Giving basic concepts regarding culture media and its classification on the basis of different properties like physical state, chemical composition and utility purposes.

1. Culture media and types
Anup Muni Bajracharya

2. Culture medium
• food that is use in the laboratory for the
growth of bacteria, molds and other micro-
organism.
• nutrient preparation in which micro-organism
are grown in the laboratory, the growth itself
is called a culture.
• Robert Koch- discovered and developed the
use of culture medium.
• the first medium in bacteriology-potato agar

3. Composition of media
i) Agar
ii) Peptone
iii) Extracts( Meat extract, yeast extract)
iv) Carbohydrates
v) Water

4. Agar
• Agar is solidifying agent
• an impure polysaccharides
obtained from certain red
marine algae.
• liquifies at about 1000c
solidified at 450c.

5. Peptone
• water soluble product
obtained from the
breakdown or
hydrolysis of animal or
plant material such as
meat scraps, muscles,
gelatin, milk protein etc.
• Hydrolysis is brought by
the action of acid and
enzymes such as trypsin
and pepsin

6. Extracts
• Eukaryotic tissues
(yeast, beef muscles,
liver,brain) are extraced
by boiling and then
concentrated to a paste
or dry to powder.
• Those which are
extracted from yeast
cells are called yeast
extracts.
Meat extract
Yeast extract

7. Carbohydrates
• The bacteriologist use
carbohydrates to enrich
media for growth,
pigmentation and to
determine whether the
organism can produce
acid or gas by using it.
• Most commonly use
carbohydrates are
glucose, sucrose,
lactose, maltose etc.

8. Water
• essential for growth of all micro-organism.
• used in microbiology lab for dissolving media

9. Classification of culture media
• On the basis of physical state of the media, it can be classified as
a) Solid media
b) Liquid media
c) Semi- solid media
• a) Solid media:- media which are solid in state. Agar is the major
solidifying agent ,added in concentration of 1.5% for plates, slant media.
Eg: Nutrient agar, Macconkey agar.
• b) Liquid media (broth):- media which are in liquid state. This form of
media don't contain agar or any solidifying agent. Eg:- Nutrient broth,
Macconkey broth.
• c) Semi- solid media:- This form of medium is prepared by adding a
small amount of agar (0.2-0.5%)to a fluid medium. The consistency of this
media is jelly like, the consistency between solid and liquid. Eg:- Hugh
Leifson's media, SIM media.

11. Chemical composition
On the basis of chemical composition, media are of two types.
a) chemically-defined (synthetic) medium
b) complex (undefined) medium
• A chemically-defined (synthetic) medium: It is one in which the
exact chemical composition is known. It is generally made from
various chemicals that are highly purified and precisely defined.
• A complex (undefined) medium is one in which the exact chemical
constitution of the medium is not known. complex media usually
contain complex materials of biological origin such as blood or milk
or yeast extract or beef extract, the exact chemical composition of
which is obviously undetermined.

12. Utility
On the basis of utility purpose media are of following types
a) Basal Media( General Purpose Media):-
• simple media which support the growth of microorganism that do
not have special nutritional requirements.
• designed to grow as many as possible of the organism commonly
used in general bacteriological laboratory.
• E.g. Nutrient agar, Nutrient broth.

13. Enriched Media
• used for the cultivation of certain microorganism
that have elaborated requirements for specific
nutrients.
• For the growth of fastidious micro-organism such
as Haemophilus influenza, Streptoccocus,
Neisseria etc.
• In such media, some addition as supplementary
foods are supplied besides the common nutrients.
Such as blood, egg, serum, vitamins ,peptones,
aminoacids to a basal media. e.g. Blood agar,
chocolate agar, egg yolk medium.

14. BLOOD AGAR
Enriched Media

15. Chocolate agar

16. Selective Media
• A selective media is one which has a components added to
it which will inhibit or prevent the growth of certain types
or species of bacteria and/or promote the growth of desired
species.
• Such media contains some selective substances that
supports the growth of desired organism while inhibiting
the growth of unwanted organism in a mixture.
• E.g. Macconkey Agar is selective media for Gm -ve bacteria
because it contains selective agents like bile salts and crystal
violet which inhibit the Gm +ve bacteria.
• XLD agar selects for Salmonella Shigella species.

18. Differential Media
• Differential media consists of indicator, dyes or
other substances to differentiate microorganism.
• These types of media are also known as indicator
media and these media incorporate some
substances i.e. changed visibly as a result of the
metabolic activities of particular organism.
• Eg: Macconkey Agar contains the indicator neutral
red which differentiate lactose fermenting from
Non- Lactose fermenting organism.

19. Macconkey Agar-Differential media

20. Blood agar- Differential
Media

21. • Enrichment media:- These are fluid media that
increases the number of pathogens by containing
enrichment and a substances that discourage the
multiplication of unwanted bacteria.
• For e.g:- Alkaline Peptone Water is used as
enrichment media for vibrio species. The pH of
the media is high (8.5-9.2) that supports the
growth of vibrio species and is inhibitory to other
organisms.

22. Transport Media
• These are media that are devised to maintain
the viability of a pathogen and to avoid over
growth of other contaminants during transit
from the patient to the laboratory.
• Their use is particularly important when
transporting microbiological specimens from
health centre to the district microbiology lab.
• E.g:- Cary and Blair medium for preserving
enteric pathogens