• Dorset egg medium is an enriched slope medium used to culture Corynebacterium diphtheriae to direct volutine granules. It is also used for maintaining control cultures.

Composition of Dorset egg medium:

• Nutrient broth……………………20 ml
• Whole fresh egg………………….80 ml

Preparation of Dorset egg medium:

• Prepare and sterilize the nutrient broth
• Wash the eggs by scrubbing them carefully with soap and water followed by rinsing in clean running water. Immerse the egg in 70% v/v ethanol (alcohol) for 10 minutes.
• As aseptically possible, break the eggs into a sterile flask (premarked to hold 80ml) which contains a few sterile beads. Mix well until egg yolks and whites are completely homogenized.
• Strainthe egg mixture through sterile gauze or muslin into a sterile bottle.
• When the nutrient broth has cooled to 45-50°C, add it aseptically to an egg mixture and mix it well.
• Dispense aseptically the medium in 3 ml amounts in sterile Bijou bottles or screw-cap tubes.
• Heat (Inspissate) at 75-80°C with the bottles in a sloped position until the medium has solidified

Quality control

• pH of medium: this should be within the range pH 7.2-7.6 at room temperature.
• Store the slopes with bottle tops tightly screwed in a cool dark place or at 2-8°C.

Use of Dorset egg medium

• used to isolate Corynebacterium diphteriae

Dorset egg medium:composition, preparation and uses

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