Culture media can be solid or liquid and are used to grow microorganisms. Solid media contains agar to solidify it and allow discrete bacterial colonies to form. Agar is extracted from seaweed and has the unique property of melting at 90°C and solidifying at 45°C, allowing solid media to be poured and incubated. Nutrient agar is a commonly used solid medium, containing peptones and beef or yeast extract for nutrients, agar for solidification, and sodium chloride to match microbial osmotic conditions. Liquid media like nutrient broth are also used but do not form discrete colonies, instead being used for bulk culture or testing liquid samples. Proper culture media, temperature, and nutrients are needed to cultivate

1. Culture Media
Solid media, Liquid media & use of agar
By
Dr C R Meera
Assistant Professor & HOD
Department of Microbiology
St. Mary’s College, Thrissur

2. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Culture Media
 A suitable culture media makes the cultivation of microorganisms possible in
laboratories.
 A culture media should contain all the necessary nutrients required for the
growth and multiplication of the organisms.
 Knowledge of normal habitat of a particular organism is useful in the selection of
media as their natural habitat reflects their nutritional requirements.
 Physical factors like optimum temperature, pH etc. also have to be maintained
properly.
 A culture media is used to grow, transport and store microorganisms

3. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Classification of Culture Media
 Culture media can be classified on the basis of several parameters
Physical
nature
• Liquid
• Solid
• Semisolid
Chemical
constituents
• Simple
• Complex
• Defined
• Semi-
defined
Function
• Supportive
• Special
Oxygen need
• Aerobic
• Anaerobic

4. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Liquid Media
 Liquid media is liquid in consistency.
 Louis Pasteur used liquid media for first time to cultivate microbes.
 In liquid media, microbes grow diffusely, so no discrete colonies are formed in
liquid media
 Disadvantages- Microbes cannot be easily identified from liquid culture
- Pure culture isolation is difficult from liquid media
 Advantages - To test large volume samples like blood and water
-Bulk culture preparation of microorganisms for antigen and
vaccine production.
 Most widely used liquid media now a days is Nutrient broth

5. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Liquid Media
 In liquid media microbes show growth patterns
Courtesy: Studyblue.com
Nutrient broth
Courtesy:blog.biomall.in

6. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Solid Media
 Solid media is solid in consistency.
 Contains the solidifying agent agar
 Earliest solid media was cooked cut potatoes used by Robert Koch
 Gelatine – next solidifying agent used - liquefied at 240 C and also digested
by proteolytic bacteria.
 Use of agar as solidifying agent was suggested to him by Frau Hesse
 Solid media are widely used than liquid media

7. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Solid Media
 Advantages:
• Microbes produce discrete colonies with particular
colony morphology
• Also exhibit other characteristics like pigmentation or
haemolysis
• Isolation of pure culture and identification of organisms
are easier
 Most widely used solid media is Nutrient agar
 Nutrient agar composition is same as nutrient broth
except the use of additional ingredient, agar.
Nutrient agar
Courtesy: emp.com

8. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Composition of Nutrient agar and Nutrient broth
Nutrient agar Nutrient broth Amount
Agar -- 20 g
Peptone Peptone 5 g
Yeast extract / Beef extract Yeast extract 3 g
NaCl (Sodium chloride) NaCl (Sodium chloride) 3 g
Distilled water Distilled water 1 Litre
pH pH 7±0.2

9. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Agar
 Universally used solidifying agent
 Agar is extracted from seaweeds or marine algae of
species Gelidium, mainly Gelidium corneum
 Long chain polysaccharides with varying amount of
inorganic salts and small quantities of protein like
substances
 Sulphuric acid esters of linear galactan
Agar powder
Courtesy: indiamart.com
Gelidium spp.
Courtesy: agephotostock.com

10. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Unique Properties of Agar
 Agar is insoluble in cold water and soluble in hot water
 Agar has no nutritive value and most microbes do not degrade it
 Most unique property of agar is that it melts at 900 C and sets at 450 C
 Also solid media with agar can be incubated at a wide range of temperatures
depending on the type of organisms cultivated.
 Usually 2% agar is used for the preparation of solid media
 Agar is commercially available as dehydrated powder or long shreds

11. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Peptone
 Peptone is another universal agent used in solid & liquid
media
 It is a complex mixture of partially digested proteins
from proteinaceous materials like meat, casein and
gelatine
 Protein molecules are broken up by acid or enzyme
hydrolysis into a series of smaller fragments like
proteoses, peptones, polypeptides and amino acids
 Peptone - usually include proteoses, polypeptides, amino
acids, variety of inorganic salts like Phosphate,
Potassium, Magnesium and riboflavin.
peptone powder
Courtesy: indiamart.com

12. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Peptone
 Peptone has nutritive value
 Main source of organic nitrogen
 Also contain vitamins and carbohydrate based on the
material digested
 Commercially different brands of peptone are now
available
 Different brands differ in composition and growth
promoting properties.

13. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Beef Extract
 Aqueous extract of lean beef tissue concentrated to paste
like form is called beef extract.
 It has nutritive value and consists of water soluble
substances of animal tissue
 Rich in protein, also contain carbohydrate, water soluble
vitamins and salts.
Beef Extract
Courtesy: alibaba.com
Yeast Extract
 It is aqueous extract of yeast cells available commercially in powder form.
 It is nutritious with rich source of B Vitamins, organic nitrogen and carbon
compounds.

14. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Sodium Chloride (NaCl)
 NaCl is not necessary for bacterial growth
 Maintains a salt concentration in the medium that is similar to the
cytoplasm of the microorganisms
 If the salt concentration is not similar, osmosis takes place transporting
excess water into or out from the cell
 Highly useful in media like blood agar which is an enriched media is usually
used to study haemolysis.
 Red Blood Cells get haemolysed when added to water or to media having
low osmotic pressure.

15. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,
Distilled water
 Distilled water is used for preparation of culture media since it is of
definite composition
 Calcium and Magnesium present in tap water react with phosphates
present in peptones, beef extract and other ingredients of culture media
 This will produce insoluble phosphates during sterilisation
 Media with insoluble phosphates throw down considerable precipitate

16. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,

17. Culture Media- Solid media, Liquid media & Use of Agar., Dr C R Meera,