Prevalence And Antimicrobial Susceptibility Of Vibrio Parahaemolyticus Isolated From Retail Shellfish In Shanghai

Vibrio parahaemolyticus is a Gram-negative,halophilic asporogenous rod bacterium.It has been the leading cause of bacterial foodborne poisoning in China according to recent official surveillance reports.As a foodborne pathogen,V.parahaemolyticus mainly transmitted by fish,shellfish and other seafood.Consumption of contaminated seafood may lead to the development of acute gastroenteritis.In this context,antibiotics have been used for therapeutic purposes in clinical treatment and aquaculture field for many years.However,the drug resistance of bacteria has emerged with the widespread utilization of antibiotics,which may result in the failure of clinical treatments.Hence,it is meaningful to have a good knowledge of the prevalence of V.parahaemolyticus in retail shellfish in Shanghai as well as its antimicrobial susceptibility.The main results obtained from the current research were described as follows:1.The preliminary isolation of Vibrio parahaemolyticus from retail shellfish in ShanghaiOne hundred and forty shellfish samples,including clam,oyster,razor clam and scallop,were randomly collected from retail markets in Shanghai between Februry 2014 and Februry 2015.According to the National Standard of the People's Republic of China GB 4789.7-2013,Thiosulphate citrate bilesalt sucrose?TCBS?Agar plates and CHROMagar^TM Vibrio?CV?were used to isolate V.parahaemolyticus isolates.As a result,176 suspected strains were detected.2.Identification and virulence genes screening of Vibrio parahaemolyticusCommercial biochemical test kit and PCR assay were used to identify suspected V.parahaemolyticus.The biochemical tests with 16items to be detected were performed according to the manufacturer's instructions.Species-specific gene irgB,previously screened in our laboratory,was used to identify suspected strains of V.parahaemolyticus.Finally,a total of 96 isolates were confirmed as being V.parahaemolyticus.These identified isolates were then screened for major virulence genes in V.parahaemolyticus.It was found that the tdh gene was positive in two isolates?2.1%?and the trh gene was negative in all isolates.3.Molecular typing of Vibrio parahaemolyticus by ERIC-PCREnterobacterial repetitive intergenic consensus?ERIC?PCR was used to type 96 V.parahaemolyticus strains.When the similarity index was set as 75%,these V.parahaemolyticus isolates were divided into 21groups.The results suggested a high level of genetic diversity among V.parahaemolyticus strains isolated from retail shellfish in Shanghai.4.Antimicrobial profile determination and resistance genes detectionThe disk diffusion method established by the Clinical and Laboratory Standards Institute?CLSI,2013?was employed to determine the antimicrobial profile of V.parahaemolyticus.A total of 18 antibiotics were used in this experiment.The results showed that these isolates had the highest resistance to ampicillin?87.5%?,followed by cephazolin?31.3%?,cephalothin?6.3%?,amoxicillin/clavulanic acid?6.3%?,piperacillin?6.3%?and amikacin?3.1%?.Though no drug resistance was shown,a large number of isolates exhibited intermediate-resistance to aztreonam?40.6%?.Furthermore,all isolates were sensitive to ceftazidime,gentamycin,nalidixicacid,norfloxacin,sulphamethoxazole/trimethoprim,imipenem and chloramphenicol.PCR test was conducted to determine the presence of 11 genes concerning antibiotic resistance.The existence frequencies of resistance genes were as follows:bla_TEM?15.6%?and bla_SHV?4.2%?.And other genes were negative in all isolates.