Culture media are the basic requirement to grow the microbes in the laboratory for various purpose like isolation, identification and research purposes.

1. Culture
Media
-Ajay Kumar
Chaurasiya

2. Culture Media
Media –Pleural
While medium is singular
Culture media are required to grow the organisms from
infected material to identify the causative agent and its basic
constituents are-
 Water : source of hydrogen and oxygen
 Electrolyte: Sodium chloride or other electrolytes
 Peptone: It is a complex mixture of partially digested protein.
It contains proteoses, amino acids, polypeptides, phosphates,
minerals (K, Mg) and accessory growth factors like nicotinic
acid and riboflavin.
 Meat extract: Available commercially as “Lab-Lamco"

3. It contains protein degradation products, inorganic salts,
carbohydrates and growth factors.
 Blood or serum: They are used for enriching culture
media. Usually 5-10% defibrinated sheep blood is used. In
certain media, serum is used.
 Agar: It is long chain polysaccharide and prepared from sea
wood (Algae -Geladium Species).
It does not provide any nutrition to the bacteria but acts as a
solidifying agent only.
-Used in concentration of 2-3%
-Melts at 980C
-Solidifies at 420C
-New Zealand agar has twice the capacity jellifying capacity
than that of Japanese agar.

4. Types of media
Media are classified in flowing ways:
1. Based on physical state
I. Liquid media
II. Semisolid media ( Agar, 0.2-0.4% which enables motile bacteria
to spread.)
III. Solid media
2. On the basis of presence of molecular oxygen and reducing
substances in the media
I. Aerobic media
II. Anaerobic media
3. Based on nutritional factors
I. Simple media
II. Complex media
III. Synthetic media
IV. Special media

5. Special media –
a) Enriched media
b) Enrichment media
c) Selective media
d) Differential media
e) Indicator media
f) Transport media
g) Sugar media
Simple media:
Nutrient broth is an example of simple medium. It contains
peptone water and meat extract 1%.when agar is added to
nutrient broth, it becomes nutrient agar. This is the simplest
and routinely employed medium in the laboratory for
diagnostic purposes.
Complex media:
All media other than simple media are complex media.

6. Synthetic media:
These are prepared from pure chemicals and the exact
composition of the medium is known. These are used for special
studied such as metabolic requirements. Dubo’s medium with
tween 80 is an example of a synthetic medium.
Special Media
Enriched media : When basal medium is added with some
nutrients such as blood, serum or egg. It is called enriched
medium. For e.g.
 Blood agar-Blood is added to nutrient agar. It may be used for
growing a number of bacteria but one specific example is
Streptococcus which requires blood for its growth.
 Loeffler’s serum slope-Serum is added for enriching the
medium. This medium is used for growing Corynebacterium
diphtheriae.
Enrichment media:
A fluid type of selective medium in which some substances are
incorporated that have either a stimulating effect on the bacteria
to be grown or inhibits its competitors or both .

7. This results in an absolute increase in the number of wanted
bacteria related to other bacteria. Such medium is called
enrichment medium.
 Tetrathionate broth-Tetrathionate is added which inhibits
coliforms while allows typhoid-paratyphoid bacilli to grow.
 Selenite F broth –Selenite has similar action as that of
tetrathionate in tetrathionate broth.
Selective media:
Selective media contain substances that inhibit all but a few
types of bacteria and facilitate the isolation of a particular
species. These media are used to isolate a particular bacteria
from specimen where mixed bacterial flora is expected.
Selective media are solid in contrast to enrichment media
which are liquid. Example of selective media are:

8.  Deoxycholate citrate agar(DCA)-Addition of deoxycholate
acts as selective agent for enteric bacilli (Salmonella,
Shigella).
 Bile salt agar(BSA)-Bile salt is a selective agent. It favors
the growth of only Vibrio cholerae where as inhibits the
growth of other intestinal organisms.
Differential media:
When a medium contains substances which help to
distinguish differing characteristics of bacteria, it is called
differential medium e.g.
 MacConkey’s medium, which contains peptone, lactose ,
agar, sodium taurocholate and neutral red. The lactose
fermenters (LF) form pink colored colonies where as non
lactose fermenters (NLF) produce colorless or pale
colonies.

