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Bacteria are free-living cells that can live inside or outside a body. Viruses are a non-living collection of molecules that need a host to survive.
Vibrio cholerae causes cholera infection.
Germ Theory
Germ Theory
Germ theory explains how germs cause disease. It took science hundreds of years to learn that germs cause disease.
In science, a "theory" is an explanation. All theories explain phenomena.
For instance, germ theory explains that a person gets sick because microorganisms attack the body.
Germ theory supplanted miasma theory. Germ theory is the basis of modern medicine.
Obsolete Theories
Obsolete Theories
Over the many years, people entertained many unusual theories including miasma theory and spontaneous generation. Miasma theory stated that disease was caused by noxious gas or night air. Miasma was thought to come from rotting matter. Spontaneous generation is discussed below.
Both miasma theory and spontaneous generation have been disproven.
An 1831 color lithograph by Robert Seymour depicts cholera as a robed, skeletal creature emanating a deadly black cloud.
Spontaneous Generation
Spontaneous Generation
Spontaneous Generation was a misguided belief that held that life came from nonliving matter. For instance, rats were thought to come from garbage. Mushrooms were thought to come from dead logs. Fleas arose from dust. No parents were thought necessary to bring about new life.
Aristotle (384 - 322 BC) supported spontaneous generation theory. Aristotle believed that "vital heat" was required for Spontaneous Generation to happen.
Spontaneous Generation was taken as scientific fact for 2000 years!
Jan Baptist van Helmont
Jan Baptist van Helmont
He is remembered today for his ideas concerning spontaneous generation. He had a theory that mice come about from rags and wheat. He was wrong, of course. (Baby mice come from mommy mice.)
Although Van Helmont was wrong about spontaneous generation, he did contribute to science. He coined the term "gas."
Perhaps his most famous experiment showed that tree mass can be attributed to water, not soil.
People believed this spontaneous generation nonsense for two thousand years.
Finally, in 1862, Louis Pasteur proved spontaneous generation to be wrong with his famous swan neck flask experiment.
Some People Who Helped Develop Germ Theory
Some People Who Helped Develop Germ Theory
Listed below are some of the important people who helped mankind understand why and how people get sick.
Robert Hooke - 1665
Robert Hooke - 1665
Robert Hooke embraced and improved the first microscopes by designing his own light microscope.
Hooke observed cork cells and coined the term cell for describing biological organisms. The term was suggested by the resemblance of plant cells to monks' cells.
Robert Hooke was an excellent illustrator and he published his findings in a book called Micrographia. His work led to cell theory.
Robert Hooke saw cells first. He called them cells.
This picture shows Robert Hooke's microscope and what he saw.
Francesco Redi - 1668
Francesco Redi - 1668
In 1668, Francesco Redi was the founder of experimental biology. He showed that maggots came from adult flies. Maggots did not spontaneously generate from rotting meat. Unfortunately, although this experiment was pretty clear, scientists continued to debate spontaneous generation for another 200 years.
Francesco Redi
Red's experiment showed that maggots come from fly eggs. If flies cannot lay eggs on the meat, there will be no maggots.
Antonie Phillips van Leeuwenhoek - 1674
Antonie Phillips van Leeuwenhoek - 1674
Microbes were first discovered by an amateur Dutch scientist named Antonie Phillips van Leeuwenhoek in the 1670s. He was a pioneer in microscopy. In fact, he was the first person to see microscopic life! He was the first to document muscle fibers, red blood cells, sperm cells, and bacteria. He was the father of microbiology.
Animicules = Protists
Dr. Edward Jenner - 1796
Dr. Edward Jenner - 1796
In 1796, Dr. Edward Jenner used Vaccinia (cowpox) to vaccinate against smallpox. He observed that milkmaids often suffered from cowpox but rarely suffered from smallpox. It occurred to him that cowpox prevented milkmaids from catching smallpox. Dr. Jenner inoculated a 13 year-old-boy with "vaccinia virus", which was known as cowpox. The boy was immune to smallpox. This was the first vaccine.
Smallpox virus, a stable DNA virus, is no longer found in the wild. However, it is reportedly held in a freezer at the CDC.
Latin word: vacca = cow. The word "vaccine" comes from "vaccinia", which is the fancy word for "smallpox."
On May 14, 1796, Dr. Edward Jenner used matter from a cowpox lesions to inoculate an 8-year-old boy, James Phipps.
Ignaz Semmelweis - 1847
Ignaz Semmelweis - 1847
Ignaz Semmelweis went insane because his peers did not accept his conclusion.
1847 - Ignaz Semmelweis proved that hand washing prevented the spread of childbirth fever. Handwashing stops the spread of disease.
Childbirth fever was caused by bacteria entering the uterus.
Prior to this discovery, many doctors were responsible for infecting many of their patients. Oops.
Dr. John Snow - 1854
Dr. John Snow - 1854
Cholera is a horrific diarrheal illness caused by Vibrio cholerae bacteria. This bacteria infects intestines. Cholera used to kill 50% of the people who got it.
