Low incidence of Vibrio vulnificus among Vibrio isolates from sea water and shellfish of the western Mediterranean coast

Investigation of potentially pathogenic Vibrionaceae in Saint-Louis city, Senegal

Introduction

as cholera, due to toxigenic bacteria Vibrio cholera (serogroups O1 and O139), is a major public health threat in Africa, the aim of this work was to investigate potentially pathogenic Vibrionaceae bacteria firstly from human stool samples, and secondly from various environmental water points of Saint-Louis city in Senegal.

Methods

a hospital-based study was conducted between 2013 and 2015. Stool samples were taken and cultured from daily incoming patients or hospitalized for acute diarrhea at Saint-Louis´ regional hospital. For environment, a monthly longitudinal sampling from January to October 2016 was carried out at 10 sites in the city. We used total DNA extracted from APW (alkaline peptone water) broth solutions and on suspect bacterial colonies to run PCR Multiplex targeting specific DNA fragments to detect Vibrio genus and specific species. In case of positivity, a simplex PCR was performed to test for cholera toxins Ctx, and V. parahaemolyticus TRH and TDH.

Results

for 43 patients screened, bacterial culture was positive in 6% of cases but no strain of V. cholerae or other Vibrio sp. was isolated. PCR on 90 APW solutions were positive for Vibrio sp.(n = 43), V. cholera(n = 27), V. mimicus(n = 16), V. parahaemolyticus(8), V. alginolyticus(n = 4), and V. vulnificus(n = 2). Unlike for those on suspected colonies which were positive for a majority of V. parahaemolyticus (n = 40) and V. cholerae non-O1 / O139 (n = 35). Six strains of V. parahaemolyticus carried TRH gene, 3 of which expressed simultaneously virulence TRH and TDH genes. For physicochemical parameters, all temperatures varied similarly according to a unimodal seasonality, as well as salinity.

Conclusion

despite the presence of natural populations of Vibrionaceae, even toxigenic ones, was noted in water environment, along with favorable habitat conditions that could play a role in transmission of Vibriosis in the Saint Louis population, we did not isolate any of them from patients screened at the hospital.

Bioprospecting for Novel Bacterial Sources of Hydrolytic Enzymes and Antimicrobials in the Romanian Littoral Zone of the Black Sea

Marine microorganisms have evolved a large variety of metabolites and biochemical processes, providing great opportunities for biotechnologies. In the search for new hydrolytic enzymes and antimicrobial compounds with enhanced characteristics, the current study explored the diversity of cultured and uncultured marine bacteria in Black Sea water from two locations along the Romanian coastline. Microbial cell density in the investigated samples varied between 65 and 12.7 × 10³ CFU·mL^-1. The total bacterial community identified by Illumina sequencing of 16S rRNA gene comprised 185 genera belonging to 46 classes, mainly Gammaproteobacteria, Alphaproteobacteria, Flavobacteriia, and 24 phyla. The 66 bacterial strains isolated on seawater-based culture media belonged to 33 genera and showed variable growth temperatures, growth rates, and salt tolerance. A great fraction of these strains, including Pseudoalteromonas and Flavobacterium species, produced extracellular proteases, lipases, and carbohydrases, while two strains belonging to the genera Aquimarina and Streptomyces exhibited antimicrobial activity against human pathogenic bacteria. This study led to a broader view on the diversity of microbial communities in the Black Sea, and provided new marine strains with hydrolytic and antimicrobial capabilities that may be exploited in industrial and pharmaceutical applications.

How Safe to Eat Are Raw Bivalves? Host Pathogenic and Public Health Concern Microbes within Mussels, Oysters, and Clams in Greek Markets

Raw-bivalves consumption is a wide trend in Mediterranean countries. Despite the unambiguous nutritional value of seafood, raw consumption of bivalves may involve risks that could pose a significant threat to consumers' health. Their filter-feeding behavior is responsible for the potential hosting of a wide variety of microorganisms, either pathogenic for the bivalves or public health threats. Under this prism, the current study was conducted in an effort to evaluate the risk of eating raw bivalves originating from the two biggest seafood markets in Thessaloniki, the largest production area of bivalves in Greece. Both microbiological and molecular methodologies were applied in order to assess the presence of various harmful microbes, including noroviruses, Bonamia, Marteilia, Esherichia coli, Salmonella, and Vibrio. Results indicated the presence of several Vibrio strains in the analyzed samples, of which the halophilic Vibrio harveyi was verified by 16S rRNA sequencing; other than this, no enteropathogenic Vibrio spp. was detected. Furthermore, although Esherichia coli was detected in several samples, it was mostly below the European Union (EU) legislation thresholds. Interestingly, the non-target Photobacterium damselae was also detected, which is associated with both wound infections in human and aquatic animals. Regarding host pathogenic microorganisms, apart from Vibrio harveyi, the protozoan parasite Marteilia refrigens was identified in oysters, highlighting the continuous infection of this bivalve in Greece. In conclusion, bivalves can be generally characterized as a safe-to-eat raw food, hosting more bivalve pathogenic microbes than those of public health concern.

