The University of Arizona Learn About Germs


UA College of Public Health






Discovery of Germs


Did you know?    In 1872 Pierre Pachet, Professor of Physiology at Toulouse made the statement “Louis Pasteur’s theory of germs is ridiculous fiction”.

Microorganisms, or life forms not visible to the naked eye, were first discovered by Anton van Leeuwenhoek in 1675 with the invention of the microscope. Yet it would take nearly 200 years for scientists to make the connection between microbes and disease.


Exploration into this mysterious world of germs began circa 1850 by a Frenchman by the name of Louis Pasteur (1822-1895). At that time Pasteur, Dean of the Faculty of Science at the University of Lille, was approached by a man who worked at a factory that produced beer from sugar beets. Much to the businessman’s lament, vats of the fermented beer were turning sour, so the businessman asked Pasteur to find out the cause.


Pasteur used a microscope to analyze the beer samples and found thousands of microorganisms. His theory was that these microbes or “germs” were not the result of the beer going sour, rather they were the cause. Pasteur went on to study other liquids such as vinegar and milk.

From his experiments with liquids, Pasteur became convinced that the air contained tiny living organisms unseen by the naked eye. These organisms could cause petrifaction of liquids and could be prevented by killing the germs with heat. Initially his beliefs were ridiculed by the medical community, but he was able to eventually prove his case beyond doubt. Indeed, we are all familiar with the term “pasteurized milk” which was named in Pasteur’s honor.


Further in his career Pasteur became convinced that microbes could affect not just liquids, but humans as well. Furthermore he believed these microbes could spread diseases among humans. . This became known as the “Germ theory of Disease”. He continued his work by searching for ways humans could be protected from getting diseases.

In 1868 Pasteur suffered a stroke that affected his ability to work independently as he had done in the past. Pasteur was inspired to put together a research team to further his studies. In 1881 Pasteur and his team found a vaccine against anthrax. A few years later Pasteur found a vaccine for rabies.


Pasteur’s discoveries inspired other researchers to perform experiments in the field of germs. Some of the more prominent scientists in this era included:

  • Edward Jenner (1749-1823). Jenner changed our world by developing the first vaccine—the vaccine for smallpox virus. But it wouldn’t be until 12 years later until the smallpox virus was discovered by Dmitri Ivanovski. In 1980 the World Health Organization declared that smallpox was extinct throughout the world
  • Joseph Lister (1827-1912). Familiar with Pasteur’s work, Lister believed that microbes in the air could cause disease to be spread in hospitals. He discovered the link between post-operative death in hospitals to lack of cleanliness . Learning that carbolic acid was being used as a disinfectant in sewers, he started using it on humans with success. He used lint soaked in carbolic acid to prevent wounds from getting infected.Lister became known as the “Father of Antiseptic Surgery” and his anticeptic principals remain the cornerstone of surgery to this day.
  • Robert Koch (1843-1910). Koch found the specific germs that caused anthrax and tuberculosis, thus confirming Pasteur’s’ research by directly linking an individual microbe with a specific disease. Most importantly, Koch developed new research techniques that influenced the work of the young scientists that followed. He discovered a way to stain and photograph germs so the rest of the world could see them. He also devised a new way to uncover which germ caused infection by perfecting techniques for growing cultures of germs on a solid medium.
  • Martinus Beijerinck (1851-1931). The son of a tobacco dealer that went bankrupt, Beijerinck devoted most of his career to the study of a contagious disease that affects tobacco plants now known as the tobacco mosaic virus. From this research he discovered and named the virus. Although he believed the virus was a liquid, Wendell Stanley (1904-1971) would later disprove this.

These early germ pioneers eventually became known as the “Microbe Hunters” in a famous book written in 1926 by Paul de Kruif. Inspired by the work of these early scientists a new generation of microbe hunters emerged. By 1900, 21 germs that caused disease had been identified. In addition to the smallpox vaccine, vaccines had been developed for typhoid fever, (1897, Almwroth Wright and David Sample) and the plague (1897, Waldemar Haffkine).


