Skill lab No. 6 - Culture Medium
Culture medium is a solution of nutrient substances, which allows the growth or culture
micro-organisms in the laboratory. It contains water and various nutrients as sources of
Carbon, Nitrogen, Sulfur, Phosphorus, Growth factors and other inorganic salts.
Indications or Need for culture
• Isolate bacteria in pure cultures.
• Demonstrate their properties.
• Obtain sufficient growth for preparation of antigens & for other tests.
• Typing bacterial isolates.
• Antibiotic sensitivity.
Types of culture media based on consistency
• Liquid Media
• Semi-Solid Media
• Solid Media (Agar)
• Firm Media or Agar (More concentrated to prevent Swarming or motility)
• Double Phase Media (Castaneda)
Liquid Media
These do not contain agar and grow a mixture of microorganisms. Liquid media are used
as primary medium to prepare inoculum for isolation of pathogens by culturing on solid media
and drug sensitivity testing. Also used for transport of specimen.
Examples: Nutrient broth, Brain Heart Infusion Broth, Peptone water etc.
Semisolid Media
These contain 0.5% agar The solidifying agents are added to the liquid medium in order
to partially solidify them. They are dispensed in petri dishes either made up of plastic or glass.
Example: Motility medium
Solid Media
These contain 2% agar added to the liquid medium in order to solidify. They are
dispensed in petri dishes either made up of plastic or glass. The growth of microbes is obtained
as colonies over the medium. The colonial morphology, pigment production, hemolysis and
other characteristics can be appreciated.
Example: Blood agar, Mac Conkey agar, Nutrient agar, Chocolate agar
Types of culture media based on their Characteristics
Simple medium/basic culture medium
Enriched medium
Selective medium
, Differential medium
Transport medium
Composite medium
Simple medium/basic culture medium: It contains basic nutrients for bacterial growth e.g
peptone water, nutrient agar, nutrient broth.
Enriched medium: It is enriched by adding blood (5 – 10%) to the medium. e.g Blood agar,
Chocolate agar etc.
Selective medium: A medium, which favors the growth of a particular type of organism and
discourage the growth of unwanted organisms e.g Lowenstein Jensen medium for
Mycobacterium tuberculosis, SS agar (Salmonella, Shigella agar) for Salmonella & Shigella.
Usually some antibiotics or chemicals are added. Tellurite Blood agar, VCNT blood agar – V:
vancomycin, C: Colistin, N: Nystatin, T: Trimethoprim.
Differential medium: It helps in the identification of different bacterial pathogens e.g Mac-
Conkey agar help in the differentiation of lactose and non-lactose fermenting gram negative
enteric rods. CLED agar, TCBS
Transport medium: These are mostly semisolid media that contains ingredients to prevent the
overgrowth of Commensals and ensure the survival of pathogens (both aerobic and anaerobic)
when specimen cannot be cultured soon after collection. e.g Cary Blair medium to preserve
enteric pathogens. Stuart medium, Amies medium
Composite Media: For identification of isolates. e.g. Triple Sugar Iron
Commonly Used Culture Media
• Nutrient agar
• Blood Agar
• McConkey Agar
• Chocolate Agar
• Cystein Lactose Electrolyte Deficient (CLED) Agar
• Mueller Hinton Agar
• Tryptic Soya broth
• Brain Heart Infusion (BHI) Broth
• Lowenstein Jensen (LJ) Agar
• Thiosulphate Citrate Bile Suscrose (TCBS) Agar
• Sabouraud Agar
Culture medium is a solution of nutrient substances, which allows the growth or culture
micro-organisms in the laboratory. It contains water and various nutrients as sources of
Carbon, Nitrogen, Sulfur, Phosphorus, Growth factors and other inorganic salts.
Indications or Need for culture
• Isolate bacteria in pure cultures.
• Demonstrate their properties.
• Obtain sufficient growth for preparation of antigens & for other tests.
• Typing bacterial isolates.
• Antibiotic sensitivity.
Types of culture media based on consistency
• Liquid Media
• Semi-Solid Media
• Solid Media (Agar)
• Firm Media or Agar (More concentrated to prevent Swarming or motility)
• Double Phase Media (Castaneda)
Liquid Media
These do not contain agar and grow a mixture of microorganisms. Liquid media are used
as primary medium to prepare inoculum for isolation of pathogens by culturing on solid media
and drug sensitivity testing. Also used for transport of specimen.
Examples: Nutrient broth, Brain Heart Infusion Broth, Peptone water etc.
Semisolid Media
These contain 0.5% agar The solidifying agents are added to the liquid medium in order
to partially solidify them. They are dispensed in petri dishes either made up of plastic or glass.
Example: Motility medium
Solid Media
These contain 2% agar added to the liquid medium in order to solidify. They are
dispensed in petri dishes either made up of plastic or glass. The growth of microbes is obtained
as colonies over the medium. The colonial morphology, pigment production, hemolysis and
other characteristics can be appreciated.
Example: Blood agar, Mac Conkey agar, Nutrient agar, Chocolate agar
Types of culture media based on their Characteristics
Simple medium/basic culture medium
Enriched medium
Selective medium
, Differential medium
Transport medium
Composite medium
Simple medium/basic culture medium: It contains basic nutrients for bacterial growth e.g
peptone water, nutrient agar, nutrient broth.
Enriched medium: It is enriched by adding blood (5 – 10%) to the medium. e.g Blood agar,
Chocolate agar etc.
Selective medium: A medium, which favors the growth of a particular type of organism and
discourage the growth of unwanted organisms e.g Lowenstein Jensen medium for
Mycobacterium tuberculosis, SS agar (Salmonella, Shigella agar) for Salmonella & Shigella.
Usually some antibiotics or chemicals are added. Tellurite Blood agar, VCNT blood agar – V:
vancomycin, C: Colistin, N: Nystatin, T: Trimethoprim.
Differential medium: It helps in the identification of different bacterial pathogens e.g Mac-
Conkey agar help in the differentiation of lactose and non-lactose fermenting gram negative
enteric rods. CLED agar, TCBS
Transport medium: These are mostly semisolid media that contains ingredients to prevent the
overgrowth of Commensals and ensure the survival of pathogens (both aerobic and anaerobic)
when specimen cannot be cultured soon after collection. e.g Cary Blair medium to preserve
enteric pathogens. Stuart medium, Amies medium
Composite Media: For identification of isolates. e.g. Triple Sugar Iron
Commonly Used Culture Media
• Nutrient agar
• Blood Agar
• McConkey Agar
• Chocolate Agar
• Cystein Lactose Electrolyte Deficient (CLED) Agar
• Mueller Hinton Agar
• Tryptic Soya broth
• Brain Heart Infusion (BHI) Broth
• Lowenstein Jensen (LJ) Agar
• Thiosulphate Citrate Bile Suscrose (TCBS) Agar
• Sabouraud Agar
