Identification of Cereulide-Producing Bacillus cereus by Nucleic Acid Chromatography and Reverse Transcription Real-Time PCR

RNA extracts were analyzed with a nucleic acid sequence-based amplification (NASBA) nucleic acid chromatography and a reverse transcription-quantitative PCR assay (RT-qPCR) based on the TaqMan probe for identification of cereulide-producing Bacillus cereus. All 100 emetic B. cereus strains were found to give positive results, but 50 diarrhea! B. cereus strains and other bacterial species showed negative results in the NASBA-chromatography. That is, the assay could selectively identify the emetic strains among B. cereus strains. Also, the B. cereus contents of more than 10(7) cfu/ml were required for the identification of the cereulide-producing strains in this assay. In qRT-PCR assays, all 100 emetic type strains of B. cereus produced 102 104 copy numbers per ng of the RNA preparation, and the strains produced 104 copies including ones which had the high vacuolation activities of HEp-2 cells.