Starch Agar 500g Each

Directions

Suspend 25 grams in 1000 ml distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 10 minutes. Mix well and pour in sterile Petri plates.

Principle And Interpretation

Starch Agar was formulated by Vedder (1) for the cultivation of Neisseria. It is recommended for the detection of starch hydrolysing microorganisms from foods (2) and clinical samples (3). Present formulation is accepted by BIS for detection of starch hydrolysis by Bacillus cereus (4).

Peptic digest of animal tissue and meat extract provide nitrogenous compounds, carbon, sulphur, trace elements etc. to the microorganisms.

Flood the surface of 24 - 48 hour old culture on Starch Agar with Grams Iodine (S013). Starch hydrolysis is seen as a colourless zone surrounding the colonies. A blue or purple zone indicates that starch is not hydrolyzed.

Quality Control

Appearance: Yellow coloured homogeneous free flowing powder

Gelling: Firm, comparable with 1.5% Agar gel

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

Reaction: Reaction of 2.5% w/v aqueous solution at 25°C. pH: 7.2±0.1

pH: 7.10-7.30

Cultural Response

Cultural characteristics observed after an incubation at 35-37°C for 18 - 48 hours. (key *- On addition of Iodine solution)

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