Objective To establish a rapid,sensitive and specific assay based on real-time PCR combined with reverse transcription for detecting and identifying viable Listeria monocytogenes.Methods The hlyA gene of Listeria monocytogenes was chosen as target,and then the primers and TaqMan probe were designed.Both ends of probe were modified with two different fluorescence groups.The PCR reaction was optimized systematically.The mRNA of Listeria monocytogenes was extracted,and then reverse transcription was performed through random primer.The cDNA Was detected by real-time PCR.Then the specificity,sensitivity and reproducibility of real-time PCR were estimated.In final,real-time PCR was applied to detect 20 mocked double-blind samplea.Results Viable Listeria monocytogenes were detected by real-time PCR accurately and quickly,and meanwhile,none of other bacteria and non-viable Listeria monocytogenes could be identified.The sensitivity was 10 CFU/ml in pure culture and 103CFU/ml for mocked samples respectively.The coefficient of variation of intra-assay and inter-assay Was less than 5%.When this assay was applied directly to identify 20 mocked double-blind samples,10 of these were positive to viable Listeria monocytogenes,5 were negative to non-viable Listeria monocytogenes,and 5 were negative to other pathogens.Conclusion It is demonstrated that real-time PCR is a reliable,accurate and feasible assay for viable Listeria monocytogenes.The establishment of this assay provided complete data for analysis and diagnosis in the field of food safety and epidemiologic survey.

Objective To develop the PCR-denaturing high performance liquid chromatography (DHPLC) for detection of E. Coli O157: H7. Methods The virulence genes of Shiga-like toxin(SLT) and rfbE were specifically amplified by 2 sets of primers. The target gene fragments of the PCR assay were 224 bp and 499 bp, respectively. Results Analysis of 37 strains demonstrated that this PCR system was specific. The detection limit of the PCR was 4 CFU/ml. Conclusion These results indicated that the multiplex PCR-DHPLC assay can be used for specific and sensitive detection of E. Coli O157:H7.