9. Indicator Media :
These media contain an indicator which changes color when a
bacterium grows in them. Salmonella enterica serotype Typhi
grow as black colonies on Wilson and Blair medium containing
sulphite.
 MacConkey ‘s medium is also an indicator medium. Due to
fermentation of lactose , there is acidic pH which forms the
pink colonies in the presence of neutral red indicator.
Transport media:
These are used in the case of delicate organisms (e.g.
gonococci) which may not survive the time taken for transit or
may be overgrown by non pathogenic bacteria(e.g. cholera
organisms).They maintain only viability.
Examples of transport media are:

10.  Stuart’s transport medium: is a non nutrient soft agar gel
containing a reducing agent to prevent oxidation, and
charcoal to neutralize bacterial inhibitors. It may be used
for organisms such as gonococci.
 Buffered glycerol saline transport medium for enteric
bacilli.
Sugar media:
Sugar media help in identification of bacteria. The term sugar
in microbiology denotes any fermentable substance. Glucose,
lactose, sucrose and mannitol are routinely employed for
fermentation tests.
Anaerobic Media:
These are used for cultivation of anaerobic bacteria e.g.
 Cooked meat broth (CMB)
 Thioglycollate broth

13. Nutrient Agar
Intended use
Nutrient Agar is used as a general purpose medium for the cultivation of less
fastidious microorganisms, can be enriched
with blood or other biological fluids.
Composition**
Ingredients Gms / Litre
Peptone 5.000
Sodium chloride 5.000
HM peptone B# 1.500
Yeast extract 1.500
Agar 15.000
Final pH ( at 25°C) 7.4±0.2
**Formula adjusted, standardized to suit performance parameters
Directions
Suspend 28 grams in 1000 ml distilled water. Heat to boiling to dissolve the
medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15
minutes. Cool to 45-50°C. If desired ,the medium can be enriched with 5-10%
blood or other biological fluids. Mix well and pour into sterile Petri plates.

14. Blood Agar Base
Intended Use:
Blood Agar Base is recommended as a base to which blood may be added
for use in the isolation and cultivation of fastidious pathogenic
microorganisms like Neisseria , Streptococci etc.
Composition**
Ingredients Gms / Litre
HM peptone B# 10.000
Tryptose 10.000
Sodium chloride 5.000
Agar 15.000
Final pH ( at 25°C) 7.3±0.2
**Formula adjusted, standardized to suit performance parameters
Directions
Suspend 40.0 grams in 1000 ml distilled water. Heat to boiling to dissolve
the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C)
for 15 minutes. Cool to 45-50°C and aseptically add 5% v/v sterile
defibrinated blood. Mix well and pour into sterile Petri plates.

15. Cooked M Medium (R.C. Medium)
Intended use
Cooked Meat Medium (R.C. Medium) is used for cultivation of aerobes and
anaerobes, especially pathogenic Clostridia from clinical, food and water samples.
This can also be used as a maintenance medium for stock cultures.
Composition**
Ingredients Gms / Litre
HMH peptone B # 98.000
Proteose peptone 20.000
Dextrose(Glucose) 2.000
Sodium chloride 5.000
Final pH ( at 25°C) 7.2±0.2
**Formula adjusted, standardized to suit performance parameters
# Equivalent to Beef heart, solids
Directions
Suspend 12.5 grams in 100 ml distilled water (or suspend 1.25 grams in 10 ml
distilled water in test tubes). Mix thoroughly and allow to stand for 15 minutes
until all the particles are thoroughly wetted. Dispense into tubes or flasks as
desired. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.