Varying Success of Relaying To Reduce Vibrio parahaemolyticus Levels in Oysters ( Crassostrea virginica)

Vibrio parahaemolyticus is the leading cause of seafood-borne human infections in the United States, and many of these illnesses are associated with consumption of raw molluscan shellfish. V. parahaemolyticus levels in shellfish vary temporally and spatially with environmental conditions in and around production areas. The objective of this study was to study the potential for reducing levels of V. parahaemolyticus in live oysters by relaying them during higher-risk warm weather to a site with elevated salinity and consistently low V. parahaemolyticus levels. The effectiveness of relaying was assessed by analyzing oyster samples collected on days 0, 2, 7, 10, and 14 for V. parahaemolyticus levels using a three-tube most-probable-number enrichment method in conjunction with genetic marker-based quantitative PCR. The salinity at the relay site was always higher than the salinity at the harvest site, with the difference between the two sites ranging from 3.4 to 19.1 ppt (average, 12 ppt) during 2011 to 2014. Oysters relayed during June, July, and August in 2011 and 2012 showed consistently reduced V. parahaemolyticus levels after 14 days, whereas relaying was less successful and V. parahaemolyticus populations changed to include trh-positive strains during 2013. When effective, relay required at least 10 days to reduce V. parahaemolyticus levels. A sample of oysters collected in August 2012, which was temperature abused to increase initial V. parahaemolyticus levels, showed a 4.5-log decrease in V. parahaemolyticus levels after 14 days of relay. These results suggest that relaying oysters to reduce V. parahaemolyticus levels holds promise, but that both microbial community and environmental conditions at relay sites can affect relay success. Further investigation to discover key factors that affect V. parahaemolyticus levels in relayed oysters may aid in developing a consistent approach for reducing V. parahaemolyticus in oysters to eliminate the risk of illness for oyster consumers.

Different abundance and correlational patterns exist between total and presumed pathogenic Vibrio vulnificus and V. parahaemolyticus in shellfish and waters along the North Carolina coast

Monitoring of Vibrio vulnificus and V. parahaemolyticus abundance is pertinent due to the ability of these species to cause disease in humans through aquatic vectors. Previously, we performed a multiyear investigation tracking Vibrio spp. levels in five sites along the southeastern North Carolina coast. From February 2013 to October 2015, total V. vulnificus and V. parahaemolyticus abundance was measured in water, oysters and clams. In the current study, pathogenic subpopulations were identified in these isolates using molecular markers, revealing that 5.3% of V. vulnificus isolates possessed the virulence-correlated gene (vcgC), and 1.9% of V. parahaemolyticus isolates harbored one or both of the virulence-associated hemolysin genes (tdh and trh). Total V. parahaemolyticus abundance was not sufficient to predict the abundance of pathogenic subpopulations. Specifically, pathogenic V. parahaemolyticus isolates were more often isolated in cooler waters and were sometimes isolated when no other V. parahaemolyticus strains were detectable. Vibrio vulnificus clinical (C-) genotypes correlated with total V. vulnificus; however, salinity, water depth and total suspended solids influenced C- and E-genotypes differently. Lastly, we documented individual oysters harboring significantly higher V. vulnificus levels for which there was no ecological explanation, a phenomenon that deserves closer attention due to the potentially elevated health hazard associated with these 'hot' shellfish.

Analysis of the bacterial microbiome in the small octopus, Octopus variabilis, from South Korea to detect the potential risk of foodborne illness and to improve product management

The small octopus (Octopus variabilis) is a popular seafood in many countries including South Korea. Because it is often consumed uncooked, the microorganisms in it often cause food poisoning. Therefore, analyzing the microbiome of the small octopus can help to understand the risk of food poisoning and manage octopus products better. A total of 40 small octopuses were collected from four sites in November and August. The microbiota was analyzed using Illumina Miseq sequencing, and the amount of bacteria was quantified by real-time PCR. In addition, we analyzed the influence of Vibrio vulnificus infection on the microbiome of the small octopus through artificial infection experiments. Bacteroidetes was the predominant phylum in August, and Proteobacteria was predominant in November. The composition of the microbiota in octopus depended on sampling region and season. The potential risk of foodborne illness from small octopus consumption might be higher in August than in November due to the abundance of potential pathogens. In the infection experiment, the proportion of V. vulnificus increased only at 27°C. The composition and functional gene profiles of the microbiota varied in a similar manner between non-infected and infected samples over time at the same temperature. These results indicated that the indigenous microbiota in small octopus could inhibit colonization by V. vulnificus during storage. Although further studies are necessary to clarify these results, our results could help us better understand food poisoning through octopus ingestion and manage products.

Culture conditions improvement of Crassostrea gigas using a potential probiotic Bacillus sp strain

It is well demonstrated that some probiotics improve rearing water quality and thereby have beneficial effects on reared organisms. We conducted this study to determine the effect of Bacillus consortium on Crassostrea gigas reared in contemned seawater with indigo dye priory treated with Bacillus or no treated. This effect was studied by assessing hemocytes death using flow cytometry analysis. We found that the percentage of decolorization of indigo dye in polluted seawater in presence of C. gigas increased from 41% to 90% when using Bacillus consortium. In these conditions, the hemocytes mortality of reared C. gigas decreased from 87% to 56%. We have demonstrated also that seawater contemned with priory treated indigo with Bacillus consortium is less toxic than seawater contemned with the no treated indigo. The percentage of hemocytes death is 81% for the contemned seawater with indigo and 56% for no contemned seawater. This consortium shows a protector effect of C. gigas against Vibrio harveyi contemning reared seawater.

Grimontia celer sp. nov., from sea water

Strain 96-237T, a Gram-reaction-negative, curved- to spiral-shaped motile bacterium, isolated from coastal marine water, was found to be related to species of the genus Grimontia by 16S rRNA gene sequence comparison, sharing 98.3 % similarity to Grimontia marina CECT 8713Tand 98.8 % to 'Grimontiaindica' AK16. Phenotypic analysis revealed that strain 96-237T is slightly halophilic, mesophilic and facultatively anaerobic, fermenting d-glucose, d-ribose, d-mannose, d-mannitol, maltose and sucrose. It was positive for oxidase and indole production and negative for arginine dihydrolase and lysine and ornithine decarboxylases. Its major fatty acids were C16 : 1ω7c/C16 : 1ω6c (SF3), C18 : 1ω7c and C16 : 0. Its DNA G+C content was 48.4 mol%. The strain was different at the species level from all other species of the genusGrimontia, with average nucleotide identity indices of 79.6 % to Grimontia. hollisae CECT 8713T, 87.8 % to G. marina CECT 5069T and 89.1 % to 'G. indica' AK16 genomes. Thus, the strain represents a novel species for which we propose the name Grimontia celer and 96-237T (=CECT 9029T =KCTC 42960T =LMG 29238T) as the type strain.

