MacConkey Agar No. 3

LAB 45

Description

A modification recommended by the W.H.O. and the Ameri Public Health Association for the isolation of Enterobacteriac from waters and sewage. The medium has been made more selec than MacConkey's original formula by the use of crystal viole well as bile salts. Gram positive organisms will not grow on medium.

Method for reconstitution

Weigh 51.5 grams of powder and add to 1 litre of deionised water. Allow to soak for 10 minutes, swirl to mix then sterilise for 15 minutes at 121˚C. Cool to 47˚C and pour into Petri dishes. Dry the surface before inoculation.

Appearance: Pale red slight violet tinge.

pH: 7.1 ± 0.2

Minimum Q.C. organisms: E. coli NCIMB 50034 Ent. faecalis (inhibition) NCIMB 50030

Storage of prepared medium: Plates - up to 7 days at 2-8˚C in the dark.

Inoculation: Surface, streaking for single colonies.

Incubation: 37˚C aerobically for 18-24 hours.

1.30

References

American Public Health Association (1950). Diagnostic Procedures and Reagents. 3rd edn. A.P.H.A., New York.

American Public Health Association (1946). Standard Methods for the examination of Water and Sewage. 9th edn. A.P.H.A., New York.