History of Microbiology: Scientists, Discoveries and Timeline

Microbiology is the study of microorganisms, including bacteria, archaea, fungi, protozoa, algae, and viruses.

Until about the 1880s, people still believed that life could form out of thin air and that sickness was caused by sins or bad odors. Diseases were thought to be caused by:

• Bad smells, treated by removing or masking the offending odor.
• An imbalance in the body’s humors, treated with bleeding, sweating, and vomiting.
• Sins of the soul, treated with prayer and rituals.

Although the concept of contagion was known, it was not attributed to tiny living creatures but to bad odors or spirits, such as the devil. Varo and Columella in the first century BC postulated that diseases were caused by invisible beings (Animalia minuta) inhaled or ingested. Fracastorius of Verona in 1546 proposed a Contagium vivum as a possible cause of infectious disease, and Von Plenciz in 1762 suggested that each disease was caused by a separate agent.

Discovery of Microbes and the Dawn of Microbiology

Zacharias Janssen (1570-1638)

• He was a Dutch spectacle maker.
• He invented the compounding of lenses.
• He used two lenses fitted in a single tube to observe an enlarged image of microscopic forms.

Robert Hooke (1635-1703)

• In the 1660s, he modified the basic design of the microscope and developed a compound microscope that was six inches long and had two convex lenses.
• He observed specimens such as leaves, thin specimens of cork, hair of peacock, seaweed, wood, and sponges under the microscope.
• He described the repetitive rectangular box-like structures as “cells.”
• In 1665, he published his observations in Micrographia.
• He described forms of fungi such as bluish mold on a piece of leather and one of the leeches in vinegar.
• His descriptions can broadly classify the white mold as Mucor.

Antonie van Leeuwenhoek (1632-1723)

• Antonie van Leeuwenhoek of Delft, Holland, was a Dutch self-made scientist and was the first person to observe and accurately describe microorganisms such as bacteria and protozoa.
• He was not the first person to observe microscopic forms but was probably the first one to report them accurately.
• He is known as the “Father of Microbiology.”
• He made 419 lenses and more than 250 microscopes. His microscopes could magnify around 50-300 times.
• He observed animal sperm, blood, cork, leaves, scrapings from his teeth, and many other materials.
• He carefully recorded his observations and descriptions in a series of letters to the Royal Society in London over a period of about 50 years.
• He described the tiny creatures as “animalcules.”
• In 1683, he published sketches showing the principal shapes of bacteria, including rods, cocci, and spiral-shaped forms.
• He is also considered the father of bacteriology and protozoology.

Spontaneous Generation and Biogenesis

When microorganisms were known to exist, most scientists believed that such simple life forms could arise through spontaneous generation. Life was thought to spring spontaneously from mud, lakes, or anywhere with sufficient nutrients.

Van Helmont (1580-1644)

• He experimentally supported abiogenesis by devising a method that supposedly produced mice.
• He placed dirty material in a vessel containing cheese and wheat and incubated it in a dark stable place for 21 days.
• He found mice near these materials and concluded that mice were produced by abiogenesis.

Francesco Redi (1626-1697)

• He was an Italian physician who opposed the theory of abiogenesis.
• He performed a three-jar experiment to disprove abiogenesis.
• He placed pieces of rotten meat in three jars. He covered one jar with parchment paper, another with fine mesh or gauze, and left the third jar open.
• The uncovered jar showed maggots and attracted flies.
• The covered jars did not show maggots or flies inside, but eggs were laid on the parchment paper and gauze.
• Redi’s experiment could not completely prove that microbial life does not originate spontaneously, but it showed that entry of flies and eggs can lead to the formation of maggots.

Louis Joblot (1645-1723)

• He performed experiments in which he observed that hay infused with water and allowed to stand for a few days showed the growth of microorganisms.
• He boiled the infusion and divided it into two vessels.
• One vessel was covered and placed in a cupboard, while the other was left open.
• The covered vessel did not show growth, while the uncovered vessel showed growth within a few days.
• When the covered vessel was opened, it showed growth after some time.
• His experiments supported biogenesis and showed that life cannot be created spontaneously.

John Needham (1713-1781)

• He was a strong proponent of abiogenesis or spontaneous generation.
• He boiled meat broth in a corked flask and, after several days, observed growth in the flask.
• He concluded that the growth resulted from spontaneous generation.
• The result was due to insufficient boiling of the broth, which failed to kill heat-resistant spores.

Lazzaro Spallanzani (1729-1799)

• He repeated Needham’s experiment but obtained the opposite result.
• He boiled meat infusion for a longer period and sealed the flask in the flame.
• After several days, he found no growth.
• He argued that prolonged boiling destroyed heat-resistant spores.
• When he opened the sealed flask and exposed it to air, microbial growth appeared in the broth.
• His experiments supported biogenesis and opposed spontaneous generation.

