Influence of water temperature and salinity on Vibrio vulnificus in Northern Gulf and Atlantic Coast oysters (Crassostrea virginica)

The interactions of Vibrio vulnificus and the oyster Crassostrea virginica

The human bacterial pathogen, Vibrio vulnificus, is found in brackish waters and is concentrated by filter-feeding molluscan shellfish, especially oysters, which inhabit those waters. Ingestion of raw or undercooked oysters containing virulent strains of V. vulnificus can result in rapid septicemia and death in 50 % of victims. This review summarizes the current knowledge of the environmental interactions between these two organisms, including the effects of salinity and temperature on colonization, uptake, and depuration rates of various phenotypes and genotypes of the bacterium, and host-microbe immunological interactions.

An 'extreme' future for estuaries? Effects of extreme climatic events on estuarine water quality and ecology

Recent climate observations suggest that extreme climatic events (ECE; droughts, floods, tropical cyclones, heat waves) have increased in frequency and/or intensity in certain world regions, consistent with climate model projections that account for man's influence on the global climate system. A synthesis of existing literature is presented and shows that ECE affect estuarine water quality by altering: (1) the delivery and processing of nutrients and organic matter, (2) physical-chemical properties of estuaries, and (3) ecosystem structure and function. From the standpoint of estuarine scientists and resource managers, a major scientific challenge will be to project the estuarine response to ECE that will co-occur with other important environmental changes (i.e., natural climate variability, global warming, sea level rise, eutrophication), as this will affect the provisioning of important ecosystem services provided by estuaries.

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.

Seasonal shifts in population structure of Vibrio vulnificus in an estuarine environment as revealed by partial 16S ribosomal DNA sequencing

Abstract The partial sequence (600 bp) containing the most variable region of Vibrio vulnificus 16S ribosomal DNA (rDNA) was determined for 208 randomly selected V. vulnificus strains isolated from Galveston Bay, TX, USA between June 2000 and June 2001. A comparative analysis of the determined partial 16S rDNA sequences revealed the existence of two different partial 16S rDNA sequences (type A and type B, 1.3% base substitutions) among the 208 V. vulnificus isolates. A higher proportion of 16S rDNA type A strains was isolated in June and July while a considerably higher proportion of type B strains was isolated in September. In addition, after no V. vulnificus strains were detected during the winter months (December-February), only type A strains were isolated during the following months (March-May). The results suggest that the relative abundance of type A and type B V. vulnificus strains in Galveston Bay varies with the season and that the differences between the two 16S rDNA types may affect the viability of these organisms in the natural environment.

Spatial and species variations in bacterial communities associated with corals from the Red Sea as revealed by pyrosequencing

Microbial associations with corals are common and are most likely symbiotic, although their diversity and relationships with environmental factors and host species remain unclear. In this study, we adopted a 16S rRNA gene tag-pyrosequencing technique to investigate the bacterial communities associated with three stony Scleractinea and two soft Octocorallia corals from three locations in the Red Sea. Our results revealed highly diverse bacterial communities in the Red Sea corals, with more than 600 ribotypes detected and up to 1,000 species estimated from a single coral species. Altogether, 21 bacterial phyla were recovered from the corals, of which Gammaproteobacteria was the most dominant group, and Chloroflexi, Chlamydiae, and the candidate phylum WS3 were reported in corals for the first time. The associated bacterial communities varied greatly with location, where environmental conditions differed significantly. Corals from disturbed areas appeared to share more similar bacterial communities, but larger variations in community structures were observed between different coral species from pristine waters. Ordination methods identified salinity and depth as the most influential parameters affecting the abundance of Vibrio, Pseudoalteromonas, Serratia, Stenotrophomonas, Pseudomonas, and Achromobacter in the corals. On the other hand, bacteria such as Chloracidobacterium and Endozoicomonas were more sensitive to the coral species, suggesting that the host species type may be influential in the associated bacterial community, as well. The combined influences of the coral host and environmental factors on the associated microbial communities are discussed. This study represents the first comparative study using tag-pyrosequencing technology to investigate the bacterial communities in Red Sea corals.

Prevalence and population structure of Vibrio vulnificus on fishes from the northern Gulf of Mexico

The prevalence of Vibrio vulnificus on the external surfaces of fish from the northern Gulf of Mexico was determined in this study. A collection of 242 fish comprising 28 species was analyzed during the course of 12 sampling trips over a 16-month period. The prevalence of V. vulnificus was 37% but increased up to 69% in summer. A positive correlation was found between the percentages of V. vulnificus-positive fish and water temperatures, while salinity and V. vulnificus-positive fish prevalence were inversely correlated. A general lineal model (percent V. vulnificus-positive fish = 0.5930 - 0.02818 × salinity + 0.01406 × water temperature) was applied to best fit the data. Analysis of the population structure was carried out using 244 isolates recovered from fish. Ascription to 16S rRNA gene types indicated that 157 isolates were type A (62%), 72 (29%) were type B, and 22 (9%) were type AB. The percentage of type B isolates, considered to have greater virulence potential, was higher than that previously reported in oyster samples from the northern Gulf of Mexico. Amplified fragment length polymorphism (AFLP) was used to resolve the genetic diversity within the species. One hundred twenty-one unique AFLP profiles were found among all analyzed isolates, resulting in a calculated Simpson's index of diversity of 0.991. AFLP profiles were not grouped on the basis of collection date, fish species, temperature, or salinity, but isolates were clustered into two main groups that correlated precisely with 16S rRNA gene type. The population of V. vulnificus associated with fishes from the northern Gulf of Mexico is heterogeneous and includes strains of great virulence potential.

