Discovery of Microorganisms
The advent of the microscope permitted the studying of microorganisms. The first microscopes were simple ground glass lenses that magnified images of previously unseen microorganisms. Among the first to observe this previously unseen and invisible microbial world were Robert Hooke and Anthony Van Leeuwenhoek.
1. Robert Hooke (1635-1703), an English mathematician and natural historian.
. He coined the term “cells” to describe the “little boxes” he
observed in examining cork slices with a compound
microscope.
. He was the first to make a known description of microorganisms.
. He made microscopic observation and the earliest description of many fungi.
. Various species of fungi were clearly identified in his
drawing and recorded in his book Micrographia.
Figure 2.1: Robert Hooke’s detailed diagram of fungi made in 1667
Source: Microorganisms in our World by Atlas R. M. (1995)
2. Anthony Van Leeuwenhoek (1632-1723) lived in Delft, Holland. . He is known as the father of bacteriology and the first
person to publish extensive and accurate observations of microorganisms.
. He was a draper and an amateur microscope builder.
. He learned lens grinding as a hobby and made over 100
simple microscopes each capable of magnifying an image about 300 times.
. By using simple microscopes, he observed microscopic
organisms which he called ‘animalcules’ .
. He discovered bacteria in 1676 while studying pepper
water infusion and reported his observations in a series of letters to Royal Society of London which published them
in 1684 in English translation.
. He made sketches of the different shapes of bacteria.
(A) (B) (C)
Figure 2.2: (A) Anthony van Leeuwenhoek (1632-1723) (B&C) Leeuwenhoek’s microscopes.
Source: Microorganisms in our World by Atlas R. M. (1995)
After Van Leeuwenhoek’s death, the study of microbiology did not develop rapidly because microscopes were rare and interest in microorganisms was not high. Scientists then were debating the theory of spontaneous generation.
The Spontaneous Generation Conflict
The concept spontaneous generation states that living organisms could develop from non-living matter. The proponents of the concept of spontaneous generation claim that living organisms could develop from non living or decomposing matter.
1. Francesco Redi (1626-1697) challenged this concept by showing that maggots on decaying meat came from fly eggs deposited on the meat, and not from the meat itself.
. He carried out a series of experiments on decaying meat
and its ability to produce maggot spontaneously.
He placed meat in three different containers, one was not
covered, and the second was covered with fine gauze to exclude flies.
. Flies laid eggs on the uncovered meat and maggots
developed.
. The two other meats did not produce maggots.
. Spontaneously, flies were attracted to the gauze-covered
container and laid their eggs on the gauze, these later produced maggots.
. Hence, it become evident that the generation of maggots
resulted from the presence of fly eggs and that meat (a non-living matter) did not spontaneously generate maggots as previously believed.
2. Louis Jablot (1670) conducted an experiment in which he divided a hay infusion that had been boiled into two containers: a heated container that was closed to the air and a heated container that was freely open to the air. Only the open vessel developed microorganisms. This further helped to disprove abiogenesis.
3. John Needham (1713-1781) showed that mutton broth boiled in flasks and then sealed could still develop microorganisms, which supported the theory of spontaneous generation.
4. Lazzaro Spallanzani (1729-1799) showed that flasks sealed and then boiled had no growth of microorganisms, and he proposed that air carried germs to the culture medium. He also commented that external air might be needed to support the growth of animals already in the medium. The latter concept was appealing to supporters of spontaneous generation.
5. Louis Pasteur (1822-1895) was a Professor of Chemistry. He devised a series of swan necked flasks known as Pasteur-flasks, filled the flasks with broth and heated the broth to sterilisation. After cooling, the flasks were opened to the air, but bends on the neck of the flasks prevented microorganisms from falling on the broth and contaminating it rather the microorganisms fell on the neck of the bottle. Pasteur proved that no growth occurred because dust and germs were trapped on the wall of the curved necks. If the neck were broken, growth will occur. By these experiments he disproved and defeated the theory of spontaneous generation.
Figure 2.3: Pasteur’s experiment with the Swan-Necked bottles that defeated the spontaneous generation theory.
Source: Amoebamike, wordpress.com
Apart from the defeat of the concept of spontaneous generation Pasteur’s contribution in microbiology included:
. Pasteurization: an effective sterilization method which involve
holding juices and milk at 62.8°C (145°F) for 30 minutes.
. The discovery of the fact that, alcoholic fermentation was indeed
a process catalyzed by yeast cells.
. The development of vaccines for the control of anthrax, fowl
cholera and rabies diseases between 1880 and 1890.
. The establishment of Pasteur Institute in 1888 in Paris, in
recognition of his research on rabies by the French government. It was originally established as a clinical centre for treating rabies, but is now a major biomedical research centre for antiserum and vaccine production.
. He postulated the Germ Theory of Disease which states that
microorganisms are the cause of infectious diseases.
. His work ushered in the Golden Age of Microbiology.
The Recognition of the Role of Microorganisms In Disease
1. Joseph Lister (1872-1912) developed a system of surgery designed to prevent microorganisms from entering wounds. He implemented the use of sterile surgical instrument, and used carbolic acid (phenol) during surgery and on wound dressings.
