Introduction of Schaedler Agar
Schaedler Agar is recommended for the enumeration of various aerobic and anaerobic bacteria present in the gastrointestinal tract. Bacteroides fragilis grew on Schaedler Agar after 48 hours of anaerobic incubation as shown above picture.
Principle of Schaedler Agar
Tryptone, proteose peptone, Soya peptone, Yeast extract, and L-cystine supply nitrogenous growth factors, vitamins, and other essential growth nutrients. Dextrose/glucose serves as an energy source. Hemin and sheep blood enhances the growth of fastidious microbes and stimulates the growth of other Bacteroides species and gram-positive spore formers. The addition of Sodium Polyanethol Sulphonate (SPS) is useful when using Schaedler Agar for blood culture. It inhibits phagocytosis and neutralizes the antibacterial activity of fresh blood components. Vitamin K1 enables the cultivation of Bacteroides melaninogenicus and stimulates the growth of other Bacteroides species and gram-positive spore-forming bacteria.
Sodium chloride maintains the osmotic equilibrium of the medium. The presence of sodium chloride in nutrient agar maintains a salt concentration in the medium that is similar to the cytoplasm of the microorganisms. Agar acts as the solidifying agent. Water is an essential ingredient for the growth and reproduction of organisms and also serves as a transport medium for the agar’s various substances.
Composition of Schaedler Agar
Ingredients Gms / Litre
- Tryptone: 5.67
- Proteose peptone: 5.0
- Soya peptone: 1.0
- Yeast extract: 5.0
- Dextrose (Glucose): 5.83
- Sodium chloride: 1.67
- Dipotassium hydrogen phosphate: 0.83
- Tris (hydroxymethyl) aminomethane: 3.0
- L-Cystine: 0.4
- Hemin: 0.01
- Agar: 15.0
Final pH ( at 25°C) 7.6±0.2
Preparation of Schaedler Agar
- Suspend 43.41 grams in 950 ml of purified/distilled or deionized water.
- Heat to boiling to dissolve the medium completely.
- Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.
- After autoclaving, leave for cooling to 45-50°C.
- Add 5% sterile defibrinated sheep blood if desired. Mix well before dispensing.
- Other supplements may also be used in this medium according to the recovery purpose of microorganisms.
- Pour the medium into each plate and leave plates on the sterile surface until the agar has solidified.
- Store the plates in a refrigerator at 2-8°C.
Storage and Shelf life of Nutrient agar
- Store at 2-8ºC and away from direct light.
- Media should not be used if there are any signs of deterioration (shrinking, cracking, or discoloration), or contamination.
- The product is light and temperature sensitive; protects from light, excessive heat, moisture, and freezing.
- Test specimens- Clinical samples – Blood, Genital specimen, Upper respiratory swab, Endotracheal Aspiration swab, or growth of bacteria
- Inoculating loop
- Bunsen burner
- Control strains (Escherichia coli ATCC 25922 and Bacteroides fragilis ATCC 25285 )
Procedure of Schaedler Agar
- Allow the plates to warm at 37°C or to room temperature, and the agar surface to dry before inoculating.
- Inoculate and streak the specimen as soon as possible after collection.
- If the specimen to be cultured is on a swab, roll the swab over a small area of the agar surface.
- Streak for isolation with a sterile loop.
- Incubate plates aerobically at 35-37ºC for 18-48 hours under anaerobic conditions or nature of recovery purposes for bacteria.
- Examine colonial characteristics.
Colony Morphology of bacteria on Schaedler Agar after 18-48 hours under anaerobic conditions-
- Bacteroides fragilis ATCC 25285: Luxuriant Growth
- Escherichia coli ATCC 25922: No growth
- Clostridium sporogenes : Dense Growth
- C. perfringens: ,,
- C. sporogenes: Luxuriant Growth
- Streptococcus pyogenes: ”
Uses of Schaedler Agar
- Schaedler Agar serves as an excellent basal media to which blood or other enrichments can be added to strengthen the recovery of fastidious anaerobic bacteria.
- Obligate aerobes and facultative anaerobes can also recover without adding supplements and anaerobic incubation.
Keynotes on Schaedler Agar
- Hemin and sheep blood stimulates the growth of fastidious microorganisms and stimulates the growth of other Bacteroides species and gram-positive spore-forming bacteria.
- Avoid overheating and photooxidation of Schaedler Agar since it will
retard the growth of bacteria.
- Schaedler Agar is the original formulation of Schaedler et al and further Mata et al modified formulation changes for the cultivation and enumeration of aerobic and anaerobic organisms. It has been modified according to the recovery of organisms.
Schaedler Agar Modifications- Uses
- Schaedler Agar (SA)+Vitamin K1+ 5% sheep blood- fastidious anaerobic bacteria (Bacteroides)
- S. Agar+Colistin and Nalidixic acid+5% sheep blood-selective isolation of the anaerobic gram (also known for Schaedler CNA Agar)-positive cocci (Peptococcus and Peptostreptococcus species)
- SA+Kanamycin and Vancomycin+5% sheep blood( also called (Schaedler KV Agar) -selective isolation of gram-negative anaerobes.
Further Readings on Schaedler Agar
- Picture source:http://www.biomerieux-culturemedia.com/product/47-schaedler-agar-+5-percent-sheep-blood