Types of culture media Flashcards
What is culture medium?
- The food material or substances required for
growing microorganisms in vitro (outside the
body). - An artificial soil that contains nutritional and
environmental requirements.
Growth of an organism is known as
culture
Basic Requirements
of Culture Medium
- Water
- Energy source
- Carbon source
- Nitrogen source
- Salts
- pH
- Adequate oxidation
- Growth factors
Uses of culture medium
It is important to grow microorganisms outside the body
for the following purposes:
1.to identify the cause of infection from the clinical
sample, so that proper treatment can be given.
2.to study the characteristics or properties of
microorganisms.
3.to prepare biological products like vaccines, toxoides,
antigens…etc.
Types of culture media
I. Classification based on physical state
a) solid medium
b) semi solid medium
c) liquid medium
II. Classification based on the presence
and absence of oxygen
a) anaerobic media
b) aerobic media
III. Classification based on nutritional factors
a) simple medium
b) complex medium
c) synthetic or defined medium
d) Special media
agar is the most commonly used solidifying agent.
Solid medium
What is agar
- Golden –yellow granular powder
- Prepared from seaweeds.
- Not affected by the growth of the bacteria
- Melts at 98oC & sets at 42oC
lower agar concentration - 0.2 to
0.5%
Such media are soft and are useful in demonstrating
bacterial motility and separating motile from non-
motile strains.
Useful in the cultivation of microaerophilic bacteria
Semi-solid media
are sometimes referred as “ broth “.
bacteria grow uniformly producing general turbidity
eg. Nutrient broth
Peptone solution
Liquid media
- eg: Nutrient broth, N. agar
- NB consists of peptone, meat extract, NaCl,
- NB + 2% agar = Nutrient agar
Simple media (basal media)
such as blood agar, it has ingredients that exact
components are difficult to estimate.
Complex media
- specially prepared media from pure chemical
substances for research purpose and composition of
every component is well known - eg: peptone water –
1% peptone + 0.5% NaCl in water.
Synthetic or defined media
Special media
- Enriched media
- Selective media
- Differential media
- Transport media
- Anaerobic media
- Substances like blood, serum, egg are added to
the simple medium. - Used to grow bacteria that are exacting in their
nutritional needs.
Ex: fastidious microorganisms - Neisseria
gonorrhoeae) - eg: Blood agar, Chocolate agar
Enriched media
BAP contains mammalian blood(usually
sheep or horse) typically at a
concentration of 5-10%, used to isolate
fastidious organisms and detect
hemolysis.
Blood agar
contain red blood cells that have been lysed by
slowly heating to 80 c .and it used for growing
fastidious bacteria, such as Haemophilus
influenzae
Chocolate agar
Shows incomplete lysis of red blood cells
Alpha Hemolysis
shows complete lysis of red blood cells resulting in complete clearing around the colonies
Beta Hemolysis
no hemolysis, resulting in no change in the medium
Gamma Hemolysis
- The inhibitory substance is added to a solid media to inhibit
commensal or contaminating bacteria such as : - Antibiotics
- Dyes
- Chemicals
- Alteration of pH
Selective media
selective for Neisseria gonorrhoeae
* It usually contains the following combination of
antibiotics:
* Vancomycin:
which is able to kill most Gram-positive organisms.
* Colistin:
which is added to kill most Gram-negative organisms except
Neisseria.
* Nystatin:
which can kill most fungi
* Trimethoprim:
which inhibits Gram-negative organisms, especially
swarming Proteus.
Thayer Martin medium
kill most Gram-positive organism
Vancomycin
Kill most Gram-negative organisms except Neisseria
Colistin
Kill most Fungi
Nystatin
Which inhibits Gram-negative organism, especially swarming Proteus
Trimethoprim