Predatory bacteria as natural modulators of Vibrio parahaemolyticus and Vibrio vulnificus in seawater and oysters

This study shows that naturally occurring Vibrio predatory bacteria (VPB) exert a major role in controlling pathogenic vibrios in seawater and shellfish. The growth and persistence of Vibrio parahaemolyticus and Vibrio vulnificus were assessed in natural seawater and in the Eastern oyster, Crassostrea virginica. The pathogens examined were V. vulnificus strain VV1003, V. parahaemolyticus O1:KUT (KUT stands for K untypeable), and V. parahaemolyticus O3:K6 and corresponding O3:K6 mutants deficient in the toxRS virulence regulatory gene or the rpoS alternative stress response sigma factor gene. Vibrios were selected for streptomycin resistance, which facilitated their enumeration. In natural seawater, oysters bioconcentrated each Vibrio strain for 24 h at 22°C; however, counts rapidly declined to near negligible levels by 72 h. In natural seawater with or without oysters, vibrios decreased more than 3 log units to near negligible levels within 72 h. Neither toxRS nor rpoS had a significant effect on Vibrio levels. In autoclaved seawater, V. parahaemolyticus O3:K6 counts increased 1,000-fold over 72 h. Failure of the vibrios to persist in natural seawater and oysters led to screening of the water samples for VPB on lawns of V. parahaemolyticus O3:K6 host cells. Many VPB, including Bdellovibrio and like organisms (BALOs; Bdellovibrio bacteriovorus and Bacteriovorax stolpii) and Micavibrio aeruginosavorus-like predators, were detected by plaque assay and electron microscopic analysis of plaque-purified isolates from Atlantic, Gulf Coast, and Hawaiian seawater. When V. parahaemolyticus O3:K6 was added to natural seawater containing trace amounts of VPB, Vibrio counts diminished 3 log units to nondetectable levels, while VPB increased 3 log units within 48 h. We propose a new paradigm that VPB are important modulators of pathogenic vibrios in seawater and oysters.

Ecology of Vibrio parahaemolyticus and Vibrio vulnificus in the coastal and estuarine waters of Louisiana, Maryland, Mississippi, and Washington (United States)

Vibrio parahaemolyticus and Vibrio vulnificus, which are native to estuaries globally, are agents of seafood-borne or wound infections, both potentially fatal. Like all vibrios autochthonous to coastal regions, their abundance varies with changes in environmental parameters. Sea surface temperature (SST), sea surface height (SSH), and chlorophyll have been shown to be predictors of zooplankton and thus factors linked to vibrio populations. The contribution of salinity, conductivity, turbidity, and dissolved organic carbon to the incidence and distribution of Vibrio spp. has also been reported. Here, a multicoastal, 21-month study was conducted to determine relationships between environmental parameters and V. parahaemolyticus and V. vulnificus populations in water, oysters, and sediment in three coastal areas of the United States. Because ecologically unique sites were included in the study, it was possible to analyze individual parameters over wide ranges. Molecular methods were used to detect genes for thermolabile hemolysin (tlh), thermostable direct hemolysin (tdh), and tdh-related hemolysin (trh) as indicators of V. parahaemolyticus and the hemolysin gene vvhA for V. vulnificus. SST and suspended particulate matter were found to be strong predictors of total and potentially pathogenic V. parahaemolyticus and V. vulnificus. Other predictors included chlorophyll a, salinity, and dissolved organic carbon. For the ecologically unique sites included in the study, SST was confirmed as an effective predictor of annual variation in vibrio abundance, with other parameters explaining a portion of the variation not attributable to SST.

Apparent loss of Vibrio vulnificus from North Carolina oysters coincides with a drought-induced increase in salinity

Despite years of successful isolation of Vibrio vulnificus from estuarine waters, beginning in 2007, it was extremely difficult to culture V. vulnificus from either North Carolina estuarine water or oyster samples. After employing culture-based methods as well as PCR and quantitative PCR for the detection of V. vulnificus, always with negative results, we concluded that this pathogen had become nearly undetectable in the North Carolina estuarine ecosystem. We ensured that the techniques were sound by seeding North Carolina oysters with V. vulnificus and performing the same tests as those previously conducted on unadulterated oysters. V. vulnificus was readily detected in the seeded oysters using both classes of methods. Furthermore, oysters were obtained from the Gulf of Mexico, and V. vulnificus was easily isolated, confirming that the methodology was sound but that the oysters and waters of North Carolina were lacking the V. vulnificus population studied for decades. Strikingly, the apparent loss of detectable V. vulnificus coincided with the most severe drought in the history of North Carolina. The drought continued until the end of 2009, with an elevated water column salinity being observed throughout this period and with V. vulnificus being nearly nonexistent. When salinities returned to normal after the drought abated in 2010, we were again able to routinely isolate V. vulnificus from the water column, although we were still unable to culture it from oysters. We suggest that the oysters were colonized with a more salt-tolerant bacterium during the drought, which displaced V. vulnificus and may be preventing recolonization.

Development and validation of a predictive model for the growth of Vibrio vulnificus in postharvest shellstock oysters

Postharvest growth of Vibrio vulnificus in oysters can increase risk of human infection. Unfortunately, limited information is available regarding V. vulnificus growth and survival patterns over a wide range of storage temperatures in oysters harvested from different estuaries and in different oyster species. In this study, we developed a predictive model for V. vulnificus growth in Eastern oysters (Crassostrea virginica) harvested from Chesapeake Bay, MD, over a temperature range of 5 to 30°C and then validated the model against V. vulnificus growth rates (GRs) in Eastern and Asian oysters (Crassostrea ariakensis) harvested from Mobile Bay, AL, and Chesapeake Bay, VA, respectively. In the model development studies, V. vulnificus was slowly inactivated at 5 and 10°C with average GRs of -0.0045 and -0.0043 log most probable number (MPN)/h, respectively. Estimated average growth rates at 15, 20, 25, and 30°C were 0.022, 0.042, 0.087, and 0.093 log MPN/h, respectively. With respect to Eastern oysters, bias (B(f)) and accuracy (A(f)) factors for model-dependent and -independent data were 1.02 and 1.25 and 1.67 and 1.98, respectively. For Asian oysters, B(f) and A(f) were 0.29 and 3.40. Residual variations in growth rate about the fitted model were not explained by season, region, water temperature, or salinity at harvest. Growth rate estimates for Chesapeake Bay and Mobile Bay oysters stored at 25 and 30°C showed relatively high variability and were lower than Food and Agricultural Organization (FAO)/WHO V. vulnificus quantitative risk assessment model predictions. The model provides an improved tool for designing and implementing food safety plans that minimize the risk associated with V. vulnificus in oysters.