F. Schulze (1815-1873)

• He performed experiments to disprove abiogenesis.
• He passed air through infusion broth after passing it through caustic potash or sulfuric acid.
• He aspirated the flask daily for three months.
• No microbial growth was observed.

Theodor Schwann (1810-1882)

• He was also an opponent of abiogenesis.
• He passed air into infusion broth through red-hot tubes.
• No growth appeared in the broth.

H. Schroder and Von Dusch

• In 1854, they performed experiments in which air was filtered through cotton wool.
• This method prevented microbial growth in boiled infusions.
• The concept led to the use of non-absorbent cotton as a stopper for test tubes so that incoming air would be sterile.

Nicolas Appert

• He followed the ideas arising from Spallanzani’s work.
• He showed that soups and liquids could be preserved by heating them extensively in thick champagne bottles.

Ignaz Semmelweis and John Snow

• They showed a growing awareness of the mode of disease transmission.

Charles Darwin

• In 1859, Darwin’s Origin of Species showed that the human body could be conceived as a creature susceptible to the laws of nature.
• He considered disease to be a biological phenomenon rather than something caused by magic.

The Golden Age of Microbiology

The Golden Age of Microbiology began with the work of Louis Pasteur and Robert Koch. During this period, the scientific community accepted their work and continued to expand it. This period marked the real beginning of microbiology as a discipline of biology.

Louis Pasteur (1822-1895)

• Pasteur provided decisive experimental evidence against spontaneous generation through his swan-neck flask experiments.
• He placed nutrient broth in the flask and boiled it to sterilize it.
• Although the flask remained open to air, no microbial growth appeared because dust particles carrying microorganisms became trapped in the long neck.
• When the neck was cut open, microbial growth appeared in the broth.
• His experiments showed that microorganisms arise from other microorganisms rather than spontaneously from inanimate matter.
• Pasteur also found that fermentation of fruits and grains, resulting in alcohol, was brought about by microorganisms.
• He determined that bacteria were responsible for the spoilage of wine.
• He proposed mild heating to destroy undesirable microorganisms without ruining the taste of the product. This process became known as pasteurization.
• Pasteur demonstrated that yeasts are responsible for alcoholic fermentation.
• In 1877, he discovered anaerobic bacteria during his study of butyric acid fermentation.
• He was the first person to use gun cotton for filtration.
• He discovered the principle of active immunization in 1880.
• He isolated the causative agent of chicken cholera and showed that older cultures could lose their ability to cause disease while stimulating protective substances in the host.
• He prepared an attenuated rabies vaccine and successfully used it to protect a young boy from rabies.
• His work led to the development of the germ theory of disease.
• He introduced sterilization techniques and developed steam sterilizers, hot air ovens, and autoclaves.
• He developed methods for preserving food through fermentation principles.
• He used nutrient broth to grow microorganisms.
• He founded the Pasteur Institute in Paris.
• Louis Pasteur is widely regarded as one of the founders of modern microbiology.

Pasteur’s major contributions include:

• Principles of fermentation.
• Pasteurization of milk.
• Sterilization techniques.
• Germ theory of disease.
• Vaccines against diseases such as anthrax, fowl cholera, and rabies.

John Tyndall (1820-1893)

• In 1877, John Tyndall gave a final blow to spontaneous generation.
• He observed that air containing germs and dust particles was visible, while air without dust particles and germs was invisible.
• He designed a chamber to demonstrate that germs are carried by dust.
• The chamber contained test tubes filled with sterile nutrient broth, and glycerol-coated surfaces trapped dust particles containing germs.
• No growth appeared when dust-free air entered the chamber.
• When dust-containing air was introduced, microbial growth appeared.
• He concluded that some bacteria exist in thermolabile and thermostable forms.
• His experiments demonstrated the presence of heat-resistant microbial forms, later understood to include bacterial endospores.
• He developed fractional sterilization, known as Tyndallisation.

Ferdinand Cohn (1828-1898)

• He confirmed the presence of endospores in bacteria.
• He discovered bacterial flagella and some bacterial pigments.

Robert Koch (1843-1910)

• Robert Koch was a German physician and bacteriologist.
• He provided direct evidence for the role of bacteria in causing disease.
• In 1876, he isolated Bacillus anthracis, the causative agent of anthrax.
• He developed methods for isolating bacteria in pure culture.
• He introduced solid culture media in 1881, initially using gelatin as a solidifying agent.
• He later used agar as a solidifying agent through the work of his assistants.
• He developed techniques for isolating bacteria and the streak plate technique.
• In 1882, he discovered Mycobacterium tuberculosis.
• He identified and characterized important bacterial pathogens, including the agents of anthrax, tuberculosis, and cholera, and established methods for linking microorganisms to specific diseases.
• He introduced staining techniques using aniline dyes.
• He described the hanging drop method for testing bacterial motility.
• He proposed Koch’s postulates, which became important guidelines for establishing the causative agent of an infectious disease.
• He observed a hypersensitivity reaction in guinea pigs already infected with tubercle bacilli when they were injected with tubercle bacilli or its protein. This reaction is called Koch’s phenomenon.