Isolation of TDA-producing Phaeobacter strains from sea bass larval rearing units and their probiotic effect against pathogenic Vibrio spp. in Artemia cultures

Fish-pathogenic Vibrio can cause large-scale crashes in marine larval rearing units and, since the use of antibiotics can result in bacterial antibiotic resistance, new strategies for disease prevention are needed. Roseobacter-clade bacteria from turbot larval rearing facilities can antagonize Vibrio anguillarum and reduce mortality in V. anguillarum-infected cod and turbot larvae. In this study, it was demonstrated that antagonistic Roseobacter-clade bacteria could be isolated from sea bass larval rearing units. In addition, it was shown that they not only antagonized V. anguillarum but also V. harveyi, which is the major bacterial pathogen in crustaceans and Mediterranean sea bass larvae cultures. Concomitantly, they significantly improved survival of V. harveyi-infected brine shrimp. 16S rRNA gene sequence homology identified the antagonists as Phaeobacter sp., and in silico DNA-DNA hybridization indicated that they could belong to a new species. The genomes contained genes involved in synthesis of the antibacterial compound tropodithietic acid (TDA), and its production was confirmed by UHPLC-TOFMS. The new Phaeobacter colonized live feed (Artemia) cultures and reduced Vibrio counts significantly, since they reached only 10(4)CFUmL(-1), as opposed to 10(8)CFUmL(-1) in non-Phaeobacter treated controls. Survival of V. anguillarum-challenged Artemia nauplii was enhanced by the presence of wild type Phaeobacter compared to challenged control cultures (89±1.0% vs 8±3.2%). In conclusion, TDA-producing Phaeobacter isolated from Mediterranean marine larviculture are promising probiotic bacteria against pathogenic Vibrio in crustacean live-feed cultures for marine fish larvae.

The Fish Pathogen Vibrio vulnificus Biotype 2: Epidemiology, Phylogeny, and Virulence Factors Involved in Warm-Water Vibriosis

Vibrio vulnificus biotype 2 is the etiological agent of warm-water vibriosis, a disease that affects eels and other teleosts, especially in fish farms. Biotype 2 is polyphyletic and probably emerged from aquatic bacteria by acquisition of a transferable virulence plasmid that encodes resistance to innate immunity of eels and other teleosts. Interestingly, biotype 2 comprises a zoonotic clonal complex designated as serovar E that has extended worldwide. One of the most interesting virulence factors produced by serovar E is RtxA1 3 , a multifunctional protein that acts as a lethal factor for fish, an invasion factor for mice, and a survival factor outside the host. Two practically identical copies of rtxA1 3 are present in all biotype 2 strains regardless of the serovar, one in the virulence plasmid and the other in chromosome II. The plasmid also contains other genes involved in survival and growth in eel blood: vep07 , a gene for an outer membrane (OM) lipoprotein involved in resistance to eel serum and vep20 , a gene for an OM receptor specific for eel-transferrin and, probably, other related fish transferrins. All the three genes are highly conserved within biotype 2, which suggests that they are under a strong selective pressure. Interestingly, the three genes are related with transferable plasmids, which emphasizes the role of horizontal gene transfer in the evolution of V. vulnificus in nutrient-enriched aquatic environments, such as fish farms.

Factors affecting the uptake and retention of Vibrio vulnificus in oysters

Vibrio vulnificus, a bacterium ubiquitous in oysters and coastal water, is capable of causing ailments ranging from gastroenteritis to grievous wound infections or septicemia. The uptake of these bacteria into oysters is often examined in vitro by placing oysters in seawater amended with V. vulnificus. Multiple teams have obtained similar results in studies where laboratory-grown bacteria were observed to be rapidly taken up by oysters but quickly eliminated. This technique, along with suggested modifications, is reviewed here. In contrast, the natural microflora within oysters is notoriously difficult to eliminate via depuration. The reason for the transiency of exogenous bacteria is that those bacteria are competitively excluded by the oyster's preexisting microflora. Evidence of this phenomenon is shown using in vitro oyster studies and a multiyear in situ case study. Depuration of the endogenous oyster bacteria occurs naturally and can also be artificially induced, but both of these events require extreme conditions, natural or otherwise, as explained here. Finally, the "viable but nonculturable" (VBNC) state of Vibrio is discussed. This bacterial torpor can easily be confused with a reduction in bacterial abundance, as bacteria in this state fail to grow on culture media. Thus, oysters collected from colder months may appear to be relatively free of Vibrio but in reality harbor VBNC cells that respond to exogenous bacteria and prevent colonization of oyster matrices. Bacterial-uptake experiments combined with studies involving cell-free spent media are detailed that demonstrate this occurrence, which could explain why the microbial community in oysters does not always mirror that of the surrounding water.

Vibrio parahaemolyticus and its specific bacteriophages as an indicator in cockles (Anadara granosa) for the risk of V. parahaemolyticus infection in Southern Thailand

Correlation between the numbers of Vibrio parahaemolyticus and its specific bacteriophages in cockles was investigated from June 2009 to May 2010 in Hat Yai, Songkhla, Thailand. Cockles obtained monthly from a local market were sampled to determine the numbers of V. parahaemolyticus and bacteriophages that could form plaques on ten strains of pandemic and nonpandemic V. parahaemolyticus. In addition, V. parahaemolyticus isolates from clinical samples from Hat Yai hospital over the same period were investigated. All 139 cockles sampled were positive for V. parahaemolyticus. However, only 76 of them were positive for bacteriophages. During the testing period, the number of bacteriophages was not significantly correlated with the incidence of V. parahaemolyticus-infected patients, but the numbers of V. parahaemolyticus isolates from the cockle samples were closely related to the number of infected patients. The bacteriophages isolated from V. parahaemolyticus also infected Vibrio alginolyticus and Vibrio mimicus, suggesting that the broad host range of phages may be a factor of providing the possibility of their participation in the processes of genetic exchange between V. parahaemolyticus and closely related Vibrio spp. In conclusion, this study indicated that the number of V. parahaemolyticus in cockles may be a useful tool for predicting the relative risk of infection by V. parahaemolyticus in this area of Thailand.