Year round patchiness of Vibrio vulnificus within a temperate Texas bay

AIMS

To investigate with high geographical resolution the small-scale spatial and temporal distribution of the pathogen Vibrio vulnificus throughout the water column in a temperate Texas bay where numerous V. vulnificus infections had been reported by the regional media the previous summer.

METHODS AND RESULTS

Surface and bottom water samples were collected from 19 sites between April 2005 and October 2006 from Matagorda Bay, TX. Physicochemical parameters were measured and V. vulnificus were analysed using quantitative polymerase chain reaction (Q-PCR) as a means of overcoming constraints of traditional culturing techniques. V. vulnificus was detected through out the year, although its temporal and spatial distribution was patchy. V. vulnificus abundances at individual sites ranged from <10 to >1·1×10(3)cellsml(-1) . No statistically reliable predictive model related to the physicochemical parameters could be developed for this pathogen.

CONCLUSIONS

This study demonstrates that year round detection of V. vulnificus while likely in the viable but nonculturable (VBNC) state during the winter months and emphasizes why physicochemical factors are insufficient metrics for robust regression modelling of this pathogen.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides an effective new tool, Q-PCR, to study environmental distribution of V. vulnificus and that in the light of the patchy distribution observed, new reliable approaches and a mechanistic understanding of pathogen ecology need to be considered to effectively model the aquatic distribution of V. vulnificus.

High numbers of Vibrio vulnificus in tar balls collected from oiled areas of the north-central Gulf of Mexico following the 2010 BP Deepwater Horizon oil spill

The Deepwater Horizon Oil Spill was the largest oil spill in USA history releasing approximately 4.9 million barrels of crude oil into the Gulf of Mexico. Soon after the spill started, tar balls and other forms of weathered oil appeared in large numbers on beaches in Mississippi and Alabama. In this study, we analyzed tar balls for total aerobic bacterial (TAB) counts and also for the presence of Vibrio vulnificus, a human pathogen known to be abundant in the Gulf Coast environment and capable of causing severe wound infections by contact with contaminated surfaces. Our results showed that TAB counts were significantly higher in tar balls than in sand and seawater collected at the same location. In addition, V. vulnificus numbers were 10× higher in tar balls than in sand and up to 100× higher than in seawater. Densities of V. vulnificus were higher than 10(5) colony forming units/g of tar ball in all samples analyzed. Our data suggest that tar balls can act as reservoirs for bacteria including human pathogens.

Temporal and spatial variability in the distribution of Vibrio vulnificus in the Chesapeake Bay: a hindcast study

Vibrio vulnificus, an estuarine bacterium, is the causative agent of seafood-related gastroenteritis, primary septicemia, and wound infections worldwide. It occurs as part of the normal microflora of coastal marine environments and can be isolated from water, sediment, and oysters. Hindcast prediction was undertaken to determine spatial and temporal variability in the likelihood of occurrence of V. vulnificus in surface waters of the Chesapeake Bay. Hindcast predictions were achieved by forcing a multivariate habitat suitability model with simulated sea surface temperature and salinity in the Bay for the period between 1991 and 2005 and the potential hotspots of occurrence of V. vulnificus in the Chesapeake Bay were identified. The likelihood of occurrence of V. vulnificus during high and low rainfall years was analyzed. From results of the study, it is concluded that hindcast prediction yields an improved understanding of environmental conditions associated with occurrence of V. vulnificus in the Chesapeake Bay.

High salinity relay as a postharvest processing strategy to reduce vibrio vulnificus levels in Chesapeake Bay oysters (Crassostrea virginica)

In 2009 the U.S. Food and Drug Administration (FDA) announced its intention to implement postharvest processing (PHP) methods to eliminate Vibrio vulnificus from oysters intended for the raw, half-shell market that are harvested from the Gulf of Mexico during warmer months. FDA-approved PHP methods can be expensive and may be associated with unfavorable responses from some consumers. A relatively unexplored PHP method that uses relaying to high salinity waters could be an alternative strategy, considering that high salinities appear to negatively affect the survival of V. vulnificus. During relay, however, oysters may be exposed to rapid and large salinity increases that could cause increased mortality. In this study, the effectiveness of high salinity relay to reduce V. vulnificus to <30 most probable number (MPN) per g and the impact on oyster mortality were assessed in the lower Chesapeake Bay. Two relay experiments were performed during the summer and fall of 2010. Oysters collected from three grow-out sites, a low salinity site (14 to 15 practical salinity units [psu]) and two moderate salinity sites (22 to 25 psu), were relayed directly to a high salinity site (≥30 psu) on Virginia's Eastern Shore. Oysters were assayed for V. vulnificus and Vibrio parahaemolyticus (another Vibrio species of concern) densities at time 0 prior to relay and after 7 and 14 days of relay, using the FDA MPN enrichment method combined with detection by real-time PCR. After 14 days, both V. vulnificus and V. parahaemolyticus densities were ≤0.8 MPN/g, and decreases of 2 to 3 log in V. vulnificus densities were observed. Oyster mortalities were low (≤4%) even for oysters from the low salinity harvest site, which experienced a salinity increase of approximately 15 psu. Results, although preliminary and requiring formal validation and economic analysis, suggest that high salinity relay could be an effective PHP method.