Koch’s Postulates

According to Koch’s postulates:

1. The microorganism should be constantly associated with the lesions of the disease.
2. It should be possible to isolate the organism in pure culture from the lesions of the disease.
3. The same disease must result when the isolated microorganism is inoculated into a suitable laboratory animal.
4. It should be possible to re-isolate the organism in pure culture from the lesions produced in the experimental animals.

An additional fifth criterion was introduced subsequently, stating that antibodies to the causative organism should be demonstrable in the patient’s serum.

Exceptions to Koch’s Postulates

It is not always possible to apply Koch’s postulates to all human diseases.

• Mycobacterium leprae and Treponema pallidum cannot be grown in vitro but can be maintained in animals.
• Neisseria gonorrhoeae has no animal model but can be grown in vitro.

Molecular Koch’s Postulates

Molecular Koch’s postulates were developed as a modification of Koch’s postulates by Stanley Falkow. They state that the gene coding for virulence should satisfy the criteria of Koch’s postulates rather than the microorganism itself.

Fanny Angelina Hesse (1850-1934)

• Fanny Angelina Hesse, one of Koch’s assistants, proposed the use of agar in culture media.
• Agar was superior to gelatin because of its higher melting and solidifying points and because most bacteria did not attack it.

Richard Petri (1852-1921)

• In 1887, Richard Petri developed the Petri dish, a container used for solid culture media.

The contributions of Robert Koch, Fanny Angelina Hesse, and Richard Petri made possible the isolation of pure cultures of microorganisms and stimulated progress in microbiology.

Development in Medicine and Surgery

Once scientists established that microbes caused disease, medical practices improved.

Joseph Lister (1827-1912)

• Joseph Lister was an English surgeon known for his contribution to antiseptic treatment and the prevention of wound infections.
• He concluded that wound infections were caused by microorganisms.
• In 1867, he developed a system of antiseptic surgery using phenol on surgical dressings.
• He also sprayed carbolic acid into the air of operating theatres to create an antiseptic environment.
• He introduced antiseptic techniques into surgery and demonstrated their value in preventing wound infections.
• He used carbolic acid during surgical procedures.
• His methods reduced wound infections.
• He was the first person to isolate Bacillus lactis in pure form in a liquid culture.
• Joseph Lister is known as the “Father of Antiseptic Surgery.”

Development of Vaccines

Vaccination was discovered before germ theory, but scientists did not fully understand its basis until the time of Pasteur.

Edward Jenner (1749-1823)

• Edward Jenner was an English physician.
• He observed that milkmaids who contracted the mild disease cowpox were subsequently protected from smallpox.
• On May 14, 1796, he demonstrated that inoculating people with material from cowpox lesions provided protection against smallpox.
• In 1798, he published his results on 23 successful vaccinators.
• The process became known as vaccination, based on the Latin word vacca, meaning cow.
• The use of material from cowpox lesions to protect against smallpox provided the foundation for vaccination.
• Jenner successfully developed the smallpox vaccine.
• Smallpox has since been eradicated.

Pasteur later applied the principle of vaccination to anthrax and rabies. He called attenuated cultures vaccines and the process vaccination.

Elie Metchnikoff (1845-1916)

• Elie Metchnikoff proposed the phagocytic theory of immunity.
• He discovered that some white blood cells protect against disease by engulfing disease-causing bacteria.
• These cells were called phagocytes and the process was called phagocytosis.
• His work established the concept of cellular immunity.
• He is associated with the discovery of phagocytosis and phagocytes.

Development of Chemotherapeutics, Antitoxins and Antibiotics

Emile Roux and Alexandre Yersin

• They demonstrated the production of toxin in filtrates of broth cultures of the diphtheria organism.

Emil von Behring and Shibasaburo Kitasato

• Both were colleagues of Robert Koch.
• In 1890, they discovered tetanus antitoxin.
• Von Behring also reported immunization against diphtheria using diphtheria antitoxin.
• The discovery of toxin-antitoxin relationships contributed to the development of immunology.