Occurrence, seasonality and infectivity of Vibrio strains in natural populations of mussels Mytilus galloprovincialis

Widespread and large-scale mortalities of bivalve molluscs significantly affect their production. A number of pathogens have been identified as the primary causes of death in oysters or clams, especially bacteria of the genus Vibrio. We evaluated the occurrence, seasonality and infectivity of Vibrio strains associated with natural mussel (Mytilus galloprovincialis) populations. In particular, different isolates of V. splendidus and V. aestuarianus were analysed because they were associated with major oyster mortalities in areas where mussels are cultured without presenting mortalities. The presence of both Vibrio spp. was analysed bimonthly in mussels, water, sediment, plankton and other associated fauna from 2 sites in Galicia (NW Spain), the region with the highest mussel production in Europe. Environmental factors were also considered. The pathogenicity of different Vibrio isolates was analysed by performing experimental infections in mussels with strains isolated from the field. Results showed that Vibrio populations were mainly influenced by changes in water temperature and salinity. V. splendidus was dominant during the warm months and V. aestuarianus was predominant throughout the cold season. The sediment was the most important natural reservoir for bacteria. Experimental infections showed the extreme resistance of mussels to bacterial pathogens. Isolates of V. splendidus and V. aestuarianus were only moderately pathogenic for mussels in intramuscular infections and bath infections, and mortalities only occurred when animals were infected with a high bacterial concentration in adverse environmental conditions (hypoxia and 25°C). Although the pathogenicity of the Vibrio strains isolated from the wild was low for mussels, their potential risk for other bivalves cannot be ignored.

New Vibrio species associated to molluscan microbiota: a review

The genus Vibrio consists of more than 100 species grouped in 14 clades that are widely distributed in aquatic environments such as estuarine, coastal waters, and sediments. A large number of species of this genus are associated with marine organisms like fish, molluscs and crustaceans, in commensal or pathogenic relations. In the last decade, more than 50 new species have been described in the genus Vibrio, due to the introduction of new molecular techniques in bacterial taxonomy, such as multilocus sequence analysis or fluorescent amplified fragment length polymorphism. On the other hand, the increasing number of environmental studies has contributed to improve the knowledge about the family Vibrionaceae and its phylogeny. Vibrio crassostreae, V. breoganii, V. celticus are some of the new Vibrio species described as forming part of the molluscan microbiota. Some of them have been associated with mortalities of different molluscan species, seriously affecting their culture and causing high losses in hatcheries as well as in natural beds. For other species, ecological importance has been demonstrated being highly abundant in different marine habitats and geographical regions. The present work provides an updated overview of the recently characterized Vibrio species isolated from molluscs. In addition, their pathogenic potential and/or environmental importance is discussed.

Host-nonspecific iron acquisition systems and virulence in the zoonotic serovar of Vibrio vulnificus

The zoonotic serovar of Vibrio vulnificus (known as biotype 2 serovar E) is the etiological agent of human and fish vibriosis. The aim of the present work was to discover the role of the vulnibactin- and hemin-dependent iron acquisition systems in the pathogenicity of this zoonotic serovar under the hypothesis that both are host-nonspecific virulence factors. To this end, we selected three genes for three outer membrane receptors (vuuA, a receptor for ferric vulnibactin, and hupA and hutR, two hemin receptors), obtained single and multiple mutants as well as complemented strains, and tested them in a series of in vitro and in vivo assays, using eels and mice as animal models. The overall results confirm that hupA and vuuA, but not hutR, are host-nonspecific virulence genes and suggest that a third undescribed host-specific plasmid-encoded system could also be used by the zoonotic serovar in fish. hupA and vuuA were expressed in the internal organs of the animals in the first 24 h of infection, suggesting that they may be needed to achieve the population size required to trigger fatal septicemia. vuuA and hupA were sequenced in strains representative of the genetic diversity of this species, and their phylogenies were reconstructed by multilocus sequence analysis of selected housekeeping and virulence genes as a reference. Given the overall results, we suggest that both genes might form part of the core genes essential not only for disease development but also for the survival of this species in its natural reservoir, the aquatic environment.

Detection and differentiation of Vibrio vulnificus and V. sinaloensis in water and oysters of a Gulf of Mexico estuary

Vibrio vulnificus is a potentially lethal human pathogen that occurs naturally in estuarine waters and shellfish. Vibrio vulnificus was quantified in water and oysters from Florida's Gulf Coast by plating on mCPC agar, enrichment and plating, and quantitative PCR (qPCR). Vibrio vulnificus was detected in 19%, 29%, and 97% of samples respectively by direct plating, qPCR, and enrichment. Only 8% of typical colonies from direct plating were confirmed by PCR for vvhA; others yielded no or atypically sized amplicons. Sequencing of the 16S rDNA of 16 vvhA-negative isolates with colony morphology typical of V. vulnificus identified 75% as V. sinaloensis. In vitro growth curves showed that V. sinaloensis grew more rapidly than V. vulnificus in seawater at temperatures ≤ 30°C. In contrast, the growth rate of V. vulnificus in alkaline peptone water was greater than that of V. sinaloensis, suggesting that these species can outcompete one another under conditions that are relevant to environmental parameters or regulatory monitoring regimes respectively. The virulence potential and ecology of V. sinaloensis are poorly understood; however, its phenotypic resemblance to V. vulnificus and the possibility that it could outcompete the pathogen in warm, estuarine waters argue for the need for a better understanding of this newly described Vibrio species.

