Explain colonies

J. McGrath jmcg at frontiernet.net
Wed Aug 20 20:42:42 EST 1997

VEIUSA at aol.com wrote:

> I am doing some research and would like an explanation on what
> colonies
> are and how they are counted, processed, picked etc..  Also what is a
> coliform and green sheen???  WOuld I use a stereo microscope to
> perform
> any of these activities???  Appreciate any feedback.  Thx in advance!
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When microbiologists grow bacterial organisms, samples are diluted in an
isotonic (similar ionic content) solutions and plated in a gelatin-like
substance called nutrient agar.  This nutrient agar contains food for
the organisms.  When a single bacterium grows is will eventually
reproduce by splitting into two new organisms; as this process repeats
over..and over...and over... the organisms form a pile of themselves on
or in the nutrient agar.  This group of microorganisms when visible on
or in the agar is termed a colony.  When coliforms are grown on specific
agar like EMB agar.  The colony appears with the classic "metallic
sheen"  This is indicative of coliform growth.  EMB agar contains
special chemicals that facilitate the green sheen when coliform growth
is present.

No you do not need a steromicrosope to observe any of these
characteristics (though one may be desired to study the fine detail and
differences is colony shape, size and texture).  Microbiologists often
utilize the old-fasioned naked eye to count and describe the colony.

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