Malt Extract Agar

LAB 37

Description

An acidic medium which will support the growth of most yeasts and moulds whilst inhibiting most bacteria. It was first described by Thom and Church in 1926 in a study of Aspergillus spp. claiming the high carbohydrate content ensured rapid growth. Selectivity can be increased by further lowering the pH with the addition, after sterilisation, of XO37 Lactic Acid. It should be noted that excess heating of this medium together with its low pH can easily result in hydrolysis of the agar gel producing soft plates.

Method for reconstitution

Weigh 50 grams of powder, disperse in 1 litre of deionised water, allow to soak for 10 minutes, swirl to mix then sterilise at 115˚C for 10 minutes. If the addition of XO37 Lactic Acid is required this should be done after sterilisation. One 5ml vial of XO37 will lower the pH of 250ml of medium to 3.5-4.0. Cool to 47˚C before making additions and pouring plates.

Appearance: Pale brown/straw, clear.

pH: 5.4 ± 0.2 (if XO37 is added pH 3.5-4.0)

Minimum Q.C. organisms: Candida spp. NCIMB 50010

Storage of Prepared Medium: Plates - up to 7 days at 2-8˚C in the dark. Capped container - up to 1 month at 15-20˚C in the dark.

Inoculation: Pour plate technique or surface streaking for single colonies.

Incubation: 25˚C aerobically for 5 days.

References

Galloway, L.D. and Burgess, R. (1952). Applied Mycology and Bacteriology, Leonard Hill, London. Thom and Church, 1926. The Aspergilli.