Kingdom prokaryotae consists of organisms with prokaryotic cells. In Greek the word pro means “before” and karyon means nucleus. Microbiologists place bacteria in two major categories: eubacteria (Greek for “true bacteria”) and a much smaller division, the archaeobacteria (Greek for “ancient bacteria”).

Discovery of Bacteria

It had long been suspected that small creatures exist which are too small to be seen with naked eye. But their discovery was linked to the invention of microscope. A Dutch Scientist “Antonie Van Leeuwenhoek” (1673) was the first to report the microbes such as bacteria and protozoa. He used a simple microscope to describe bacteria and protozoa with accurate drawings and descriptions and called these small creatures as “animalcules”. He firstly. Observed small creatures in rain water, then confirmed these in saliva, vinegar, infusions and other substances.

The progress in understanding the nature and importance of these tiny organisms has been slow. The existence of microbes was further confirmed by Louis pasteur’s work. Pasteur went on making many discoveries in the field of microbiology and medicine. His main achievements are the development of vaccines for disease anthrax, fowl cholera and rabies. He also made significant contributions in development of pasteurization process and development of fermentation industries. He proved that microorganisms could cause disease.

Robert Koch formulated the ‘germ theory of disease’. The isolated typical rod-shaped bacteria with squarish ends (bacilli) from the blood of sheep that had died of anthrax. Then he discovered bacteria that caused tuberculosis and cholera. He formulated four postulates, which are the main pillars of the germ theory of disease. These are used to find out whether the organisms found in disease lesions is the causal agent of the disease or not.

  1. A specific organism can always be found in association with a given disease.
  2. The organism can be isolated and grown in pure culture in the laboratory.
  3. The pure culture will produce the disease when inoculated into susceptible animal. it is possible to recover the organism in pure culture from experimentally infected animal.

Koch and his colleagues invented many techniques concerning inoculation, isolation, media preparation, maintenance of pure cultures and preparation of specimens for microscopic examination.


Occurrence Of Bacteria

Bacteria are wide spread in their occurrence. They are found almost everywhere, in air, land, water, oil deposits, food, decaying organic matter, plants, man and animals. Their kind and number vary according to locality and environmental conditions. Some bacteria are always present and contribute towards the natural flora. Others are present in specific environments such as hot springs, alkaline/acidic soil, highly saline environments, in highly polluted soils and waters.