Germ Theory is the concept that microorganisms can cause disease, and this theory is the foundation of modern medicine. Here is a summary of some key discoveries.

Key in the development of Germ Theory, and the understanding of infectious disease, was the refutation of spontaneous generation; the idea that, in modern times, living things can arise from non-living matter.

Aristotle & Abiogenesis

According to Aristotle, it was readily observable that aphids arise from the dew on plants, fleas from putrid matter, and mice from dirty hay; and this belief remained unchallenged for more than two thousand years.

What was actually being observed in many instances was the appearance of visible organisms or populations of organisms which arose from microscopic precursors. For example it only takes one bacterial cell to, in a matter of days, give rise to millions of daughter cells, or minute aphid eggs to quickly give rise to visible adult aphids.

Important Early Microbiologists

There were many involved in the triumph of Germ Theory, but here is a summary of some of the key players. Those italicized are covered in this article.

• van Leeuwenhoek, Anton (1670s)
• Semmelweis, Ignaz (1840s)
• Snow, John (1850s)
• Pasteur,Louis (1860s)
• Lister, Joseph (1860s)
• Koch, Robert (1870s)
• Domagk, Gerhard & Fleming, Alexander (1920s & 1930s)

Louis Pasteur, Mythbuster (1860s)

Pasteur, a French scientist who made great contributions to our understanding of microbiology and for whom the process of “pasteurization” is named, brought to light strong evidence that microbes arise from other microbes, not spontaneously.

Pasteur’s Swan-Necked Flasks

Pasteur created unique glass flasks with unusual long, thin necks that pointed downward. These “swan-necked” flasks allowed air into the container but did not allow particles from the air to drift down into the body of the flask.

The End of Abiogenesis

After boiling nutrient broths in his special flasks, Pasteur found that these swan-necked containers would remain free of microbes until he broke the necks of the flasks, allowing particles from the air to drift in. It was the carefully controlled experiments of Pasteur that finally put to rest the debate over spontaneous generation.

Joseph Lister the Father of Modern Antisepsis (1860s)

Despite previous discoveries to the contrary, the prevailing belief remained that wound infection due to tissue exposed to stinking "miasma" in air, and it was still considered unnecessary for surgeon to wash hands before seeing a patient.

Lister read a paper by Pasteur showing that rotting could occur if micro-organisms present and thought that perhaps microorganisms were causing the rotting wounds.

In his publication, Pasteur had suggested three different methods to eliminate microorganisms:

• filter them out
• heat them up
• expose them to chemical solutions

The first two methods were inappropriate for use in human wounds, so Lister experimented with the third.

Carbolic acid was used at the time for deodorizing sewage, so Lister tried spraying instruments, surgical incisions, wounds and dressings with solution. It markedly reduced the incidence of gangrene. This led to the rise of sterile surgery and Lister being recognized as the father of antiseptic surgery.

Robert Koch’s Postulates (1870s)

Koch, a German physician, developed a sequence of experimental steps for directly relating a specific microbe to a specific disease, and in doing so was able to isolate:

• Bacillus anthracis (the bacterium causing anthrax)
• Mycobacterium tuberculosis (the bacterium causing tuberculosis)
• Vibrio cholera (the bacterium causing cholera)

In addition to his postulates, Koch played an important role in the use of agar as solid medium, and invented nutrient broth and nutrient agar for controlled growth of microorganisms in the laboratory setting.

The Discovery of Antimicrobials (1930s)

Gerhard Domagk and Sulfa Drugs

German pathologist and bacteriologist, Domagk discovered that the dye Prontosil was effective against a wide range of bacteria. The sulfanilamide portion of the Prontosil molecule is responsible for its antibacterial effect, hence, sulfa drugs. In 1939, Domagk received the Nobel Prize in Medicine for this discovery.

Alexander Fleming and Penicillin

Fleming, a British bacteriologist, discovered penicillin by accident when observing that some of the bacterial colonies he was studying were disappearing on plates that were contaminated with mold. Fleming extracted the compound in the mold that was responsible for destruction of the bacterial colonies. The product of the mold was named penicillin, after the Penicillium mold from which it was derived.

For more information on the History of Microbiology and Germ Theory, see Science Prof Online and the Suite101 articles Early Germ Theory of Disease and Spontaneous Generation.

Sources

Bauman, R. (2005) Microbiology.

Park Talaro, K. (2008) Foundations in Microbiology.