Study on the detection of live Shigella in food using propidium monoazide combined with quantitative PCR

To resolve the problem that PCR assay cannot effectively discriminate between live and dead bacteria,a detection method for live Shigella was developed by propidium monoazide( PMA) combined with quantitative PCR technique. The results showed that the sample bacteria were added with 10 ~ 20 μg /mL of PMA,and were treated with strong illumination for 3 ~ 5 min to induce covalent cross- linking of PMA with the DNA from the bacteria with damaged cell membrane,while hydrolyzing free PMA. The quantitative detection for live bacteria in food could be achieved when the proportion of live bacteria was greater than 1%. The results indicate that the method of PMA combined with quantitative PCR avoids false- positive results.