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History of Microbiology

History of Microbiology

Microorganisms are so minute that they cannot be seen clearly with the human eye, hence before the development of microscopes, the presence of the microbial world was unknown.

Zacharias Jansen unintentionally discovered the telescope and microscope’s basic operating principles in 1609. (Dutch spectacle maker).

Professor Athanasius Kircher was the first to use the microscope in medicine (1602- 1680).

He analysed the blood of plague patients and, using a microscope, discovered innumerable masses of tiny worms that were unseen to the naked eye. He said that the plague’s primary causes were these worm-like entities.

English physicist Robert Hooke (1635–1703) used a straightforward lens to magnify objects in 1665. Slices of cork from an oak tree’s bark were studied by him.

He observed that the cork was made of tiny boxes that he referred to as ‘cells’. The credit for developing a compound microscope with multiple lenses and describing the world of microbes goes to Robert Hooke.

Antony Van Leeuwenhoek (1632-1723) was the greatest of all microscopists. He made many observations through the microscope. Leeuwenhoek’s microscope consists of a spherical lens mounted between two small metal plates. The culture or specimen was placed on the point of a blunt pin attached to the back plate and was brought into focus by manipulating the screw.

He was the first to observe and accurately describe the shape of human red blood cells as well as the little agents of disease ‘animalcules’.

He took the scarf from the root of the decayed tooth and mixed it with clean rainwater and saw the mobility in animalcules. In 1683, he described and sketched different forms of animalcules such as rods, spheres, and spiral shapes which are nothing but the morphological forms of bacteria. This was the first recorded observation of bacteria.

He discovered major classes of bacteria, protozoa, algae, yeasts, erythrocytes, and spermatozoa.

Antony Van Leeuwenhoek, (Dutch merchant) had little formal education but his keen interest in nature made him examine a variety of materials. Glass grinding and preparation of lenses was his hobby and this led him to assemble 250 simple microscopes.

He often used a magnifying glass to study the weaves of the various types of cloth. He observed and measured a large number of minute living organisms, including bacteria and protozoa, and communicated this to the Royal Society of London in 1684.

He discussed his research on the bacteria that acetic acid inhibits in his letter from 1684. In the form of a protracted string of letters written in Dutch, Leeuwenhoek communicated his discoveries to the Royal Society. The Proceedings of the Royal Society received and published the majority of these letters in English.

1. Contributions of Louis Pasteur

  • The credit for providing a foundation for bacteriology as science goes to Louis Pasteur (1822-1895), the French organic chemist.

Louis Pasteur was the first scientist who demonstrated that air contains microscopically observable organized structures. He passed a large quantity of air through a tube that contained a plug of guncotton to serve as a filter. The guncotton was then removed and dissolved in a mixture of alcohol-ether and the sediment was examined microscopically. He found that this sediment contained not only organic matter but also a large number of small microorganisms.

He performed a series of experiments to prove that although microorganisms were present in the air they were not spontaneously produced. Pasteur took boiled meat and infused it with several swan-neck flasks .

The flask’s apertures were fully accessible to the air, but they were curved such that any flying dust particles would fall to the lower portion of the neck due to gravity. After sterilising the soup with heat, the flasks were placed in an incubator. Despite the contents of the flasks being exposed to air, no growth took place.

History of Microbiology

Due to the dust and bacteria being trapped on the walls of the curved necks, Pasteur noted that no growth occurred; however, if the necks were cut off so that the dust dropped directly into the flask, microbial growth started right away.

Pasteur demonstrated that bacteria do not spontaneously arise from inanimate substances in 1861, putting an end to the debate between spontaneous generation and biogenesis.

Pasteur also showed that microorganisms are not evenly distributed in the atmosphere and that their number varies from place to place. For this experiment, he took a large number of sealed flasks containing boiled and cooled infusions and opened a few at a time, for a short period, at various places and then resealed them.

