2. What is culture media ?
■ Culture media are mediums that provide essential nutrients and minerals to
support the growth of microorganisms in the laboratory.
■ Microorganisms have varying nature, characteristics, habitat, and even
nutritional requirements, thus it is impossible to culture them with one type
of culture media.
■ However, there are also microorganisms that can’t grow on a culture media at
all in any condition – these are called obligate parasites.
3. Advantages
Culturing micro-organisms is essential for :
■ Identification of microbial species
■ Isolating pure culture
■ Studying biochemical reactions
■ Testing microbial contamination
■ Testing viable counts
■ Testing antibiotic sensitivity
■ Storing culture stocks
■ Diagonsing infectious disease
■ Obtaining antigens
4. Classifiaction and types of
culture media
■ Growing microorganisms in the lab involve mimicking the organisms’ natural
habitat or environment, and this is possible in the laboratory by formulating
culture media that meets their requirements.
■ Therefore, many culture media were developed by scientists according to the
microbial species to be cultured.
■ The basic media contains :
Carbon and energy source
Nitrogen source
Growth factors
Some trace elements
5. ■ Some commonly used media components include :
Peptone Malt extract
Agar Meat extract
Water Yeast extract
Casein hydrolysate
■ In addition, the pH of the medium should be set accordingly.
■ However, some additional components or nutrients are added to the media
when growing specific microorganisms.
6.
7. Classification of culture media based on
consistency
1. Solid media
■ In these media, 1.5 - 2 % concentration of agar is added.
■ Most commonly, 1.3% agar is used to prepare solid media in labs.
■ Sometimes, in the place of agar, some other inert solidifying agents are used,
such as gellatin.
Uses : To grow microorganisms in their full physical form.
Perepare bacterial pure culture .
Isolate bacteria to study colony.
8. Advantages
(a) Bacteria can be identified by studying the colony character.
(b) Mixed bacteria can be seperated.
Diadvantages
(a) Large volumes of inoculas cannot be accommodated in solid media
(b) At times, solid media dehydrates, thus losing its ability to support bacterial
growth.
Examples: blood agar, nutrient agar,
McConkey agar, and chocolate agar.
9. Composition of Nutrient Agar Medium
(NAM)
Peptone – 5 gm
Beef extract – 3 gm
Sodium chloride – 5 gm
Agar – 15 gm
Distilled water – 1000ml
10. 2. Semi-solid media / Floppy media
■ This media has 0.2-0.5% agar concentration.
■ it appears as a soft, jelly-like substance due to the reduced agar
concentration.
Uses: It’s mainly used to study the motility of microorganisms.
Distinguish between motile and non motile strains.
Advantages
(a) This media allows motile bacteria to move and grow in the medium.
Diadvantages
(a) Tedious nature of the method
(b) Uncertainity of the results
(c) Difficulty of identifying the motility when only few cells are motile.
11. Examples: Hugh and Leifson’s oxidation fermentation medium, Stuart’s and Amies
media, and Mannitol motility media.
12. 3. Liquid media
■ These media do not contain any traces of solidifying agents, such as agar or
gelatin.
■ Large growth of bacterial colonies can be observed in the media.
■ Liquid media are also called broths, they allow for uniform and turbid growth
of bacterial strains when Incubated at 37ºC for 24hrs.
Uses : It is used for the profuse growth of microorganisms and fermentation
studies.
Advantages
(a) It offers a uniform culture condition for the growth of bacteria .
(b) It is easy to sterilize .
13. Disadvantages
(a) Sometimes bacteria growing in liquid media may lack some characteristics.
(b) Also, it may be challenging to isolate various types of bacteria, especially
when they are from a fixed population.
Examples:Tryptic soy broth, phenol red carbohydrate broth, MR-VP broth, and
nutrient broth.
14. Classification based on the
nutritional components
1. Simple media :It’s a general-purpose media that supports the growth of non-
fastidious microbes, and it is primarily used for the isolation of microorganisms.
Examples : nutrient broth, peptone water, and nutrient agar.
2. Compelx media: These are media containing nutrients in unknown quantities that
are added to bring about a particular characteristic of a microbial strain
Examples: tryptic soy broth, blood agar, and nutrient broth.
3. Synthetic media: Synthetic media is a type of chemically defined media and is
produced from pure chemical substances.
Examples: Czapek Dox Medium
15. Classification based on
application
■ Basal media: These are routinely used simple media having carbon and nitrogen
sources that boost the growth of many microorganisms. They are also known as
general-purpose media and are considered non-selective media.
The basal media do not require enrichment sources for the growth of non-
fastidious bacteria and are suitable for growing Staphylococcus and Enterobacteriaceae.
Examples:nutrient broth, nutrient agar, and peptone water.
■ Enriched media: This media is prepared by adding additional substances like blood,
serum, or egg yolk in the basal medium. It’s used to grow fastidious microorganisms
as they require additional nutrients and growth-promoting substances.
Examples:chocolate agar, blood agar, and Loeffler’s serum slope.
16. ■ Selective media: This media allows the growth of certain microbes while
inhibiting the growth of others. It’s an agar-based medium that is used to isolate
microorganisms in labs.
The selective growth of microbes is decided by adding substances like
antibiotics, dyes, bile salts, or by pH adjustments.
Examples: Mannitol salt agar, crystal violet blood agar,etc.
■ Enrichment media: It’s a liquid medium, used to increase the relative
concentration of certain microbes before culturing them on a solid medium
plate.
It’s also used in isolating fecal and soil microorganisms.
Examples: selenite F broth which is used to isolate Salmonella typhi from a fecal
sample, tetrathionate broth, and alkaline peptone water.
17. ■ Differential or indicator media: It contains certain indicators like dyes or
metabolic substrates in the medium composition which gives different colors to
colonies of different microbial species when they utilize or react with these
components.
It allows the growth of more than one microorganism, however, the bacterial
colonies are differentiated based on their color when a chemical change occurs in
the indicator, such as neutral red, phenol red, methylene blue.
Examples: Blood agar, Mannitol salts agar, MacConckey agar, Thiosulfate citrate
bile salts sucrose (TBCS)agar.
18. ■ Transport media: Transport media are useful for clinical specimens which are
required to be transferred immediately to labs to maintain the viability of
potential pathogens and to prevent overgrowth of commensals or
contaminating microorganisms.
Examples:
(a) Sach’s buffered glycerol saline - It’s used to transport feces from patients
suspected to be suffering from bacillary dysentery.
(b) Pike’s medium - throat specimen containing Streptococci is transported using
this medium.
19. ■ Storage media: It’s used to store microorganisms for a longer period.
Examples: chalk cooked meat broth and egg saline medium.
20. Conclusion
■ Culture media is a source of nutrients and growth factors required for the
growth of microorganisms and even plants in laboratory conditions.
■ Every organism has different nutritional requirements based on its habitat or
living conditions. Therefore, a single formulation of culture media can’t be used
to grow all organisms in labs.
■ Many types of culture media have been developed by scientists to grow
selective or desired microorganisms.
■ These are classified based on their nutrient composition, consistency, and
application or use in life science laboratories.
■ Culture media serve several purposes in labs like isolating specific strains of
microorganisms, identifying disease-causing pathogens, preparing pure culture
of a microbial species, distinguishing bacterial species, and studying their
responses to certain antibiotics.
21. ■ Thus, before deciding which culture media to use, it is critical to determine the
purpose of your study and in some cases the type of microorganism you want
to study.
■ This narrows down your choices and helps you to choose which media is best
for your experiment, without wasting your time and effort.