Occurrence and potential pathogenesis of Vibrio cholerae, Vibrio parahaemolyticus and Vibrio vulnificus on the South Coast of Sweden

During the summer of 2006, several wound infections - of which three were fatal - caused by Vibrio cholerae were reported from patients who had been exposed to water from the Baltic Sea. Before these reports, we initiated a sampling project investigating the occurrence of potential human pathogenic V. cholerae, Vibrio vulnificus and Vibrio parahaemolyticus in The Sound between Sweden and Denmark. The Blue mussel (Mytilus edulis) was used as an indicator to follow the occurrence of vibrios over time. Molecular analyses showed high frequencies of the most potent human pathogenic Vibrio spp.; 53% of mussel samples were positive for V. cholerae (although none were positive for the cholera toxin gene), 63% for V. vulnificus and 79% for V. parahaemolyticus (of which 47% were tdh(+) and/or trh(+)). Viable vibrios were also isolated from the mussel meat and screened for virulence by PCR. The mortality of eukaryotic cells when exposed to bacteria was tested in vivo, with results showing that the Vibrio strains, independent of species and origin, were harmful to the cells. Despite severe infections and several deaths, no report on potential human pathogenic vibrios in this area had been published before this study.

Genomic and metabolic profiling of nonulosonic acids in Vibrionaceae reveal biochemical phenotypes of allelic divergence in Vibrio vulnificus

Nonulosonic acids (NulOs) encompass a large group of structurally diverse nine-carbon backbone α-keto sugars widely distributed among the three domains of life. Mammals express a specialized version of NulOs called sialic acids, which are displayed in prominent terminal positions of cell surface and secreted glycoconjugates. Within bacteria, the ability to synthesize NulOs has been demonstrated in a number of human pathogens and is phylogenetically widespread. Here we examine the distribution, diversity, evolution, and function of NulO biosynthesis pathways in members of the family Vibrionaceae. Among 27 species of Vibrionaceae examined at the genomic level, 12 species contained nab gene clusters. We document examples of duplication, divergence, horizontal transfer, and recombination of nab gene clusters in different Vibrionaceae lineages. Biochemical analyses, including mass spectrometry, confirmed that many species do, in fact, produce di-N-acetylated NulOs. A library of clinical and environmental isolates of Vibrio vulnificus served as a model for further investigation of nab allele genotypes and levels of NulO expression. The data show that lineage I isolates produce about 20-fold higher levels of NulOs than lineage II isolates. Moreover, nab gene alleles found in a subset of V. vulnificus clinical isolates express 40-fold higher levels of NulOs than nab alleles associated with environmental isolates. Taken together, the data implicate the family Vibrionaceae as a "hot spot" of NulO evolution and suggest that these molecules may have diverse roles in environmental persistence and/or animal virulence.

Vibrio vulnificus oysters: pearls and perils

Vibrio vulnificus is a naturally occurring bacterium found ubiquitously in coastal waters. Infection with this organism, which is often associated with eating raw oysters, is the leading cause of seafood-related deaths in the United States. This article reviews the current scientific literature on this potentially lethal pathogen and discusses the prognosis, treatment, and prevention of V. vulnificus infections.

Mathematical Modeling of Vibrio vulnificus Infection in Korea and the Influence of Global Warming

OBJECTIVES

To investigate the possible link between Vibrio vulnificus population size in seawater and water temperature.

METHODS

We collected incidence and water temperature data in coastal regions of Korea and constructed a mathematical model that consisted of three classes; susceptible fish, infected fish available to humans, and infected humans.

RESULTS

We developed a mathematical model to connect V. vulnificus incidence with water temperature using estimated bacterial population sizes and actual coastal water temperatures.

CONCLUSION

Increased V. vulnificus population sizes in marine environments may increase the risk of infection in people who eat at coastal restaurants in Korea. Furthermore, we estimated the near-future number of infected patients using our model, which will help to establish a public-health policy to reduce the disease burden.

Comparison of the effects of environmental parameters on growth rates of Vibrio vulnificus biotypes I, II, and III by culture and quantitative PCR analysis

Vibrio vulnificus is a natural inhabitant of estuarine waters. The three known biotypes include (i) most human pathogens, (ii) primarily eel pathogens, and (iii) pathogens associated with fish and with human wound infections in Israel. Despite the frequently lethal consequences of V. vulnificus infections, the growth rates of the various biotypes and their response to environmental changes are not well characterized. We compared the specific growth rates (μ) of a representative of each biotype by culture and quantitative PCR (qPCR) analysis in a defined medium under varied pH, temperature, and salinity. Growth rates based on culturable concentrations were always higher than those based on qPCR estimates; however, both enumeration methods yielded comparable results on the influence of environmental factors on growth rates. Temperature (25°C, 30°C, 37°C), pH (7.0, 8.0), and salinity (5 to 40‰) all had significant effects on the μ of each biotype. Temperature had the greatest effect on the μ of biotype 1 (CMCP6), whereas salinity had the greatest effect on the μ of biotypes 2 (ATCC 33147) and 3 (302/99). The biotypes' growth rates varied significantly; biotype 1 grew most rapidly, while biotype 3 grew most slowly. The highest growth rates were achieved at 37°C, pH 7.0, and salinities of 15 to 30‰ (μ = 4.0, 2.9, and 2.4 generations h(-1) for biotypes 1, 2, and 3, respectively). Other strains of the biotypes yielded comparable results, suggesting that the physiological responses of the biotypes are differentially affected by parameters that are highly variable both in estuarine environments and between the free-living and pathogen states of V. vulnificus.

A comprehensive review of Vibrio vulnificus: an important cause of severe sepsis and skin and soft-tissue infection

Vibrio vulnificus is a halophilic Gram-negative bacillus found worldwide in warm coastal waters. The pathogen has the ability to cause primary sepsis in certain high-risk populations, including patients with chronic liver disease, immunodeficiency, iron storage disorders, end-stage renal disease, and diabetes mellitus. Most reported cases of primary sepsis in the USA are associated with the ingestion of raw or undercooked oysters harvested from the Gulf Coast. The mortality rate for patients with severe sepsis is high, exceeding 50% in most reported series. Other clinical presentations include wound infection and gastroenteritis. Mild to moderate wound infection and gastroenteritis may occur in patients without obvious risk factors. Severe wound infection is often characterized by necrotizing skin and soft-tissue infection, including fasciitis and gangrene. V. vulnificus possesses several virulence factors, including the ability to evade destruction by stomach acid, capsular polysaccharide, lipopolysaccharide, cytotoxins, pili, and flagellum. The preferred antimicrobial therapy is doxycycline in combination with ceftazidime and surgery for necrotizing soft-tissue infection.

