culturing of microorganism
culturing of microorganism

Cultural techniques are used to isolate pathogens in pure
cultures so that they can be identified.
1- the culture media used for growing microorganisms
contains required nutreins in the correct amount, and PH
(6.5-7.5) of the medium are also correct.
2- the microorganisms are incubated in an atmosphere
(aerobic, anaerobic) and temperature (35-37C) most suited
to their metabolism.
3- the culture media used for growing microorganisms should
contain water and sources of nitrogen, carbon, menirals
and essential vitamins.
Classification of culture media
according to physical condition:

a. solid medium: contain 2% agar.
usually prepared in petridises

b. semisolid media: contain 0.4% agar

c. liquid medium: do not contain agar
and prepared in tubes.
Phenomena of bacterial growth

In liquid medium

On plate
Classification of culture media
according to basic ingredients

a. Minimal essential growth medium: such as nutreint
agar and nutrient broth that will support the growth of
M.O. that do not have special nutritional requirements.

b. Enrichment medium: these are required for the
growth of organisms special nutritional requirements
such as H. influenza, Neisseria species, ex. Chocolate agar
Classification of culture media according to
basic ingredients

c. Selective medium: contain substances (antibiotics) which inhibits
the growth of one organism to allow the growth of another to be
growe clearly demonstrated.

d. Differential medium: which contain dyes to differentiate
microorganisms. They distinguish between bacteria by incorporating
an indicator which changes color when acid is produced following
fermentation of a specific carbohydrate.

Many media used to isolate pathogens are both selective
and enrichment or both selective and differential.
Differential Media

Differentiates between different organisms
growing on the same plate
 Example:
– Blood Agar Plates (TSA with 5% sheep blood)
 used to differentiate different types of Streptococci
Alpha Hemolytic Streptococci
Incomplete lysis of RBC’s
Beta Hemolytic Streptococci
Complete lysis of RBC’s
Gamma Hemolytic Streptococci
No lysis of RBC’s
Selective and Differential
Media

Mannitol Salt Agar
– used to identify Staphylococcus aureus

Mannitol Salt Agar
– High salt conc. (7.5%) inhibits most bacteria
– sugar Mannitol
– pH Indicator (Turns Yellow when acid)
Selective and Differential
Media

MacConkey’s Agar
– used to identify Salmonella

MacConkey’s Agar
– Bile salts and crystal violet (inhibits Gram (+)
bacteria)
– lactose
– pH Indicator
Many Gram (-) enteric non-pathogenic bacteria can
ferment lactose, Salmonella can not
1. Obligate Aerobes
2. Obligate Anaerobes
3. Facultative Aerobes
Facultative Anaerobes
4. Microaerophilic
Microaerophilic Bacteria
A. Candle Jar
16 %
4%
O2
CO2