culture media and its types

1. CULTURE MEDIA
BY
DR. Ahmed Khadri
DEPT. OF ORAL MAXILLOFACIAL
PATHOLOGY & MICROBIOLOGY

2. Introduction
• Its utility in diagnosing infectious diseases
• Isolating a bacterium from sites in body
normally known to be sterile is an indication
of its role in disease process
• Initial step in studying the morphology and
identification
• Bacteria have to be cultured in order to obtain
antigens from developing serological assays or
vaccines

3. • Certain genetic studies and manipulations of
the cells also need that bacteria be cultured in
vitro
• Culturing bacteria also provide a reliable way
estimating their numbers (viable count).
• Culturing on solid media is another convenient
way of separating bacteria in mixtures.

4. History
• Louis pasteur – used simple broths made up of
urine or meat extracts
• Robert koch – used potato pieces to grow
bacteria
• Fanny Eilshemius’s suggestion – agar was used to
solidify culture media
• Before agar, gelatin was tried to be used as
solidifying agent.
• Gelatin had some inherent problems; it existed as
liquid at normal incubating temperatures (35-37
C) and was digested by certain bacteria.

5. Composition of culture media
• Bacteria infecting humans are
chemoorganoheterotrophs.
• When culturing bacteria, it is very important
to provide similar environmental and
nutritional conditions that exist in its natural
habitat
• Hence an artificial culture medium must
provide all the nutritional components that a
bacteria gets in its natural habitat

6. • Most often a culture medium contains water,
a source of carbon and energy, source of
nitrogen, trace elements and some growth
factors
• Besides these, the pH of the medium must be
set accordingly
• Some of the ingredients of culture media
include water, agar, peptone, casein
hydrolysate, meat extract, yeast extract and
malt extract.

7. Preparation and preservation
• Care must be taken to adjust the pH of the
medium before autoclaving
• E.g. Phenol red, neutral red, bromothymol
blue, bromocresol purple etc.
• Dehydrated media are commercially available
and must be reconstituted as per
manufacturers’ recommendation
• Most culture media are sterilized by
autoclaving

8. • Certain media that contain heat labile
components like glucose, antibiotics, urea,
serum, blood are not autoclaved
• Certain highly selective media such as Wilson
and Blair’s medium and TCBS agar need not be
sterilised
• Once prepared, media may be held at 4-5 C in
the refrigerator for 1-2 weeks
• Certain liquid media in screw capped bottles
or tubes or cotton plugged can be held at
room temperature for weeks.

9. Types of culture media
I. Based on their consistency
a) solid medium
b) liquid medium
c) semi solid medium
II. Based on the constituents/ ingredients
a) simple medium
b) complex medium
c) synthetic or defined medium
d) Special media

10. Special media
– Enriched media
– Enrichment media
– Selective media
– Indicator media
– Differential media
– Sugar media
– Transport media
– Media for biochemical reactions
III.Based on Oxygen requirement
- Aerobic media
- Anaerobic media

11. Solid media – contains 2% agar
• Colony morphology, pigmentation, hemolysis can be
appreciated.
• Eg: Nutrient agar, Blood agar
Liquid media – no agar.
• For inoculum preparation, Blood culture, for the
isolation of pathogens from a mixture.
• Eg: Nutrient broth
Semi solid medium – 0.5% agar.
• Eg: Motility medium

13. Simple media / basal media
- Eg: Nutrient Broth, N.agar
- NB consists of peptone, meat extract, NaCl,
- NB + 2% agar = Nutrient agar

14. Complex media
• Media other than basal media.
• They have added ingredients.
• Provide special nutrients
Synthetic or defined media
• Media prepared from pure chemical substances
and its exact composition is known
• Eg: peptone water – 1% peptone + 0.5% NaCl in
water

15. Enriched media
• Substances like blood, serum, egg are added
to the basal medium.
• Used to grow bacteria that are exacting in
their nutritional needs.
• Eg: Blood agar, Chocolate agar

16. Blood agar Chocolate agar

17. Enrichment media
• Liquid media used to isolate
pathogens from a mixed culture.
• Media is incorporated with
inhibitory substances to suppress
the unwanted organism.
• Eg:
– Selenite F Broth – for the isolation of
Salmonella, Shigella
– Alkaline Peptone Water – for Vibrio
cholerae

18. Selective media
• The inhibitory substance is added to a solid
media.
Eg:
• Mac Conkey’s medium for gram negative
bacteria
• TCBS – for V.cholerae
• LJ medium – M.tuberculosis
• Wilson and Blair medium – S.typhi
• Potassium tellurite medium – Diphtheria bacilli

19. TCBS
Mac Conkey’s medium

20. Potassium Tellurite media LJ media

21. Indicator media
• These media contain an indicator which
changes its colour when a bacterium grows in
them.
• Eg:
– Blood agar
– Mac Conkey’s medium
– Christensen’s urease medium

23. Urease medium

24. Differential media
• A media which has substances incorporated in
it enabling it to distinguish between bacteria.
• Eg: Mac Conkey’s medium
– Peptone
– Lactose
– Agar
– Neutral red
– Taurocholate
• Distinguish between lactose fermenters & non
lactose fermenters.

25. • Lactose fermenters – Pink colonies
• Non lactose fermenters – colourless colonies

26. Sugar media
• Media containing any fermentable substance.
• Eg: glucose, arabinose, lactose, starch etc.
• Media consists of 1% of the sugar in peptone
water.
• Contain a small tube (Durham’s tube) for the
detection of gas by the bacteria.

28. Transport media
• Media used for transporting the
samples.
• Delicate organisms may not
survive the time taken for
transporting the specimen without
a transport media.
• Eg:
– Stuart’s medium – non nutrient soft
agar gel containing a reducing agent
– Buffered glycerol saline – enteric
bacilli

29. Anaerobic media
• These media are used to grow anaerobic organisms.
• Eg: Robertson’s cooked meat medium, Thioglycolate
medium.

30. Reference
• Text book of microbiology Ananthnarayan
• Pareja practical book of microbiology
• Cp Baveja diagnostic text book of microbiology