USES OF NUTRIENTS AGAR:
1) It is frequently used for isolation and
purification of cultures.
2) It can also be used as a means for
producing the bacterial lawns needed for
antibiotic sensitivity tests. In actuality,
antibiotic sensitivity testing is typically
performed on media specially formulated
for that purpose.
oSELECTIVE MEDIA
- Selective media are used for growth of only
selected microorganism. For example, if a
microorganism is resistant to a certain
antibiotic,such as ampicillin or tetracyline, then
that antibiotic can be added to the medium to
prevent other cells, which do not possess the
resistance, from growing.
- YM (yeast extract, malt extract agar) has a low
pH, deterring bacterial growth.
- MacConkey agar is for Gram-negative bacteria
oDEFFERENTIAL MEDIA
- Differential or indicator media distinguish one
microorganism type from another growing on the
same medium. This type of media uses the
biochemical characteristics of a microorganism
growing in the presence of specific nutrients or
indicators (such as nuetral red, phenol red, eosiny,
or methylene blue)added to the medium to visibly
indicate the defining characteristics of a
microorganism.
Example of Differential Media include:
- Blood agar (used in strep test) contains bovine
heart blood that becomes transparent in the
presence of B-hemolytic organisms such as
streptococcus pyogenes and staphylococcus
aureus.
- MacConkey agar is differential for lactose
fermentation.
oTRANSPORT MEDIA
- Transport media should fulfill these criteria:
- Temporary storage of specimens being
transported to the laboratory for cultivation
- Maintain the viability of all organisms in the
specimen without altering their concentration
- Contain only buffers and salt
- Lack of carbon, nitrogen, and organic growth
factors so as to prevent microbial
multiplication
- Transport media used in the isolation of
anaerobes must be free of molecular oxygen
Example of Transport media include:
- Treoglycolate broth is for strict anaerobes.
- Stuart transport medium is a non-nutrient soft
agar gel containing a reducing agent to prevent
oxidation, and charcoal to neutralize.
- Certain bacterial inhibitors are used for
gonococci, and buffered glycerol saline for
enteric bacili.
oENRICHED MEDIA
Enriched media contain the nutrients required to
support the growth of a wide variety of organisms,
including some of the more fastidios ones.they are
commonly used to harvest as many different type of
microbes as are prsent in the specime. Blood agar is
an enriched medium in which nutritionally rich
whole blood suplements the basic nutrients.
Chocolate agar is enriched with heat-treated blood
(40-45 degree celsius) which turn brown and gives
the medium the color for which it is named.
PREPARATION OF NUTRIENT AGAR
1) Suspend 28g of nutrient agar powder in 1
liter of distilled water.
2) Heat this mixture while stirring to dissolve
all components.
3)Autoclave the dissolved mixture at 121
degress celsius for 15 minutes.
4)Once the nutrient agar has been autoclave,
allow to cool but not solidify.
5)Pour nutrient agar into each plate and leave
plates on the sterile surface until the agar
solidified.
6) Replace the lid of each petri desh and store
the plates in a refrigerator.
WHY DO WE REQUIRE A
MEDIA?
Microorganism need nutrients, a source of
energy and certain environmental
conditions in order to grow and produce. In
the environment, microbes have adapted to
the habitats most suitable for their needs,
whereas in laboratory, these requirements
must be met by a culture medium.
This is basically an aqueous solution to
which all necessary nutrients have been
added.
COMPO
SITION
The general composition of a medium is as follows:
H-donors and acceptors (approximately 1-15)
C-source (approximately 1-20 g/L)
N-source (approximately 0.2-2 g/L)
Other inorganic nutrients e.g S,P (50 mg/L)
Trace elements (0.1-1 mg/L)
Growth factors (amino acid, purines,
pyrimidine’s, occasionally 50 mg/L, vitamins
occasionally 0.1-1 mg/L)
Solidifying agent (e.g agar 10-20 g/L)
Solvent (usually distilled water)
Buffer chemicals
PREPA
Require amountRATIO
of chemicals is dissolve in
Nusing
distilled water OF Erlenmeyer flasks or
rimless clean test tubes.
MEDIA
pH is adjusted by adding 1N of NaOH or
N/10th of HCI.
15ml capacity of test tube 5ml of liquid
medium is taken .
250ml flask 100ml of media.
These are plugged with non absorbent
cotton and are covered using brown paper.
This is kept for autoclaving – sterilization
done at 15lbs/inch^2 at a temperature
of 121 degree celsius for 15min.
Later cooled down and poured in petri
plates or test tubes which solidifies to
form a medium.
MAJOR TYPES
oCULTURE MEDIA
- Culture media contains all the elements
that most bacteria need for growth and
are not selective, so they are used for the
general cultivation and maintenance of
bacteria kept in laboratory culture
collections.
o MINIMAL MEDIA
- Minimal media are those that contain the
minimum nutrients possible for colony
growth, generally without the presence of
amino acid, and are often used by
microbiologists and geneticists to grow
“wild-type” microorganism.
PREPARATION OF
BIOLOGICAL MEDIA
MEDIA: A
growth
medium or
culture
medium is
It is either
an organic
or a
synthetic
substance
that
provides
both the
biophysical
and the
