Description
Presumptive B. cereus are determined quantitatively by plating known amounts of sample on Bacillus cereus selective agar (mandatory). After incubation at 30 degrees C for 24 ± 3 hours, typical bluish colonies surrounded by egg yolk reaction (lecithinase activity) are counted. Alternatively, plating on B. cereus selective agar (mandatory) and blood agar in parallel can be performed, especially when low counts are expected. On blood agar presumptive B. cereus form colonies with a hemolytic zone.