Modified Soyabean Casein Digest Agar

Composition

Formula adjusted, standardized to suit performance parameters

Directions

Suspend 55 grams in 1000 ml distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Mix well and pour into sterile Petri plates.

Principle And Interpretation

Soyabean Casein Digest Agar was initially developed for the cultivation of very fastidious microorganisms without addition of serum, blood or any other enrichment agent. As a general purpose medium, Soyabean Casein Digest Agar supports the growth of most organisms both aerobes and facultatives. Soyabean Casein Digest Broth possesses superior growth-promoting properties which makes it particularly suitable for the tube dilution method for antibiotic sensitivity testing.

Modified Soyabean Casein Digest Agar is recommended as Medium-B by British Pharmacopoeia for microbiological assay of polymyxin B, colistin sulphate and colistimethate sodium (1). The combination of casein enzymic hydrolysate and papaic digest of soyabean meal makes this media nutritious by providing amino acids and long chain peptides for the growth of microorganisms. Glucose serves as immediate carbon source whereas dipotassium phosphate buffers the medium. Sodium chloride maintains the osmotic balance of media. Depending on the growth requirement, polysorbate 80 is included in the media, which serves as fatty acid source.

Quality Control

Appearance: Cream to yellow homogeneous free flowing powder

Gelling: Firm, comparable with 1.5% Agar gel

Colour and Clarity of prepared medium: Yellow coloured clear to slightly opalescent gel forms in Petri plates

Cultural Response: M1329: Cultural characteristics observed after an incubation at 35-37°C for 18-48 hours.

Storage and Shelf Life

Store below 30°C in tightly closed container and the prepared medium at 2 - 8°C. Use before expiry date on the label.

Reference

1. The British Pharmacopoeia, 2003, Volume IV, The Stationery Office Limited, UK.