Classification of Culture Media

When it comes to culturing bacteria, it is crucial to create the same environmental and nutritional conditions as those found in the natural environment. The majority of culture mediums contain water, which is a major source of carbon and energy and nitrogen. It also contains trace elements, as well as some growth factors. In addition, the pH as well as oxygen tension and Osmolarity must also be considered. Some of the components of media for culture include: Although tap water is appropriate for the use of culture media, it shouldn’t be used in the event that it contains a significant amounts of minerals. In these instances the use of demineralised or distillated water is recommended.

Peptone is one of the byproducts of digestion of proteins. Proteins are usually derived from the heart muscle, casein fibrin, soya flour or casein and digested with proteolytic enzymes like papain, pepsin, or trypsin. The final product is composed of amino acids in addition to a variety of inorganic salts, including magnesium, potassium and phosphates.

Casein hydrolysate can be obtained by the hydrolysis of casein, a milk protein with HCl and trypsin. Meat extract is derived from the extraction of hot water from lean beef. It is then concentrated through the process of evaporation. The yeast extract is made from the washed yeast cells and includes a wide variety of amino acids growth factors, growth factors and organic salts.

What is a Culture Medium?

The culture medium is affectionately described as a growth medium since it provides a specific space for the growth of microbial life. The medium can be solid, liquid, or an solid based on the application method and the bacteria we have. The fundamental ingredients that are the same for all culture media include electrolytes such as water, salt chloride and peptone and meat or beef extracts. Not just microbes but every kind or cell (plant as well as animal) can be grown using media for culture.  


Louis Pasteur used simple broths composed of meat or urine extracts. Robert Koch realized the importance of solid media and utilized potato pieces to cultivate bacteria. It was because of the advice of Fannie Eilshemius who was the wife of Walther Hesse (who was an assistant to Robert Koch) that agar was utilized to make solid culture media. Before the invention of agar, efforts were made to use gelatin as a an agent for solidification. Gelatin was not without its own issues; it was a liquid at normal temperatures (35-37oC) but was consumed by certain bacteria. 

Principle of culture media

The elements in culture media can range from pure chemical compounds to more complex substances like digests or extracts of animal and plant tissues. If all the components of a medium for culture are identified, both quantitatively and qualitatively, it is termed Chemically defined medium. They are of tremendous importance in studying the nutritional needs of microorganisms, or in studying the variety of their metahlic actions. In a highly complex medium the precise chemical composition of corn is not fully understood, and this kind of medium is typically made from complex substances, e.g., body fluids, tissue extracts and infusions.

Commonly Used Constituents in Culture Media

1. Carbohydrates

Alcohols and carbohydrate are used as energy and carbon sources that stimulate the proliferation of microorganisms. Carbohydrates can also assist in the identification of microorganisms and differentiation.

2. Agar 

Agar is the main ingredient used to solidify microbiological media. It is a non-pure polysaccharide gum derived from specific marine algae. It is added in the form of an insoluble powder at a higher than or less standard amount (1.5 percent in slanted and plates, 0.5% or less for “semisolid media) generally after other components of the medium are added and dissolving in water. Agar disintegrates at around 100 degrees Celsius Agar-containing media which is heated will not begin to be solid until the temperature has been decreased to 43 degrees. Once it has solidified, the medium won’t melt until brought back to around 100 degrees Celsius.

Commonly Used Constituents in Culture Media
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Uses of agar

  • It is among the most important ingredients for the production of semisolid or solid media.
  • It serves as an agent of solidification in the culture medium.
  • This is made from seaweeds belonging to genera that are red algae such as Gelidium as well as Gracilaria.
  • It’s a sulphated, polymer mostly composed of D-galactose.
  • Agar is a popular for its ability to solidify because it doesn’t affect the development of microorganisms. Agar is also utilized in the pharmaceutical and food industries.
  • The purified form of Agar is known as Agarose. It is made by stripping all pectin in the Agar. It is utilized in the Molecular Biology laboratory for the separation of DNA molecules using electrophoresis on gels.

Why agar is used as an ideal solidifying agent?