Development of Antibiotics


Did you know?    Sir Alexander Flemming said “Nature makes penicillin. I just fount it”.The 1900’s was marked by the discovery of antibiotics. Antibiotics (Greek “anti” meaning against and “bio” meaning life) are chemicals which can kill or stop the growth of a germ. (Antibiotics are discussed in more detail in section, Prevention of Disease.) The discovery of antibiotics was arguably one of the most important medical advances in history.

  • Paul Ehrlich (1854-1915). Ehrlich was a German scientist who won the 1908 Nobel Prize in Physiology or Medicine. Although Alexander Fleming is probably better known for his work with antibiotics (see below) Ehrilch came up with the idea that chemicals might exist that can kill germs infecting a person, while not killing the person. In a 17 year journey, he developed the first anti microbial drug, using an arsenic compound, to treat syphilis. He also coined the term "chemotherapy" and came up with the concept of a “magic bullet”. Ehrlich also demonstrated that antibodies are responsible, in part, for immunity, thus paving the way for research into vaccinations.. The movie “The Magic Bullet” is a story of his life, primarily on his cure for syphilis. Other antibiotic discoveries were on the horizon:
  • Alexander Fleming. As with many discoveries, the antibiotic that came to be known as penicillin was found by accident. One morning in the year 1928, Professor Alexander Fleming was looking at some petri dishes he had previously inoculated with staphyloccus bacteria as part of a research project. One of the plates was contaminated with mold. All around the mold was a clear area where no bacteria were growing. He concluded that something in the mold was killing the bacteria. Alexander Fleming grew the mold in a pure culture and found that it produced a substance that killed some of the germs. He concluded that something in the mold was killing the disease-causing bacteria and named the substance penicillin.
  • Howard Florey , Ernst Chain and Charles Fletcher. Ten years later Howard Florey (1898-1968) and Ernst Chain (1906-1979), working at Oxford University , isolated penicillin, the bacteria killing substance found in the mold. In 1941 Charles Fletcher( born 1923) used penicillin on a patient for the first time and found it was able to kill off some of the infection. Soon after this, Flory convinced an American drug company to mass produce the penicillin, By D-day (June 6 1944) penicillin was nicknamed the wonder drug and in 1945 Fleming, Chain and Florey were awarded the Nobel Prize for medicine.
  • Andrew J Moyer (1899-1959). Moyer was an expert in the nutrition of molds and developed methods to increase the production of penicillin. He was granted a patent for a method of the mass production of penicillin in May 1948.
  • Selman Waksman and Boyd Woodruff. In 1940 Selman Waksman (1888-1973) and H. Boyd Woodruff (born 1917) discovered actinomycin, the first antibiotic obtained from a group of soil organisms called actinomycetes. Tetracycline is also isolated from this group of organisms. In 1944 Waksman discovered streptomycin and within 20 years there would be several antibiotics effective for the treatment of tuberculosis. Waksman was the person to suggest the word "antibiotic" to describe the group of compounds produced by one microorganism that inhibit or kill other microorganisms. For his efforts he was awarded the Nobel Prize.
  • Lloyd Conover. In 1955 Lloyd Conover (born 1923)patented the antibiotic tetracycline, which became the most prescribed broad spectrum antibiotic in the United States within 3 years.


Later Discoveries

Did you know?  “Science consistently produces a new crop of miraculous truths and dazzling devices every year, truths and devices that enrich our lives and grow up out of the graciously willing puzzles of the unknown in an orderly but unpredictable way, out of a process of observation, hypothesis, experiment, conclusion; a process that as far as we know, was first proposed and adopted, only a few hundred years ago by a number of Europeans faced with a new world to explore and some worn out scholastic tools passed down from the ancient Greeks to explore it with.”
A quote from Nobel Prize Winner Kary Mullis from his website 2002


Jonas Salk and Albert Sabin. The polio vaccines were developed by Jonas Salk (1914-1995) and Albert Sabin (1906-1993) in 1952 and 1962 respectively. Other post 1945 vaccines included measles, rubella, chicken pox, hepatitis, lyme disease and anthrax vaccines.


