Zacharias Janssen (1570-1638)
- Dutch spectacle maker
- He invented 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 1660’s modified the basic design of the microscope and developed a compound microscope that was six inches long and had two convex lenses which very much resembles the design of the modern microscope.
- He observed specimens of various things under the microscope such as the leaves, thin specimens of cork, hair of peacock, seaweed, wood, sponges, etc.
- He described the repetitive rectangular box-like structures as “cell”
- In 1665 he published his observations in his Micrographia
- He described the forms of fungi such as bluish mold on a piece of leather and one of the leeches in vinegar
- The descriptions by Hooke can broadly classify the white mold as Mucor.
Antony van Leeuwenhoek (1632-1723)
- He was a self-made scientist and explores in Delft, Holland.
- He was not the first person to observe microscopic forms but probably the first one to report it.
- Antony Van Leeuwenhoek is known as the Father of Microbiology
- He made 419 lenses and more than 250 microscopes. The highest magnification at which he observed was 200-300 times.
- He observed a variety of things like sperms of animals, blood, cork, leaves, scrapings from his teeth, and many more.
- In a series of his letters written to the British Royal Society he carefully recorded his observations and descriptions. In one of his letters, he described the tiny creatures as ‘animalcules’.
- He also described the shapes of bacteria in these letters. In 1683 he published a sketch of the principle shape of bacteria, rods, cocci, and spiral-shaped.
Van Helmont (1580-1644)
- He experimentally supported abiogenesis by devising a method that produced mice.
- He placed dirty material in a vessel containing cheese, wheat and incubated this 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 and opposed the theory of abiogenesis.
- He performed a 3 jar experiment to disprove abiogenesis.
- He placed pieces of rotten meat in 3 jars. He covered one jar with parchment paper, the other with fine mesh or gauze, and the third jar was left open.
- The jar left uncovered showed maggots and attracted flies, whereas the jars covered did not show maggots or flies in the jar but eggs were laid on the parchment paper and the gauze.
- Experiment by Redi could not completely prove that microbial life does not originate spontaneously but it proved that entry of flies and eggs in the jars can lead to the formation of life and life cannot be created spontaneously.
Louis Joblot (1645-1723)
- He performed experiments in which he observed that hay when infused with water and allowed to stand for a few days shows the growth of microorganisms.
- He boiled the infusion and divided it into two vessels. One vessel was covered and placed in a cupboard, the other was left open.
- The covered vessel did not show any growth upon standing but the uncovered vessel showed growth within a few days. When he opened the covered vessel, it showed growth after some time.
- Hence he 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 conducted an experiment in which he boiled the meat broth in a corked flask and upon standing for a few days he observed growth in the flask. He concluded that this was due to spontaneous generation.
- This result was due to insufficient boiling of the broth and hence it failed to kill the heat-resistant spores in the broth.
Lazzaro Spallanzani (1729-1799)
- He repeated the experiment of John Needham but arrived at an opposite end.
- He boiled the meat infusion for a longer period and sealed the flask in the flame.
- Upon keeping the flask for a few days he did not find any growth in the flask. He examined the meat broth from various flasks.
- He argued that prolonged boiling destroyed the heat-resistant spores, and to prove this he opened the sealed flask and exposed it to air. Within a short time, the opened flask showed growth in the broth.
- He performed experiments to disprove the theory of abiogenesis.
- He passed air through his infusion broth after passing it through caustic potash or sulphuric acid and aspirated the flask daily for 3 months.
- At the end of 3 months, no microbial growth was observed in the flask.
- He was also an opponent of abiogenesis.
- He passed the air into his infusion broth through red hot tubes and proved that growth was absent in the broth.
H. Schroder and Von Dusch
- In 1854 these two scientists performed similar experiments in which air was filtered through cotton wool.
- This method prevented microbial growth in boiled infusions. This concept is used even today in the labs.
- The non-absorbent cotton is used as a stopper for test tubes so that air entering will be sterile.
Louis Pasteur (1822-1895)
- To disprove the theory of spontaneous generation Louis Pasteur in 1862 designed a special flask with a long neck called ‘Swan necked Flask’ or ‘S-shaped flask.
- He placed the nutrient medium and boiled it to ensure sterilization. Though the flask was kept open no growth was seen in the medium due to the long neck.
- Later when the neck of the flask was cut open, the nutrient broth was exposed to air soon microbial growth was seen in the nutrient medium.
- He was also the first person to use gun cotton for filtration.
- In 1877 Louis Pasteur discovered the anaerobic bacteria during his study on butyric acid fermentation.
- He also solved the problem of the souring of wine due to the presence of bacteria in France. He proposed boiling the fruit juice to kill contaminants. This process is known as ‘Pasteurisation’.
- He discovered microorganisms called ‘Yeast’ which are responsible for the conversion of sugar into alcohol.
- He discovered the principle of active immunization in 1880.
- He isolated the causative agent of chicken chlorella (Pasturela spp) and after his experiments, for several weeks he concluded that the older cultures lose their ability to cause disease which is known as pathogenicity or virulence, but it stimulates the host to produce certain substances which may protect the host against subsequent exposure to the pathogen.
