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Introduction to Lab 6: Ex. Preparation of Culture Media Media facts Preparation Sterilization Aseptic technique. Introduction to Lab 7: Ex. Preparation of Culture Media The purpose of this exercise is to introduce the concept of growing
The purpose of this exercise is to introduce the concept of growing
microorganisms in the lab in order to be able to study them.
Culture is the term given to microorganisms that are cultivated in
the lab for the purpose of studying them.
Medium is the term given to the combination of ingredients that
will support the growth and cultivation of microorganisms by
providing all the essential nutrients required for the growth
(that is, multiplication) in order to cultivate these
microorganisms in large numbers to study them.
can be grown in cultures are bacteria and fungi.
Algae and protozoa require many different nutrients in minute
quantities that are difficult to anticipate and prepare in the lab.
These organisms have different nutritional requirements and
thus various kinds of culture media have been developed.
Primary ingredients required by all living organisms include:
a carbon source, water, minerals, and a nitrogen source.
Living cells need nutrients required for their structure (biosynthesis)
as well as nutrients to provide them with energy to perform all
of their various life processes.
Nutrients are acquired from the environment in which they live in
their natural habitat.
Most of these nutrients are then processed within the cell through a
variety of metabolic pathways to be incorporated in different
The process of building complex structures from simple building
blocks is called anabolism.
The process of breaking up complex materials to harvest the energy
in them is called catabolism.
The ability to use particular compounds is dependent upon the
genetic makeup (DNA) that the cells have.
culture media with varying needs, culture media have also
been formulated with different ingredients.
Culture media may be found in one of three states:
liquid (called broth)
Media are solidified by the addition of solidifying agents such as
agar (inert compound).
Varying the concentration of agar will yield varying degrees
Complex (Non-synthetic) media
Synthetic media contain only ingredients for which a complete
chemical formula is known.
Complex media contain at least one ingredient for which a chemical
formula is not known (such as milk, egg, malt, animal tissues)
Culture media can also be classified based on the function they
perform in determining various characteristics of organism
that are able to grow on/in them
e.g. Differential, Selective media.
This is important because organisms vary in their
requirement for different environments.
One such property is:
pH (which is a measure of the amount of hydrogen ions in
a particular medium).
This has to be monitored during the preparation of media since this
will influence the kind of organisms that are able to grow in the
The pH of the medium will thus determine which organisms are
able to grow on the medium.
For example, fungi prefer acidic media for their growth while bacteria
grow on neutral pH media.
particular organisms on/in them.
It is important that these media are devoid of any other living
This is possible through the process of sterilization
(a process by which all living organisms and their spore forms
are killed and the medium is made sterile)
Culture media are most commonly sterilized through the process of
autoclaving (using high temperatures that will kill all living
organisms under increased pressure for specified periods of time –
in an appliance called the autoclave)
-They will be sterilized in an autoclave and poured into Petri dishes.
-These will then be used for the next exercise to be done in the lab.
The 3 media that are to be prepared are:
Dextrose Starch Agar (DSA)
Malt Agar (MA)
Nutrient Agar (NA)
Be able to assign functions to each of the ingredients for any culture
medium – that is identify the source of:
carbon, nitrogen, minerals
and any other specific function they may perform
(such as solidification)
Most common sources:
- carbon are sugars (carbohydrates)
- nitrogen are proteins (partially degraded – peptone)
- animal tissue extracts as a source for minerals
Gelysate peptone- 5.0g (source of carbon and nitrogen);
Beef extract - 3.0g (secondary source of carbon and nitrogen and
primary source of minerals),
Agar -15.0g (solidifying agent – if this were not added
medium would be a broth)
These are various techniques that are used to
minimize the introduction of microorganisms into media
especially during transfer processes, such as –
pouring of media into Petri dishes,
inoculation of cultures
These techniques include:
cleaning the bench top work areas with disinfectant solution
washing hands before starting work
other specific techniques that will be demonstrated in the lab.