Bacillus Cereus Supplement ISO

Description

These media permit an easy and ready detection of a small number of Bacillus cereus in the presence of a large number of food contaminants: Bacillus cereus grows in very typical colonies and it allows a rapid macroscopic identification.

• PEMBA: blue colonies, surrounded by a clear zone of egg yolk.
• MYP: brilliant pink opaque colonies, with clear lecithinase halo.

Technique

Collect, dilute and prepare samples and volumes as required according to specifications, directives, official standard regulations and/or expected results.

Reconstitute the vial with the sterile diluent in aseptic conditions and add it to 450 mL of melted agar base cooled to 50 °C, previously supplemented also with 50 mL of sterile Egg Emulsion.

Do not overheat once supplemented.

Pour the complete medium into Petri dishes and, once solidified on a flat surface, spread the plates either by streaking or by spiral method.

Incubate the plates in aerobic atmosphere at 30 ± 1 °C for 24-48 h.

Incubation times longer than those mentioned above or different incubation temperatures may be required depending on the sample or the specifications.

After incubation, count all the colonies that have appeared on the surface of the agar.

Presumptive isolation of Bacillus cereus must be confirmed by further microbiological and biochemical tests.

Reconstitute the original freeze-dried vial by adding 6 mL of sterile distilled water.

Note: each vial is sufficient to supplement 500 mL of Bacillus cereus Agar Base.

Physical/chemical control

Microbiological control

Reconstitute 1 vial as indicated in Composition; shake and dissolve completely.

Distribute the complete medium, cooled to 50 °C, in plates.

Inoculate: practical range 100 ± 20 CFU, min. 50 CFU (productivity) / 10⁴-10⁶ (selectivity).

Aerobiosis. Incubation at 35 ± 2 °C, reading at 24-48 hours.

Sterility control

Add 5 mL of the sample to 100 mL of TSB and to 100 mL of Thioglycollate.

Incubation 48 hours at 30-35 °C and 48 hours at 20-25 °C: NO GROWTH.

• 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.