History of Microbiology


The microscope

  • Zacharias Janssen

In 1590, Zacharians Janssen developed the first compound microscope in Middleburg, Holland, Janssen’s microscope consisted of three tubes. One tube served as the outer casing and contained the other two tubes. At either ends of the inner tubes were lenses used for magnification. Janssen’s design enabled scientists to enlarge the image of a specimen three and nine times the specimen’s actual size.

  • Robert Hooke

In 1665, Robert Hooke, an English scientist, popularized the use of the compound microscope when he placed lenses over slices of cork and viewed little boxes that he called cells. It was his discovery that led to the development of cell theory in the nineteenth century by Mathias Schleiden. Theoder Schwann, and Rudolf Virchow, Cell theory states that all living things are composed of cells.

  •  Antoni van Leeuwenhoek

Hooke’s experiments with a crude microscope inspired Antoni van Leenwenhoek to further explore the micro world. Van Leeuwenhock, an amateur lens grinder, improved Hooke’s microscope by grinding lenses to achieve magnification. His microscope required one lens. With his improvement, van Leeuwenhock became the first person to view a living microorganisms, which he called Animalcules. This discovery took place during the 1600s, when scientists believed that organisms generated spontaneously and did not come from another organisms. This sounds preposterous today; however, back then scientists were just leaning that a cell was the basic component of an organism.

Origin of Organisms

  • Francesco Redi

In 1668, Italian physician Francesco Redi developed an experiment that demonstrated that an organisms did not spontaneously appear. He filled jars with rotting meat. Some jars he sealed and other he left opened. Those that were open eventually contained maggots, which is the larval stage of the fly. The other jars did not contain maggots because flies could not enter the jar to lay eggs on the rotting meat. His critics stated that air was the ingredient required for spontaneous generation of an organism. Air was absent from the sealed jar and therefore no spontaneous generation could occur, they said Redi repeated the experiment except this time he placed a screen over the opened jars. This presented flies from entering the jar. There weren’t any maggots on the rotting eat.

Until that time scientists did not have a clue about how to fight disease. However, Redi’s discovery gave scientists an idea. They used Redi’s findings to conclude that killing the microorganisms that caused a disease could prevent the disease from occurring. A new microorganisms could only be generated by another microorganisms when it underwent a reproductive process. Kill that microorganism and you will not have new microorganisms, the theory went – you could stop the spread of the disease. Scientists called this the Theory of Biogenesis. The Theory of Biogenesis states that a living cell is generated from another living cell.

  • Louis Pasteur

Although the Theory of Biogenesis disproved spontaneous generation, spontaneous generation was hotly debated among the scientific community until (1861) when Louis Pasteur, a French scientific, resolved the issue once and for all. Pasteur showed that microorganisms were in the air. He proved that sterilized medical instruments became contaminated once they were exposed to the air.

Pasteur came to this conclusion by boiling beef broth in several short-necked flasks. Some flasks were left open to cool. Other flasks were sealed after boiling. The opened flasks became contaminated with microorganisms while no microorganisms appeared in the closed flasks. Pasteur concluded that airborne microorganisms had contaminated the opened flask.

In a follow-up experiment, Pasteur placed beef broth in an open long-necked flask. The neck was bent into an S-shape. Again he boiled the beef broth and let it cool. The S shaped neck trapped the airborne microorganisms. The beef broth remained uncontaminated even after months of being exposed to the air. The very same flask containing the original beef broth exists today in Pasteur Institute in Paris and still shows no sign of contamination. Pasteur’s experiments validated that microorganisms are not spontaneously generated. Based on Pasteur’s findings, concerned effort was launched to improve sterilization techniques to prevent microorganisms from reproducing. Pasteurization, one of the best known sterilization techniques, was developed and named for Pasteur. Pasteurization kills harmful microorganisms in milk, alcoholic beverages, and other foods and drinks by heating it enough to kill most bacteria that cause spoilage.

  • John Tyndall and Ferdinand Cohn

The work of John Tyndall and Ferdinand Cohn in the late 1800s led to one of the most important discoveries in sterilization. They learned that some microorganisms are resistant to certain sterilization techniques. Until their discovery, scientists had assumed that no microorganisms could survive boiling water, which became a widely accepted method of sterilization. This was wrong. Some thermophiles resisted heat and could survive a bath in boiling water. This means that there was not one magic bullet that killed all harmful microorganisms.

Germ theory

Until the late 1700s, not much was really known about diseases except their impact. It seemed that anyone who came in contact with an infected person contracted the disease. A disease that is spread by being exposed to infection is called a contagious disease. The unknown agent that causes the disease is called a contagion. Today we known that a contagion is a microorganisms, but in the 1700s many found it hard to believe something so small could cause such devastation.

  • Rober Koch Koch made some observations on the disease caused Bacillus anthracci called anthrax.Based on his findings, Koch developed the Germ Theory. The Germ Theory states that a disease-causing microorganisms should be present in animals infected by the disease and not in healthy animals. The microorganisms can be cultivated away from the animal and used to inoculate a healthy animal. The healthy animal should then come down with the disease. Samples of a microorganism taken from several infected animals are the same as the original microorganism from the first infected animals.