Agar is a great solidifying agent because it :

  • Inert to bacteria, i.e. no influence on bacterial growth,
  • It is still solid at 37degC and
  • It’s transparent.

3. Body Fluids

Defibrinated or whole blood plasma, serum, or other bodily fluids are typically added to media for culture in order to aid in the cultivation and isolation of numerous pathogens. Body fluids are a source of many growth factors, and/or chemicals that detoxify inhibitors.

4. Buffers

These substances are added to ensure the optimal pH range for the organism. Substances such as potassium and sodium phosphates as well as calcium carbonate, keep pH from undergoing drastic changes that would otherwise be caused by the microbial production of organic bases or acids.

5. Extracts (Beemeast)

Eucaryotic tissues (yeast muscles, beef brain, liver and so on.) are extracted through boiling and then pressed into the form of a paste or dried into powder. Extracts of this kind are often utilized as a source of amino acids and vitamins, and coenzymes. They include many of the elements needed for growth by the most meticulous organisms. Minerals and trace elements and often sugar are also found.

6. Peptones

The complex mixtures of organic and inorganic substances are derived from the digesting protein-rich tissues from animals and plants , including carcass scraps of meat, beef muscle gelatin and the milk proteins (casein) as well as soybean meal. Peptones are mainly composed of peptides and one amino acid. As crude digests of complicated materials they include a wide assortment of organic and inorganic substances. Examples include Tryptone (a digestion of the pancreas made of the casein), Phytone (a papaic digest of soybean meal) and Peptone (a digest made from muscle from beef).

7. pH Indicators

A pH indicator for acid is typically added to different media to monitor variations in the hydrogen ion concentration in the course of the growth of an organism. This is the case for example in Carbohydrate Fermentation Broth Kligler Iron Agar, Simmons Citrate Agar, MacConkey Agar and the Glucose OIF Medium. Brom-thymol blue, brom-cresol purple as well as phenol red, are frequently employed. For each indicators, pH that is acidic changes the indicator yellow.

8. Reducing Agents

Certain chemicals can promote growth by reducing the oxidation reduction potential of the environment. Cystine and Thioglycollate are two reducing agents commonly used in cultivating anaerobes.

9. Selective Agents

Antimicrobial substances like the crystal violet and bile sodium salts, bright green, potassium tellurite sodium azide, and antibiotics can be utilized in selective media to inhibit or stop the growth of specific groups of microorganisms and allow the expansion of the desired organisms. These are generally bacteriostatic agents.

Classification of Culture Media
Classification of Culture Media | Image Source:×613.jpg

Classification of Culture Media based on Consistency

*Media for Bacterial Culture may be classified at minimum three ways. Based on Consistency, based on the nutrition, and on its function.

  1. liquid media
  2. semi-solid media
  3. solid media

A. Liquid media

  • They can be used in bottles, test tubes or flasks.
  • Liquid media can be referred to in the form of “broths” (e.g nutritional broth).
  • In liquid medium, the bacteria develop uniformly, causing general turbidity.
  • Certain aerobic bacteria as well as ones that contain fimbriae (Vibrio and Bacillus) are well-known to develop as a thin film known as’surface”pellicle” over the top of an unaffected broth.
  • Bacillus anthracis is known for its ability to create stalactite growth in the ghee-containing broth. Sometimes , the initial turbidity could be followed by a clearing through autolysis, which is observed in penumococci.
  • The long chains that comprise Streptococci when developed in liquid media are likely to form a knot and then sink to the bottom, creating small deposits. 

Disadvantages of Liquid media

  • The characteristics of bacteria aren’t evident in liquid media, and the the presence of multiple kind of bacteria is not detectable.
  • Identification of mixed cultures within liquid mediums requires the transfer of subculture to solid media, so that the isolated colonies can be separated to determine their identity.
  • Growth in liquid media isn’t usually quantifiable.
  • Bacteria that are grown in liquid cultures usually create colloidal suspensions

Application of Liquid media

  • It is employed for large-scale expansion, e.g. the culture of blood in liquid medium. The mixed organisms are not able to be distinguished
  • Liquid media are generally utilized when a huge amount of bacteria need to be produced.
  • They can be used to cultivate bacteria when the number of organisms in the inoculum are thought to be low.
  • Inoculating the liquid medium can also help to reduce any inhibitors that hinder bacteria’s growth.
  • This is the method that can be used to use blood samples.
  • The process of culturing with liquid media may be used to determine a the viable counts (dilution techniques).

