Introduction to Lab 6: Ex. Preparation of Culture Media

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Introduction to Lab 6 Ex. Preparation of Culture
Media Media facts Preparation Steriliz
ation Aseptic technique
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Introduction to Lab 7 Ex. Preparation of Culture
Media 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.
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Among the different kinds of microorganisms the
two groups that 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.
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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 ways. 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.
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Since there are different kinds of organisms that
can be grown in 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) semi-solid solid. Media are solidified
by the addition of solidifying agents such as
agar (inert compound). Varying the
concentration of agar will yield varying degrees
of solidification.
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Culture media may be classified as Synthetic
media (Defined) 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.
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The ingredients in a medium will affect the
chemical nature of the medium. 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 medium. 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.
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The primary function of culture media is to be
able to grow particular organisms on/in them.
It is important that these media are devoid of
any other living organisms. 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)
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-3 different culture media will be prepared in
the class. -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
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For example Nutrient Agar 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) Aseptic Technique 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.
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Aseptic Techniques
protective clothing hand washing bench
cleaning loop flaming pipettors