Lipid globule staining to aid in differentiating Bacillus species

The use of the lipid globule stain to aid in differentiating the Bacillus cereus group (i.e., B. cereus, B. cereus var. mycoides, and B. thuringiensis) from other Bacillus species was investigated. Smears from colonies grown on suitable agar were made on precleaned slides, stained, and examined microscopically for characteristic deep blue lipid globules. The study included a total of 649 cultures of Bacillus species plus 143 incompletely characterized Bacillus isolates from food. Only B. cereus, B. cereus var. mycoides, B. thuringiensis, B. megaterium, and B. sphaericus were consistently positive for lipid globules, although at times, a few cells of B. aneurinolyticus and B. thiaminolyticus were also positive. The lipid globule stain procedure is of value in differentiating Bacillus species, especially when performed by an experienced analyst and used in conjunction with tests for cell and spore morphology.