Example of Liquid media

1. Peptone water

  • Composition: Peptone, sodium chloride, water
  • Applications: Routine culture, the base for sugar fermentation test, indole test

2. Nutrient broth

  • Composition: Peptone water, meat extract
  • Applications: Routine culture

3. Glucose broth

  • Composition: Nutrient broth, glucose
  • Applications: Blood culture, culture of fastidious organisms, such as streptococci

4. Brain heart infusion broth 

  • Composition: Sodium citrate, sodium chloride, Whole blood, bone sodium phosphate, dextrose marrow, body fluid peptone, brain and heart culture infusion broth (ox), sodium polyanethol sulfonate (SPS)

5. Alkaline peptone water

  • Composition: Peptone water (pH 8.6)
  • Applications: Enrichment medium for Vibrio

6. Selenite-F broth

  • Composition: Peptone water, sodium selenite
  • Applications: Enrichment medium for feces for Salmonella and Shigella

7. Tetrathionate broth

  • Composition: Nutrient broth, sodium thiosulfate, calcium carbonate, iodine solution
  • Applications: Culture of feces for Salmonella

8. Robertson’s cooked meat (RCM) broth

  • Composition: Nutrient broth, predigested cooked meat of ox heart 
  • Applications: Anaerobic bacterial culture

B. Solid media

  • Any liquid medium is made solid through the addition of specific substances that help in the process of solidification.
  • Agar agar (simply called Agar) is one of the widely utilized solidifying agent. It is a unbranched polysaccharide made from cell membranes of a few varieties of algae, such like the ones in Gelidium.
  • Agar is comprised of two polysaccharides with long chains (70 percent agarose, and 30 percent of agarapectin).
  • Agar melts at 95degC , and it solidifies at temperatures of 42oC. It does not provide any nutritional properties and isn’t hydrolyzed by the majority of bacteria, and is generally free of growth-promoting or growth retarding substances.
  • Agar powders are available.
  • New Zealand agar and Japanese agar are used most often in concentrations of 2and 4 percent respectively, to create an agarmedium-like solid.

Advantages of solid media

  • Bacteria can be identified by looking at the colony’s character.
  • It is possible to separate mixed bacteria.


  • Solid media cannot handle large inocula volumes, usually larger than 0.05ml.


  • Solid media are used to isolate bacteria in pure cultures.

Example of solid media

1. Nutrient agar

  • Composition: Nutrient broth, agar 2%
  • Applications: Routine culture

2. MacConkey medium

  • Composition: Peptone, lactose, sodium taurocholate, agar, neutral red 
  • Applications: Culture of Gram-negative bacteria, such as Escherichia coli

3. Blood agar

  • Composition: Nutrient agar, 5% sheep or human blood
  • Applications: Routine culture, culture of fastidious organisms, such as Streptococcus spp.

4. Chocolate agar

  • Composition: Heated blood agar
  • Applications: Culture of Haemophilus influenza and Neisseria

5. Deoxycholate citrate agar

  • Composition: Nutrient agar, sodium deoxycholate, sodium citrate, lactose, neutral red, etc.
  • Applications: Culture of Shigella spp. and Salmonella spp.

6. Thiosulfate citrate bile salt bile salt sucrose agar

  • Composition: Thiosulfate, citrate, bile salt, sucrose, bromothymol blue, thymol blue
  • Applications: Culture of Vibrio cholerae

7. Loeffler’s serum slope

  • Composition: Nutrient broth, glucose, horse serum
  • Applications: Culture of Corynebacterium diphtheriae

8. Lowenstein- Jensen medium

  • Composition: Coagulated hen’s egg, mineral salt solution, asparagine, malachite green
  • Applications: Culture of Mycobacteriu tuberculosis

B. Semisolid media

  • The reduction of that amount by 0.2-0.5 percent produces a semi-solid medium.
  • They are surprisingly soft and can be useful for showing the motility of bacterial cells (U-tube and Cragie’s Tube).
  • Certain transport media, like Stuart’s as well as Amies Media are semisolid in their consistency. Hugh and Leifson’s oxidation ferment test medium and the mannitol-based motility medium are semi-solid.

