What is Starch casein agar (SCA)?
Starch casein agar is a nutrient medium for the growth and cultivation of saccharolytic marine bacteria.
- Starch casein agar, as the name suggests, has starch has the primary source of carbohydrates.
- This media is primarily used for the isolation and cultivation of actinomycetes for various sources like soil and marine sediments.
- Starch Casein agar consists of seawater which contains various nutrients, vitamins, and sea salt that support the growth of marine inhabitants, and actinomycetes constitute a considerable proportion of the population of soil, lakes, and river muds.
- The starch present in the agar allows the saccharolytic organism enough nutrients to produce their proteins and carbohydrates.
- Actinomycetes are fungi-like organisms that have recently been of more interest due to their roles not only in therapeutic applications but also in the recycling of organic matter.
- Traditionally, actinomycetes have been isolated from terrestrial sources, but recently the availability of actinomycetes in marine sediments has been discovered.
- Marine sediments are known potential sources for isolation of novel actinomycetes yielding new products and are recognized as a source of novel antibiotics and anticancer agents.
Composition of Starch casein agar (SCA)
Starch casein agar consists of starch as the primary source of carbon along with casein as a source of protein and seawater. The exact composition of Starch Casein agar is given below:
|2.||Casein (Vitamin free)||0.30|
|Final pH at 25°C: 7.3 ±0.2|
The composition of the HiMedia Starch Casein Agar is given below:
|Final pH at 25°C: 7.2 ±0.2|
Principle of Starch casein agar (SCA)
- Starch Casein agar is made with various nutrients which allow the growth of a wide variety of microorganisms that do not usually don’t grow on a primary medium like Nutrient agar as they require specific nutrients or supplements.
- The primary constituents of the media are starch, casein, and seawater. In addition to these nutrients, some vitamins and some trace ingredients necessary for the growth of bacteria are also added.
- The starch is the source of carbon required for saccharolytic organisms like Actinomycetes or other marine bacteria.
- The casein is the primary source of protein which is essential for the formation of amino acids in the bacteria. It also contains other components like some vitamins, different trace minerals, organic compounds, and salts, which further enhance the growth of different organisms.
- Besides, seawater contains sea salt that provides complex ionic sources that make the medium suitable for marine microbial flora and also buffers the medium. It also prevents the change in pH of the medium during growth.
- The distilled water provides a medium to dissolve the nutrients so that it is easier for the bacteria to absorb them.
- Agar is the solidifying agent that provides a stable surface for the organism to grow on, which allows for the observation of colony morphology and enumeration of the organism.
- The medium is made up of these nutrients that are essential for a variety of organisms, which makes it a general media that can be used for various purposes.
Preparation of Starch casein agar (SCA)
- In a beaker, 63 grams of the dehydrated powder or lab-prepared media is added to 1000 milliliters of distilled or deionized water.
- The suspension is then heated to boiling to dissolve the medium completely.
- The dissolved medium is then autoclaved at 15 lbs pressure (121°C) for 15 minutes.
- Once the autoclaving process is complete, the beaker is taken out and cooled to a temperature of about 40-45°C.
- The media is then poured into sterile Petri plates under sterile conditions.
- Once the media solidifies, the plates can be placed in the hot air oven at a lower heat setting for a few minutes to remove any moisture present on the plates before use.
- The media in the powder form should be stored between 10 to 30°C in a tightly closed container, and the prepared medium should be stored at 20-30°C.
- After opening, the product should be appropriately stored when dry, after tightly capping the bottle in order to prevent lump formation as the medium is hygroscopic in nature and thus, absorbs moisture relatively quickly.
- The container should be stored in a dry ventilated area protected from extremes of temperature and sources of ignition.
- The product should be used before the expiry date on the label.
Result Interpretation on Starch casein agar (SCA)
Figure: Left (a and b): Streptomycete colonies on Starch Casein Agar (Source: Mustafa Oskay). Right: Pure culture of Actinomycetes on Starch Casein Agar after 5 days of cultivation (Source: Saroj Khadka). Down: Streptomyces coelicolor klmp33 on starch casein agar (Source: https://doi.org/10.1007/s40195-013-0217-6)
The media forms yellow-colored, clear to slightly opalescent gel on Petri plates. The following table demonstrates the growth of important medical bacteria and Actinomycetes with their colony morphologies on Starch Casein Agar:
|1.||Actinomycetes||Luxuriant||White to light yellow colored colonies with powdery colonies. Some colonies might be circular to pinpoint colonies that are powdery on the top surface and mucoid at the bottom within 1-3 days of incubation. Complete powdery colonies form after 7 days of incubation.|
|2.||Streptococcus limosus||Good-luxuriant||Smooth colorless colonies with a diameter range of 2-4 mm. The coloration of the colonies might differ.|
|3.||Streptomyces praecox||Good-luxuriant||Golden yellow colored circular, convex and smooth colonies of the diameter range of 2-4 mm; opaque colonies.|
|4.||Vibrio cholerae||Good-luxuriant||Circular, colorless to yellow colored colonies of the size 0-5 to 1 mm in diameter. Light yellow colored with low convex elevation; mucoid colonies.|
Uses of Starch casein agar (SCA)
- Starch Casein agar is used for the isolation of saccharolytic bacteria, mostly of marine origins.
- It is the standard medium for the isolation and cultivation of actinomycetes from various terrestrial and marine environments.
- It can also be used for the studies related to the microbial ecosystem of an environment as it helps the growth of bacteria, fungi, and actinomycetes.
- Starch Casein Agar is recommended by standard methods for the isolation and preservation of actinomycetes cultures for a longer period of time.
Limitations of Starch casein agar (SCA)
- The nutritional variations present on the media might result in poor growth in such media.
- For the confirmation of the organism, a variety of biochemical tests should be performed.
References and Sources
- Starch M-protein Agar. M801. HiMedia Laboratories.
- Mohseni, M., Norouzi, H., Hamedi, J., & Roohi, A. (2013). Screening of antibacterial producing actinomycetes from sediments of the caspian sea. International journal of molecular and cellular medicine, 2(2), 64–71.
- Oskay, Mustafa. (2009). Comparison of Streptomyces diversity between agricultural and non-agricultural soils by using various culture media. Scientific Research and Essays. 4. 997-1005.