ABSTRACT
A new EMA real-time fluorescence PCR method was developed to detect alive Listeria monocytogenes in foods.The specific primers and probe were designed based on the conserved inlA gene.The pretreatment conditions including EMA of different concentrations and irradiating times were optimized.The detection limit and inhibition rate to dead bacteria of this method were confirmed by using direct plating method.The detection specificity was evaluated by using 35 L.monocytogenes strains,25 non-L.monocytogenes strains and 92 non-Listeria strains.Simulation detection experiments were performed on 15 beverage samples and 15 cooked meat samples supplemented separately with inactivated L.monocytogenes,alive L.monocytogenes and Staphylococcus aureus.Results showed that the Ct of EMA real-time fluorescence PCR for alive L.monocytogenes was Ct=38.46-3.30 × log (R2=0.999).The detection limit was 55 cfu per reaction.Inhibition rate of DNA of inactivated strains was over 99.98％.The Ct of 35 L.monocytogenes strains were between 16.21 and 29.38,while 25 non-L.monocytogenes strains and 92 non-Listeria strains had Ct ＞35.The variation coefficient of CT was less than 5％ when the experiments were repeated.Results of 30 simulation samples were consistent with that by using standard method.The test time by using newly developed EMA real-time fluorescence PCR was shortened from 3-5 days to about 10 h.The newly developed EMA real-time fluorescence PCR method for alive L.monocytogenes is rapid,convenient,specific and sensitive and could be applyed in foods inspection.