Paul Ehrlich (1854-1915)

• He was the first to report the acid-fast nature of the tubercle bacillus.
• He developed techniques to stain tissues and blood cells.
• He proposed a toxin-antitoxin interaction called the Ehrlich phenomenon.
• He introduced methods of standardizing toxin and antitoxin.
• He proposed the side-chain theory for antibody production.
• In 1904, he found that Trypan Red was active against trypanosomes causing African sleeping sickness.
• He introduced the concept of the “magic bullet.”
• In 1910, in collaboration with Sakahiro Hata, he introduced Salvarsan (arsenobenzol) for the treatment of syphilis caused by Treponema pallidum.
• His work laid important foundations for chemotherapy.
• Paul Ehrlich is known as the “Father of Chemotherapy.”
• The bacterial genus Ehrlichia was named after him.

Gerhard Domagk (1895-1964)

• In 1935, Gerhard Domagk experimented with synthetic dyes.
• He reported that Prontosil, a red dye used for staining leather, was active against pathogenic streptococci and staphylococci in mice.
• Jacques and Therese Trefouel showed that Prontosil was broken down in the body to sulfanilamide, the true active factor.
• Domagk received the Nobel Prize in 1939 for the discovery of the first sulfa drug.

Alexander Fleming (1881-1955)

• Alexander Fleming was a Scottish physician and bacteriologist.
• In 1928, he discovered the antibiotic penicillin.
• He had been interested in finding substances that could kill pathogens, particularly because of his work on wound infections during World War I.
• Penicillin was discovered when a bacterial culture became contaminated with a fungal colony and the bacterial colonies around the fungus showed poor growth.
• The antibacterial compound was named penicillin.
• Penicillin became widely used to treat bacterial infections.

Selman Waksman (1888-1973)

• Selman Waksman and Albert Schatz discovered streptomycin in 1943, and it was reported in 1944.
• Streptomycin was used in the treatment of tuberculosis caused by Mycobacterium tuberculosis.
• Waksman received the Nobel Prize in 1952 for his discovery of streptomycin.

By 1950, other microorganisms producing antibiotics had also been identified:

• Chloramphenicol from Streptomyces venezuelae by Paul R. Burkholder in 1947.
• Aureomycin from Streptomyces aureofaciens by B. M. Dugger in 1948.
• Terramycin from Streptomyces rimosus by Finlay, Hobby, and collaborators in 1950.

By the early 20th century, microbiology had expanded into specialized fields including bacteriology, immunology, virology, microbial physiology, and microbial genetics.

Other Important Contributors in Microbiology

Hans Christian Gram (1853-1938)

• In 1884, Hans Christian Gram developed the Gram staining method.
• The method differentiates bacteria into Gram-positive and Gram-negative bacteria.
• It is an important staining procedure used to identify bacteria.

Sergei Winogradsky (1853-1953) and Martinus Beijerinck (1851-1931)

• They demonstrated the importance of microorganisms in biogeochemical cycles such as carbon, nitrogen, and sulfur cycles.
• Winogradsky developed a column that demonstrated different microenvironments and showed sites where different microorganisms grow.

Beadle (1903-1989) and Tatum (1909-1975)

• Their work with mutants of the fungus Neurospora established a connection between microbiology and genetics.
• They proposed the one gene, one enzyme hypothesis.

Embden, Meyerhof, and Parnas

• They discovered the important enzymatic pathway involved in the breakdown of glucose into pyruvate.
• This metabolic pathway is known as glycolysis.

Max Delbrück and Salvador Luria

• They analyzed mutations in bacteria and provided a foundation for microbial genetics.

Frederick Griffith (1877-1941)

• He performed experiments to identify the transforming principle in organisms.
• He showed that bacteria can transform genetic material through the process of transformation.

Avery, McLeod, and McCarty

• They studied transformation in Streptococcus pneumoniae.
• They confirmed that DNA, rather than protein, was the transforming principle.
• Their discovery contributed to major advances in genetics.

Rosalind Franklin (1920-1958)

• She performed X-ray crystallography to study the structure of DNA.
• Her work provided major clues about the structure of DNA.

James Watson and Francis Crick

• In 1953, they published a paper describing the structure of DNA.
• They described DNA as having a double-helix structure.

Meselson and Stahl

• Through a series of experiments, they demonstrated the semiconservative replication of DNA.
• Their discovery provided evidence for the mechanism of DNA replication.

Kary Mullis (1944-2019)

• Kary Mullis discovered the polymerase chain reaction (PCR).
• PCR allows DNA to be amplified to produce multiple copies.
• The process can be performed over a short period and is widely used.

Development of Microbiology in the 20th Century: Era of Molecular Biology

By the end of the 19th century, microbiology had developed into an established branch of biology.

In later years, microorganisms became ideal tools for studying various life processes. Their relative simplicity, short life span, and genetic homogeneity provided useful models for understanding physiological, biochemical, and genetic processes.

Molecular biology made major advances in understanding the genetic code, DNA regulation, and RNA translation into proteins. Researchers increasingly used bacterial cells to study these processes, revealing many principles of genes and enzymes.

Major Discoveries and Milestones in the History of Microbiology

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