Out of the 20 flasks which he opened and resealed on a dusty road, 8 showed spoilage, while out of the 20 that he opened on the top of a mountain, only 5 showed spoilage and out of the 20 that he opened near a glacier, only 1 showed spoilage. After incubation, only those flasks carrying micro-organisms from the air showed growth and spoilage. From these experiments, Pasteur concluded that air contained microorganisms, and their number varied from place to place.

Pasteur made an intensive study of beer and wine fermentation. He found that wine spoilage was caused by the growth of undesirable contaminating microorganisms. After some experimentation, he showed that wine did not undergo spoilage if it was held for a few minutes at 50 to 60°C. This gave rise to the new process of preserving wine, fruit juices, milk, etc., and was called ‘Pasteurisation’.

Pasteur studied several other fermentation processes and showed that not only each type of fermentation was accomplished by a specific type of microorganism but also that each fermentation required specific environmental conditions.

He showed that the agent responsible for alcoholic fermentation could flourish in an acid medium while microorganisms for lactic fermentation could grow best only at a neutral pH. During the studies on butyric acid fermentation, Pasteur discovered the existence of life in the absence of oxygen. He reasoned that oxygen was inhibitory to the growth of butyric acid bacteria.

Pasteur also found that many other microorganisms, including yeast, could grow either in the presence or in the absence of oxygen. He designated life in the presence of oxygen as ‘aerobic’, in the absence of oxygen as ‘anaerobic’, and in the presence or absence of oxygen as ‘facultative anaerobic’.

By claiming that boiling made the fluids sterile, Pasteur established the field of sterilisation. He soon discovered that even after boiling, regular water still contained some germs. Pasteur established the process of sterilising fluid material by heating it to 120°C under pressure (autoclave). He also popularised the technique of dry heating glassware to 170°C for sterilisation. Many other researchers paid great attention to Pasteur’s accomplishments in sterilising.History of Microbiology History of Microbiology History of Microbiology History of Microbiology History of MicrobiologyvHistory of Microbiology History of Microbiology

Tyndall conducted an important experiment and found that when bacteria were dormant, they were relatively resistant to boiling when they were actively growing. He popularised the process of sterilising through repeated heating with timed intervals. Tyndallization is the term for this technique.History of Microbiology

In 1880, Pasteur isolated the bacterium responsible for chicken cholera and grew it in pure culture. But on the day of his public demonstration, he failed to repeat his experimental results. The chicken survived after injecting the isolated bacterial culture and this result surprised him. In subsequent experiments, he concluded that on long preservation or subculturing, the virulence power of the pathogenic bacteria was destroyed.History of Microbiology

Such microbial culture with decreased virulence was referred to as attenuated culture. Such attenuated culture does not cause infection but induces immunity in the host.History of Microbiology

Pasteur further introduced a vaccine for anthrax and rabies. He knew that the causative agent of rabies attacked the brain and spinal cord. He took spinal cords from rabbits that died from the disease and suspended these cords in dry sterile air. Through this process, the rabies microorganisms in the nervous tissue lost their virulence and the emulsion of the spinal cord was used as a vaccine. It was found to be effective in dogs. Joseph Meister was the first boy cured of rabies by this vaccine.History of Microbiology

2. Robert Koch and Anthrax

  The first direct demonstration of the role of bacteria in causing the disease was provided by Robert Koch (1843-1910).

He was a German physician, who first isolated Bacillus anthracis, the causative agent of anthrax. His method of preparing, fixing, and staining film preparation of bacteria using aniline dyes, opened a new area in bacteriological techniques. In 1881, he described his method of preparing cultures on solid media, and the isolation of pure strains of bacteria from single colonies was made possible.