Advantages of Semisolid media

  • Semi-Solid Media allows bacteria to move around and expand in the medium unlike solid media.
  • High melting point material for the formation
  • Extending die life
  • Less casting imperfections (shrinkage oxides, voids, porosity)
  • Laminar filling behaviour, Fine grain structure
  • Forging intricate parts, lower power of making

Disadvantages of Semisolid media

  • High cost billets are made using electromagnetically processing (Thixo)
  • Initial investment is high, but it will be a long way to the point of mass-production (Thixo)
  • Control of cycle time to ensure mass production
  • Induction heating stage to fix the problem of cycle time (Thixo,
  • Liquid segregation after forming

Application of Semisolid media

  • Semi-Solid Media are utilized to measure the motility of bacterial cells

Example of Semisolid media

  • Certain transport media like Stuart’s or Amies Media are semi-solid in their consistency.
  • Hugh & Leifson’s Oxidation Fermentation test medium and the mannitol-based motility medium are semi-solid.

C. Biphasic media

  • Sometimes the culture system consists of solid and liquid medium inside the exact same container. This is referred to in biphasic medium (Castaneda technique for the blood-culture).
  • The inoculum is added into the liquid medium. When subcultures are being created the bottle is turned so that the liquid can flow across the medium. This eliminates the requirement to open the bottle of culture to make subculture.
  • In addition to eggs, agar, and serum can also be used to make culture media more solid. Although egg yolk and serum are typically liquids however, they can be made solid through coagulation with heat.
  • Mediums that contain serum, like Loeffler’s serum slope as well as egg-containing media like Lowenstein Jensen medium, and Dorset egg medium are cured as well as disinfected via an inspissation process.

Classification of culture media based on the nutritional component

1. Simple media

The most basic media are nutrient broth as well as peptone water. They serve as the base for other media.


  • Nutrient broth: Nutrient broth can be described as a basic liquid medium made of peptone, extracts from meat as well as sodium chloride and water. The addition of 0.5 percent glucose to the nutritional broth results in glucose broth.
  • Nutrient agar: Nutrient Agar can be described as a straightforward solid medium. Themedium is frequently used to isolate a variety of species of bacteria in clinical samples.

2. Complex media

Complex media are composed of a number of complex ingredients, that are composed of a mix of several chemicals with unknown amounts. This is an unspecified medium since amino acid sources contain various compounds, with the precise composition that is unknown. The complex media comprise:

  • Water,
  • A carbon source , such as glucose that is used to stimulate growth of bacterial,
  • Different salts are needed to promote bacterial growth.
  • A good source of amino acids along with nitrogen (e.g. beef, the extract of yeast).


The majority of media, other than the basal media are generally referred to as complex media for instance;

  • chocolate agar, 
  • MacConkey agar, 
  • Robertson’s cooked meat (RCM) medium, 
  • Lowenstein–Jensen (LJ) medium

3.  Define Media/Synthetic medium

A clearly defined medium, also referred to a synthetic medium, has certain quantities of each ingredient. The chemicals employed are well-known and does not contain yeast, animals or plant tissues. The media comprise:

  • Vitamins and trace elements;
  • A clearly defined Carbon source as well as a nitrogen source that is required by some microbes. Glycerol or glucose is frequently utilized as carbon sources, and ammonium salts or nitrates are organic nitro-gen sources.


  • Dubos medium that has Tween 80 provides an illustration of the type of medium.

Classification of culture media based on functional use or application

1. Basal medium

  • This medium aids in the growth of a variety of microorganisms, which don’t require any particular nutrient supplement.
  • Basal media are fundamentally simple media that can support most non-fastidious bacteria.
  • It is a typical lab medium that has Carbon or Nitrogen as sources, along with a few minerals.
  • It’s also referred to as general use medium.
  • It is used to subculturing pathogens.
  • This is an non-selective media that was designed to encourage development of diverse variety of heterotrophic species.
  • Example: Peptone water, Nutrient Agar or Nutrient Broth. 

