This document discusses various methods for preserving bacteria, including periodic transfer to fresh media, refrigeration, cryopreservation, storage in water, agar slant culture, porcelain bead technique, storage in silica gel, preservation in soil, and lyophilization. Lyophilization, or freeze drying, is described as one of the best preservation methods as it reduces the risk of intracellular ice crystallization by removing water from specimens, effectively preventing damage and allowing bacteria to remain viable for up to 30 years. The lyophilization process involves freezing, primary drying, secondary drying, and packaging stages.

1. SUBMITTED TO
DR. KAMAL KHILARI
PROFESSOR
DEPTT OF PLANT PATHOLOGY
PRESERVATION OF BACTERIA
PRESENTED BY
ANKIT KUMAR SINGH
M.Sc. PLANT PATHOLOGY

2. Why to Preserve Bacteria ?
 Even death is not completed without bacteria .Anton Von
Leeuwenhoek
 In nature there are only 1% bacteria which is pathogenic
and harmful to Animalia and Plantae.
 99% of bacterial populations are of economic importance
for human beings and plants.
 In soil for nutrient uptake in food industry,in sewage
treatment,in medical industry.
 So the preservation of bacteria is one of the most profitable
practice economically as well as environmentally.

3. Introduction
Once a microorganism has been isolated and
grown in pure culture, it becomes necessary to
maintain the viability and purity of the
microorganism by keeping the pure culture free
from contamination.
Normally in laboratories, the pure cultures are
transferred periodically on to or into a fresh
medium (subculturing) to allow continuous
growth and viability of microorganisms.
 The transfer is always subject to aseptic
conditions to avoid contamination.

4.  Since repeated subculturing is time consuming,
it becomes difficult to maintain a large number
of pure cultures successfully for a long time.
 In addition, there is a risk of genetic changes
as well as contamination. Therefore, it is now
being replaced by some modern methods that
do not need frequent subculturing.
 These methods include refrigeration, paraffin
method, cryopreservation, and lyophilization
(freeze drying).

5. Preservation Methods of Bacteria
 Periodic transfer to fresh media
 Preservation in mineral oil
 Refrigeration
 Cryopreservation
 Storage in water
 Agar slant culture
 Porcelain bead technique
 Storage in silica gel
 Preservation in soil
 Lyophilization

6. • Strains can be maintained by periodically preparing a fresh
culture from the previous stock culture.
• The culture medium, the storage temperature, and the time
interval at which the transfers are made vary with the species .
• The temperature and the type of medium chosen should support
a slow rather than a rapid rate of growth so that the time interval
between transfers can be as long as possible.
• Many of the more common heterotrophs remain viable for
several weeks or months on a medium like Nutrient Agar.
• The transfer method has the disadvantage of failing to prevent
changes in the characteristics of a strain due to the development
of variants and mutants.
1.Periodic Transfer to Fresh Media

8.  This is a simple and most economical method of maintaining pure
cultures.
 In this method, sterile liquid paraffin is poured over the slant (slope)
of culture and stored upright at room temperature. The layer of
paraffin ensures anaerobic conditions and prevents dehydration of
the medium.
 This condition helps microorganisms or pure culture to remain in a
dormant state and, therefore, the culture can be preserved form
months to years (varies with species).
 Advantage: we can remove some of the growth under the oil with a
transfer needle, inoculate a fresh medium, and still preserve the
original culture.
 The simplicity of the method makes it attractive, but changes in the
characteristics of a strain can still occur.
2.Paraffin Method/ preservation by overlaying
cultures with mineral oil

10. Pure cultures can be successfully stored at 0-4°C either in
refrigerators or in cold-rooms.
 This method is applied for short duration (2-3 weeks for
bacteria and 3-4 months for fungi) because the metabolic
activities of the microorganisms are greatly slowed down
but not stopped.
Thus their growth continue slowly, nutrients are utilized
and waste products released in medium.
This results in finally the death of the microbes after
sometime.
Refrigeration

12. Cryopreservation
 Cryopreservation (i.e., freezing in liquid nitrogen at -196°C or
in the gas phase above the liquid nitrogen at -150°C) helps
survival of pure cultures for long storage times.
 In this method, the microorganisms of culture are rapidly
frozen in liquid nitrogen at -196°C in the presence of
stabilizing agents such as glycerol or Dimethyl Sulfoxide
(DMSO) that prevent the cell damage due to formation of ice
crystals and promote cell survival.
 This liquid nitrogen method has been successful with many
species that cannot be preserved by lyophilization and most
species can remain viable under these conditions for 10 to 30
years without undergoing change in their characteristics,
however this method is expensive.