- Pasteur also prepared an attenuated rabies vaccine and tried it on a young boy which protected him from rabies.
John Tyndall (1820-1893)
- In 1877 the final blow to the spontaneous generation was given by physicist John Tyndall.
- While studying optical properties he observed that the air containing germs and dust particles was visible while the air that does not have dust particles and germs is invisible.
- He also designed a chamber to prove that germs are carried by dust.
- The chamber contained a rack of test tubes filled with sterile nutrient broth. The inner parts of the chamber were coated with glycerol to trap the dust particles containing germs.
- This system was allowed to stand for several days and no growth was seen in the test tubes. This could have been due to dust-free air.
- When dust containing air was introduced into the chamber microbial growth appeared in a brief period.
- Tyndall also concluded that some bacteria exist in two phases- thermolabile and thermostable.
- His observations stated that the thermolabile forms can be destroyed by significant boiling while thermostable forms are resistant to heat. This confirmed the presence of endospore in certain bacteria.
- He also developed a method of fractional sterilization known as Tyndallisation.
Ferdinand Cohn (1828-1898)
- He confirmed the presence of endospores in bacteria.
- He also discovered bacterial flagella and some bacterial pigments.
Robert Koch (1843-1910)
- A German bacteriologist is known for the isolation of microorganisms causing Anthrax and Tuberculosis.
- He also developed solid media for culturing bacteria and various techniques to isolate bacteria.
- He developed the streak plate technique to isolate bacteria.
- The postulates given by Koch proved as guidelines to identify the causative agent of an infectious disease.
Joseph Lister (1827-1912)
- He is known as the Father of Antisepsis developed antiseptic surgical procedures.
- He used carbolic acid for antiseptic surgical procedures.
- This reduced the rate of wound infections.
- He was the first person to isolate bacteria (Bacillus lactis) in pure form in a liquid culture form.
Paul Ehrlich (1854-1915)
- He discovered a synthetic drug, arsenic chemotherapeutic derivative ‘Salvarsan’ known as ‘Magic bullet’.
- The drug was effective against Syphilis.
Hans Christian Gram (1853-1938)
- He developed the most important staining method in 1884 to visualize bacteria known as Gram Staining.
- Based on the differences in the peptidoglycan content in the cell wall of bacteria, they acquire different colors.
- Bacteria are differentiated into Gram-Positive (Violet) and Gram-negative (Pink) by the staining procedure.
- It is the basic staining procedure used to identify bacteria.
Alexander Fleming (1881-1955)
- In 1928 discovered the antibiotic Penicillin which has been extensively used since then.
- He discovered that this was effective against several Gram-positive bacteria which caused diseases like gonorrhea, scarlet fever, and many more.
Edward Jenner (1749-1823)
- The concept of vaccination was invented by this British physician.
- He successfully developed a vaccine against smallpox and today smallpox has been eradicated from society.
S. Winogradsky (1853-1953) and M.W. Beijerinck (1851-1931)
- They discovered the importance of microbes in biogeochemical cycles like carbon, nitrogen, and sulfur cycles.
- Winogradsky also developed a column that demonstrated the various microenvironments and showed different sites in which different microorganisms grow.
Beadle (1903-1989) and Tatum (1909-1975)
- With the discovery of mutants from the fungus Neurospora by Beadle and Tatum the connection between microbiology and genetics was established.
- They also put forward the one gene, one enzyme hypothesis.
Embden, Meyerhof, and Parnas
- The important enzymatic pathway of the breakdown of glucose into pyruvate was discovered by them.
- The metabolic pathway is known as Glycolysis.
Elie Metchnikoff (1845-1916)
- In 1892 Elie Metchnikoff discovered the process of phagocytosis and the phagocytes.
- This was an important discovery in the clinical microbiology sector.
Delbruck and Luria
- They analyzed the mutations in bacteria and provided a base for microbial genetics.
Frederick Griffith (1877-1941)
- He performed experiments to identify the transforming principle in organisms.
- He showed that bacteria can transform the genetic material through the process of transformation.
Avery, McLeod, and McCarty
- They discovered the process of transformation in Streptococcus pneumoniae and confirmed that the transforming principle in organisms is the DNA and not protein.
- After this discovery, great advancement was seen in the field of genetics.
Rosalind Franklin (1920-1958)
- She was the first person to perform X-Ray crystallography for identifying the structure of DNA.
- The major clues for the structure of DNA were discovered by her.
James Dewey Watson (1928) and Francis Harry Compton Crick (1916-2004)
- They published a brief paper describing the structure of DNA in 1953.
- They described that the genetic material – DNA has a double helix structure.
M. Meselson (1930) and F. Stahl (1929)
- Through the series of experiments they discovered the semi-conservative replication process of DNA.
- This discovery proved the hereditary observed in organisms.
Kary Mullis (1944-2019)
- He discovered a method to amplify the DNA and develop multiple copies by using the process of PCR (Polymerase Chain Reaction).
- This process is widely used and can be performed over a short period.
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