Diversity and pathogenecity of Vibrio species in cultured bivalve molluscs

Shellfish production is seriously affected by bacterial pathogens that cause high losses in hatcheries and in the aquaculture sector. A number of Vibrio species are considered important pathogens and have provoked severe mortality outbreaks. The pathologies caused by vibrios in bivalves have been described since the 1960s; however, over recent years, successive episodes of high mortality have been recorded due to these microorganisms. The present work provides an updated overview of the different studies performed in relation with the diversity of Vibrio spp. associated to bivalves. Special attention is given to the main Vibrio diseases and implicated species affecting the different life stages of cultured bivalves.

Detection of Vibrio vulnificus in seafood, seawater and wastewater samples from a Mediterranean coastal area

Vibrio vulnificus is an opportunistic human pathogen that may cause gastroenteritis, severe necrotizing soft-tissue infections and primary septicaemia, with a high lethality rate. Illness is associated to ingestion of seafood or to the exposure of contaminated water. The aim of this work was to determine the occurrence of V. vulnificus in water and seafood samples from a coastal area near the Mediterranean (Valencia, Spain). A TaqMan probe-based real-time PCR assay was optimised and applied to 22 sea water, 42 raw sewage and 40 seafood samples. Results were compared with those obtained for culture isolation. The detection level of the PCR assay was 10 CFU g⁻¹ in inoculated samples. Seven seawater, four shellfish and six wastewater samples were positive by real time PCR. V. vulnificus was isolated from two oyster, three sea water and two wastewater samples. All the strains were obtained after 20 h enrichment, except for wastewater strains, which were isolated directly from the sample. To our knowledge, this is the first report on the isolation of V. vulnificus from sewage in Spain. Our results about the presence of V. vulnificus in food and environmental samples are strong enough to consider that the organism may represent a human health hazard in our geographical area.

Emerging Vibrio species: an unending threat to public health in developing countries

Discharge of inadequately treated sewage effluents into the environment in developing countries has increased over the years, leading to deterioration of water quality of major watersheds in developing nations and consequently an increased incidence of emerging pathogens such as Vibrio species, the prevalence of which has been generally underestimated in developing nations. This review underscores the need for a proactive approach to risk factors for emerging Vibrio infections, so as to establish adequate prevention measures.

Distribution, genetic richness and phage sensitivity of Vibrio spp. from coastal British Columbia

This study examined the distribution, susceptibility to viral infection and genetic diversity of Vibrio spp. in the coastal waters and sediments of British Columbia during summer (July and August). Abundances of presumptive Vibrio spp. ranged from 1.5 to 346 ml(-1) within the water column (1-291 m); whereas, abundances at the water-sediment interface were much higher (up to approximately 3 x 10(4)Vibrio spp. cc(-1)), and decreased with sediment depth (down to 30 cm). The genetic diversity of Vibrio spp. isolates was not tied to the location from which they originated and was only influenced in a minor way by the type of environment. However, the environment had a greater effect on phage-typing patterns. Vibrio parahaemolyticus isolates from environments with high abundances of cells (sediments and oysters) were generally more susceptible to viral infection than those from the water column which were highly resistant. Therefore, although Vibrio spp. were widespread in the areas investigated, the results show that there is segregation of bacterial host strains in different environments, under differing selection pressures, which ultimately will affect in situ phage production.

Occurrence of Vibrio spp. in blue mussels (Mytilus edulis) from the German Wadden Sea

The present study aimed at determining the contamination of blue mussels grown in Germany with relevant bacterial organisms. Seasonal variations were examined. For that purpose, mussel samples were taken regularly between June 2004 and May 2005 in seven shellfish-growing areas of the German Wadden Sea. A total of 90 samples were analysed. The analysis included the compulsory microbiological parameters Escherichia coli and Salmonella spp., as well as the determination of the contamination with Vibrio spp. Although the analysed mussels complied with the legislation in force, potential human pathogens were detected in a wide range of samples. Vibrio spp. was detected in 74.4% of the samples analysed in this study. Among Vibrio isolates, Vibrio alginolyticus was the species most frequently detected (51.2%), followed by Vibrio parahaemolyticus (39.5%). Vibrio vulnificus was detected in 3.5% of the samples. V. parahaemolyticus and V. vulnificus were not found in samples collected at low water temperatures. The results indicate that blue mussels from shellfish-growing areas in the German Wadden Sea regularly contain pathogens relevant to public health. They also show that E. coli is not a reliable indicator for the contamination with Vibrio spp. To improve consumer protection, it therefore seems necessary to extend the analysis of mussels for direct human consumption by additional parameters.

Use of multiparameter analysis for Vibrio alginolyticus viable but nonculturable state determination

BACKGROUND

Vibrio alginolyticus is known to enter into a viable but nonculturable (VBNC) state in response to environmental conditions unfavorable to the growth. Cells in VBNC condition pose a public health threat because they are potentially pathogenic.

METHODS

We constructed a pathway for the identification of the most significant variables and the characterization of those variables able to discriminate the groups under investigation. Different parameters measured by the image processing software were chosen as the most representative of V. alginolyticus cell morphology (length index for dimension) and metabolic activity (density profile indexes). To detect relationships between the groups of treatment performed, we carried out a principal components analysis (PCA).

RESULTS

The PCA analysis indicated that increasing coccoid shape transformation was related to both metabolic and dimension variations, delineating a well defined graph profile. Indeed, we discovered that specific morphological variations occur when cells in the culturable state pass into VBNC condition, namely comma-shaped culturable bacteria are converted into coccoid-shaped VBNC cells. The results were also supported by scanning electron microscopy analysis.

CONCLUSIONS

This technique allows the analysis of a large number of vibrio samples in a short period of time. The obtained multiparameter information may complement genetic/molecular analyses facilitating, in an automatic fashion, further studies to evaluate the potential risk of this pathogen in the environment. It may also be a useful tool for large-scale cell biology studies and high content screening.