2. Enriched media

  • The media are created by adding serum, blood eggs, and serum to the base media to meet the nutritional needs of more precise and meticulous bacteria.
  • The media that are enriched are always solid media.
  • It’s used to create highly specialized organisms (nutritionally demanding) that are highly specific in their nutritional requirements.
  • Highly discerning organisms have a complex requirement of certain nutrients, such as vitamins and growth-promoting substances and are not easily satisfied or contented by the normal natural nutrients.
  • Blood Agar is a rich medium that is nutrients-rich whole blood supplements provide the essential nutrients.
  • Chocolate agar is enhanced with blood that has been heated (80degC) and transforms into brown, giving the medium the colour for the reason it’s called.
  • Example: Blood agar, chocolate agar, Loeffler’s serum slope etc are few of the enriched media. 

3. Enrichment media

  • The Enrichment Medium is liquid.
  • It is utilized to cultivate specific microorganisms that are only present in smaller numbers as well as other microorganisms that are that are present in sufficient numbers.
  • A medium for enrichment provides the nutrients and conditions for environmental that favor the growth of desired microorganism.
  • It is used to cultivate microorganisms that are present in soil or in faecal samples that are extremely small in numbers.
  • Example: Selennite F Broth has been used in the past to separate Salmonella Typhi, which is found in low concentration in the samples of faeces. It is then cultured in an enrichment media containing Selenium. Selenium helps to promote an increase in the size of the organism and increases the amount of detectable levels when in comparison to the intestinal flora. The selenite sulfate of sodium inhibits a variety that are Gram positive or Gram negative such as Enterococci and Coliforms.

4. Selective medium

  • Selective media contains several agents (selective components) which block unwanted organisms, but permit the organisms you want to grow.
  • The growth of undesirable microbes is prevented by adding the bile salts, antibiotics, and dyes.
  • Any media that is agar can be modified to make it selective through the using inhibitory agents that do not affect the pathogen.
  • Many methods of making an agent selective may involve the adding dyes, antibiotics chemical compounds, changes in pH or the mix of them.
  • Example: Succinate Broth, Mannitol salt agar, MacConkey Agar, Nitrogen-Free Broth.

Mannitol salt agar

Mannitol salt agar is selectiv for Staphylococci. The medium is enriched with 77 percent Sodium chloride which blocks the expansion of other bacterial populations however it allows for the development of Staphylococci. Furthermore, it includes Phenol red dye that indicates acid production. Staphylococcus makes use of Mannitol and creates acid that alters the color of the Phenol red indicator from yellow to red. Salmonella-Shigella (SS) agar is selective for Salmonella.

MacConkey Agar

This is an illustration of a medium that has specific agents are added that directly inhibit the growth of undesirable organisms in the maximum extent that is possible. The specific agents selected for this medium are bile salts, crystal violet block gram-positive bacteria and allow the nearly-exclusive growth of gram negative bacteria.

Nitrogen-Free Broth

The medium is made selective through the elimination of a crucial element. No nitrogen compounds are found. Thus, the only organisms that are able to grow after being inoculated into the medium are those that can make use of the gaseous nitrogen (N2) which is absorbed through the air. They are nitrogen fixing bacteria. Although this medium does not make use of the use of selective agents, it remains restricting to a large number of different organisms.

Succinate Broth

In this case the nutrient that is used by the organism of interest – and a few others – is used as the sole carbon source. This medium is utilized to enrich the non-sulfur photosynthesis bacteria that are purple The majority of other organisms are to not metabolize succinate in the conditions of anaerobic digestion. This is yet another instance of a medium that is restricted Not using selective agents. 