2. Robert Koch (1843-1910) was a German physician. He was the first to directly prove the role of microorganisms in causing diseases. He established the relationship between Bacillus anthracis and the disease it causes, anthrax. Using mice as experimental animals, he demonstrated that when a small amount of blood from a diseased mouse was injected into a healthy mouse, the healthy mouse quickly developed anthrax. From this work he developed Koch’s postulates which states that:
i. The suspected disease-causing organism should be present
in all cases of the disease and absent from healthy animals.
ii. The suspected organism must be cultivated in a pure
culture away from the animal body.
iii. The isolated organism must cause the disease when inoculated into a healthy susceptible animal. iv. The organism must be re- isolated from these experimental
animals and culture again in the laboratory after
which it should still be the same as the original organism.
Figure 2.4: Diagrammatic illustration of Koch’s Postulates
Using these principles, Koch discovered causative organisms of anthrax (1876), tuberculosis (1882) and cholera (1883).
. He was the first to grow bacteria on solid culture media to get
pure culture; hence he developed the pure culture concept and
developed different solid media.
. Koch’s discovery of solid culture media and pure culture concept
supplied the most needed tools for the development of microbiology as a field of science.
For his contribution on tuberculosis, he was awarded the 1905
Nobel Prize for Physiology or Medicine. Today, “Molecular Koch’s postulates” have been established in light of advances in the molecular biology of pathogenic microbes.
3. Edward Jenner (ca. 1798) used a vaccination procedure to protect individuals from smallpox. 4. Emil Von Behring (1854-1917) and Shibasaburo Kitasato (1852-1931) induced the formation of diphtheria tetanus antitoxins in rabbits which were effectively used to treat humans, thus demonstrating humoral immunity.
The Development of Microbiology in this Century
Microbiology established a closer relationship with other disciplines during the 1940s because of its association with genetics and biochemistry.
1. George W. Beadle and Edward L. Tatum (ca. 1941) studied the relationship between genes and enzymes using the bread mould, Neurospora.
2. Salvadore Lurai and Max Delbruck (ca. 1943) showed that mutations were pontaneous and not directed by the environment.
3. Oswald T. Avery, Colin M. Mcleod, and Maclyn McCarty (1944) provided evidence that deoxyribonucleic acid (DNA) was the genetic material and carried genetic information during transformation.
Era of Molecular Microbiology
This Began in the 1970s with the following:
. Advancement in the knowledge of bacterial physiology, biochemistry and genetics.
. Genetic manipulation which involves the transfer of DNA from
one organism into another or a bacterium and the proteins encoded by the DNA harvested led to the development of the
field of Biotechnology.
. DNA sequencing revealed the phylogenetic (evolutionary) relationships among bacteria which led to revolutionary new concepts in microbial systematic.
. In 1990s, DNA sequencing gave birth to the field of genomics.
SELF-ASSESSMENT EXERCISE
Observe a decay meat under the microscope and discuss your findings in the discussion forum.
CONCLUSION
To conclude, the history of microbiology from 19th century to date has been rich with contributions of many scientists who developed the field to what it is today. It is imperative to you as nursing students to know these personalities and acknowledge their various individual contributions towards the development of microbiology
SUMMARY
In this unit you have been exposed to the circumstances that lead to the discovery of microorganisms, the spontaneous generation conflict, recognize the role of microorganisms in disease causation, the development of microbiology in this century and the era of molecular microbiology.
TUTOR-MARKED ASSIGNMENT
1. Write short note on Robert Hooke and Anthony Van Leeuwenhoek contribution to the discovery of microorganisms (LO1)
2. State the concept of spontaneous generation (LO2)
3. Discuss the experiments that were performed to disprove the concept of spontaneous generation (LO2).
4. Explain the steps involved in using Koch’s postulate to establish the link between a suspected microorganism and a disease (LO3).
5. Explain development of microbiology in this century (LO4).
6. Explain the era of molecular biology (LO5).
REFERENCES /FURTHER READING
Atlas, R.M. (1995). Microorganisms in Our World. Mosby Year Book. Inc.
Kayser, F.H., Bienz, K.A., Eckert, J. & Zinkernagel, R.N. (2005). Kayser, Medical Microbiology. Thieme, Stuttgart, Germany
Markey, B., Leonard, F., Archambault, M., Cullinane, A. & Maguire, D. (2013). Clinical Veterinary Microbiology. 2nd Edition. MOSBY ELSEVIER
Medigan, M.T. et al. (2009). Brock Biology of Microorganisms. 12th Edition. Pearson Education Inc. Pelczar, M.J., Chan, E.C.S. & Krieg, R.N. (2001). Microbiology. 5th Edition. McGraw-Hill.
Mitchell, R. & Gu, J.-D. (editors) (2010). Environmental Microbiology. 2nd Edition. Hoboken, New Jersey, John Wiley & Sons, Inc, Wiley-Blackwell
Struthers, K. (2017). Clinical Microbiology. 2nd Edition. CRC Press, Taylor & Francis Group.
Talaro, K.P. & Talaro, A. (2002). Foundations in Microbiology. 4th Edition. The McGraw-Hill Companies.
Willey, J.M., Sherwood, L.M & Woolverton, C.J. (2008). Microbiology. 7th Edition. Boston Bur Bridge, IL: McGraw-Hill Higher Education.
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