Four steps used by Koch to study microorganisms are referred to as Koch’s Postulates.

Koch’s Possulates state:

  1. The microorganism must be present in the diseased animals and not presence in the healthy animal.
  2. Cultivate the microorganism away from the animal in a pure culture.
  3. Symptoms of the disease should appear in the healthy animal after the healthy animal is inoculated with the culture of the microorganisms.
  4. Isolate the microorganism from the newly infected animal and culture it in the

laboratory. The new culture should be the same as the microorganism that was cultivated from the original diseased animal.

Koch ‘s work with anthrax also developed techniques for growing a culture of microorganisms. He eventually used a gelatin surface to cultivate microorganisms.

Gelatin inhibited the movement of microorganisms. As microorganisms reproduced, they remained together, forming a colony that made them visible without a microscope. The reproduction of microorganisms is called colonizing. The gelatin was replaced with agar that is derived from seaweed and still used today. Richard Petri improved on Koch’s cultivating technique by placing the agar in a specially designed disk that was later called the Petri dish which is still used today.


The Variola virus was once of the most feared villains in the late 1700s. The variola virus causes smallpox. If variola didn’t kill you, it caused pus-filled blisters that left deep scars that pitted nearly every part of your body. Cows were also susceptible to a variation of variola called cowpox. Milkmaids who tended to infected cows contracted cowpox and exhibited immunity to the smallpox virus.

  • Edward Jenner

Edward Jenner, an English physician, discovered something very interesting about both smallpox and cowpox in 1796. Those who survived smallpox never contracted smallpox again, even when they wee later exposed to someone who was infected with smallpox.

Milkmaids who contracted cowpox never caught smallpox even though they were exposed to smallpox. Jenner had an idea. He took scrapings from a cowpox blister found on a milkmaid and, using a needle scratched the scrapping into the arm of James Phipps, an 8-year-old. Phipps became slightly ill when the scratch turned bumpy. Phipps recovered and was then exposed to smallpox. He did not contract smallpox because his immune system developed antibodies that could fight off variola.

Jenner’s experiment discovered how to use our body’s own defense mechanism to prevent disease by inoculating a healthy persons with a tiny amount of the diseasecausing microorganism. Janner called this a vaccination, which is an extension of the Latin word vacca (cow). The person who received the vaccination became immune to the disease-causing microorganism.

  • Elie Metchnikoff

Elie Metchnikoff, a nineteeth-century Russian zoologist, was interested by Jenner’s work with vaccinations. Metchnikoff wanted to learn how our bodies react to vaccination by exploring our body’s immune system. He discovered that white blood cells (leukocytes engulf and digest microorganisms that invade the body. He called these cells phagocytes, which means “cell eating”. “Metchnikoff was one of the first scientists to study the new area of biology called immunology, the study of the immune system.

Killing the Microorganism

  • Ignaz Semmelwees

Great studies were made during the late 1800s in the development of antiseptic techniques. It began with a report by Hungarian physician Ignaz Semmelweis on a dramatic decline in childbirth fever when physicians used antiseptic techniques when delivering babies. Infections become preventable through the use of antiseptic techniques.

  • Joseph Lister

Joseph Lister, an English surgeon, developed one of the most notable antiseptic techniques. During surgery he sprayed carbolic acid over the patient and then bandged the patient’s wound with carbolic acid-soaked bandages. Infection following surgery dramatically dropped when compared with surgery performed without spraying carbolic acid. Carbolic acid, also known as phenol was one of the first surgical antiseptic.

  • Paul Ehrlich

Antiseptics prevented microorganisms from infecting a person, but scientists still needed a way to kill microorganisms after they infected the body. Scientists needed a magic bullet that cured diseases. At the turned of the nineteeth century, Paul Ehrlich, a German chemist, discovered the magic bullet. Ehrich blended chemical elements into a convocation that, when inserted into an infected area, killed microorganisms without affecting the patient. Today we call Ehrlich’s concoction a drug. Ehrlic’s innovation has led to chemotherapy using drugs that are produced by chemical synthesis.

  • Alexander Fleming

Scientists from all over set out to use Ehrlich’s findings to find drugs that could make infected patients well again. One of the most striking breakthroughs came in 1929 when Alexander Fleming discovered Penicillin snotatum, the organism that synthesizes penicillin. Penicillium notatum is a fungus that kills the Staphyloccus aureus microorganism and similar microorganisms. Fleming grew cultures of Staphyloccus aureus, a bacterium, in the laboratory. He was also conducting experiments with Penicillium notatum, a mold. By accident the Staphyloccous aureus was contaminated with the Penicillium notatum, causing the Staphyloccocus to stop reproducing and die. Penicillium notatum became one of the first antibiotic. An antibiotic is a substance that kills bacteria.