Bacterial Culture Media: Classification, Types, Uses

By Acharya Tankeshwar •  Updated: 05/04/22 •  7 min read

Culture media contains nutrients and physical growth parameters necessary for microbial growth. If a culture medium meets a bacterial cell’s growth requirements, then that cell will multiply to sufficient numbers to allow visualization by the unaided eye.

All microorganisms cannot grow in a single culture medium and in fact, many can’t grow in any known culture medium. Organisms that cannot grow in the artificial culture medium are known as obligate parasitesMycobacterium leprae, Rickettsia, Chlamydia, and Treponema pallidum are obligate parasites.

Common bacterial culture media

Classification of Bacterial Culture Media

Bacterial culture media can be classified on the basis of composition, consistency, and purpose.

On the Basis of Consistency

Solid Medium

Solid culture media contain agar at a concentration of 1.5-2.0% or some other mostly inert solidifying agent. Solid medium has a physical structure and allows bacteria to grow in physically informative or useful ways (e.g. as colonies or in streaks). Solid culture media are useful for isolating bacteria or for determining the colony characteristics of the isolate. MacConkey agar, chocolate agar, nutrient agar, blood agar, etc are some examples of solid culture media.

Semisolid Medium

Semisolid culture media are prepared with agar at concentrations of 0.5% or less. Semisolid medium has a soft custard-like consistency and is useful for the cultivation of microaerophilic bacteria or for the determination of bacterial motility. Motility test medium, Stuart’s and Amies transport media, etc are semisolid media.

Liquid (Broth) Medium

These media contain specific amounts of nutrients but don’t have a trace of gelling agents such as gelatin or agar. Broth medium serves various purposes such as propagation of a large number of organisms, fermentation studies, and various other tests. e.g. sugar fermentation tests, MR-VP broth.

On the Basis of Functional Use

Nutrient Agar
Nutrient Agar

Many special-purpose media are needed to facilitate the recognition, enumeration, and isolation of certain types of bacteria. To meet these needs, numerous media are available.

Bacteria with complex nutritional requirements are called fastidious bacteria. Special nutritional supplements must be added to culture media to grow such bacteria. Bacteria having relatively basic and straightforward nutritional requirements are easy to grow in a lab, they are known as nonfastidious bacteria.

General-Purpose Media

Basal media also called general-purpose media are basically simple media that support the growth of most non-fastidious bacteria. Peptone water, nutrient broth, and nutrient agar (NA) are considered basal media. These media are generally used for the primary isolation of microorganisms.

Enriched Media

Blood Agar

Addition of extra nutrients in the form of blood, serum, egg yolk, etc, to the basal medium makes an enriched medium. Enriched media are used to grow nutritionally exacting (fastidious) bacteria. Blood agar, chocolate agar, Loeffler’s serum slope, etc are a few examples of enriched media. Blood agar is prepared by adding 5-10% (by volume) blood to a blood agar base. Chocolate agar is also known as heated blood agar or lysed blood agar.

Selective and Enrichment Media

These media are designed to inhibit unwanted commensal or contaminating bacteria and help to recover pathogens from a mixture of bacteria. While selective media are agar-based, enrichment media are liquid. Both these media serve the same purpose. Any agar media can be made selective by the addition of certain inhibitory agents that don’t affect the pathogen of interest. Various approaches to making a medium selective include addition of antibiotics, dyes, chemicals, alteration of pH, or a combination of these.

Selective Media

Principle: Differential growth suppression
Selective medium is designed to suppress the growth of some microorganisms while allowing the growth of others. Selective medium is an agar-based (solid) medium so that individual colonies may be isolated.

Examples of selective media include

  1. Thayer Martin Agar used to recover Neisseria gonorrhoeae contains antibiotics; vancomycin, colistin, and nystatin.
  2. Mannitol Salt Agar and Salt Milk Agar used to recover S.aureus contains 10% NaCl.
  3. Potassium tellurite medium used to recover C.diphtheriae contains 0.04% potassium tellurite.
  4. MacConkey’s Agar used for Enterobacteriaceae members contains bile salt that inhibits most gram-positive bacteria.
  5. Pseudosel Agar (cetrimide agar) used to recover Pseudomonas aeruginosa contains cetrimide (antiseptic agent).
  6. Crystal Violet Blood Agar used to recover S. pyogenes contains 0.0002% crystal violet.
  7. Lowenstein Jensen Medium used to recover M.tuberculosis is made selective by incorporating malachite green.
  8. Wilson and  Blair’s Agar for recovering S. typhi is rendered selective by the addition of dye brilliant green.
  9. Selective media such as TCBS Agar used for isolating Vibrio cholerae from fecal specimens have elevated pH (8.5-8.6), which inhibits most other bacteria.
LF and NLF colonies in MacConkey Agar
Lactose fermenting (pink) and non-lactose-fermenting (colorless/pale) colonies in MacConkey Agar

