he is sometimes known as the father of bacteriology, a title shared with Louis Pasteur.

Koch’s first important discovery was on anthrax, a disease that killed large numbers of livestock and some humans. Rod-shaped structures had been observed in the blood of infected animals, but the cause of the disease was still uncertain.

Koch found that the disease could be spread by the blood of infected animals, and hypothesised that it was caused by living bacteria. He developed sophisticated techniques for observing bacterial growth on microscope slides, and saw that anthrax could form spores that survived desiccation, but produced more bacteria when put back into a moist environment. This explained how contaminated soil could remain toxic for years.

Although others had earlier determined that germs cause disease – notably Pasteur and Joseph Lister – Koch was the first to link a specific bacterium, in this case bacillus anthracis, to a specific disease.

Koch learned that dyes helped to make bacteria visible and identifiable under the microscope, and published the first photographs of bacteria. Koch’s assistant, Julius Petri, designed a shallow dish for culturing bacteria, and another of his assistants discovered that agar from seaweed made an effective medium.

Koch’s postulates

Tuberculosis was then responsible for one in seven deaths in Europe. Koch discovered rod-shaped bacteria, called bacilli, in patients’ tissues, but needed more evidence that they were the cause of the disease. He formulated four conditions that came to be known as Koch’s postulates:

1. the organism was present in every case of the disease
2. it could be cultured outside the body
3. inoculation of the culture caused the disease in an animal
4. the organism could be found in that animal

Culturing the bacilli was difficult, but Koch eventually succeeded in growing them on coagulated blood serum, and found that inoculating animals with the bacilli caused tuberculosis. He also found that sputum from patients was the main way the disease spread. This led to strategies to prevent disease by sterilising clothes and bed sheets and prohibiting public spitting.

He went on to discover the bacteria that cause cholera, and demonstrate the importance of a clean water supply to prevent the disease. Robert Koch was awarded the 1905 Nobel Prize in Physiology or Medicine for his work on tuberculosis.