Chromogenic medium for detection of Bacillus cereus in food and environmental samples

DESCRIPTION
ChromaticTM Bacillus cereus is a chromogenic medium used with supplements for the isolation, differentiation and enumeration of Bacillus cereus from a wide variety of foods including both raw and cooked food as well as sauces, soups and other food mixtures.

PRINCIPLE
Peptone is a source of amino acids, nitrogen, carbon, minerals and vitamins essential for bacterial growth. Yeast extract provides vitamins particularly of B-group. Di-sodium phosphate and potassium phosphate are the buffer system. Sodium pyruvate is an energy source. The chromogenic mix allows the identification of bacteria on the basis of the colony color. Agar is the solidifying agent. This medium is completed after the addition of Chromatic™ Bacillus cereus Supplement (ref. 81097) consisting of an enrichment supplement and a selective supplement. Selectivity is due to the combination of two antibiotics: polymyxin B and trimethoprim. Polymyxin B inhibits most Gram-negative organisms and some Gram-positive bacteria including some bacilli other than B. cereus. Trimethoprim, which blocks folic acid synthesis necessary for cellular replication, is active against many Gram-positive bacteria including S. aureus, Enteroccus spp and some non-cereus Bacillus spp.

TYPICAL FORMULA (g/l)

PREPARATION
Suspend 39 g of powder in 1 liter of deionized or distilled water. Bring to boil and shake until completely dissolved. Sterilize at 121°C for 15 minutes. Cool up to 45-50°C. Aseptically, add rehydrated content of 2 vials (10 ml) of Selective Supplement and 2 vials (40 ml) of Enrichment Supplement, both supplements contained in ChromaticTM Bacillus cereus Supplement. Mix well and pour in Petri dishes.

TECHNIQUE
Prepare the sample by diluting 1:10 (w/v) with Buffered Peptone Water (ref. 24099) or Ring's Solution (ref. 81059). Homogenize for 1 minute by using an appropriate laboratory blender and spread the material over the agar surface. Alternatively, inoculate the medium by direct streaking of the sample onto plate. Incubate aerobically at 30°C for 18-24 hours.

INTERPRETATION OF RESULTS
Examine for typical blue-green colonies of Bacillus cereus surrounded by a opaque halo. Confirm the presumptive identification by a validated method.
Note: that Bacillus cereus strains which do not produce the enzyme β-glucosidase cannot cleave the chromogenic substrate thereby forming white colonies with opaque halo.

STORAGE
The powder is very hygroscopic, store the powder at 10-30°C, in a dry environment, in its original container tightly closed and use it before the expiry date on the label or until sings of deterioration or contamination are evident. Store prepared plates at 2-8°C away from light.

WARNING AND PRECAUTIONS
The product does not contain hazardous substances in concentrations exceeding the limits set by current legislation and therefore is not classified as dangerous. it is nevertheless recommended to consult the safety data sheet for its correct use. The product is designed for professional use only and must be used by properly trained operators.

DISPOSAL OF WASTE
Disposal of waste must be carried out according to the national and local regulations in force.

PRESENTATION
Dehydrated medium

STORAGE
10-30°C

APPEARANCE OF THE MEDIUM
Powder medium
Appearance: free-flowing, homogeneous,
Colour: yellowish
Ready-to-use medium
Appearance: slightly opalescent
Colour: light straw

SHELFLIFE
2 years

PACKAGING

QUALITY CONTROL

1. Control of general characteristics, label and print
2. Microbiological control
   Supplement: ChromaticTM Bacillus cereus Supplement
   Inoculum for productivity: 50-100 CFU
   Inoculum for selectivity: 10⁴-10⁶ CFU
   Incubation Conditions: 18-24 h at 30 ± 2°C, in aerobiosis

REFERENCES

1. ISO 7932:2004. Horizontal method for the enumeration of presumptive Bacillus cereus.
2. ISO 16140:2003. Microbiology of food and animal feeding stuffs - Protocol for the validation of alternative
3. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook Bacillus cereus and other Bacillus spp. (2003) U.S. Food & Drug Administration (C.F.S.A.N)
4. Handbook of Culture Media for Food Microbiology (2003) Volume 37. Chapter 4. Media for Bacillus spp. and related genera relevant to foods. Edited by Corry, J. E. L., Curtis, G. D. W. and Baird, R. M. Publisher - Elsevier, Amsterdam.

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