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 Microorganisms are kept for:
 Control the culture media (testing
media).
 Control the biochemical &
sensitivity testing.
 For teaching purpose.
 For further identification.

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 The bacteria are vary in their ability
to remain a life after they complete
their growth. There are different
methods for preservation of
microorganisms:
 Moist storage.
 Cold storage.
 Dry storage.
 Freeze drying storage (The best one).
 In this method keep the organisms
by serial subculture (interval time)
to keep it is life.
 Use different types of media
according to the type of
microorganisms
 Choice media with low nutritional
substances.
 Semi-solid media (Nutrient agar).

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 Cooked meat media (CMM).
 Blood broth.
 Dorset egg.
 Egg saline.
 Skimmed milk.
 Semi-solid media:
 Staphylococci: Subculture every 1-2 month.
 Enterobacterieace: Subculture every 3
month.
 Blood broth:
 Streptococci: all of them except
pneumococci every one month.
 Dorset egg, Egg saline & skimmed
milk:
 Used for many organisms at least every 6
month subculture.
 CMM:
 Clostriia: subculture every 6-12month.

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 Method:
 Use screw capped container.
 After inoculation (stabbing), incubate
over night.
 Sealing by paraffin wax – fill the
container.
 Make at least duplicate every organism.
 Advantage:
 Easy.
 Practical.
 Disadvantage:
 Cannot prevent mutation.
 There is chance for drying &
contamination.

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 Use low temperature for
preservation the microorganisms.
 Use different degree of temperature:
 4 - 8 C° domestic refrigerator.
 -20 C° - -40 C° deep freezer.
 -70 C° - -80 C° ultra deep freezer.
 -70 C° solid CO2 (Micro-bank methods).
 -196 C° liquid nitrogen methods.
 Some organisms like Niesseria and H.
influenzae cannot preserve by this method.
 4 - 8 C° or -20 C° - -40 C° keep the organisms
for short time.
 -70 C° culture the organism in tube and then
inserted in container CO2.
 Adv. : keep organism for long time – no change
and no need for subculture.

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 Disadv. : expensive – regular filling with
CO2.
 -80 C° ultra deep freezer:
When used it need certain precautions to
avoid ice crystals and concentration of
salt (destroy the organisms) by using:
 Glycerol – Sugar – Dimethyl sulphoxide
(DMSO).
 -196 C° (liquid nitrogen):
 Rapid freezing and rapid rewarming will
avoid formation of ice crystal, and viability
does not affected.
 Disadv: have some disadvantage of
CO2.
 Micro-bank system:
 Commercial supplied cryovials which
are screw capped 2ml container.
 Method: Bacterial suspension add to
the vial which contain
cryopreservative. The organism
absorbed by the glass beads in the vial,
the excess fluid is absorbed and
discarde (storge at -70 C°).

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 Done by several method:
 Filter paper disc methods: Thick
suspension of organism is prepared,
and impregnate the disc of filter paper
with it. Drying take place in a desiccant
under vacuum, over reducing
substance such as phosphorus peroxide
(P2O5), and lastly impregnated with
paraffin oil.
 Slamp method: Similar to previous
method
with some modification in the
reducing substance which is
incorporated in the medium (10%
gelatin with ascorbic acid – paper is
impregnated with the paraffin oil
before the culture – dry as describe
above).
 L. method (La page method):
Drying in bottle or prefer tubes or
capillary tube seal it and kept for long
time.

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