Starch Casein Agar (SCA) Composition, Principle, Preparation

What is Starch casein agar (SCA)?

  • Starch casein agar (SCA) is a nutrient medium specifically designed for the growth and cultivation of saccharolytic marine bacteria. As its name suggests, the primary source of carbohydrates in SCA is starch. This medium is widely used for isolating and cultivating actinomycetes, which are fungi-like organisms, from various sources such as soil and marine sediments.
  • Actinomycetes are a significant part of the microbial population found in soil, lakes, and river muds. While they were traditionally isolated from terrestrial sources, it was discovered several decades ago that mycelium-forming actinomycetes can also be recovered from marine sediments. This finding opened up new possibilities for exploring the diversity of actinomycetes and their potential for producing novel bioactive compounds.
  • Marine sediments are known to be rich sources of actinomycetes that yield new products, including antibiotics and anticancer agents. These microorganisms have a substantial impact on the environment as they play a vital role in decomposing and transforming complex organic residues. Additionally, actinomycetes are of interest not only for their therapeutic applications but also for their involvement in the recycling of organic matter.
  • Starch casein agar provides an ideal environment for the growth of saccharolytic marine bacteria and actinomycetes. The inclusion of seawater in the medium ensures the presence of complex ionic sources, nutrients, vitamins, and sea salt, which support the growth of marine microorganisms. Furthermore, the starch present in SCA serves as a rich carbohydrate source, providing the saccharolytic organisms with the necessary nutrients to produce proteins and carbohydrates.
  • Overall, starch casein agar is a valuable tool in the study of saccharolytic marine bacteria and actinomycetes. It allows researchers to isolate and cultivate these microorganisms from various environmental sources, including marine sediments, facilitating the exploration of their potential in the development of new bioactive compounds with therapeutic and ecological applications.

Composition of Starch casein agar (SCA)

The composition of Starch casein agar (SCA) includes the following ingredients:

  1. Soluble starch: 10.0 grams per liter
  2. Casein (Vitamin free): 0.30 grams per liter
  3. KNO3: 2.0 grams per liter
  4. MgSO4.7H2O: 0.05 grams per liter
  5. K2HPO4: 2.0 grams per liter
  6. NaCl: 2.00 grams per liter
  7. CaCO3: 0.02 grams per liter
  8. FeSO4.7H2O: 0.01 grams per liter
  9. Agar: 18.0 grams per liter

The HiMedia Starch Casein Agar has a slightly different composition, which is as follows:

  1. Starch: 10.0 grams per liter
  2. Casein: 1.0 gram per liter
  3. Seawater: 37.0 grams per liter
  4. Agar: 15.0 grams per liter

In both compositions, starch serves as the primary source of carbon, providing a rich carbohydrate substrate for the microorganisms. Casein, a protein source, is included to support the growth and metabolism of the organisms. The addition of seawater in the HiMedia version of SCA provides various nutrients, vitamins, and sea salt, creating a suitable environment for the growth of marine microorganisms. Agar is added as a solidifying agent, allowing the medium to solidify and provide a solid surface for bacterial growth.

The final pH of Starch casein agar at 25°C is maintained at approximately 7.3 ± 0.2 in the first composition and 7.2 ± 0.2 in the HiMedia composition. This pH range is favorable for the growth of the target microorganisms and helps maintain the stability of the medium during incubation.


Principle of Starch casein agar (SCA)

The principle of Starch casein agar (SCA) revolves around providing a nutrient-rich environment that supports the growth of a wide range of microorganisms. It is designed to overcome the limitations of primary media like Nutrient agar by incorporating specific nutrients or supplements required by certain microorganisms.

The main components of SCA are starch, casein, and seawater. Starch serves as the primary source of carbon, providing saccharolytic organisms such as Actinomycetes or marine bacteria with the necessary carbon for energy and growth. Casein, on the other hand, acts as the primary source of protein, enabling the synthesis of amino acids in bacteria. Additionally, SCA contains various vitamins, trace minerals, organic compounds, and salts, which further enhance the growth of different microorganisms.