Detection and differentiation of Vibrio vulnificus in seawater and plankton of a coastal zone of the Mediterranean Sea

Vibrio vulnificus, a human and animal pathogen, is present in low numbers in the Mediterranean Sea. Seawater and plankton samples were collected from a marine coastal zone of the Straits of Messina in the Mediterranean Sea (Italy) in order to investigate V. vulnificus as free-living (>0.2 microm) and associated with small (>64 microm) and large plankton (>200 microm) utilizing cultural and molecular techniques. Characteristic colonies, grown on thiosulfate, citrate, bile salts and sucrose agar plates, were identified using a biochemical protocol system. A PCR assay was used to confirm isolates and to directly detect V. vulnificus in environmental concentrated samples. Specific primers were used to target the structural cytotoxin/hemolysin gene and the variable regions of 16S rRNA species-specific for V. vulnificus. In addition, a tri-primer PCR of 16S rRNA was used for the differentiation of V. vulnificus strains. Direct detection in marine samples was more frequent than isolation of culturable forms. All isolates were assigned to V. vulnificus biotype 1, 16S rRNA type B. These results confirm the low incidence of V. vulnificus in Mediterranean coastal waters. The isolation of cultivable forms is limited to the warmest months. 16S rRNA primers were the most sensitive molecular tool as they allowed detection of V. vulnificus in 79.1% of samples. Due to the low incidence of V. vulnificus in the Mediterranean coastal environment, its detection requires a molecular approach. The occurrence of V. vulnificus as plankton-associated confirms the role of plankton as a potential reservoir for this pathogen.

A persistent, productive, and seasonally dynamic vibriophage population within Pacific oysters (Crassostrea gigas)

In an effort to understand the relationship between Vibrio and vibriophage populations, abundances of Vibrio spp. and viruses infecting Vibrio parahaemolyticus (VpVs) were monitored for a year in Pacific oysters and water collected from Ladysmith Harbor, British Columbia, Canada. Bacterial abundances were highly seasonal, whereas high titers of VpVs (0.5 x 10(4) to 11 x 10(4) viruses cm(-3)) occurred year round in oysters, even when V. parahaemolyticus was undetectable (< 3 cells cm(-3)). Viruses were not detected (<10 ml(-1)) in the water column. Host-range studies demonstrated that 13 VpV strains could infect 62% of the V. parahaemolyticus strains from oysters (91 pairings) and 74% of the strains from sediments (65 pairings) but only 30% of the water-column strains (91 pairings). Ten viruses also infected more than one species among V. alginolyticus, V. natriegens, and V. vulnificus. As winter approached and potential hosts disappeared, the proportion of host strains that the viruses could infect decreased by approximately 50% and, in the middle of winter, only 14% of the VpV community could be plated on summer host strains. Estimates of virus-induced mortality on V. parahaemolyticus indicated that other host species were required to sustain viral production during winter when the putative host species was undetectable. The present study shows that oysters are likely one of the major sources of viruses infecting V. parahaemolyticus in oysters and in the water column. Furthermore, seasonal shifts in patterns of host range provide strong evidence that the composition of the virus community changes during winter.

Methods for isolation and confirmation of Vibrio vulnificus from oysters and environmental sources: a review

The gram-negative bacterium Vibrio vulnificus is a natural inhabitant of estuarine waters and poses a significant health threat to humans who suffer from immune disorders, liver disease, or hemochromatosis (iron overload). V. vulnificus enters human hosts via wound infections or consumption of raw shellfish (primarily oysters), and infections frequently progress to septicemia and death in susceptible individuals. Prevalence in waters and shellfish is not correlated with fecal indicator organisms; therefore, species-specific detection and enumeration of V. vulnificus in the environment has become a priority for agencies that are responsible for shellfish safety. The many selective-differential media developed for isolation of Vibrio spp., and specifically for V. vulnificus detection, are reviewed here; however, none of the media developed to date combines the sensitivity to low numbers with the specificity necessary to inhibit growth of other organisms. Therefore, immunological and molecular protocols are needed for confirmation of the identity of the organism and are discussed in detail. Methods under development that hold promise for rapid, accurate, and sensitive detection and enumeration of the organism include multiplex and real-time PCR. Developing technologies that have proven useful for detection and investigation of other pathogens such as biosensors, spectroscopy and microarrays may provide the next generation of tools for investigation of the prevalence and ecology of V. vulnificus.

Protocol for specific isolation of virulent strains of Vibrio vulnificus serovar E (biotype 2) from environmental samples

The eel pathogen Vibrio vulnificus biotype 2 comprises at least three serovars, with serovar E being the only one involved in both epizootics of eel vibriosis and sporadic cases of human infections. The virulent strains of this serovar (VSE) have only been recovered from clinical (mainly eel tissue) sources. The main objective of this work was to design and validate a new protocol for VSE-specific isolation from environmental samples. The key element of the new protocol is the broth used for the first step (saline eel serum broth [SEB]), which contains eel serum as a nutritive and selective component. This approach takes advantage of the ability of VSE cells to grow in eel serum and thus to separate themselves from the pool of competitors. The growth yield in SEB after 8 h of incubation was 1,000 times higher for VSE strains than for their putative competitors (including biotype 1 strains of the species). The selective and differential agar Vibrio vulnificus medium (VVM) was selected from five selective media for the second step because it gave the highest plating efficiency not only for the VSE group but also for other V. vulnificus groups, including biotype 3. The entire protocol was validated by field studies, with alkaline peptone water plus VVM as a control. V. vulnificus was isolated by both protocols, but serovar E was only recovered by the new method described here. All selected serovar E isolates were identified as VSE since they were virulent for both eels and iron-overloaded mice and resisted the bactericidal action of eel and iron-overloaded human sera. In conclusion, this new protocol is a suitable method for the isolation of VSE strains from environmental samples and is recommended for epidemiological studies of the pathogenic serovar E.

