Ready-to-use media
Bacillus Cereus Selective Agar (MYP)
Selective solid medium, according to Mossel, for the isolation and identification of Bacillus cereus from food samples according to ISO standards.
- Cat. No.
- LC-945
- Category
- Ready-to-use media
- Format
- 20 plates, 90 mm
- ISO 17025 quality control
- Yes
- Storage
- 2 to 14 °C
- Minimum guaranteed shelf life
- 1 month
- Standards
- ISO 7932
Mossel's formulation is developed to detect and enumerate B. cereus in any food stuff. It is both selective and differential for this microorganism. Polymyxin addition inhibits most of the accompanying bacteria, but does not affect the growth of B. cereus. This bacterium does not ferment mannitol and thus there is no change in the colour of the indicator around the colonies. The lecithinase activity of B. cereus produces a halo or zone of white precipitate around the colonies.
Key features
Applications
Selective enumeration of Bacillus cereus.
Industry
Food.
Standards
ISO 7932.
Presentation
20 prepared plates, 90 mm, with 21 ± 2 mL.
Description and technique
Description
A count of B. cereus over 100,000 cells/g of food sample is considered hazardous, since the accumulated phosphorylcholine may cause toxic symptoms in children. For this reason a viable enumeration must be performed to evaluate the real population of cells.
Technique
For plate inoculation, follow the laboratory's standard methods or the applicable norms (spiral plating method, ecometric methods, streak plating, dilution banks, spread plating with Drigalski rod, among them).
According to the authors, dehydrated or dry samples must be treated in the following way: 20 g of sample is mixed with 90 mL of Tryptone Water for a minimum period of 1 hour, at room temperature. Afterwards, add an additional 90 mL of Tryptone Water and homogenize. If necessary, dilute 1:10. Proceed to a 1/10 serial dilution bank using Tryptone Water as the diluent if necessary. With a Drigalski loop, spread aliquots of 0.1 mL over the surface of the agar plates and let the agar medium absorb the aliquots. Incubate the plates at 30 °C for 18-24 hours to allow spore germination before giving definite results.
Suspected colonies have the following appearance: irregular borders, pink colour becoming purple in the centre, with a halo of white precipitate (mannitol +). Colonies with yellow halos must be discounted (mannitol -).
Confusion with other colonies of Gram-positive bacilli is possible, and hence confirmation tests must be carried out, i.e. glucose fermentation, gelatine degradation and nitrate reduction.
Presentation
| Presentation | 20 prepared plates, 90 mm |
|---|---|
| Filling | 21 ± 2 mL |
| Packaging | 1 box with 2 packs of 10 plates/pack. Single cellophane. |
Composition
| Ingredient | g/L |
|---|---|
| Peptone from casein | 10.000 |
| Mannitol | 10.000 |
| Sodium chloride | 10.000 |
| Meat extract | 1.000 |
| Phenol red | 0.025 |
| Agar | 12.000 |
| Polymyxin B sulphate | 100,000 IU |
| Egg yolk | 100 mL |
Quality control
Physical/chemical control
| Color | Orange |
|---|---|
| pH | 7.2 ± 0.2 at 25 °C |
Microbiological control
Inoculate: practical range 100 ± 20 CFU; min. 50 CFU (productivity) / 10⁴-10⁶ (selectivity).
Microbiological control according to ISO 11133:2014/Amd 1:2018.
Aerobiosis. Incubation at 30 ± 1 °C, read after 24-48 h.
| Microorganism | Growth |
|---|---|
| Bacillus cereusATCC 11778, WDCM 00001 | Good - pink colonies with halo of precipitation |
| Escherichia coliATCC 25922, WDCM 00013 | Inhibited |
| Bacillus subtilisATCC 6633, WDCM 00003 | Yellow colonies without halos |
Sterility control
Incubation 48 hours at 30-35 °C and 48 hours at 20-25 °C: NO GROWTH.
Check at 7 days after incubation in same conditions.
Bibliography
- ATLAS, R.M. & L.C. PARKS (1993) Handbook of Microbiological Media. CRC Press. London.
- CORRY, J.E.L., G.D.W. CURTIS & R.M. BAIRD. (2003) Handbook of Culture Media for Food Microbiology. Elsevier Sci. B.V. Amsterdam. The Netherlands.
- DOWNES, F.P. & K. ITO (2001) Compendium of methods for the microbiological examination of foods. 4th ed. APHA. Washington DC. USA.
- FIL-IDF 181:1998 Provisional Int. Standard. Dried Milk Products. Enumeration of Bacillus cereus - Most probable number technique.
- ISO 7932 Standard (2004) 3rd ed. Microbiology of food and animal feeding stuffs. Horizontal method for the enumeration of presumptive Bacillus cereus. Colony count technique at 30 °C.
- ISO 11133:2014/Amd 1:2018. Microbiology of food, animal feed and water. Preparation, production, storage and performance testing of culture media.
- ISO 21871 Standard (2006) Microbiology of food and animal feeding stuffs - Horizontal method for the determination of low numbers of presumptive Bacillus cereus - Most probable number technique and detection method.
- MOSSEL, D.A.A., KOOPMAN, M.J. & JONGERIUS, E. (1967) Enumeration of Bacillus cereus in foods. Appl. Microbiol. 15:650-653.
- PASCUAL ANDERSON, Mª R. (1992) Microbiología Alimentaria. Díaz de Santos, S.A. Madrid.
What you receive
The product
Shipped under controlled temperature when the product requires it.
Lot certificate
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