Classical Laboratory Methods and Pure Cultures


Microorganisms are abundantly found in nature in sufficiently large populations invariably comprised
of a plethora of different species. It is, however, pertinent to state here that to enable one to carry
out an elaborated study with regard to the characteristic features of a specific species it is absolutely
necessary to have it separated from all the other species.
Laboratory Methods : Well defined, articulated, and explicite laboratory methods have been
adequately developed which enable it to isolate a host of microorganisms representing each species,
besides to cultivate each of the species individually.
Pure Culture : Pure culture may be defined as — ‘the propogation of microorganisms or of
living tissue cells in special media that are conducive to their growth’.
In other words it may also be explained as the growth of mass of cells belonging to the same
species in a laboratory vessel (e.g., a test tube). It was indeed Joseph Lister, in 1878, who first and
foremost could lay hand on pure cultures of bacteria by the aid of ‘serial dilution technique’ in liquid
media.
Example : Lister diluted milk, comprising of a mixture of bacteria, with a specially designed
syringe until a ‘single organism’ was strategically delivered into a container of sterile milk. The container
on being subjected to incubation for a definite period gave rise to a bacteria of a single type, very
much akin to the parent cell. Lister termed it as Bacterium lactis.

Colonies : Koch meticulously devised methods for the specific study of microorganism. He
smeared bacteria on a sterile glass slide, followed by addition of certain specific dyes so as to observe
the individual cells more vividly under a microscope. Koch carefully incorporated some specific solidifying
agents, such as : gelatin, agar into the media in order to obtain characteristic isolated growths of
organisms usually called as colonies. Importantly, each colony is essentially comprised of millions of
individual bacterial cells packed tightly together.
Now, from these identified colonies one may transfer pure cultures to other sterile media. However,
the development of a liquefiable solid-culture medium proved to be of immense fundamental
importance.
Example : Koch thoroughly examined material obtained from subjects suffering from pulmonary
tuberculosis, and succeeded in the isolation of the tubercle bacillus Mycobacterium tuberculosis.
In conclusion, one may summarize the remarkable importance of ‘pure cultures’ toward the
overwhelming development in the field of microbiology, because by the help of pure-culture techniques
several intricate and complicated problems could be answered with reasonable clarification and
complete satisfaction, namely :
􀂳 Microorganisms causing a large number of infections,

􀂳 Certain specific fermentative procedures,
􀂳 Nitrogen-fixation in soil,
􀂳 High-yielding alcohol producing strains from ‘malt wort’, and ‘molasses’,
􀂳 Selected good cultures for making top-quality wines, and
􀂳 Specific cultures for manufacturing dairy products viz., cheeses, yogurt.
Futuristic Goals
The futuristic goals of ‘pure cultures’ are exclusively based upon the following two cardinal
aspects, namely :
(a) better understanding of the physiology of individual microorganisms present in the pure
culture, and
(b) ecological relationships of the entire microbial populations in a given environment.
Thus, the following new horizons in the domain of microbiology may be explored with great
zeal and gusto :
􀁏 Advancements in marine microbiology,
􀁏 Rumen microbiology,
􀁏 Microbiology of the gastro-intestinal tract (GIT), and
􀁏 Several other systems.




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