Seawater is an essential component of SCA as it provides complex ionic sources that are suitable for marine microbial flora. It acts as a buffer, helping to maintain the pH of the medium during bacterial growth. The inclusion of seawater ensures that SCA is suitable for the cultivation of marine microorganisms and supports their specific nutritional requirements.

Distilled water is used in the preparation of SCA to dissolve the nutrients, making it easier for bacteria to absorb them and utilize them for growth and metabolism.


Agar is added to SCA as a solidifying agent. It forms a gel-like matrix when heated and solidifies as it cools, providing a stable surface for microorganisms to grow on. This allows for the observation of colony morphology and enables the enumeration of organisms present in the medium.

Overall, the principle of Starch casein agar lies in its formulation with a variety of essential nutrients that support the growth of diverse microorganisms. This makes it a versatile medium that can be used for various purposes in microbiology, allowing for the cultivation and study of microorganisms that may not grow on primary media alone.


Intended Use

Starch Casein Agar is recommended for the detection of marine saccharolytic bacteria.

Type of Specimen: Marine isolates.


Preparation of Starch casein agar (SCA)

To prepare Starch casein agar (SCA), follow the steps below:

  1. Measure 63 grams of the dehydrated powder or lab-prepared media and add it to a beaker containing 1000 milliliters of distilled or deionized water.
  2. Heat the suspension in the beaker, stirring gently, until it reaches a boiling point. This will help dissolve the medium completely.
  3. After the medium has dissolved, transfer the beaker to an autoclave and autoclave it at 15 pounds of pressure (121°C) for 15 minutes. Autoclaving is crucial to sterilize the medium and eliminate any contaminants.
  4. Once the autoclaving process is finished, carefully remove the beaker from the autoclave and allow it to cool. The medium should be cooled to a temperature of approximately 40-45°C. Be cautious while handling the hot beaker to avoid burns.
  5. With sterile precautions, pour the cooled medium into sterile Petri plates. Maintain aseptic techniques throughout the process to prevent contamination.
  6. Allow the poured medium to solidify in the Petri plates. This typically takes a few minutes as the medium cools and solidifies.
  7. If there is any residual moisture on the plates, place them in a hot air oven at a lower heat setting for a few minutes. This step helps remove excess moisture from the plates, ensuring their optimal performance.

Once the plates have cooled and dried, they are ready to be used for various microbiological applications such as isolation and cultivation of microorganisms on Starch casein agar (SCA). It is important to handle the plates under sterile conditions to maintain the integrity of the medium and prevent contamination.

Storage and Shelf Life of Starch casein agar (SCA)

To ensure the longevity and quality of Starch casein agar (SCA), follow these guidelines for storage:

  1. Powder form storage: Store the powdered medium in a tightly closed container within a temperature range of 10 to 30°C. It is important to keep the container sealed to prevent moisture absorption.
  2. Prepared medium storage: Once the medium is prepared, it should be stored at a temperature range of 20 to 30°C. Use appropriate storage containers such as Petri plates or bottles with tight caps to maintain sterility and prevent contamination.
  3. Protection against moisture: Starch casein agar is hygroscopic, meaning it has a tendency to absorb moisture. To prevent lump formation and maintain the quality of the medium, ensure that the container is tightly capped after opening. Store the medium in a dry environment and avoid exposure to humid conditions.
  4. Dry and ventilated storage area: Store the containers in a dry and well-ventilated area. This helps to minimize the risk of moisture absorption and maintain the integrity of the medium. Additionally, protect the containers from extreme temperatures and sources of ignition to ensure the safety and stability of the medium.
  5. Adherence to expiry date: It is crucial to use the Starch casein agar before the expiry date mentioned on the label. Expired media may not provide accurate and reliable results, so it is important to monitor and adhere to the expiration dates for optimal performance.

By following these storage recommendations, you can maintain the quality and effectiveness of Starch casein agar, both in its powdered form and as prepared medium, ensuring its suitability for microbiological applications.

