Study On Isolation, Identification And Inhibition Of Listeria Monocytogenes In Food

In this paper, the contamination of Listeria monocytogenes (L.monocytogenes) of seven kinds of food in three seasons was investigated. The suspicious strains were isolated and identified by physiological and biochemical methods and polymerase chain reaction (PCR). The aspects of time consuming and accuracy were compared between the two methods. In addition, the NaCl concentration, pH and temperature range for L. monocytogenes growth was determined by studying its growth characteristics of L. monocytogenes, and the inhibition effect of six kinds of spice on growth of L. monocytogenes were also investigated.The results obtained are as follows:A total of184food samples were examined during2008～2009, of which22samples were positive for L.monocytogenes. The positive rates of L.monocytogenes were16.13%for summer,4.84%for winter and5%for spring. Ranked from high to low, the positive rates of L.monocytogenes of seven kinds of food were20%for raw meat,13.79%for cooked meat products,11.11%for raw beef,7.7%for raw chicken,4%for raw mutton, and no found for milk and vegetable.This thesis studied the characteristic of L.monocytogenes, and the range of L.monocytogenes growth NaCl concentration, pH and temperature was finded out. And the optimum NaCl concentration is0～10mg/mL, pH is7～8, temperature is30～40℃癈. When the NaCl concentration is higher than110mg/mL, the temperature is higher than55℃, the pH is lower than3and higher than11, all the L.monocytogenes died after24hours.The inhibitions of the six kind of spices for L.monocytogenes were determined. The minimum inhibitory concentrations(MIC) of the spices is6.25mg/mL for cloves and vanilla,12.5mg/mL for anise tree, fennel, cinnamon and cassia bark. When the concentration is12mg/mL for cloves,11mg/mL for vanilla,16mg/mL for anise tree,14mg/mL for fennel,16mg/mL for cassia,18mg/mL for cassia bark, all of the L.monocytogenes died after24hours.