Role of GacA in virulence of Vibrio vulnificus

The GacS/GacA two-component signal transduction system regulates virulence, biofilm formation and symbiosis in Vibrio species. The present study investigated this regulatory pathway in Vibrio vulnificus, a human pathogen that causes life-threatening disease associated with the consumption of raw oysters and wound infections. Small non-coding RNAs (csrB1, csrB2, csrB3 and csrC) commonly regulated by the GacS/GacA pathway were decreased (P<0.0003) in a V. vulnificus CMCP6 ΔgacA : : aph mutant compared with the wild-type parent, and expression was restored by complementation of the gacA deletion mutation in trans. Of the 20 genes examined by RT-PCR, significant reductions in the transcript levels of the mutant in comparison with the wild-type strain were observed only for genes related to motility (flaA), stationary phase (rpoS) and protease (vvpE) (P=0.04, 0.01 and 0.002, respectively). Swimming motility, flagellation and opaque colony morphology indicative of capsular polysaccharide (CPS) were unchanged in the mutant, while cytotoxicity, protease activity, CPS phase variation and the ability to acquire iron were decreased compared with the wild-type (P<0.01). The role of gacA in virulence of V. vulnificus was also demonstrated by significant impairment in the ability of the mutant strain to cause either skin (P<0.0005) or systemic infections (P<0.02) in subcutaneously inoculated, non-iron-treated mice. However, the virulence of the mutant was equivalent to that of the wild-type in iron-treated mice, demonstrating that the GacA pathway in V. vulnificus regulates the virulence of this organism in an iron-dependent manner.

Relationships between environmental factors and pathogenic Vibrios in the Northern Gulf of Mexico

Although autochthonous vibrio densities are known to be influenced by water temperature and salinity, little is understood about other environmental factors associated with their abundance and distribution. Densities of culturable Vibrio vulnificus containing vvh (V. vulnificus hemolysin gene) and V. parahaemolyticus containing tlh (thermolabile hemolysin gene, ubiquitous in V. parahaemolyticus), tdh (thermostable direct hemolysin gene, V. parahaemolyticus pathogenicity factor), and trh (tdh-related hemolysin gene, V. parahaemolyticus pathogenicity factor) were measured in coastal waters of Mississippi and Alabama. Over a 19-month sampling period, vibrio densities in water, oysters, and sediment varied significantly with sea surface temperature (SST). On average, tdh-to-tlh ratios were significantly higher than trh-to-tlh ratios in water and oysters but not in sediment. Although tlh densities were lower than vvh densities in water and in oysters, the opposite was true in sediment. Regression analysis indicated that SST had a significant association with vvh and tlh densities in water and oysters, while salinity was significantly related to vibrio densities in the water column. Chlorophyll a levels in the water were correlated significantly with vvh in sediment and oysters and with pathogenic V. parahaemolyticus (tdh and trh) in the water column. Furthermore, turbidity was a significant predictor of V. parahaemolyticus density in all sample types (water, oyster, and sediment), and its role in predicting the risk of V. parahaemolyticus illness may be more important than previously realized. This study identified (i) culturable vibrios in winter sediment samples, (ii) niche-based differences in the abundance of vibrios, and (iii) predictive signatures resulting from correlations between environmental parameters and vibrio densities.

Relationship between differential retention of Escherichia coli and Enterococcus faecalis and variations in enzyme activity in the scallop Patinopecten yessoensis

Uptake of Escherichia coli and Enterococcus faecalis and variations of trypsin amylase activity acid phosphatase and superoxide dismutase in tissue of the scallop Patinopecten yessoensis were detected. The results showed that P. yessoensis accumulated E. faecalis in larger numbers and more rapidly than E. coli, both with the highest concentration in the digestive tract and lowest in hemolymph. Compared to E. coli, all scallops exposed to E. faecalis showed significantly higher trypsin and AMS activity. SOD activity in hemocytes and ACP activity in hemolymph was significantly higher in the treatments with 5 log(10)CFU/ml E. coli than with E. faecalis. But no significant differences in ACP activity of P. yessoensis exposed to a 3 log(10)CFU/ml inoculum of both bacteria were recorded. In conclusion, the mass retention of gut microflora in P. yessoensis is positively correlated with digestive enzymes activity and negatively correlated with ACP activity in the hemocyte.

Bacterial and viral pathogens in live oysters: 2007 United States market survey

Two samples of market oysters, primarily from retail establishments, were collected twice each month in each of nine states during 2007. Samples were shipped refrigerated overnight to five U.S. Food and Drug Administration laboratories on a rotating basis and analyzed by most probable number (MPN) for total and pathogenic Vibrio parahaemolyticus and V. vulnificus numbers and for the presence of toxigenic V. cholerae, Salmonella spp., norovirus (NoV), and hepatitis A virus (HAV). Levels of indicator organisms, including fecal coliforms (MPN), Escherichia coli (MPN), male-specific bacteriophage, and aerobic plate counts, were also determined. V. parahaemolyticus and V. vulnificus levels were distributed seasonally and geographically by harvest region and were similar to levels observed in a previous study conducted in 1998-1999. Levels of pathogenic V. parahaemolyticus were typically several logs lower than total V. parahaemolyticus levels regardless of season or region. Pathogenic V. parahaemolyticus levels in the Gulf and Mid-Atlantic regions were about two logs greater than the levels observed in the Pacific and North Atlantic regions. Pathogens generally associated with fecal pollution were detected sporadically or not at all (toxigenic V. cholerae, 0%; Salmonella, 1.5%; NoV, 3.9%; HAV, 4.4%). While seasonal prevalences of NoV and HAV were generally greater in oysters harvested from December to March, the low detection frequency obscured any apparent seasonal effects. Overall, there was no relationship between the levels of indicator microorganisms and the presence of enteric viruses. These data provide a baseline that can be used to further validate risk assessment predictions, determine the effectiveness of new control measures, and compare the level of protection provided by the U.S. shellfish sanitation system to those in other countries.

