An improved selective and diagnostic medium for the isolation and enumeration of Bacillus cereus in foods

Abstract

The use and performance of an improved diagnostic and selective medium, PEMBA (polymyxin pyruvate egg yolk mannitol bromothymol blue agar), for the detection of Bacillus cereus in foods is described. The distinct colonial appearance of B. cereus on PEMBA permitted the recognition of both strains: those that do precipitate egg yolk and those that do not react with egg yolk. A staining procedure, used to demonstrate microscopically both the presence of lipid globules in vegetative cells and spore morphology of isolates, proved a rapid and reliable confirmatory test which gave complete agreement with a battery of biochemical tests used for this purpose. The quantitative recovery of B. cereus on PEMBA from 143 food samples was not significantly different from counts on KG (Kim and Goepfert), MYP (mannitol egg yolk phenol red), and McClung's media, and the selectivity of PEMBA was generally superior.