Microbiology is a science that deals with the study of living organisms that can not be seen by the naked eye. These can be seen with the aid of microscopes, which magnify objects. Many scientists contributed to the science of microbiology.
Louis Pasteur (1822-1895)
Louis Pasteur was a French chemist and a crystallographer. His contribution to microbiology is so great that he is considered to be the “ Father of Microbiology”.
Contribution to science as a chemist
He was working with tartaric acid crystals. He could pick up the dextro and levo rotatory crystals by seeing the morphology of the crystals. Later he was called to solve some of the problems in fermentation industry and turned his attention to biological process of fermentation.
Contribution to wine industry
1. He discovered that alcohol production from grape juice was due to Yeast
2. He found out that large amounts of lactic acid production was due to the presence or contamination of rod shaped bacteria.
3. He observed that the process of alcohol production i.e. FERMENTATION took place in the absence of air.
4. He coined the terms aerobic to describe those organisms requiring air and anaerobic to describe those organisms which do not require air for their growth.
Contribution to modern microbiology
Pasteur disproved the theory of spontaneous generation. The theory proposed that living organisms originated spontaneously, particularly from decaying organic matter. He disproved it.
Pasteur’s swan neck flask
Pasteur poured meat infusions into flasks and then drew the top of each flask into a long curved neck that would admit air but not dust. He found that if the infusions were heated, they remained sterile (free from any growth) until they were exposed to dust. He opened them on a dusty road and resealed them and demonstrated the growth of microorganisms in all the flasks. The unopened flasks were sterile.
Thus he disproved the theory of spontaneous generation
Edward Jenner 1796
It was an ancient observation that persons who had suffered from a specific disease such as small pox or mumps, resisted the infection on subsequent exposures. They rarely contracted it second time. Such acquired resistance is specific. Edward Jenner a country doctor in England noted a pustular disease on the hooves of horses called the grease. This was carried by farm workers to the nipples of cows (cow pox). This was again carried by milk maids. They got inflamed spots on the hands and wrists. The people who got this cow pox were protected from small pox. He reported that 16 farm workers who had recovered from cow pox were resistant to small pox infection.
He took the material from the cow pox and inoculated into the cut of an 8 year old boy on 14 May 1796. Two months later Jenner inoculated the same boy with material taken from small pox patients.
This was a dangerous but accepted procedure of that time and the procedure was called variolation. The boy was protected against small pox. His exposure to the mild disease cow pox had made him immune to the disease small pox.
In this manner Jenner began the science of Immunology, the study of the body’s response to foreign substances.
Robert Koch (1843-1910)
Robert Koch was a German physician.
1. For the first time he showed the evidence that a specific germ (Anthrax bacillus) was the cause of a specific disease (spleenic fever in sheep)
2. He established that a specific germ can cause a specific disease and introduced scientific approach in Microbiology
3. He discovered Bacillus anthracis (Anthrax bacillus), Mycobacterium tuberculosis, and Vibrio cholerae.
4. He modified Ziehl-Neelsen acid fast staining procedure which was introduced by Ehrlich.
5. He devised the solid medium to grow the microorganism to get single colonies.
6. He introduced Koch’s thread method to find out the efficacy of disinfectants
7. He established certain rules that must be followed to establish a cause and effect relationship between a microorganism and a disease. They are known as Koch’s Postulates.
8. He also described the Koch’s Phenomenon.
Robert Koch developed powerful method to isolate the organisms in pure culture from diseased tissue. He also perfected the techniques of identification of the isolated bacteria.
The need for Koch’s postulates
In those days there were no perfect techniques to identify the organisms. Solid media and staining techniques were not available. So the etiological role of organisms was not known.
To prove the etiology there were not strict criteria. So there was a need to establish criteria.
1. The organism should be regularly seen in the lesions of the disease.
2. It should be isolated in pure culture on artificial media.
3. Inoculation of this culture should produce a similar disease in experimental animals.
4. The organism must be recovered from the lesions in these animals.
The organism should be found in lesions of the disease
All the causative agents of the disease are seen in the particular diseases. If we take pneumococci as example, they are seen in all the pneumonia cases.
It should be isolated and grown in solid media
Pneumococci are grown in solid media and are isolated from the diseases. Some organisms do not grow on solid media or the solid media are not developed yet.
Example: Mycobacterium leprae and
The organisms should produce the exact disease in experimental animals
Almost all the pathogenic organisms produce the same disease in experimental animals. Usually rats, mice, rabbits or guinea pigs are used as experimental animals.
Pneumococci produce pneumonia in animals. Salmonella species do not produce typhoid fever in rat, mice or rabbit. So chimpanzee is taken as experimental animal and it produces fever in chimpanzee.
It should be isolated from the diseased animal also
Pneumococci are isolated from the experimental animals also
Modern addition to Koch’s Postulates
Today we recognize additional criteria of causal relation between a microorganism and a disease.
The important one is the demonstration of abnormally high concentration of specific circulating antibodies to the organism in the infected host.
Or, the presence of abnormally high degree of specific immunity or hypersensitivity to the infecting agent in a recently recovered host.
Some organisms have not yet been grown in artificial culture media
Example: Mycobacterium leprae and Treponema pallidum.
Usefulness of Koch’s Postulates
1. It is useful in determining pathogenic organisms
2. To differentiate the pathogenic and nonpathogenic microorganism
3. For the classification of organisms
4. To detect the susceptibility, resistance of the laboratory animals.
Koch has done a valuable work in the field of Microbiology and has made postulates, which have merits, demerits and limitations with modern omission and addition.