14. STORAGE IN WATER
 Agar culture discs or bacterial cells are
submerged in glass Vials half filled with sterile
distilled water that can be sealed or plugged
with cotton and stored in a refrigerator or at
room temperature.
 SeveralAgrobacterium,corynebacterium,Psued
omonas and Xanthomonas spp can be stored in
sterile water for 2 to 3 years.

16.  All microbiology laboratories preserve micro-
organisms on agar slant.
 The slants are incubated for 24hr or more and are then
stored in a refrigerator.
 These cultures are periodically transferred to fresh
media.
 Time intervals at which the transfers are made which
varies with the origin and condition of growth.
AGAR SLANT CULTURE:FOR PRESERVATION
OF BACTERIA

17. PORCELAIN BEAD TECHNIQUE
 This technique is used mainly for preservation of
Rhizobium and Septorium nodorum .
 Half filled screw cap small glass bottle with silica gel
crystal indicator dye ( blue when dry and pink when wet )
are covered with a 1to 1.5 semi thick cotton cap and
sterilized with dry heat for 2 to 3 hour 160 centigrade temp.
beads are sterilized in a closed container by dry heat.
Bacteria grown in liquid culture broth in tubes can be use
directly .

19. Storage in Silica Gel
 CMI recommends using silica gel for long term
storage when lyophilization or liquid nitrogen storage
is not available. its comparable to these method for
long term preservation of culture .
 the method was developed for storage of Neurospora
spp. sporulating fungi an several bacterial stored in
silica gel and protected by skim milk remain viable for
4 to 5 years reviable of culture are easy and the same
storage container can be used for successive sampling.

20. STORAGE IN SOIL
Storing organisms in soil fall into two groups;
[1]sterile soil infested with small amount of inoculum,immediately
dried and stored in refrigerator.
[2]Soil infested with the organism,than incubated allowing
The organism to grow;thus the mycelium and propagative unit of
second generation are preserved.
The soil preservation method is useful for fungi,and by this method
actinomycetes are maintained in soil for 4 to 5 years,and there are
several bacterial spp which are also maintained in soi for several
years.

22. LYOPHILZATION
Freeze drying is a stabilizing process in
which a substance is first frozen and then
the quantity of the solvent is reduced, first
by sublimation (primary drying stage)
and then desorption (secondary drying
stage) to values that will no longer
support biological activity or chemical
reactions.

24. Introduction :
• Better preservation occurs with freeze-drying than with other
methods because freeze-drying reduces the risk of
intracellular ice crystallization that compromises viability
• Removal of water from the specimen effectively prevents this
damage
• Lyophilization is greatest with gram-positive bacteria (spore
formers in particular) gram-negative
bacteria, but overall,
and decreases with
the viability of bacteria can be
maintained for as long as 30 years

25. • Large numbers of vials of dried microorganisms can be stored
with limited space, and organisms can be easily transported
long distances at room temperature
• The process combines freezing and dehydration- Organisms
are initially frozen and then dried by lowering the atmospheric
pressure with a vacuum apparatus
• Specimens can be connected individually to the condenser
(manifold method) or can be placed (in a chamber) where they
are dehydrated in one larger airspace
Contd.

26. STEPS INVOLVED IN LYOPHILIZATION
FREEZINGSTAGE
PRIMARY DRYINGSTAGE
SECONDARYDRYINGSTAGE
PACKING

27. Lyophilization Process

28.  StorageVials
 Glass vials are used for all freeze-driedspecimens
 When freeze-drying is performed in a chamber, double glass vials
are used
 (chamber method) : an outer soft glass vial is added for
protection and preservation of the dehydrated specimen
 Silica gel granules are placed in the bottom of the outer vial
before the inner vial is inserted and cushioned withcotton
 Manifold method- a single glass vial is used
 storage vial must be sealed to maintain the vacuum and the dry
atmospheric condition
 Cryoprotective Agents
– Two most commonly used agents are
 Skim milk for chamber lyophilization, and
 sucrose for manifold lyophilization

29. Advantages ofLyophilization
 Removal of water atlow
temperature
 Thermolabile materials canbe
dried.
 Sterility can bemaintained.
 Reconstitution iseasy

30. Disadvantages of Lyophilization
 Many biological molecules are damaged by the stress
associated with freezing, freeze-drying, or both.
 E.g. the process of drying causes extensive damage to
molds, protozoa, and most viruses
 Hence, these microorganisms can not be stored by
this method
 The product is prone to oxidation, due to high porosity
and large surface area. Therefore the product should be
packed in vacuum or using inert gas
 Cost may be an issue, depending on the product