  • John Franklin Enders, Thomas H. Weller, and Frederick Chapman Robbins. In 1949, John Franklin Enders (1897-1985), Thomas H Weller (born 1915) and Frederick Chapman Robbins (1916-2003).worked together and came up with a technique to grow poliovirus in cultures of human tissues. This gave virologists a tool for the isolation and study of viruses. They were awarded the Nobel Prize in 1954.
  • Joshua Lederberg, Norton Zinder, Alfred Hershey and Martha Chase. Scientists researching viral genetics during this time included Joshua Lederberg (1925-2008) and Norton Zinder (born 1928) who studied the transfer of genetic information. Alfred Hershey (1908-1997)and Martha Chase (1927-2003) postulated that only DNA is needed for viral replication.
  • Howard Temin and David Baltimore. In 1970 Howard Temin (1934-1994) and David Baltimore (born 1938), working in independent laboratories, discovered the reverse transcriptase enzyme in RNA viruses.
  • Luc Montagnier and Robert Gallo.One of the major diseases in the modern world is HIV/AIDS. The HIV virus was first discovered by Luc Montagnier (born 1932) and Robert Gallo (born 1937) in 1980. Combination drug therapies have been developed and research is ongoing to find a cure or vaccination.

Molecular Biology

  • George Beadle and Edward Tatum. In 1941 George Beadle (1903-1989) and Edward Tatum (1909-1975) demonstrated an important relationship between genetics and microbiology while working with isolated mutants of the fungus Neurospora. They were awarded the Nobel Prize in 1958. Their discovery paved the way for the study of mutations and DNA.
  • Oswald Avery, Colin MacLeod and Maclyn McCarty. In 1944 Oswald Avery (1877-1955), Colin MacLeod (1909-1972), and Maclyn McCarty (1911-2005) established that DNA (Deoxyribonucleic acid) was the genetic material in bacteria.
  • Francis Crick, Maurice Wilkins and James Watson. One of the most significant and well known discoveries was made by Francis Crick (1916-2004), Maurice Wilkins (1916-2004), and James Watson (born 1928), who described the double-helix structure of DNA and developed methods to sequence DNA. These discoveries formed the foundation for today’s advances in the field of molecular biology. All three scientists were awarded the Nobel Prize in 1962.
  • Walter Gilbert, Fred Sanger and Paul Berg. More exact sequencing techniques were developed by Walter Gilbert (born 1932), Fred Sanger (born 1918) and Paul Berg (born 1926), and were awarded the Nobel Prize in 1980.
  • Kary Mullis. In 1980 Kary Mullis (born 1944) isolated a heat stable enzyme from the bacteria Thermus aquaticus and developed the polymerase chain reaction technique (PCR). PCR was a revolution in molecular biology, allowing for a very small amount of a sequence of DNA to be the amplified into a very large amount. Mullis was awarded the Nobel Prize in 1993.
  • J. Craig Ventor and Francis Collins. In the 1990’s an international team of scientists began the Human Genome Project, with the goal of mapping the entire human genome. In 2000, J. Craig Ventor (born 1946) and Francis Collins (born 1950) announced the completion of the Human Genome project. Ventor was listed on the Time 100 list of the most influential people in the world in both 2007 and 2008.



Stanley Prusiner. In the early 80’s Stanley Prusiner (born 1942) discovered that disease can be caused by a class of infectious proteins (not containing a nucleus) he termed “prions”. Initially Prusiner received much skepticism from the scientific community. However, in 1997 Prusiner was awarded the Nobel Prize for his work. The proteins cause scrapie in sheep, mad cow disease, and spongiform diseases such as Creutzfeldt-Jakob disease in humans. Currently there is no cure for this disease.