Updated perspectives on emerging vibrios associated with human infections

This review describes the ecological, clinical and epidemiological features of emerging vibrios and discusses what laboratory methods are being used for the detection of pathogenic vibrios in clinical, environmental and food samples. After selecting articles illustrative of the current scientific research on pathogenic vibrios, the review focuses on the need for better insight into the risk factors of emerging infections to establish adequate prevention procedures.

Influence of aquatic microbiota on the survival in water of the human and eel pathogen Vibrio vulnificus serovar E

The eel and human pathogen Vibrio vulnificus serovar E (biotype 2) is seldom isolated from natural waters, although it can survive in sterilized artificial seawater microcosms for years. The main objective of the present study was to investigate whether aquatic microbiota can limit its survival and recovery from water samples. A set of preliminary experiments of survival in microcosms containing natural seawater and water from eel farms showed that the persistence of this pathogen was mainly controlled by grazing, and secondarily by bacterial competition. The bacterial competition was further analysed in artificial seawater microcosms co-inoculated with selected virulent serovar E (VSE) strains and potential competitors. Competitors included V. vulnificus biotype 1 isolates and strains of selected species that can grow on the selective media designed for V. vulnificus isolation from water samples. Evidences of bacterial competition that was detrimental for VSE recovery were recorded. Thus, some species produced a deleterious effect on VSE strains under starvation, and others were able to use the resources more efficiently under nutrient input. These results suggest that an overgrowth of more efficient competitor bacteria in conventional media used for isolation of V. vulnificus could mask the recovery of VSE strains and explain the scarcity of reports on the isolation of this human and eel pathogen from natural waters.

Determination of Vibrio scophthalmi and its phenotypic diversity in turbot larvae

The association of Vibrio scophthalmi with turbot larvae was assessed, by molecular methods with a species-specific probe, in the rearing stages of turbot (Scophthalmus maximus) larvae using a routine batch of production at a fish farm. The phenotypic diversity of this bacterial species was also studied to identify predominant phenotypes at successive stages of larval development. Vibrio scophthalmi was detected in all turbot larvae samples except in the sample from day 0 after hatching. The percentage of V. scophthalmi in the intestinal microbiota increased throughout larval development. Vibrio scophthalmi was also detected in live food (brine shrimps) and water from the tanks, but not in the sediment. All turbot larvae, 15-57 day old, showed several V. scophthalmi phenotypes, and a pattern of successive waves of phenotypes was observed during successive larval stages. This indicates that certain strains may colonize the intestine more efficiently and thus maintain their population for longer than other strains. Vibrio scophthalmi populations from turbots of different origin were very similar, suggesting that irrespective of geographical area, turbot populations share similar V. scophthalmi strains. Vibrio scophthalmi strain was not isolated from other cultured fish, only turbot larvae, at the same hatchery receiving water from the same supply.

Infections related to the ingestion of seafood Part I: viral and bacterial infections

Foodborne diseases cause an estimated 76 million illnesses in the USA each year. Seafood is implicated in 10-19% of these illnesses. A causative agent can be traced in about 44% of seafood-related outbreaks, viruses accounting for around half of these illnesses. Although viruses are the most common cause of seafood-related infections, most hospitalisations and deaths are due to bacterial agents. A wide variety of viruses, bacteria, and parasites have been implicated in seafood-related outbreaks, which are reported worldwide. The factor most commonly associated with infection is consumption of raw or undercooked seafood. People with underlying disorders, particularly liver disease, are more susceptible to infection. The first part of this two-part review summarises the general incidence of seafood-related infections and discusses the common viral and bacterial causes of these infections. For each agent, the microbiology, epidemiology, mode of transmission, and treatment are discussed. In the May issue of the journal we will discuss parasites associated with seafood consumption, the safety of seafood, and the measures put in place in the USA to increase its safety.

Virulence and molecular typing of Vibrio harveyi strains isolated from cultured dentex, gilthead sea bream and European sea bass

Vibrio harveyi was isolated from internal organs or ulcers of diseased and apparently healthy gilthead sea bream (Sparus aurata) and European sea bass (Dicentrarchus labrax) cultured in several fish farms located on the Spanish Mediterranean coast. The prevalence of the bacterium was significantly higher in European sea bass than in gilthead sea bream, and was closely related to the season in both fish species, occurring almost exclusively on warm months (June to November). After phenotypic characterization, a selection of forty five isolates from gilthead sea bream, sea bass, and several isolates previously obtained from common dentex (Dentex dentex) of the same area, were molecularly typed by automated ribotyping and random amplified polymorphic DNA (RAPD) analysis. Cluster analysis of data established 8 RAPD types and 13 ribotypes among wild isolates, and the combination of both techniques allowed to define fourteen different groups and a clear discrimination of all outbreaks and samplings. Several strains isolated from diseased gilthead sea bream and sea bass and also from asymptomatic sea bream, were tested for virulence in both fish species by intracoelomic injection. All the isolates (11) were pathogenic for sea bass, with nine out of the eleven LD50 values ranging from 1.5 x 10(5) to 1.6 x 10(6) cfu/fish. Gilthead sea bream was unaffected by the seven tested strains, even by those more virulent for sea bass, and only one strain caused a 10% mortality at 4.2 x 10(7) cfu/fish. This is the first report on virulence of V. harveyi for sea bass.

Vibrios isolated from the cultured manila clam (Ruditapes philippinarum): numerical taxonomy and antibacterial activities

AIMS

A numerical taxonomic study of halophilic Vibrio isolated from healthy and brown ring disease (BRD) affected manila clams (Ruditapes philippinarum), harvested from the Atlantic coast of south-western Spain, was performed.