5. Differential medium

  • Differential medium differentiates between various kinds of bacteria. It also allows an in-depth identification of microorganisms based on their biological charaterstics, as they produce a noticeable change within the media.
  • We can identify haemolytic as well as non-haemolytic types of bacteria by with the help of blood Agar.
  • Differential medium can also be referred to as indicator medium since it differentiates an organism from another that is growing on the same plate through the production of pigments because of its biochemical and physiological properties.
  • Example: MacConkey agar medium, Carbohydrate Fermentation Broth, etc.  

MacConkey Agar

This medium is employed in plates. Organisms that ferment lactose present in the medium lower the pH because of the acid production. The indicator for pH (neutral red) turns red and the colonies will appear reddish. On the other plate, colonies that are not lactose-fermenting will appear white. (As this medium also appears in the above category, it is termed a selective-differential medium.)

Carbohydrate Fermentation Broth

The medium is utilized in tubes, mostly together with Durham tubes. Organisms that ferment the specific carbohydrate present in the media (e.g. sucrose, lactose or glucose) could cause the indicator’s pH to change color. Additionally, if insoluble gas (H2) is released as a result of fermentation, a bubble can be observed inside an inverted Durham tube.

Eosin Methylene Blue (EMB) agar medium 

Eosin Methylene Blue (EMB) Agar medium can also be a differentiating medium. It’s used to distinguish the fermentors of lactose from non-lactose. It contains lactose sugar as well as two dyes, namely Eosin the Y form as well as Methylene blue. The dyes work as an inhibiting agents against Gram-positive bacteria. For example, lactose fermentors like faecal Escherichia coli have a metallic sheen, while non lactose fermentors like Enterococcus don’t have metallic sheen.

Other examples 

Other examples of different media are Motility Medium (exploiting a morphological characteristic that produces flagella), Nutrient Gelatin, Starch Agar, Kligler Iron Agar and Blood Agar.

6. Anaerobic medium

  • Anaerobic medium is a type of medium that is used to cultivate anaerobes.
  • Anaerobic bacteria require specialized media to grow since they require low oxygen levels as well as a lower oxidation-reduction capacity and more nutrients.
  • Anaerobes’ media may need to be supplemented with vitamins such as vitamin K and hemin.
  • Boiling the medium helps eliminate any oxygen that is dissolved.
  • The addition of the glucose 1%, 0.1 percent thioglycollate 0.1 percent ascorbic acid, 0.05 percent cysteine and red hot iron particles can reduce the volume of a medium.
  • Example: Robertson cooked meat medium, Thioglycolate broth, etc

i) Robertson cooked meat medium

Robertson cooked meat is often used to cultivate Clostridium Spps medium contains the following: a 2.5 millimeter column of heart and 15ml of nutrient broth. Before using the medium, it must be heated in a water bath to eliminate oxygen dissolved and sealed by sterilized liquid paraffin.

ii) Thioglycolate broth

Within this environment Sodium theoglycollate can be used for reducing agents that helps ensures an oxygen tension that is low by removing the molecular oxygen from the air. Methylene blue, also known as resazurin, is an indicator of oxidation reduction potential which is present into the thioglycollate media. When the methylene concentration is reduced, the blue is colorless.

iii) Methylene blue or resazurin

Methylene blue, also known as Resazurin, is an indicator of oxidation reduction potential that is present into the medium. In a reduced state it is colorless.

7. Transport medium

  • Transport media are employed to ensure the viability of certain delicate organisms within clinical specimens while they are transported in the laboratory.
  • They usually contain buffers as well as salt.
  • They are deficient in carbon, nitrogen and organic growth fac-tors which is why they cannot allow microbial multiplication.
  • Transport medium is used to store an interim storage for specimens which are transported to the laboratory to be used for cultivation.
  • It preserves the viability of every organism within the specimen, without changing their concentration.
  • These media stop the drying (desiccation) of the specimen, ensure the pathogen to the commensal ratio and limit the growth of undesirable bacteria.
  • Certain the media (Stuart’s and Amie’s) are semi-solid and consistent.
  • The charcoal addition helps neutralize inhibitory elements.
  • Cary Blair medium and Venkatraman Ramakrishnan medium can be used to transfer the feces of suspected cholera patients.
  • Sach’s buffered glycerol saline utilized to transfer excretions from patients believed to have dysentery caused by bacillary bacteria.
  • Example: Stuart’s transport medium for Neisseriagonorrhoeae that lacks Carbon, Nitrogen and organic growth factors. Other examples of transport media are Cary Blair and Amies.

