| Vibrio parahaemolyticus is one of the main causes of aquatic product-related infectious diarrhea in China.With the changes of People's Daily dietary nutrition requirements,aquatic products have become one of the better choices for consumers to supplement high quality protein.In recent years,due to the extensive use of antibiotics in aquaculture and medical industry,the drug resistance of V.parahaemolyticus has increased.It is undoubtedly posed a great challenge to the control of food safety.The purpose of this study was to investigate the contamination and drug resistance of V.parahaemolyticus in aquatic products in Chengdu.We detected the harboring rate of its virulence genes.Multilocus sequence typing was used to analyze their genetic diversity.1.From October 2018 to October 2019,590 samples of various aquatic products were collected,including clam,short necked clam,solenstrictus,crab,prawn,crayfish,frog and eel.According to GB4789.7-2013,sample processing,pure culture and partial biochemical tests were performed,and 16S rDNA sequencing was used to complete the isolation and identification of V.parahaemolyticus.The results showed that the total contamination rate of 590 samples was 26.9%,and that of seafood was 30.1%.No cultureable V.parahaemolyticus was isolated from freshwater products.The contamination rates of prawn,solenstrictus,short necked clam,clam and crab were 45.2%,35.2%,11.4%,20.5% and 42.9%,respectively.The highest separation rate was 42.0% in summer.Nine O antigen serogroups were produced by 159 strains of V.parahaemolyticus.The dominant O antigen serogroups were O1(42.1%),O4(16.3%)and O3(15.1%).There were differences in O antigen serogroup typing due to different species,collecting season and collection locations.2.The Kirby-Bauer disk diffusion method was used to detect 159 strains of V.parahaemolyticus isolates,and a total of 13 antibacterial drugs were tested.The results showed that the isolates had the highest resistance to ampicillin(92.4%),followed by amoxicillin(65.4%),and the resistance rates to ceftiophen and cefuroxime were relatively low(23.3% and 18.2%).Most of the isolates were sensitive to compound sulfamethoxazole,tetracycline,amikacin,cefazolin and cefepime.The drug-resistant strains accounted for 4.4%,7.5%,6.9%,8.8%,9.4%.All isolates were sensitive to chloramphenicol,gentamicin,ciprofloxacin,and ofloxacin.4.4% of the isolates do not have drug resistance,and 7.5% of the isolates are multi-drug resistant strains.All isolates produced a total of 25 drug resistance patterns with significant resistance.3.Three genes related to hemolytic toxin were amplified by PCR.The results showed that the harboring rates of tdh and trh virulence genes in the isolates were4.4% and 11.9%.1.9% of the isolates carried two virulence genes.Three strains,from prawns and clams,carried two virulence genes at the same time.The detection rate of tlh gene was 100.0%.4.Seven housekeeping genes of V.parahaemolyticus were amplified by PCR,and their products were detected by electrophoresis.Finally,the products were purified and sequenced.20 isolates were not successfully matched,and the rest were divided into 72 ST types,of which ST1801(8.2%),ST392(7.5%)and ST124(6.3%)had higher separation rates.The 72 ST types included 72 monomers with no pandemic clones.The dominant ST type was different in different species and collection seasons.The drug resistance of the same ST type isolates was different.In summary,we investigates the contamination of V.parahaemolyticus in common aquatic products in Chengdu.We systematically analyzed the pollution rate,drug resistance,and virulence gene distribution in some aspects.From the perspective of food safety,the test results can provide certain data support for the prevention and control of foodborne diseases caused by the bacterium,and provide a certain scientific basis for its transmission and traceability investigation.We can also provide basic data for the research on the transmission of V.parahaemolyticus and the risk assessments of food safety. |
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