METHODS AND RESULTS

Characterization of 123 presumptive Vibrio spp. was carried out using 94 phenotypic tests. Simple matching and Jaccard similarity coefficients were used for numerical analysis. Cluster analysis by the unweighted pair group method with arithmetic averages yielded 15 phena defined at 0.81 similarity. Large phena corresponded to Vibrio tubiashii, V. splendidus biotype I and V. harveyi (phena 1, 5 and 9, respectively). The species V.splendidus biotype II, V. natriegens, V. mediterranei and V. alginolyticus were also represented. The inhibitory effect of diffusible extracellular products of the isolates against 27 strains of V.tapetis, the aetiological agent of BRD, was also investigated. Only five V. tubiashii isolates inhibited the growth of V. tapetis strains. The antimicrobial effect was inhibited by heating and depended on the culture medium.

CONCLUSIONS

The main Vibrio species associated with manila clams were V. tubiashii, V.spendidus and V. harveyi. The antagonistic relationship established between V. tapetis and the Vibrio spp. clam microbiota may explain the failure of isolation in plating medium of V.tapetis from BRD-affected clams on the south Atlantic coast of Spain.

SIGNIFICANCE AND IMPACT OF THE STUDY

Some of the strains isolated from manila clams correspond to agarolytic strains that constitute phenon 7 and they do not fit into any of the currently described Vibrio species.

Comparison of selective media for the detection of Vibrio vulnificus in environmental samples

AIMS

To compare two selective agars, cellobiose-colistin (CC) agar and a modification of the Vibrio vulnificus medium (VVMc agar), for the isolation of Vibrio vulnificus from environmental samples.

METHODS AND RESULTS

The efficiencies of recovery of V. vulnificus collection strains on CC, VVM, VVMc and on thiosulphate-citrate-bile salts-sucrose (TCBS) agar were compared and similar efficiencies were obtained. A slightly higher recovery was observed on VVMc agar. The detection of V. vulnificus in environmental samples (eels and water) was performed by combining culture-based methods (CC and VVMc agars) with DNA-based methods using species-specific probes based on the cytolysin-haemolysin and the 16S rDNA genes. A lower accompanying microbiota was found on CC agar than on VVMc agar.

CONCLUSION

The comparison between CC and VVMc agars confirms that both are useful for the detection of V. vulnificus in environmental samples. However, the use of any of these media should be combined with a species-specific probe.

SIGNIFICANCE AND IMPACT OF THE STUDY

The combined use of a selective medium and a specific probe provides a feasible method for the detection of V. vulnificus for epidemiological and ecological studies.

Ribotyping of vibrio populations associated with cultured oysters (Ostrea edulis)

The intraspecific variability of Vibrio splendidus, V. harveyi and V. tubiashii recovered from oysters (Ostrea edulis) collected at the Mediterranean coast near Valencia, Spain, was analyzed by ribotyping. The two former species represented the most abundant ones, and the third one was the only species described as pathogenic for oysters. A total of 115 environmental strains were studied, 84 of V. splendidus, 23 of V. harveyi and 8 of V. tubiashii. Chromosomal DNA was digested with KpnI and hybridized with an oligonucleotide probe complementary to a highly conserved sequence in the 23S rRNA gene. Ribotyping among natural populations of the three species rendered 5 to 9 bands, and showed a high genetic diversity, with a ratio no. of strains/no. of ribotypes between 1.1 and 1.5. Cluster analysis of V. splendidus ribotypes suggests a seasonal pattern of incidence, with those ribotypes corresponding to winter and spring samples being maintained in the oysters over the year.

Potentially pathogenic vibrios in brackish waters and mussels

Water and mussel samples were collected from two brackish lakes, used as mussel farms, at different times of the year, for the quantitative analysis of Vibrio spp. and for the isolation of potentially pathogenic species. The isolates underwent cultural and biochemical tests selected for rapid identification. Glucose oxidizing-fermenting and O/129 sensitive strains were distinguished on the basis of the following tests: sucrose and cellobiose utilization, sulphatase activity and polymyxin B resistance performed, respectively, on TCBS, CPC and SPS media. Responses to the presence of beta-galactosidase, salt requirement and growth on triple sugar iron medium were also added. A total of 125 from 152 isolates were referred to the species Vibrio fluvialis (55 strains), V. alginolyticus (40), V. parahaemolyticus (11), V. vulnificus (10) and V. mimicus (9). The remaining 27 isolates were not identified. The isolation of potentially pathogenic vibrios from cultivated mussels is a risk for health of people consuming raw seafood. Therefore, a long-term monitoring programme should also include the search for these bacterial species.

Genetic relatedness among environmental, clinical, and diseased-eel Vibrio vulnificus isolates from different geographic regions by ribotyping and randomly amplified polymorphic DNA PCR

Genetic relationships among 132 strains of Vibrio vulnificus (clinical, environmental, and diseased-eel isolates from different geographic origins, as well as seawater and shellfish isolates from the western Mediterranean coast, including reference strains) were analyzed by random amplified polymorphic DNA (RAPD) PCR. Results were validated by ribotyping. For ribotyping, DNAs were digested with KpnI and hybridized with an oligonucleotide probe complementary to a highly conserved sequence in the 23S rRNA gene. Random amplification of DNA was performed with M13 and T3 universal primers. The comparison between ribotyping and RAPD PCR revealed an overall agreement regarding the high level of homogeneity of diseased-eel isolates in contrast to the genetic heterogeneity of Mediterranean isolates. The latter suggests the existence of autochthonous clones present in Mediterranean coastal waters. Both techniques have revealed a genetic proximity among Spanish fish farm isolates and a close relationship between four Spanish eel farm isolates and some Mediterranean isolates. Whereas the differentiation within diseased-eel isolates was only possible by ribotyping, RAPD PCR was able to differentiate phenotypically atypical isolates of V. vulnificus. On the basis of our results, RAPD PCR is proposed as a better technique than ribotyping for rapid typing in the routine analysis of new V. vulnificus isolates.