Environmental occurrence and clinical impact of Vibrio vulnificus and Vibrio parahaemolyticus: a European perspective

Vibrio vulnificus and Vibrio parahaemolyticus are ubiquitous Gram-negative bacterial pathogens found naturally in marine and estuarine waters, and are a leading cause of seafood-associated bacterial illness. These pathogens are commonly reported in the USA and in many Asian countries, including China, Japan and Taiwan; however, there is growing concern that V. vulnificus and V. parahaemolyticus may represent an important and increasing clinical problem in Europe. Several factors underlie the need for a greater understanding of these non-cholera vibrios within a European context. First, there is a growing body of evidence to suggest that V. vulnificus and V. parahaemolyticus infections are increasing, and tend to follow regional climatic trends, with outbreaks typically following episodes of unusually warm weather. Such findings are especially alarming given current predictions regarding warming of marine waters as a result of global climatic change. Second, a myriad of epidemiological factors may greatly increase the incidence as well as clinical burden of these pathogens - including increasing global consumption and trade of seafood produce coupled to an increase in the number of susceptible individuals consuming seafood produce. Finally, there is currently a lack of detailed surveillance information regarding non-cholerae Vibrio infections in Europe, as these pathogens are not notifiable in many countries, which probably masks the true clinical burden of many human infections. This review will present a pertinent overview of both the environmental occurrence and clinical impact of V. vulnificus and V. parahaemolyticus in Europe.

Foodborne pathogens in retail oysters in south China

OBJECTIVE

To investigate the occurrence of important foodborne pathogens in shellstock Pacific oysters in the food markets in South China.

METHODS

From July 2007 to June 2008, retail oysters were collected in different seasons from South China and analyzed for the prevalence and levels of Listeria monocytogenes, Vibrio vulnificus and Vibrio parahaemolyticus.

RESULTS

None of L. monocytogenes could be detected in any of the 202 oyster samples tested, while E vulnificus and V. parahaemolyticus could be detected in 67 (54.9%) and 109 (89.3%) of the 122 oyster samples analyzed, respectively, with an MPN (most probable number) value greater than or equal to 3. V. vulnificus and V. parahaemolyticus with a more than 102 MPN/g were found in 36 (29.5%) and 59 (48.4%) of the 122 oyster samples, respectively. The tdh and trh genes were detected in 4 (0.3%) and 8 (0.6%) of the 1 349 V parahaemolyticus isolates, respectively. Of the 122 samples, 4 (3.3%) was positive for either tdh or trh. The levels of V. vulnificus and total V. parahaemolyticus in oysters in South China varied in different seasons.

CONCLUSION

V. vulnificus and pathogenic V. parahaemolyticus are frequently found in oysters in south China, which may pose a potential threat to public health. Data presented here will be useful for the microbiological risk assessment in oysters in China.

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.

Ecology of Vibrio vulnificus and Vibrio parahaemolyticus in brackish environments of the Sada River in Shimane Prefecture, Japan

While there are several studies on the ecology of Vibrio vulnificus and Vibrio parahaemolyticus in estuarine water environments around the world, there is little information on the distribution of both organisms during the cold-weather months. Thus, we conducted a multi-year study on the ecology of both organisms in brackish environments of the Sada River, a drainage canal flowing slowly into the Japan Sea from Lake Shinji in Shimane Prefecture, Japan. Water samples were collected twice a month at five sites from August 2000 to May 2002. Both organisms were enumerated in 10 l water, 100 g sediment and 10 g shellfish by the most probable number (MPN) procedure. Isolates were confirmed as V. vulnificus using hemolysin gene PCR. During the last 7 months (including winter) of the study, water and sediment samples were also analyzed for the presence of both organisms. V. parahaemolyticus was isolated from river mouths and coastal environments of average salinity > or = 4.4+/-2.0 ppt throughout the year at cell concentrations of 10(-3) to 10(1) MPN ml(-1). Similar concentrations of V. vulnificus were isolated from coastal environments of average salinity 24.0+/-5.4 ppt, except for two times when water moved to the upper reaches due to high tide and V. vulnificus was rifted to the upper reaches. These findings suggest that both organisms are continuously distributed in the Sada estuary throughout the year regardless of water temperature.

Incidence of Vibrio vulnificus in estuarine waters of the south Texas Coastal Bend region

AIMS

To determine the occurrence of the human pathogen, Vibrio vulnificus, in south Texas coastal waters.

METHODS AND RESULTS

Coastal waters were sampled monthly between August 2006 and July 2007. Water temperature, dissolved oxygen, pH, salinity, conductivity and turbidity were measured during each sampling event. Culture-based techniques utilizing Vibrio vulnificus agar (VVA) and membrane-Enterococcus indoxyl-beta-D-glucoside agar (mEI) were used to assess the occurrence and levels of V. vulnificus and the faecal contamination indicator group, enterococci, respectively. Vibrio vulnificus isolates were confirmed using colony-blot hybridization with the species-specific VVAP probe. Vibrio vulnificus was isolated at all sites throughout the year even when the water temperature dropped to 9.71 degrees C. Significant correlations were found between concentrations of V. vulnificus and the abiotic factors, water temperature (P = 0.002) and dissolved oxygen (P = 0.028), as well as between concentrations of V. vulnificus and enterococci (P < 0.001).

CONCLUSIONS

This study demonstrated the year-round presence of V. vulnificus in coastal waters of south Texas.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings indicate that the potential for human exposure to the pathogen, V. vulnificus, exists throughout the year. It also suggests that routinely monitored data might be used to predict the occurrence of the pathogen.