Till 1881, solid media using potato and gelatin were in practice for the isolation of fungi. Robert Koch added nutrient agar, a solid transparent medium for the isolation of bacteria.History of Microbiology

In 1882, he discovered Mycobacterium tuberculosis, and in 1883 Vibrio cholera. In 1905, Koch was awarded the Nobel Prize in Medicine for this discovery. “Koch phenomenon’ is the immunity to the second infecting dose of the tubercle bacillus. Koch was Director of the Prussian Institute of Infectious Diseases which was eventually renamed The Robert Koch Institute.History of Microbiology

Their most notable contribution of Koch was the establishment of the causal relationship between microorganisms and a specific disease by applying a set of criteria referred to as Koch’s postulates. According to these postulates, a microbe may be accepted as a causative agent of an infectious disease only if it satisfies the following conditions.History of Microbiology

The postulates are:

  1. The microorganisms must be present in every case of the disease.
  2. The microorganisms must be isolated from the diseased animal and grown in pure culture.
  3. The disease must be reproduced when a pure culture of the microorganisms is inoculated into a susceptible host.
  4. The same microorganism must be reisolated from the experimentally infected host.

3. Germ Theory of Disease

Pasteur investigated silkworm disease and proved that the disease was due to a protozoan parasite. Even before Pasteur had proved by experiments that bacteria are the causative agent of some diseases: Girolamo Fracastoro 1546 wrote a treatise in which he said the disease was caused by minute “seed” and was spread from person to person. In 1762, Von Plenciz not only stated that living agents are the cause of diseases but suspected that different germs were responsible for different diseases. The first man to present real evidence that living organisms were the cause of the disease was Augustino Bassi (1773-1856). In 1836, he demonstrated that a fungus that caused disease in silkworms could be transmitted from one silkworm to another silkworm.

Lord Joseph Lister (1827-1912), a famous English surgeon in 1867, introduced antiseptics for the prevention and cure of wound infections. He developed a system of antiseptic surgery designed to prevent microorganisms from entering wounds by the application of phenol on surgical dressings. He also heats and sterilized the instruments to be used during surgery. Joseph Lister was the first to introduce aseptic techniques for the control of microbes by the use of physical and chemical agents. Because of his important contributions, Lister is known as the father of antiseptic surgery.History of Microbiology History of Microbiology History of Microbiology History of Microbiology

The confirmed evidence that microorganisms cause disease, came from experiments performed by Robert Koch. The proofs which support the Germ theory of disease became ‘Koch Postulates’. Richard Petri, Koch’s assistant designed a special plate for old solid culture media. This plate has great significance in microbiology and is referred to as the Petri plate’. The period from 1857 to 1914 is considered the ‘golden age of microbiology’ Because the most significant advances made during this period led to the establishment of microbiology as a science.History of Microbiology

4. Discovery of Chemotherapeutic Agents

Paul Ehrlich (1854-1915) 1904 found that the dye Trypan red was active against the trypanosome that causes African sleeping sickness. This dye with antimicrobial activity was referred to as a ‘magic bullet’. Subsequently, in 1910, Ehrlich in collaboration with Takahiro Hata, a Japanese physician, introduced the drug Salvarsan (arsenobenzol/ 606 arsenic) as a treatment for syphilis caused by Treponema pallidum.History of Microbiology

Ehrlich continued his experimentation until in 1912 he discovered neosalvarsan. This gave him the title “the father of chemotherapy. He coined the word ‘chemotherapy’ meaning the treatment of infectious diseases with chemicals that are antagonistic to the pathogen without damaging the host.History of Microbiology

Ehrlich tested new dyes and aniline pigments as histological stains and showed that all dyes can be classified as acidic, basic, or neutral. He developed differential staining methods. for red and white blood cells laying the foundation of hematology.History of Microbiology

In 1882, Ehrlich developed a staining procedure to demonstrate the acid-fast property of tubercle bacilli which is known as the Ziehl- Nelson staining technique. Ehrlich propounded a new theory in the field of immunology, explaining the production of antibodies that he quantified in various sera and formulated the standardization of antitoxin into units related to a fixed and invariable standard. In 1908, Paul Ehrlich received the Nobel Prize in Medicine for his studies on immunity.