| Vibrio parahaemolyticus is a Gram-negative pathogen,which widely exists in aquaculture.Recently,the V.parahaemolyticus in aquatic animals in South China also has a high detection rate.The bacteria is known to infect a variety of aquatic animals such as fish,shrimp and shellfish.It has come up with one of the main pathogens of aquatic animals.In addition,the bacteria can also infect humans,causing abdominal pain,vomiting,dehydration and even death in severe cases,which poses a serious threat to aquaculture and human beings.In order to explore the epidemiological characteristics and genetic diversities of V.parahaemolyticus in aquaculture in South China,504 aquatic animal samples were detected in this study.98 strains of V.parahaemolyticus isolated from these samples were identified and antimicrobial susceptibility test,virulence gene detection and genotyping were carried out.This study will comprehensively help to grasp the epidemic information of V.parahaemolyticus.It can not only provide data supporting the comprehensive prevention and control of V.parahaemolyticus disease in aquaculture enterprises but also offer scientific basis and theoretical references to the effective prevention and control of related diseases.The main results of this study are as follows:1.From July 2015 to July 2017,an epidemiological survey of V.parahaemolyticus in fish,shrimp,and shellfish collected from 11 provinces in South China was carried out.A total of 504 samples were collected,including 224 fish samples,112 shellfish samples and 168 shrimp samples.The prevalence rates of V.parahaemolyticus were 9.38%,30.36% and 25.60%,respectively in the above three samples.In summer(33.33%),the prevalence rate of V.parahaemolyticus was higher than that in winter(14.01%).The results of this experiment indicated that the prevalence of V.parahaemolyticus in aquatic animals in South China was severe,and summer was the most suitable season for the growth and reproduction.2.The susceptibility of the 98 V.parahaemolyticus isolates to 15 antibiotics was examined by the disk-diffusion method.The results showed that the highest resistance frequency was found to ampicillin(79.59%),followed by Streptomycin(68.37%),and also showed resistance to cefazolin,kanamycin,etc.Besides,all the examined isolates were susceptible to meropenem,imipenem,cefotaxime,and cefoxitin.However,68.38% of the strains were resistant to more than three antibiotics in terms of the multidrug resistance analysis.The results showed that the drug resistance of V.parahaemolyticus strains was common,so this result can provide an effective reference for aquaculture enterprises to avoid the indiscriminate use of antibiotics.3.Through the detection of the main virulence genes,8.16% and 12.24% of the98 V.parahaemolyticus strains were found to carry the tdh,or trh gene,respectively.Nevertheless,none of them carried both the tdh and trh genes synchronously.Among all the samples of the three aquatic animals,the proportion of strains isolated from fish samples carrying a virulence gene tdh or trh was the highest(33.33%).Therefore,the experimental results suggestted that aquaculture enterprises should strengthen the early warning of the pathogen in fish aquaculture.4.ERIC-PCR typing analysis of 98 V.parahaemolyticus strains showed that the strain could amplify 5-10 bands with sizes ranging between 100 bp to 6000 bp.The analysis of the ERIC-PCR patterns revealed that those strains could be divided into six clusters A,B,C,D,E,and F at a relative similarity coefficient of 0.67.Most isolates were distributed among the A and D clusters.However,significant correlations between the different sample types and the ERIC-PCR clusters were not detected.A total of 86 STs were obtained among the 98 V.parahaemolyticus isolates by MLST typing,which were divided into 5 clusters I,II,III,IV and V.ERIC-PCR and MLST typing revealed the genetic relatedness and genetic diversity within these isolates,which is of great significance for the scientific prevention and control of V.parahaemolyticus diseases by aquaculture enterprises. |
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