Vibrio vulnificus cytolysin induces apoptosis in HUVEC, SGC-7901 and SMMC-7721 cells via caspase-9/3-dependent pathway

Vibrio vulnificus cytolysin (VVC) is known to be a pore-forming toxin which shows cytotoxicity for mammalian cells in culture and induces apoptosis in endothelial cells. In order to determine whether VVC induces apoptosis in vascular endothelial cells and tumor cells, the cytotoxicity induced by recombinant VVC (rVVC) and its potential mechanism in HUVEC, SGC-7901 and SMMC-7721 cells were investigated. Our study demonstrated that rVVC induced the release of intracellular K(+) from all the target cells, yet lactate dehydrogenase was not released by rVVC. It indicates that osmotic lysis might not contribute to the cytolysin-induced cytotoxicity. The study also demonstrated that rVVC induced apoptosis in HUVEC, SGC-7901 and SMMC-7721 cells in time- and dosage-dependent manners, which was associated with the activation of caspase-9 and -3, but not caspase-8. During the apoptotic process of the target cells, rVVC labeled with FITC was monitored to attach initially to the surface of the cells and entered the cytoplasma subsequently. These findings suggest that VVC may be not only a pore-forming toxin, but also a transmembrane toxin with powerful ability to induce apoptosis in human vascular endothelial cells and tumor cells.

The crystal structure of galacto-N-biose/lacto-N-biose I phosphorylase: a large deformation of a TIM barrel scaffold

Galacto-N-biose/lacto-N-biose I phosphorylase (GLNBP) from Bifidobacterium longum, a key enzyme for intestinal growth, phosphorolyses galacto-N-biose and lacto-N-biose I with anomeric inversion. GLNBP homologues are often found in human pathogenic and commensal bacteria, and their substrate specificities potentially define the nutritional acquisition ability of these microbes in their habitat. We report the crystal structures of GLNBP in five different ligand-binding forms. This is the first three-dimensional structure of glycoside hydrolase (GH) family 112. The GlcNAc- and GalNAc-bound forms provide structural insights into distinct substrate preferences of GLNBP and its homologues from pathogens. The catalytic domain consists of a partially broken TIM barrel fold that is structurally similar to a thermophilic beta-galactosidase, strongly supporting the current classification of GLNBP homologues as one of the GH families. Anion binding induces a large conformational change by rotating a half-unit of the barrel. This is an unusual example of molecular adaptation of a TIM barrel scaffold to substrates.

Salinity and temperature effects on physiological responses of Vibrio fischeri from diverse ecological niches

Vibrio fischeri is a bioluminescent bacterial symbiont of sepiolid squids (Cephalopoda: Sepiolidae) and monocentrid fishes (Actinopterygii: Monocentridae). V. fischeri exhibit competitive dominance within the allopatrically distributed squid genus Euprymna, which have led to the evolution of V. fischeri host specialists. In contrast, the host genus Sepiola contains sympatric species that is thought to have given rise to V. fischeri that have evolved as host generalists. Given that these ecological lifestyles may have a direct effect upon the growth spectrum and survival limits in contrasting environments, optimal growth ranges were obtained for numerous V. fischeri isolates from both free-living and host environments. Upper and lower limits of growth were observed in sodium chloride concentrations ranging from 0.0% to 9.0%. Sepiola symbiotic isolates possessed the least variation in growth throughout the entire salinity gradient, whereas isolates from Euprymna were the least uniform at <2.0% NaCl. V. fischeri fish symbionts (CG101 and MJ101) and all free-living strains were the most dissimilar at >5.0% NaCl. Growth kinetics of symbiotic V. fischeri strains were also measured under a range of salinity and temperature combinations. Symbiotic V. fischeri ES114 and ET101 exhibited a synergistic effect for salinity and temperature, where significant differences in growth rates due to salinity existed only at low temperatures. Thus, abiotic factors such as temperature and salinity have differential effects between free-living and symbiotic strains of V. fischeri, which may alter colonization efficiency prior to infection.

Identification of lacto-N-Biose I phosphorylase from Vibrio vulnificus CMCP6

A beta-1,3-galactosyl-N-acetylhexosamine phosphorylase (GalGlyNAcP) homolog gene was cloned from Vibrio vulnificus CMCP6. In synthetic reactions, the recombinant enzyme acted only with GlcNAc and GalNAc as acceptors in the presence of alpha-d-galactose-1-phosphate as a donor to form lacto-N-biose I (LNB) (Galbeta1 --> 3GlcNAc) and galacto-N-biose (GNB) (Galbeta1 --> 3GalNAc), respectively. GlcNAc was a much better acceptor than GalNAc. The enzyme also phosphorolysed LNB faster than it phosphorolysed GNB, and the k(cat)/K(m) for LNB was approximately 60 times higher than the k(cat)/K(m) for GNB. This result indicated that the enzyme was remarkably different from GalGlyNAcP from Bifidobacterium longum, which has similar activities with LNB and GNB, and GalGlyNAcP from Clostridium perfringens, which is a GNB-specific enzyme. The enzyme is the first LNB-specific enzyme that has been found and was designated lacto-N-biose I phosphorylase. The discovery of an LNB-specific GalGlyNAcP resulted in recategorization of bifidobacterial GalGlyNAcPs as galacto-N-biose/lacto-N-biose I phosphorylases.

Dynamics and predictive modelling of Vibrio spp. in the Neuse River Estuary, North Carolina, USA

Vibrio spp. are naturally occurring bacteria in marine and estuarine environments around the world. The genus includes several human and animal pathogens that can negatively impact human health, seafood and aquaculture. Vibrio spp. populations are capable of rapid adaptation in response to changing environmental conditions, making them dynamic over short-term and seasonal scales. Temperature, vertical mixing, tidal flushing, climate, precipitation and nutrient loading can change the estuarine environment and subsequently alter microbial community structure, including Vibrio spp., affecting estuarine water quality and public health. To describe these dynamics, Vibrio spp. concentrations and a range of microbial, physical and chemical measures were monitored every 2 weeks and after storm events for 19 months in the Neuse River Estuary (NRE). Results showed clear seasonal and geographic trends in Vibrio spp. abundance. Multiple regression analysis revealed a strong relationship to temperature and salinity, with additional minor influences of chlorophyll a and dissolved organic carbon. Similar models based on easily measured environmental parameters should be pursued for individual Vibrio species in the NRE and other estuarine environments. Predictive models provide useful information for managers, researchers and modellers of estuarine ecosystems.

