Epidemiological Investigation And Virulence Gene Detection Of Shellfish Vibrio In Shandong Province

The beach shellfish breeding industry is an important pillar of the fishery economy of our province.In recent years,the breeding varieties and modes have become increasingly diversified,the farming technology has gradually improved,and the output has been increasing.However,with the rapid development of shellfish farming and pollution of farming environment,the disease is becoming more and more serious.Among them,vibriosis causes serious damage to the shellfish breeding industry.Therefore,the epidemiological survey of shellfish Vibrio is necessary,and prevention technology of that is urgent to be solved.This study carried out an epidemiological survey of Vibrio in Ruditapes philippinarum,Razor clam,Speckle arrises clam,Glossaulax didyma,Rapana venosa,Pectinidae,Anadara subcrenata,Oyster and Mytilidae from seven coastal aquaculture areas,mainly in Binzhou,Qingdao,Yantai,Weihai and Dongying in Shandong during 2017 and 2018.Through the analysis and comparison of isolated Vibrio,understanding the epidemic of shellfish vibriosis.The drug susceptibility test was carried out on three kinds of Vibrio with high separation rate,and the drug resistance was studied.At the same time,the distribution of virulence genes of each Vibrio was studied.In this study,a total of 155 strains of bacteria were isolated,belonging to 27 different species,including 24 species of Vibrio and 3 species of other bacteria.The isolated Vibrio includes Vibrio alginolyticus,Vibrio harveyi,Vibrio parahaemolyticus,Vibrio hangzhouensis,Vibrio natriegens,Vibrio owensii,Vibrio chagasii and so on.The other bacteria include Photobacterium damsetae,Enterobacter cloacae and Photobacterium swingsii.The statistical results show that the detection rate of Vibrio harveyi,Vibrio alginolyticus and Vibrio parahaemolyticus was higher,which were 23%,24% and 9% respectively.The overall detection rate of Vibrio was 95%,and other bacteria were 5%.The detection rate of Vibrio harveyi and Vibrio alginolyticus was annually above 20%,and the detection rate ofother Vibrio was relatively low.The detection rate of Vibrio in different shellfish was different.The separation rate of Vibrio parahaemolyticus in Mytilidae,Anadara subcrenata and Razor clam was high,which were 62%,18% and 22% respectively.The isolation rate of Vibrio harveyi in Mactra veneriforimis,Anadara subcrenata and Ruditapes philippinarum was higher,which were 38%,35% and 28% respectively.The isolation rate of Vibrio alginolyticus in Oyster,Razor clam and Ruditapes philippinarum was 41%,36% and 21%,respectively.The detection rates of different Vibrio in different regions were different,and the detection rate of Vibrio harveyi in Binzhou,Dongying and Weifang was higher,which were 25%,44%and 28% respectively.The detection rate of Vibrio alginolyticus in Rizhao,Weihai and Yantai was 52%,43% and 37%.The detection rate of Vibrio parahaemolyticus in Binzhou and Rizhao was 18% and 13%.In this study,the susceptibility test was carried out on three kinds of Vibrio with high separation rate in the past two years using ampicillin,amoxicillin,piperacillin,cefuroxime,cefotaxime,streptomycin,gentamicin,kanamycin,amikacin,enrofloxacin,nalidixic acid,erythromycin,tetracycline,compound sulfamethoxazole,florfenicol and aztreonam.The drug susceptibility results showed that the sensitivity of florfenicol and nalidixic acid to Vibrio reached 100%.The sensitivity of compound sulfamethoxazole and erythromycin to Vibrio reached 95%,and no drug-resistant strains appeared.Antibiotics such as nozafloxacin,tetracycline and aztreonam were more than 90% sensitive to Vibrio and no resistant strains.90.8% and 86.2% of Vibrio showed resistance to ampicillin and amoxicillin,only 2% and 1%showed sensitivity respectively.The sensitivity of Vibrio to cefotaxime and kanamycin was about 50%,the resistance rates were 18.4% and 10.3%,respectively and the resistance rate of piperacillin was 8%.In this test,virulence genes were detected in the isolated Vibrio.The virulence genes detected include tdh,trh,ure C,lux R,Omp W,vvh A,and vac O.The results showed that the detection of tox R gene,pap6 gene and lux R gene in Vibrio harveyi was 47%,39% and 28%,respectively.The detection rate of vscC2 gene in Vibrio parahaemolyticus was up to 35%,while the detection rate of ure C gene and trh gene was 14% and 21%.The detection rate of Omp W gene in Vibrio alginolyticus was 29%.Through the epidemiological investigation of shellfish vibriosis in Shandong Provinceduring 2017 and 2018,we mastered the epidemic situation of shellfish vibriosis,providing a basis for the control and prevention of vibriosis.Sensitivity test provides a scientific method for drug control of shellfish vibriosis.At the same time,the distribution of major virulence genes was detected in some isolated Vibrio species,providing relevant information for the identification of virulence strains,and offering a scientific basis for effectively preventing large-scale outbreaks of vibriosis,which has important research significance.