Conventional identification of Bacillus cereus sensu lato isolates from soil and milk powder samples

The isolates were obtained from soil and milk powder samples by the spread plate method using a highly selective Bacillus cereus agar (BCA) (Oxoid) supplemented with egg yolk emulsion and polymyxin B. The BCA plates were incubated at 30 degrees Celsius for 24 hr and observed the plates for typical colony growth.

The B. cereus (presumptive) colonies on BCA appear turquoise-peacock blue colonies with precipitation. The bacterial cells under microscope are 4-5 micron long and 1.0 - 1.5 micron wide with square ends and rounded corners with spores located centrally or at paracentral position. The biochemical tests used here are based on the following observations: blood hemolysis, presence of hydrogen sulfide and indole, fermentation of lactose, ability to reduce nitrate, hydrolysis of starch, reaction with Voges-Proskauer medium, and motility (Table 1).