Study On The Typing Technology For Listeria Monocytogenes Isolated From Food And Its Application In Traceability

In this study,Vitek-2 Compact was applied to confirm the 105 strains Listeria monocytogenes,including one standard strain of Listeria monocytogenes and 104 strains of Listeria monocytogenes isolated from various foods in our laboratory.As expecting,all the 105 strains were identified as Listeria monocytogenes.Strain typing methods can evaluate the relationship of strains isolated from different resources,depending on their biochemical traits or genomic characteristics.Therefore,the source of the infection can be traced back.Repetitive sequence-based PCR(rep-PCR)has been recognized as an effective method for bacterial strain typing.Recently,rep-PCR has been commercially adapted to an automated format known as the DiversiLab typing system.DiversiLab typing system is considered as a quick,convenient and high efficient typing method.Serotyping and DiversiLab typing system were applied to type and analyze the 105 strains Listeria monocytogenes in this study.The main results were as follows:By serotyping,the 105 strains were divided into 6 serum types:1/2a,1/2b,1/2c,3b,4b and 1/2,all of which were pathogenic.The Listeria monocytogenes’s main serotypes were 1/2 a,1/2b and 1/2c which accounting for 93.33%of the total number.In order to establish the typing method including the steps of DNA extraction,rep-PCR,chip priming,chip electrophoresis and electrophoretic pattern assessment for Listeria monocytogenes,105 strains of the Listeria monocytogenes have been typed by the DiversiLab typing system.And then the DiversiLab database of Listeria monocytogenes was established based on the platform of the DiversiLab typing system software.According to cluster analysis for the DiversiLab data,all of 105 strains were divided into 2 major groups(Ⅰ and Ⅱ)at the similarity coefficient below 70%,69 strains were divided into major group Ⅱ with the average similarity coefficient was above 70%,and another 36 strains were divided into major group Ⅰ with the average similarity coefficient above 80%.All the strains were divided into 18 groups at the similarity coefficient as 95%;the similarity exists among strains within each group.All the strains were divided into 34 groups at the similarity coefficient as 97%;the strains could not be distinguished within each group.The result of cluster analysis of the database showed that strains from the same food enterprises with same serotype were similar or indistinguishable,which meant they might come from the same pollution sources.At the same time,some of the strains isolated from different places,different food enterprises had high degree similarity;strains of this genotype may be epidemic one.The result of cluster analysis based on DiversiLab data were closely related with the serotype,of which,1/2b,3b,4b and 1/2 were divided into major group Ⅰ,1/2a and 1/2c were divided into major group Ⅱ.Discriminatory of DiversiLab typing is higher than that of serotyping,the strains with same serotype could be divided into different categories.In this study,all the strains belonging to serotype 1/2a were divided into 13 groups at the similarity coefficient as 95%(xviii,xvii,xvi,xv,xiv,xiii,xii,xi,x,ix,vii,vi,v);all the strains belonging to serotype 1/2c were divided into 3 groups at the similarity coefficient as 95%(xvi,ix,viii);all the strains belonging to serotype 1/2b were divided into 4 groups at the similarity coefficient as 95%(iv,iii,ii,i);all the strains belonging to serotype 4b were divided into 2 groups at the similarity coefficient as 95%(iv,iii).In major group Ⅱ,5 strains(L110,L037,L042,L038 and L036)were isolated from imported food,whose serotype didn’t show consistency with the strains isolated from domestic food.Finally,the DiversiLab typing system has been applied as a prospect application based on the HACCP system.The traceability frameworks of the roasted meat,frozen roast eel and the frozen shrimp(breeding)were established.The traceability framework based on the DiversiLab typing will indicate the direction of the traceability when the food enterprise is polluted by the Listeria monocytogenes in the future.The application of these achievements would have an important meaning not only for the enterprises’economic benefits,but also for the food safety and the security of people’s physical health.