Bacillus Cereus Agar

Bacillus cereus Agar is a selective medium for the detection, isolation and quantification of?Bacillus?cereus?in foods. In this medium, the low Peptone level and the addition of Sodium Pyruvate improve egg yolk precipitation, thus enhancing bacterial sporulation. The selective agent Polymyxin B suppresses the growth of most bacteria but allows that of?B.?cereus. Typical?B.?cereus?colonies are crenated, filamentous and peacock-blue, surrounded by a precipitate due to the hydrolytic activity of the enzyme lecitinase on the egg yolk suspension. After 48 hours of incubation, the center of the colony presents a grayish color. The pH indicator Bromothymol Blue detects mannitol utilization by other bacteria of the?Bacillus?group, which unlike?B.?cereus?form yellow colonies on this medium. Other egg yolk-reacting microorganisms able to grow on this medium such as?Staphylococcus?aureus,?Serratia?marcescens?or?Proteus?vulgaris?can be distinguished from?B.?cereus?by the color and shape of their colonies, as well as by the presence of a lightening reaction on the egg yolk.?