Epidemiological survey of Vibrio vulnificus infection in Japan between 1999 and 2003

The frequency of Vibrio vulnificus infection is very rare and there are many questions regarding its epidemiology in Japan. To investigate the clinical course and epidemiology of V. vulnificus infection in Japan, we performed a retrospective questionnaire survey in which 1693 hospitals from all over Japan were surveyed, including advanced life saving emergency centers and dermatology institutions. Of the 1693 hospitals, we received answers from 1045. Ninety-four cases were confirmed as V. vulnificus infections during 1999 and 2003. Sixty-eight (72.3%) of the 94 patients had the septic type infection with a mortality rate of 75.0% (51/68 patients died). The prognosis of patients with the septic type was worse than that of the wound type (P < 0.001). V. vulnificus infections occurred from June to November and none occurred in winter. Many infections occurred in western Japan with the majority of infections (50/94) occurring in Kyushu. In particular, 43 infections occurred in marine coastal areas of the Ariake and Yatsushiro Seas, which have many tidelands. Seventy-seven of 89 patients (86.5%) had liver function impairment as an underlying disease, and 53 (59.6%) had liver cirrhosis, of whom nine (10.1%) suffered from liver cancer. The incidence of V. vulnificus infection was different according to districts. Geographic and climatic factors also contributed to the occurrence of V. vulnificus infection.

The ecology of Vibrio vulnificus, Vibrio cholerae, and Vibrio parahaemolyticus in North Carolina estuaries

While numerous studies have characterized the distribution and/or ecology of various pathogenic Vibrio spp., here we have simultaneously examined several estuarine sites for Vibrio vulnificus, V. cholerae, and V. parahaemolyticus. For a one year period, waters and sediment were monitored for the presence of these three pathogens at six different sites on the east coast of North Carolina in the United States. All three pathogens, identified using colony hybridization and PCR methods, occurred in these estuarine environments, although V. cholerae occurred only infrequently and at very low levels. Seventeen chemical, physical, and biological parameters were investigated, including salinity, water temperature, turbidity, dissolved oxygen, levels of various inorganic nutrients and dissolved organic carbon, as well as total vibrios, total coliforms, and E. coli. We found each of the Vibrio spp. in water and sediment to correlate to several of these environmental measurements, with water temperature and total Vibrio levels correlating highly (P<0.0001) with occurrence of the three pathogens. Thus, these two parameters may represent simple assays for characterizing the potential public health hazard of estuarine waters.

Occurrence, seasonality and genetic diversity of Vibrio vulnificus in coastal seaweeds and water along the Kii Channel, Japan

Vibrio vulnificus is a ubiquitous toxigenic bacterium found in a coastal environment but little is known about its occurrence and seasonality among seaweeds, which are widely consumed as seafood in Japan. Therefore, we have observed the bacterium's abundance in seawater and seaweed samples from three areas of the Kii Channel, Japan, during June 2003 to May 2004. A total of 192 samples were collected: 24 from each source in summer, autumn, winter and spring. The samples were selectively cultivated following the most probable number (MPN) technique. Vibrio vulnificus population ranged from 0 to 10(3) MPN 100 mL(-1) seawater or 10 g seaweeds; higher counts were observed during summer. The optimum temperature, salinity and pH for the bacterium were 20-24 degrees C, 24-28 p.p.t. and 7.95-8.15, respectively. However, seaweeds always contained higher V. vulnificus than seawater. Among 280 V. vulnificus strains, detected by species-specific colony hybridization and PCR, 78, 74, 11 and 16 were from seaweeds and 46, 42, 2 and 11 were from seawater during summer, autumn, winter and spring, respectively. Ribotyping of 160 selected strains revealed a higher genotypic diversity (18 patterns) among strains from seaweeds than from seawater (10 patterns). Seaweeds can thus act as a potential habitat for V. vulnificus and are more unsafe for consumption during summer.

Survival of and in situ gene expression by Vibrio vulnificus at varying salinities in estuarine environments

The opportunistic human pathogen Vibrio vulnificus survives in a wide range of ecological environments, which demonstrates its ability to adapt to highly variable conditions. Survival and gene expression under various conditions have been extensively studied in vitro; however, little work has been done to evaluate this bacterium in its natural habitat. Therefore, this study monitored the long-term survival of V. vulnificus in situ and simultaneously evaluated the expression of stress (rpoS, relA, hfq, and groEL) and putative virulence (vvpE, smcR, viuB, and trkA) genes at estuarine sites of varying salinity. Additionally, the survival and gene expression of an rpoS and an oxyR mutant were examined under the same conditions. Differences between the sampling sites in the long-term survival of any strain were not seen. However, differences were seen in the expression of viuB, trkA, and relA but our findings differed from what has been previously shown in vitro. These results also routinely demonstrated that genes required for survival under in vitro stress or host conditions are not necessarily required for survival in the water column. Overall, this study highlights the need for further in situ evaluation of this bacterium in order to gain a true understanding of its ecology and how it relates to its natural habitat.

Evaluation of postharvest-processed oysters by using PCR-based most-probable-number enumeration of Vibrio vulnificus bacteria

Postharvest processing (PHP) is used to reduce levels of Vibrio vulnificus in oysters, but process validation is labor-intensive and expensive. Therefore, quantitative PCR was evaluated as a rapid confirmation method for most-probable-number enumeration (QPCR-MPN) of V. vulnificus bacteria in PHP oysters. QPCR-MPN showed excellent correlation (R(2) = 0.97) with standard MPN and increased assay sensitivity and efficiency.