Bacillus Cereus Medium
Use and description: Solid selective medium, according to Mossel, for the detection and enumeration of Bacillus cereus. The principle of the medium relies on the inability of B. cereus to ferment mannitol (pink colonies) and on the manifestation of lecithinase when supplemented with egg yolk. Polymixin-B can be added to increase selectivity, in the presence of high number mold cycloheximide (40 mg/L) can be the right agent.
Composition per liter: Agar……………………………………13.000 g Peptone………………………………...10.000 g Mannitol……………………………….10.000 g Sodium chloride……………………….10.000 g Meat extract……………………………..1.000 g Phenol red…………………..…………...0.025 g
Final pH of the ready to use medium: 7.2 ± 0.2
Medium preparation: Add 44.0 grams of dehydrated culture medium to 900 ml of distilled water. Sterilize in the autoclave at 121oC for 15 minutes. Cool to 50oC and then add 100 ml of sterile egg yolk emulsion (MMS01) and 100 mg of Polymixin-B (MMS02). Homogenize well and distrtibute into plates. Do not reheat or remelt complete medium.
Quality specifications: Dehydrated medium: homogeneous, greenish-beige fine powder. Ready to use medium: slightly opaque and yellow to yellow-green.
Microbiological response:
Storage: Dehydrated medium should be stored between 10 to 25oC. Once opened, place the container in a dark, dry place. The dehydrated medium should not be used if there is any lump or the color has changed from the original. |
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