Enrichment Media

Enrichment medium is used to increase the relative concentration of certain microorganisms in the culture prior to plating on a solid selective medium. Unlike selective media, enrichment culture is typically used as a broth medium. Enrichment media are liquid media that also serves to inhibit commensals in the clinical specimen. Selenite F broth, tetrathionate broth, and alkaline peptone water (APW) are used to recover pathogens from fecal specimens.

Differential/ Indicator Media

Certain media are designed in such a way that different bacteria can be recognized on the basis of their colony color. Various approaches include incorporation of dyes, metabolic substrates, etc, so that those bacteria that utilize them appear as differently colored colonies. Such media are called differential media or indicator media. Differential media allow the growth of more than one microorganism of interest but with morphologically distinguishable colonies.
Examples of differential media include:

  1. Mannitol salts agar (mannitol fermentation = yellow)
  2. Blood agar (various kinds of hemolysis i.e. α, β and γ hemolysis)
  3. MacConkey agar (lactose fermenters, pink colonies whereas non-lactose fermenter produces pale or colorless colonies.
  4. TCBS (Vibrio cholerae produces yellow colonies due to fermentation of sucrose)

Transport Media

Clinical specimens must be transported to the laboratory immediately after collection to prevent overgrowth of contaminating organisms or commensals and maintain the viability of the potential pathogens. This can be achieved by using transport media. Such media prevent drying (desiccation) of a specimen, maintain the pathogen to commensal ratio, and inhibit the overgrowth of unwanted bacteria. Some of these media (Stuart’s & Amie’s) are semi-solid. The addition of charcoal serves to neutralize inhibitory factors.

Anaerobic Media

Anaerobic bacteria need special media for growth because they need low oxygen content, reduced oxidation-reduction potential, and extra nutrients.

Media for anaerobes may have to be supplemented with nutrients like hemin and vitamin K. Such media may also have to be reduced by physical or chemical means. Boiling the medium serves to expel any dissolved oxygen. The addition of 1% glucose, 0.1% thioglycollate, 0.1% ascorbic acid, 0.05% cysteine, or red hot iron filings can render a medium reduced. Before using, the medium must be boiled in a water bath to expel any dissolved oxygen and then sealed with sterile liquid paraffin.

Robertson Cooked Meat (RCM) medium that is commonly used to grow Clostridium spp contains a 2.5 cm column of bullock heart meat and 15 ml of nutrient broth. Thioglycollate broth contains sodium thioglycollate, glucose, cystine, yeast extract, and casein hydrolysate.

Methylene blue or resazurin is an oxidation-reduction potential indicator that is incorporated into the medium. Under the reduced conditions, methylene blue is colorless.

Assay Media

These media are used for the assay of vitamins, amino acids, and antibiotics. For e.g., antibiotic assay media are used for determining antibiotic potency by the microbiological assay technique.
Other types of medium include;

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

39 responses to “Bacterial Culture Media: Classification, Types, Uses”

  1. pooja says:

    What is CRA media for azospirillum isolation

  2. Neelam Devi says:

    Thank you sir……for useful n knowledgeable contents

  3. kenson munthali says:

    can u help me on can one prepare a nutrient agar to culture bactria

  4. PAUL says:

    Can you mix blood Agar and nutrient Agar and if yes , what are the results?

  5. Kelechi Ukaegbu-Obi says:

    I am working on biogas production using human excreta and cassava peels. can you suggest the various media I should use for isolation and identification of organisms; since it’s an anaerobic process.

  6. Abdulrahman Hamid says:

    I think it will be more interesting if the different medias type will be cited with common example of bacteria… thank you.

  7. sisay says:

    i am happy withn your explanations

  8. Nahom Getachew says:

    Your blog is really helpful, excellent pictures.

  9. Anastasia says:

    Is there any difference between peptone water and peptone broth?

  10. Tom says:

    May I ask which Sources you used for this article?

  11. Peace says:

    Plz I need references on this article. Plz how do I get it

  12. caryl says:

    Hi, we did an experiment using peptone media to check if the water we collected from wells was safe, after 24 hours we found that the water with the peptone media turned dark and slimy. Was that caused by the peptone? Thank you.

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