In the 1800s, people believed that cholera was transmitted by "Miasma", a poisonous cloud. They did not believe in germ theory.
It was Robert Koch who discovered cholera bacillus, Vibrio cholerae in the year 1884.
In August 1854, a cholera outbreak occurred in Soho. Dr. John Snow proved that cholera was caused by drinking water that was tainted with human waste.
Dr. Snow collected death data and plotted cases of cholera on a map. Dr. Snow determined that the Broad Street pump was the site of infection.
Dr. Snow was the first doctor to trace cholera. He was our first epidemiologist. His peers at the time did not appreciate his efforts.
It wasn't until 1884 that Robert Koch discovered cholera bacillus, Vibrio cholerae.
Louis Pasteur - 1862
Louis Pasteur - 1862
Louis Pasteur was a French chemist and microbiologist who finally put the spontaneous generation issue to rest in 1862. His elegant experiment allowed air to enter the flask while trapping microbes. The broth remained sterile.
Pasteur showed that air alone does not support growth. Further, he showed that the broth could support growth once microbes were introduced.
Microbial growth comes from microbes - not the broth itself.
The theory of spontaneous generation was dead.
Louis Pasteur in his lab.
Pasteur's Swan Neck Flask
Life comes from life
Life comes from life
Louis Pasteur showed (with swan neck flasks) that microorganisms only came from other microorganisms and that a sterile broth would remain so -unless contaminated by life.
Life comes from preexisting life. Omne vivum ex vivo!
Pasteurization - 1863
Pasteurization - 1863
Louis Pasteur also showed that heating food would kill microbes that would make the food go bad. This process is now called Pasteurization. Pasteurization is used to treat milk and other foods.
Louis Pasteur
Disease Discoveries
Disease Discoveries
From 1877 to 1887, Pasteur employed these fundamentals of microbiology in the battle against infectious diseases.
He went on to discover three bacteria responsible for human illnesses: staphylococcus, streptococcus and pneumococcus.
"Coccus" indicates that the bacteria are round.
Vaccines
Vaccines
Louis Pasteur discovered the method of weakening virulent microorganisms. His method is the basis of vaccination.
Vaccines contain a weak or dead germ. Sometimes vaccines contain only the proteins of germs. Vaccines are safe ways to teach your immune system how to fight off the real germ.
Louis Pasteur developed vaccines against chicken cholera, anthrax, and swine erysipelas.
Rabies Vaccine -1885
Rabies Vaccine -1885
After mastering his method of vaccination, Louis Pasteur applied this concept to rabies. On July 6, 1885, Pasteur tested his pioneering rabies treatment on man for the first time: the young Joseph Meister was saved.
Rabies
Joseph Lister - 1865
Joseph Lister - 1865
1865 - Joseph Lister proved that chemicals –specifically phenol (a.k.a., carbolic acid) - can be used to prevent infection. An antiseptic is a chemical that prevents infection.
Carbolic acid sprays on the open wound during surgery. The chemical kills germs.
Robert Koch - Nobel Prize Winner (1905)
Robert Koch - Nobel Prize Winner (1905)
Robert Koch
In 1882, Robert Koch discovered tubercle bacillus that caused tuberculosis.
He also discovered cholera bacillus, Vibrio cholerae in the year 1884.
1890 – Robert Koch created experimental steps for directly relating a specific microbe to a specific disease:
1. Germ must be found in all sick animals, but not in healthy animals. a
2. Germ must be grown in culture.
3. Cultured germ should make healthy animals sick. b
4. Germ must be found in sick animal.
a. Sometimes healthy animals are carriers. (cholera and typhoid)
b TB, cholera and HIV-infection don’t always result in sickness
In the late 1800s, Louis Pasteur and Robert Koch helped develop the science of bacteriology when they discovered a link between bacteria, fermentation, and disease.
Koch and Pasteur independently provided experimental evidence anthrax was caused by anthrax bacillus. Their work established the germ theory of disease.
Sir Alexander Fleming - Nobel Prize Winner (1945)
Sir Alexander Fleming - Nobel Prize Winner (1945)
In 1928, Alexander Fleming discovered penicillin by accident. Penicillin is an antibiotic, which is used to treat bacterial infections.
Howard Walter Florey discovered Alexander Fleming's work on penicillin about 10 years later. He purified the active ingredients, tested the antibiotic on mice, and saw that it worked.
Antibiotics helped us win World War Two. He was awarded the Nobel Prize for physiology or medicine in 1945 for work on penicillin.
Jonas Salk - Polio Vaccine
Jonas Salk - Polio Vaccine
In 1955, Jonas Salk made the Polio vaccine. He successfully disabled the virus so that it could not infect humans. The virus still had recognizable antigens.
Poliovirus attacks the coating of nerve cells. Paralysis is often the result.
Polio Virus
Polio Virus
Victims
Victims
Iron Lung
Iron Lung
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