Culture media are mixtures that support microbial growth. They are used to isolate microbes, study properties, and perform quality control tests. There are several types including solid, liquid, and semi-solid media made with varying ingredients from simple to complex. Common culture methods to isolate microbes or study properties include streak, lawn, stab, pour plate, and liquid cultures. Preparing quality culture media and properly executing culture techniques are both important for effective microbial growth, though challenges can arise from media calculations, weighing, documentation, and sterilization.
3. Definition
Culture media, also known as growth
media, are specific mixtures of
nutrients and other substances that
support the growth of
microorganisms such as bacteria and
fungi (yeasts and molds).
4. Introduction
Culture media are used for quality control tests of
nonsterile raw materials and finished products as well
as for microbial contamination (sterility) tests in
applications such as hygiene monitoring, sterilization
process validation and determination of the
effectiveness of preservatives and antimicrobial
agents.
Microbial enumeration tests for nonsterile products
are performed according to the harmonized test
procedures of the European, US and Japanese
pharmacopoeias. These tests, formerly known as
Microbial Limit Tests (MLT), determine the bioburden
of the product sample.
5. Types of culture media
I. Based on their consistency
a) solid medium
b) liquid medium
c) semi solid medium
II. Based on the constituents/
ingredients
a) simple medium
b) complex medium
c) synthetic or defined medium
●●●
6. Types of culture media
Solid media – contains 2% agar
Colony morphology, pigmentation, hemolysis can be
appreciated.
Eg: Nutrient agar, Blood agar
Liquid media – no agar.
For inoculum preparation, Blood culture, for the
isolation of pathogens from a mixture.
Eg: Nutrient broth
●●●
7. Types of culture media
Semi solid medium – 0.5% agar.
Eg: Motility medium
●●●
8. Types of culture media
Based on the constituents/ ingredients
Simple media / basal media
- Eg: NB, NA
- NB consists of peptone, meat extract, NaCl,
- NB + 2% agar = Nutrient agar
●●●
9. Types of culture media
Complex media
Media other than basal media.
They have added ingredients.
Provide special nutrients
Synthetic or defined media
Media prepared from pure chemical substances
and its exact composition is known
Eg: peptone water – 1% peptone + 0.5% NaCl in
water
10. CULTURE METHODS
Culture methods employed depend on the purpose for
which they are intended.
The indications for culture are:
To isolate bacteria in pure cultures.
To demonstrate their properties.
To obtain sufficient growth for the preparation of
antigens and for other tests.
For bacteriophage & bacteriocin susceptibility.
To determine sensitivity to antibiotics.
To estimate viable counts.
Maintain stock cultures.
●●●
12. CULTURE METHODS
STREAK CULTURE
Used for the isolation of bacteria in pure culture from clinical
specimens.
Platinum wire or Nichrome wire is used.
One loopful of the specimen is transferred onto the surface
of a well dried plate.
Spread over a small area at the periphery.
The inoculum is then distributed thinly over the plate by
streaking it with a loop in a series of parallel lines in different
segments of the plate.
On incubation, separated colonies are obtained over the last
series of streaks.
●●●
13.
14. CULTURE METHODS
LAWN CULTURE
Provides a uniform surface growth of the bacterium.
Uses
For bacteriophage typing.
Antibiotic sensitivity testing.
In the preparation of bacterial antigens and
vaccines.
Lawn cultures are prepared by flooding the surface
of the plate with a liquid suspension of the
bacterium.
●●●
15. CULTURE METHODS
STROKE CULTURE
Stroke culture is made in tubes
containing agar slope / slant.
Uses
Provide a pure growth of
bacterium for slide agglutination
and other diagnostic tests.
●●●
16. CULTURE METHODS
STAB CULTURE
Prepared by puncturing a suitable medium
– gelatin or glucose agar with a long,
straight, charged wire.
Uses
Demonstration of gelatin liquefaction.
Oxygen requirements of the bacterium
under study.
Maintenance of stoke cultures.
●●●
17. CULTURE METHODS
POUR PLATE CULTURE
Agar medium is melted (15 ml) and cooled to 45oC.
1 ml of the inoculum is added to the molten agar.
Mix well and pour to a sterile petri dish.
Allow it to set.
Incubate at 37oC, colonies will be distributed
throughout the depth of the medium.
Uses
Gives an estimate of the viable bacterial count in a
suspension.
For the quantitative urine cultures.
●●●
18. CULTURE METHODS
LIQUID CULTURES
Liquid cultures are inoculated by touching with a
charged loop or by adding the inoculum with pipettes or
syringes.
Uses
Blood culture
Sterility tests
Continuous culture methods
Disadvantage
It does not provide a pure culture from mixed
inocula.
20. Conclusion
The preparation of culture media and their underlying
culture technique goes hand in handand affect each
other in either a good or bad way. When the
preparation of a culture media isalready poor that is,
it was not sterilized properly or that the experimenter
made some form ofmistake on the culture process,
even though the culture technique is good, the output
or thegrowth of bacteria would be influenced by the
quality of media used.
For the culture technique, itgoes to say that if the
culture technique was executed in an unsatisfactory
manner then microbialgrowth would still be affected.
