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The word microbiology is derived from the Greek word, MICRO means small, BIOS means life and LOGIA means study. It is the study of microscopic organisms either unicellular, multicellular or acellular.

Microbiology include disciplines of Virology, mycology and bacteriology etc.

  • Eukaryotic microorganisms exhibit cell organelles and include fungi, protists and algae.
  • Prokaryotic microorganisms are conventionally classified as lacking organelles and include Eubacteria, Archaebacteria.
  • Microbiologist traditionally relayed on culture, staining and microscopy. However, if only 1 percent of microbes present in the environment are culture able. Microbiologist often relay on extraction or detection of nucleic acid either DNA or RNA.
  • Viruses are not always classified as organisms as they have been identified either as very simple microorganisms or very complex molecules.
  • Prions are never considered microorganisms and they have been investigated by virologist as the clinical effects traced to them were originally presumed due to chronic viral infection and virologist identified them as infectious proteins, e.g. mad cow disease in cattle and Scrapie disease in sheep.

Branches of Microbiology:

Two main branches

  1. Pure microbiology
  2. Applied microbiology

Pure microbiology:

  • Bacteriology: study of bacteria
  • Mycology: study of fungi
  • Phycology: study of algae
  • Immunology: study of immune system
  • Virology: study of viruses
  • Microbial physiology: study of microbial cell function. It includes the study of microbial growth, metabolism and cell function.
  • Microbial cytology: study of microscopic and sub-microscopic details of organisms.
  • Microbial genetics: study of organization and regulation of genes in microbes in relation to their cellular function.

Applied microbiology:

  • Veterinary microbiology: study of microbes of veterinary importance such as probiotics and pathogens which are related to veterinary medicine.
  • Pharmaceutical microbiology: study of microorganisms which are related to the production of antibiotics, enzymes, vitamins, biologics and other pharmaceutical products and those microbes which cause pharmaceutical contamination and spoilage.
  • Microbial biotechnology: manipulation of microorganisms at genetics and molecular level to generate useful products e.g. generation of insulin from E. coli.
  • Food microbiology: study of microorganism causing food spoilage and food borne illness. It is all the use of microbes to produce food.

History of Microbiology:

Recent discovery of Mycobacterium Tuberculosis, DNA in the three thousand years old Egyptian mummies reminds us that microorganisms have been around us for a much longer period of time. Infect Bacterium ancestors were the firsts living cells to appear on the earth. Golden age of microbiology:

From 1857-1940 has been named Golden age of microbiology. During this period, rapid advancement spread hold mainly by Pasture & Robert Koch lead to the establishment of microbiology as a science. During this era

  • Discovery of immunity
  • Discovery of disease causing agent

Robert Koch a German physician discovered the cause of Anthrax (Bacillus anthracis) in the 1870s.

Koch postulates:

  1. Same pathogen must be present in every case of the disease.
  2. Pathogen must be isolated from the diseased host & grown in a pure culture
  3. Pathogen from the pure culture must cause the disease when it is inoculated into susceptible lab. Animal
  4. The same pathogen must be isolated from the inoculated animal and it must be same as original organism


Edward Jenner a young British Physician used scraping of cowpox blister to vaccinate against sheep pox.


Microorganism like yeast converts sugar to alcohol in the absence of air this process is called fermentation. It is used to make wine & beer. In the presence of air, bacteria convert alcohol into acetic acid or vinegar.


It is the heat treatment of beverage & milk at 72 ̊ ̊ ̊ C for 30 min to kill microorganism (which causes spoilage of liquid) in food without compromising on its quality. Now a day it is only used for milk product.

Germ theory of diseases:

Microorganisms are the cause of disease. In 1860s English surgeon Joseph Lister use phenol, Carbolic acid as a disinfectant & antiseptic solution. This practice reduced the incidence of infection & death others surgeon readily adopted it. Lister technique was the earliest medical attempt to control infection caused by microorganism.

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