Rapid detection of Listeria monocytogenes by PCR

To establish a rapid method by amplification of the hly gene of this organism with PCR for the detection of Listeria monocytogenes in pure culture, and mimic contaminated water; milk and raw pork and for the application of this method in the routine food examination,it was found that the PCR products could be detected in 34 strains of L.monocytogenes, but not found in other Listeria spp, including L.innocua, L.ivanovii, L.seelgeri, L.welshimeri, L.grayi, and also not found in other non Listeria species.These results indicate the primer set (827 bp fragment at hly 3' end) was highly specific for L.monocytogenes. The detection limit of this PCR assay was 10 5 CFU/ml of pure cell culture. However, this method of assay could detect as few as 10 CFU of L.monocytogenes in the mimic contaminated pork (25 g) or contaminated water and milk(25ml), at 30℃ for 16 hours,or in LEB medium at 30℃. Further study showed this PCR assay could detect as few as 6.5 pg DNA of L.monocytogenes and the total assay time was approximately 24 hours.From 169 food samples in Yangzhou area, 8 samples were proved to be positive for L.monocytogenes by means of this method of assay, and the results were quite consistent with those detected by conventional biochemical testings. It is concluded this method of PCR assay is highly sensitive, specific and easy to handle, and can be used as a rapid detection method to find out L.monocytogenes in water, milk, pork and other food products.