Bacillus Cereus Medium

Phenol Red Egg Yolk Polymyxin Agar ( P.R.E.P. ) Mannitol Egg Yolk Polymyxin Agar

LAB 73

Description

Introduced by Mossel and his co-workers in 1967 for the enumeration of Bacillus cereus in foods, this formula was shown to be the most effective for this purpose by Inal in 1972. Two reactions on this medium differentiate B. cereus from other members of the Bacillus group, these are mannitol fermentation and lecithinase production. Mannitol fermentation on this medium produces a yellow colour, B. cereus is mannitol negative and produces red colonies. The lecithinase production of B. cereus is indicated by a white precipitate around the colonies. Polymyxin is added to suppress coliforms but some Proteus spp and Gram positive cocci may grow through.

Method for reconstitution

Weigh 46 grams of powder, disperse in 900ml of deionised water. Allow to soak for 10 minutes, swirl to mix then sterilise by autoclaving at 121˚C for 15 minutes. Cool to 47˚C and aseptically add 100ml of X073 egg yolk emulsion and 2 vials of X074 Polymyxin.

Appearance: Pink, opaque gel.

pH: 7.2 ± 0.2

Minimum Q.C. organisms: B. cereus NCIMB 50014

E. coli (inhibition) NCIMB 50034

Storage of Prepared Medium: - up to 7 days at 2-8˚C in the dark. Inoculation: Surface, spreading or streaking for single colonies. Incubation: 30˚C aerobically for 24-48 hours.

References

Inal, T.: Vergleictiende Untersuchungen über die Selektivmedien zum qualitativen und quantitativen Nachweis von Vacillus cereus in Lebensmitteln.

Mitteilung I. : Fleischwritsch, 51: 1629-1632 (1971). I V. Mitteilung: Fleischwritsch, 52: 1160-1162 (1972).

Mossel, D.A.A., Koopman, M.J. and Jongerius, E. (1967). Enumeration of Bacillus cereus in foods. Appl. Microbiol. 15: 650-653. Thatcher, F.S., Clarke, D.S. (1978) Micro-organisms in foods. Volume 1 second edition. University of Toronto.

BS5763 Part 1L:1994. ISO7932:(1993) 3/100