Genetic Characterization of Vibrio vulnificus Strains from Tilapia Aquaculture in Bangladesh

Abstract

Outbreaks of Vibrio vulnificus wound infections in Israel were previously attributed to tilapia aquaculture. In this study, V. vulnificus was frequently isolated from coastal but not freshwater aquaculture in Bangladesh. Phylogenetic analyses showed that strains from Bangladesh differed remarkably from isolates commonly recovered elsewhere from fish or oysters and were more closely related to strains of clinical origin.Vibrio vulnificus causes severe wound infections and lifethreatening septicemia (mortality, Ͼ50%), primarily in patients with underlying chronic diseases (10,19,23) and primarily from raw oyster consumption (21). This Gram-negative halophile is readily recovered from oysters (27,35,43) and fish (14) and was initially classified into two biotypes (BTs) based on growth characteristics and serology (5,18,39). Most human isolates are BT1, while BT2 is usually associated with diseased eels (1, 39). An outbreak of wound infections from aquacultured tilapia in Israel (6) revealed a new biotype (BT3). Phenotypic assays do not consistently distinguish biotypes (33), but genetic analyses have helped resolve relationships (20). A 10-locus multilocus sequence typing (MLST) scheme (8, 9) and a similar analysis of 6 loci (13) segregated V. vulnificus strains into two clusters. BT1 strains were in both clusters, while BT2 segregated into a single cluster and BT3 was a genetic mosaic of the two lineages. Significant associations were observed between MLST clusters and strain origin: most clinical strains (BT1) were in one cluster, and the other cluster was comprised mostly of environmental strains (some BT1 and all BT2). Clinical isolates were also associated with a unique genomic island (13).The relationship between genetic lineages and virulence has not been determined, and confirmed virulence genes are universally present in V. vulnificus strains from both clinical and environmental origins (19,23). However, segregation of several polymorphic alleles agreed with the MLST analysis and correlated genotype with either clinical or environmental strain origin. Alleles include 16S rRNA loci (15, 26, 42), a virulence-correlated gene (vcg) locus (31, 41, 42), and repetitive sequence in the CPS operon (12). DiversiLab repetitive extrageneic palindromic (rep-PCR) analysis also confirmed these genetic distinctions and showed greater diversity among clinical strains (12).Wound infections associated with tilapia in Israel implicated aquaculture as a potential source of V. vulnificus in human disease (6,40). Tilapia aquaculture is increasing rapidly, as shown by a 2.8-fold increase in tons produced from 1998 to 2007 (Food and Agriculture Organization; http://www.fao.org /fishery/statistics/en). Therefore, presence of V. vulnificus in tilapia aquaculture was examined in Bangladesh, a region that supports both coastal and freshwater sources of industrial-scale aquaculture. V. vulnificus strains were recovered from market fish, netted fish, and water samples, and the phylogenetic relationship among strains was examined relativ...

Prevalence of Vibrio parahaemolyticus , and Vibrio vulnificus in blue crabs (Callinectes sapidus ), seawater and sediments of the Maryland Coastal Bays

“…However, Kim and Jeong (2001) studied oysters, sediment and seawater samples from South Korea and found that 65% of samples overall were C type and 35% were E type. Mahmud et al (2010) characterized V. vulnificus strains from fish and seawater in Bangladesh and found that these strains were different compared with fish and oyster samples from other locations, with C type strains (78%) comprising the majority of the samples. It is possible that E type strains are more prevalent in fish and shellfish from the United States, while clinical (C type) V. vulnificus strains are more common in fish and shellfish in Asia, but further studies are needed to confirm this observation.…”

Genotype Is Correlated with but Does Not Predict Virulence of Vibrio vulnificus Biotype 1 in Subcutaneously Inoculated, Iron Dextran-Treated Mice

“…Therefore, a more comprehensive analysis of virulence of vcgC genotype strains from the environment should be performed. In a recent analysis of 33 V. vulnificus biotype 1 strains isolated from aquacultured fish or pond water in Bangladesh, 100% of the strains were profile 2 (40). Preliminary examination of these strains also shows a range of virulence potentials in this mouse model (P. A. Gulig et al, unpublished data).…”

Major foodborne pathogens in fish and fish products: a review

“…Meanwhile, biotype 2 was more often isolated from fish and humans (Gauthier 2015). V. vulnificus biotype 3 has not been associated with the consumption of seafood despite the observed linkage of bacteria isolates from human and fish tested with variable tandem repeat (VNTR) and multilocus sequence typing (MLST) methods (Broza et al 2009;Mahmud et al 2010). V. parahaemolyticus can be classified according to serotype, however, classifications based on the presence of particular genes have been made: V. parahaemolyticus strains are considered Bpathogenic^if the thermostable direct hemolysin (tdh) and/or TDH-related hemolysin (trh) genes are present (Drake et al 2007).…”