8. Antibiotic sensitivity medium

  • Antibiotic sensitive medium is a type of microbiological growth media that is often used to conduct test of sensitivity to antibiotics. 
  • Example: Muller- Hinton agar medium. This is an inherently nonselective, non-differential medium. It is a suitable medium for the growth of all kinds of microorganisms. It has starch, which absorbs toxins that are released by bacteria. Thus, toxins do not affect antibiotics. A concentration of 1.7 percent is utilized in this medium, which permits the better distribution of antibiotics.

9. Storage Media.

  • Media is used to store the bacteria for a prolonged length.
  • Examples: Egg saline medium, chalk cooked meat broth

10. Sugar media

Sugar media is essentially composed of the 1% of “sugar”,which in microbiology refers to any substance that is fermentable including sucrose, glucose lactose, mannitol, and lactose that is used regularly for tests of fermentation. Sugar media has the following characteristics:

  • It’s composed in 1% sugar within peptone
  • The indicator for sugar mediums is the Andrade’s indicator which is made up of 0.005 percent acid fuchsin, in 1N NaOH. Acid production following fermentation of sugar is reflected by the change in the color of the medium from pink because of the presence of the indicator.
  • Durham’s tube is positioned inverted within the sugar tube in order to demonstrate gas production. Gas production is demonstrated by the demonstration of a gas bubbles in Durham’s tube.

Dehydrated media are now readily available in diagnostic labs due to their simplicity and easier to make. The dehydrated media are prepared by reconstituting it in the distillation process and sterilizing prior to use.

Other solidifying agents

In addition to eggs, agar and serum can also be used to make culture media more solid. Serum-containing mediums like Loeffler’s serum slope as well as egg-containing media like Lowenstein Jensen (LJ) medium, and Dorset egg medium are able to be solidified and disinfected through an inspissation process.

Preparation and preservation

  • It is important to regulate to the correct pH level of the media prior to autoclaving.
  • The various pH indicators being used comprise phenol red, neutral red bromothymol blue, purple bromocresol, and so on.
  • Dehydrated media can be purchased commercially and can be reconstituted according to the manufacturer’ guidelines.
  • The majority of culture media are sterilized through autoclaving. Certain media that have heat labile components such as glucose antibiotics, urea blood, and serum do not require autoclaving. The components are removed and added after the medium has been autoclaved.
  • Certain media that are highly selective like Wilson or Blair’s media, as well as TCBS Agar does not need to be sterilized.
  • After it has been prepared, the media may be stored at 4-5oC and stored in refrigerators for up to 1-2 weeks.
  • Certain liquids contained in screw-capped bottles, tubes or cotton plugged bottles can be stored by bringing them to room temperature over the course of up to a week.

Why do bacteria have to be grown (cultured) in the laboratory on artificial culture media?

  • One of the main reasons is its use in the diagnosis of infectious illnesses. The ability to isolate an organism from areas that are normally thought as sterile is an indication of the role it plays in the process of disease. In fact, separating an organism from a medical specimen can be the very first step in proving its position as an etiologic factor.
  • Culturing bacteria is also an first step in studying its morphology as well as its recognition.
  • Bacteria must be grown to extract antigens for serological tests or vaccines.
  • Certain genetic research and manipulations of cells require that the bacteria be grown in the laboratory in.
  • Culturing bacteria can also be an accurate method of estimating their number (viable number).
  • Growing on solid substrates is also a effective method to separate bacteria from mixtures.

Application of Culture Media

It is crucial to develop microorganisms in the outside of your body for the following reasons:

  • To determine the root of infection in the clinical sample to ensure that the proper treatment be administered.
  • To investigate the specific characteristics or characteristics of microorganisms.
  • For the preparation of biological products, such as toxoides, vaccines, antigens…etc.
  • In addition to that of the development of bacteria the culture media can also be used to store and transport microorganisms and cells.



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