M.R.S. Agar

(de Man, Rogosa and Sharpe Agar)

LAB 93

Description

This medium was developed for the cultivation and enumeration of Lactobacillus spp. from various sources and is intended as a substitute for Tomato Juice Agar. The medium is suitable for most lactic acid bacteria. When acidified to pH 5.4 M.R.S. Agar can be used to enumerate Lactobacillus bulgaricus in yoghurts. Tween 80, sodium acetate, magnesium and manganese sulphates act as growth stimulants.

Method for reconstitution

Weigh 70 grams of powder and add 1 litre of deionised water. Allow to soak for 10 minutes, swirl to mix. Heat to dissolve and sterilise by autoclaving at 121˚C for 15 minutes. Cool to 47˚C and adjust pH if the acidified medium is required.

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

Inoculation: Surface, spread to cover surface, or use pour plate technique.

Incubation: 25˚C microaerobically for 2-5 days.

Interpretation: Count all colonies exhibiting typical morphology.

Growth Characteristics

Lactobacillus bulgaricus

References

de Man, J.C.,. Rogosa, M and Sharpe, M.E. (1960). A medium for the cultivation of lactobacilli. J. Appl. Bacteriol. 23: 130-135.