Result Interpretation on Starch casein agar (SCA)

Interpreting the results on Starch casein agar (SCA) involves observing the colony morphology and growth characteristics of different microorganisms. The following information outlines the growth patterns and colony morphologies of specific organisms on SCA:

  1. Actinomycetes:
    • Growth: Luxuriant
    • Colony Morphology: White to light yellow colored colonies with powdery texture. Some colonies may appear circular to pinpoint with a powdery top surface and a mucoid bottom within 1-3 days of incubation. Complete powdery colonies develop after 7 days of incubation.
  2. Streptococcus limosus:
    • Growth: Good-luxuriant
    • Colony Morphology: Smooth colorless colonies with a diameter range of 2-4 mm. The colonies may exhibit variations in coloration.
  3. Streptomyces praecox:
    • Growth: Good-luxuriant
    • Colony Morphology: Golden yellow colored circular colonies that are convex and smooth. The diameter of these colonies ranges from 2-4 mm, and they appear opaque.
  4. Vibrio cholerae:
    • Growth: Good-luxuriant
    • Colony Morphology: Circular colonies that are colorless to yellow in color. The size of these colonies ranges from 0.5 to 1 mm in diameter. They exhibit a light yellow coloration with low convex elevation and a mucoid appearance.

When interpreting the results on Starch casein agar, it is essential to compare the observed colony morphologies and growth characteristics with known reference strains or literature descriptions to identify the specific microorganisms present. The observations can provide valuable insights into the identification, characterization, and differentiation of different bacteria and actinomycetes on this medium.

Morphological appearance of two actinomycete isolates grown on Starch Casein Agar
Morphological appearance of two actinomycete isolates grown on Starch Casein Agar | Image Source:

Quality Control

The quality control of Starch casein agar (SCA) involves assessing several parameters to ensure its performance and reliability. The following information outlines the key quality control measures for SCA:

  1. Appearance: The SCA powder should have an off-white to yellow color, indicating its proper formulation and consistency. It should be homogeneous and free-flowing, ensuring easy handling and preparation.
  2. Gelling: The medium’s gelling property is evaluated by comparing it with a 1.5% agar gel. The gelled SCA should exhibit a firm consistency, similar to the reference agar gel, indicating its ability to solidify properly.
  3. Color and Clarity of prepared medium: Once prepared, SCA should form a yellow-colored clear to slightly opalescent gel in the petri plates. This demonstrates that the medium has been correctly prepared and provides the appropriate visual background for observing microbial growth.
  4. Reaction: The pH of a 6.3% aqueous solution of SCA should be measured at 25°C. The desired pH range is 7.2 ± 0.2, indicating the medium’s proper buffering capacity and suitability for microbial growth.
  5. pH: The pH range of the SCA medium should fall between 7.00 and 7.40. This range ensures the medium’s stability and compatibility with the growth requirements of target microorganisms.
  6. Cultural Response: To assess the medium’s performance, it should be inoculated with specific test organisms and incubated at 35-37°C for 18-48 hours. The cultural response is then evaluated by observing the growth characteristics of the organisms, including colony morphology, size, and coloration.
  7. Organism Inoculum Growth: The number of colony-forming units (CFUs) is determined by inoculating the SCA with a known concentration of the test organisms. The growth response is assessed by counting the colonies formed and comparing them to the expected range of growth.
  8. Recovery: The recovery rate is calculated by determining the percentage of organisms that successfully grow on the SCA medium compared to the initial inoculum. A recovery rate of at least 50% indicates satisfactory performance.

By conducting these quality control tests, the consistency and reliability of Starch casein agar can be ensured, providing researchers and laboratory personnel with a dependable medium for microbial cultivation and analysis.

Uses of Starch casein agar (SCA)

Starch casein agar (SCA) has several uses in microbiology, particularly in the isolation and cultivation of specific microorganisms. The following points highlight the key applications of SCA:

  • Isolation of saccharolytic bacteria: SCA is commonly used for the isolation of saccharolytic bacteria, particularly those of marine origins. The medium provides the necessary nutrients and carbohydrates for the growth of these bacteria, facilitating their isolation and subsequent study.
  • Isolation and cultivation of actinomycetes: SCA serves as the standard medium for the isolation and cultivation of actinomycetes from diverse environments, including terrestrial and marine sources. Actinomycetes are filamentous bacteria that have gained significant attention due to their potential for producing bioactive compounds.
  • Studies of microbial ecosystems: Due to its composition, SCA supports the growth of not only bacteria but also fungi and actinomycetes. This makes it useful for studies related to the microbial ecosystem of various environments. Researchers can use SCA to assess the diversity and dynamics of microbial communities and their interactions within a particular habitat.
  • Preservation of actinomycetes cultures: SCA is recommended by standard methods for the isolation and long-term preservation of actinomycetes cultures. The medium provides a suitable environment for the growth and maintenance of actinomycetes over an extended period, allowing researchers to store and access cultures for future studies and applications.

In summary, Starch casein agar finds utility in the isolation of saccharolytic bacteria, the cultivation of actinomycetes, investigations of microbial ecosystems, and the preservation of actinomycetes cultures. Its versatility and effectiveness in supporting the growth of specific microorganisms make it a valuable tool in various areas of microbiology research.

Limitations of Starch casein agar (SCA)

Starch casein agar (SCA) has a few limitations that should be taken into consideration when using this medium. Here are the key limitations:

  • Nutritional variations: While SCA provides a rich nutrient composition, the specific nutritional requirements of some microorganisms may not be fully met by this medium. As a result, certain organisms may exhibit poor growth or fail to grow altogether on SCA. To overcome this limitation, additional specific supplements or selective media may be required to support the growth of certain microorganisms.
  • Confirmation of organisms: While SCA can facilitate the isolation and cultivation of target microorganisms, it may not be sufficient for confirming the identity of the organisms. To accurately identify and confirm the presence of specific microorganisms, additional biochemical tests are necessary. These tests provide further information about the metabolic capabilities and characteristics of the organisms.

It is important to note these limitations and consider them when using Starch casein agar. While SCA is a useful medium for various purposes, including the isolation and cultivation of certain microorganisms, its application may require additional supplementation or confirmation methods to overcome these limitations and ensure accurate results.


What is Starch Casein Agar (SCA)?

Starch Casein Agar is a nutrient medium used for the isolation and cultivation of saccharolytic bacteria, actinomycetes, and other microorganisms from various sources.

What is the purpose of using seawater in Starch Casein Agar?

Seawater provides nutrients, vitamins, sea salt, and acts as a buffer in the medium, making it suitable for marine microbial flora and supporting the growth of marine microorganisms.

What are the key components of Starch Casein Agar?

The main components of Starch Casein Agar include soluble starch as a carbon source, casein as a protein source, seawater for complex ionic sources, vitamins, trace minerals, and agar as a solidifying agent.

How is Starch Casein Agar prepared?

To prepare Starch Casein Agar, the dehydrated powder or lab-prepared media is dissolved in distilled or deionized water, heated to dissolve the medium completely, autoclaved for sterilization, cooled, and poured into sterile Petri plates for solidification.

What is the recommended pH range of Starch Casein Agar?

The final pH of Starch Casein Agar at 25°C is typically around 7.2 ± 0.2, providing an optimal pH environment for microbial growth.

What organisms can be cultivated on Starch Casein Agar?

Starch Casein Agar supports the growth of saccharolytic bacteria, actinomycetes, and other microorganisms. It can be used for the isolation and cultivation of various terrestrial and marine organisms.

Can Starch Casein Agar be used for microbial ecosystem studies?

Yes, Starch Casein Agar can be used for studying microbial ecosystems as it supports the growth of bacteria, fungi, and actinomycetes, providing a versatile medium for microbial community analysis.

Are there any limitations to using Starch Casein Agar?

Starch Casein Agar may have nutritional variations that can result in poor growth for some microorganisms. Additionally, the medium may require additional biochemical tests for confirming the identity of organisms.

How should Starch Casein Agar be stored?

The powdered form should be stored in a tightly closed container at 10-30°C. Prepared media should be stored at 20-30°C. It is important to protect the medium from moisture and extreme temperatures.

What is the shelf life of Starch Casein Agar?

The shelf life of Starch Casein Agar depends on the manufacturer and should be used before the expiry date mentioned on the label to ensure optimal performance.


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