Pollution Distribution And Molecular Subtyping Of Vibrio Vulnificus Clam (Anadara Subcrenata),in Zhoushan

Vibrio vulnificus belongs to gram-negative vibrio.It is a kind of bacteria inhabiting the ocean.It can be isolated from oysters,clams and other marine products,as well as from the water environment of rivers and estuaries.Food poisoning caused by ingestion of food contaminated with Vibrio vulnificus is one of the most serious foodborne diseases.But its harm lies not in the gastroenteritis caused by it,but in the cellulitis and septicemia caused by it.Zhoushan has a geographical position and abundant seafood resources.Oysters,clams and other shellfish are often eaten raw because of their delicious meat.Therefore,the possibility of Vibrio vulnificus infection is very high.There are many cases of food poisoning caused by Vibrio vulnificus every year.The study was investigated the prevalence of V.vulnificus in clams in Zhoushan City in 2015,analyzed the molecular characteristics of the shellfish strains contaminated by Vibrio vulnificus,and studied the molecular genetic relationship of V.vulnificus from different sources with clinical isolates,analyzed the prevalence of V.vulnificus in Zhoushan City,and provided relevant factors for food risk investigation.It also provides some support for the traceability of diseases caused by Vibrio vulnificus and its molecular epidemiology.The main results obtained are as follows:(1)Through the investigation of the prevalence of V.vulnificus in clam in zhoushan,the contamination of V.vulnificus in Zhoushan City was serious and the pollution level was high.The positive rate of V.vulnificus infection in summer and autumn was higher than that in spring and winter.It can be concluded that the positive rate of V.vulnificus was related to the temperature.Compared two sampling links of the farm and the retail market,the pollution rate and level of the farm were higher than retail market,and the pollution degree of V.vulnificus in the two sampling links was significantly different.Combining the pollution characteristics of two sampling links in four seasons,it was found that the pollution level of farms was the highest in summer and autumn,while the retail markets was the highest in winter.(2)Molecular typing analysis of V.vulnificus in clams in Zhoushan City was carried out by PFGE method.The isolation rate was 60.81%,and the result was obvious.However,the phylogenetic relationship between the shellfish strains was relatively distant,which suggested that there were significant differences in the maps between shellfish strains with the same or different virulence related genotypes isolated from the clams in zhoushan area,indicating that there were extensive genetic diversity and instability in the shellfish strains contaminated with V.vulnificus.(3)According to the results of molecular typing,three groups of shellfish strains have certain kinship,and one group of shellfish strains indicates the existence of the same genotype in farms and retail markets.Combining with the shellfish strain information,it shows that there was certain genetic stability of V.vulnificus in the same farm,and it has retrospective significance.(4)By cluster analysis of clinically isolated strains and shellfish strains,the results of the three groups were obtained,and the MPN values of the shellfish strains were all > 30MPN/g,indicating that the level of pollution affected the probability of infection with V.vulnificus.In summary,the prevalence of V.vulnificus in clam in Zhoushan City was serious,and the degree of prevalence was related to season and sampling links.At the same time,the molecular typing results showed that although the typing effect was obvious,the clustering analysis results were very dispersed and there was extensive genetic diversity and instability.There were also cases related to clustering in the same farm,and at a certain level of pollution,there was a correlation between disease-causing strains and shellfish-producing strains.This study will provide us understand the pollution situation and molecular characteristics of V.vulnificus in zhoushan,investigate the risk of pollution source through sporadic cases,and prevent the outbreak of foodborne diseases.