This is an improvement in sensitivity compared with recent reports on detection of Salmonella. Live Salmonella cells were detected from

spiked lettuce samples at the concentration of 101 CFU/g with 12-h enrichment [34]. Another study reported that the detection limit of PMA-LAMP (loop-mediated isothermal amplification) was 6.1 × 103-104 CFU/g in spiked produce and PMA-PCR was up to 100-fold less sensitive compared with qPCR assay [32]. It is noteworthy to mention that this SB273005 PMA-qPCR assay reported here appears to be BKM120 more sensitive. Two factors might explain this: first, it may be due to the qPCR assay we developed in this study, which offers higher sensitivity with detection limit as low as 3 CFU; whereas the two previous assays used longer amplicons (269 bp and 285 bp) in their qPCR assays [32, 34], which

would make the qPCR assay less efficient LEE011 in vitro compared with the assays with shorter amplicons; second, it might be due to the usage of our previously modified PMA-treatment procedure, which was shown to increase the PMA-qPCR efficiency [21]. With this modified PMA-treatment procedure, not only could we achieve a relatively small C T value difference (0.5) between treated and untreated live cells (Figure 1A), but we were also able to obtain efficient inhibition (17-C T -value difference, 128,000-fold) of DNA amplification with dead cells (Figure 1B). These improvements made it possible for efficient Glutamate dehydrogenase and accurate differentiation

of live Salmonella cells from dead cells by this PMA-qPCR assay [37]. Furthermore, we have successfully applied this assay to detect live Salmonella cells from beef (Additional file 2: Table S2) and environmental water samples [41]. It may be applied to other food matrices as well, fostering improvement of accurate monitoring Salmonella. Conclusions We have developed a PMA-qPCR assay for selective detection of live Salmonella cells from dead cells in food. This assay is sensitive and specific and has been validated with a large number of Salmonella strains. We were able to differentiate live Salmonella cells from live/dead cell mixtures. This PMA-qPCR has been applied for selective detection of live Salmonella cells in spiked spinach. It allows selective detection of 30 CFU/g Salmonella from spiked spinach with 4-h enrichment. Additionally, we evaluated the effect of amplicon length on PMA-mediated inhibition of DNA amplification of dead cells. The limitation of this PMA-qPCR assay is that PMA treatment slightly increases the cost and reduces the sensitivity of PCR assay. Methods Bacterial strains Salmonella Enteritidis (SARB16) was used in designed experiments of optimization, sensitivity, and spinach spiking.