A quantitative real-time PCR method for monitoring Clostridium botulinum type A in rice samples.

A quantitative real-time PCR using SYBR Green dye was developed to target the neurotoxin type A (boNT/A) gene of Clostridium botulinum type A. Primer specificity was confirmed by analyzing 63 strains including 5 strains of C. botulinum type A and 11 of non-type A C. botulinum. The highly similar amplification efficiencies of the real-time PCR assay were observed for 5 strains of C. botulinum type A. The DNA extraction with NucliSENS miniMAG provided sufficient performance to obtain the purified DNA from steamed rice samples and to develop the standard curve for the enumeration of C. botulinum in steamed rice samples. The real-time PCR assay could detect 10 cells per milliliter of 10 x rice homogenate, thus indicating that more than 100 C. botulinum cells per g of rice sample was quantifiable by the real-time PCR assay. The inoculation of aseptic rice samples with low numbers of C. botulinum type A cells revealed that the fate of inoculated C. botulinum type A cells in rice samples could be monitored accurately by the real-time PCR assay. These results indicate that the real-time PCR assay developed in this study provides rapid, effective, and quantitative monitoring of C. botulinum in steamed rice samples.