Culture media to grow organisms from infected material to identify the causative agents
1.
2. Culture media are required to grow the
organisms from infected material to identify
the causative agent.
The basic constituents of culture media are:
1. Water
2.Electrolyte
3.Peptone
4.Meat extract
5.Blood or serum
6.Agar
3. TYPES OF MEDIA
1.Based on physical state
a. Liquid media
b. Semisolid media
c. Solid media
2.On the basis of presence of molecular oxygen
and reducing substances in the media
a. Aerobic media
b. Anaerobic media
3.Based on nutritional factors
a. Simple media
b. Complex media
4. c. Synthetic media
d. Special media
- Enriched media
- Enrichment media
- Selective media
- Differential media
- Indicator media
- Transport media
- Sugar media
5. Simple media
Nutrient broth is an example of simple
medium. It contains peptone water and
meat extract 1
When glucose is added to nutrient
broth, it becomes Glucose broth.
When 2-3 agar is added to nurient
broth, it becomes nutrient agar.
6. Complex media:
All media other than simple media are
complex.
Complex media have added ingredients for
bringing out certain properties or providing
special nutrients required for the growth of the
bacterium
Synthetic media:
These are prepared from pure chemicals and
the exact composition of the medium is known.
These are used for special studies such as
metabolic requirements.
dubo’s medium with tween 80 is one example
of synthetic medium.
7. Special media:
Enriched media:
When basal medium is added with some nutrients
such as bool, serum or egg.
e.g., Blood agar – Blood is added to nutrient agar.
It may be used for growing a number of bacteria
like Streptococcus which requires blood for its
growth.
Loeffler’s serum slope – Serum is added for
enriching the medium. This medium is used for
grouping Corynebacterium diptheriae.
These media are employed to grow organisms
which are more exacting in their nutritional needs.
8. Enrichment media:
Some substances are incorported in the liquid
medium which have a stimulating effect on the
bacteria to be grown or inhibits its competitors.
This results in an absolute increase in the number
of wanted bacteria related to other bacteria.
These are very useful for culture of faeces where
the nonpathogenic ones tend to overgrow the
pathogenic ones.
e.g., Tetrathionate broth and Selenite ‘F’ broth –
Inhibits coliforms while allows typhoid-
paratyphoid bacilli to grow.
9. Selective media:
These media are used to isolate a particular
bacteria from specimens where mixed bacterial
flora is expected. This is solid media.
e.g., Deoxycholate citrate agar (DCA) – selective
agent for enteric bacilli ( Salmonella, Shigella )
Bile salt agar(BSA) - Selective growth of Vibrio
cholerae where as inhibits the growth of other
intestinal organisms.
10. Differential media:
This medium helps to distinguish differing
characteristics of bacteria.
e.g., MacConkey’s medium – distinguishes lactose
fermenters (LF) form pink coloured colonies where
as non- lactose fermenters (NLF) produce
colourless or pale coloured colonies.
11. Indicator media:
These media contain an indicator which changes
colour when a bacterium grows in them.
e.g., Wilson and Blair medium(WBBS) – Salmonella
typhi grows as black colour colonies.
Blood agar and MacConkey agar are also indiactor
medium.
12. Transport media:
These media are used for growth of delicate
organisms which may not survive the time taken
for transit or may be overgrown by nonpathogenic
bacteria.
e.g., Stuart’s transport medium – used for the
growth of gonococci.
Bufferd glycerol saline – used for the growth of
enteric bacilli.
13. Sugar media:
This media hepls in identification of bacteria.
Glucose, lactose, sucrose, mannitol are routinely
employed for fermentation tests.
A small tube (Durham’s tube) is kept inverted in
the larger sugar tube to detect gas production.
The colourless medium turns pink with prodution
of acid by bacteria and gas prodution is indicated
by gas bubbles accumulated in Durham’s tube.
Hiss’s serum sugars for pneumococcus.
14. Anaerobic media:
These are used for cultivation of anaerobic
bacteria
- Cooked meat broth (CMB)
- Thioglycollate broth.
