Detection of non-emetic and emetic Bacillus cereus by propidium monoazide multiplex PCR (PMA-mPCR) with internal amplification control

Bacillus cereus is an etiological agent of food-borne disease that can cause a type of emesis. To develop a sensitive and reliable diagnosis technique for detecting all the species of the B. cereus group, specific primers were designed to target a recently discovered part of the cereulide synthetase gene (cesB) for emetic B. cereus and 16S rRNA for non-emetic B. cereus. To detect PCR signals only from viable cells, propidium monoazide (PMA) was selected to eliminate the false-positive results. In addition, an internal amplification control (IAC) was applied to meet diagnostic multiplex PCR requirements that will prevent the occurrence of false-negative results. The inclusivity and exclusivity of the mPCR assay were estimated using a panel of 100 strains, including 2 emetic B. cereus, 77 non-emetic B. cereus and 21 non-Bacillus strains. The limit of detection (LOD) for dead B. cereus without PMA treatment in pure bacteria culture was 4.0 × 102 CFU/mL, as low as 7.5 × 100 CFU/mL for viable B. cereus without PMA treatment, and 7.5 × 101 CFU/mL for viable B. cereus with PMA treatment. B. cereus in spiked food produce was detected specifically and sensitively at 1.0 × 103 CFU/g which was the lowest concentration detected. This novel PMA-mPCR-IAC assay is rapid and reliable, providing an efficient diagnostic tool with promising application in monitoring food samples.