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What is Microbiology – History of Microbiology

Microbiology: 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

Koch’s Postulates :  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.

Koch’s Postulates
  • 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

Postulate 1 :  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.

Postulate 2:  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   Treponema pallidum

Postulate 3:  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.

Postulate 4 :  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

Limitations : 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.

Conclusions :   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

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