Vibrio parahaemolyticus and related halophilic Vibrios

Differential replication dynamics for large and small Vibrio chromosomes affect gene dosage, expression and location

Background

Replication of bacterial chromosomes increases copy numbers of genes located near origins of replication relative to genes located near termini. Such differential gene dosage depends on replication rate, doubling time and chromosome size. Although little explored, differential gene dosage may influence both gene expression and location. For vibrios, a diverse family of fast growing gammaproteobacteria, gene dosage may be particularly important as they harbor two chromosomes of different size.

Results

Here we examined replication dynamics and gene dosage effects for the separate chromosomes of three Vibrio species. We also investigated locations for specific gene types within the genome. The results showed consistently larger gene dosage differences for the large chromosome which also initiated replication long before the small. Accordingly, large chromosome gene expression levels were generally higher and showed an influence from gene dosage. This was reflected by a higher abundance of growth essential and growth contributing genes of which many locate near the origin of replication. In contrast, small chromosome gene expression levels were low and appeared independent of gene dosage. Also, species specific genes are highly abundant and an over-representation of genes involved in transcription could explain its gene dosage independent expression.

Conclusion

Here we establish a link between replication dynamics and differential gene dosage on one hand and gene expression levels and the location of specific gene types on the other. For vibrios, this relationship appears connected to a polarisation of genetic content between its chromosomes, which may both contribute to and be enhanced by an improved adaptive capacity.

Detection of Vibrio parahaemolyticus in tropical shellfish by SYBR green real-time PCR and evaluation of three enrichment media

A rapid, sensitive and highly reproducible SYBR green based real-time PCR assay was developed for detection of tdh positive pathogenic Vibrio parahaemolyticus. Minimum detection limit was 0.1 pg of pure V. parahaemolyticus genomic DNA with typical R(2) values >0.99 and coefficient of variation (CV) values ranging from 1.2 to 4.2 on three different days. The method was also used to evaluate the effect of three different enrichment media alkaline peptone water (APW), sodium taurocholate (ST) broth and salt polymyxin broth (SPB) on detection of V. parahaemolyticus. Crude lysates were directly used for real-time PCR. Without enrichment, the detection limit of pure cultures was 10(1) CFU/ml for ST broth and 10(2) CFU/ml in APW and SPB but for shrimp homogenates spiked with pure culture, the minimum detection limit was 10(2) CFU/ml for all three broths with a linear detection range of 10(2)-10(6). Without enrichment, detection in ST broth was more efficient than APW and SPB. After 6 h enrichment, limit of detection was found to be 1 CFU in all three media. However, for iced shrimp, the limit of detection was 10(2) after 6 h enrichment. No significant difference was seen between different enrichment media with respect to tdh gene detection of V. parahaemolyticus. The methodology developed here can be useful for rapid detection of tdh positive V. parahaemolyticus by laboratories involved in monitoring programmes for pathogenic V. parahaemolyticus.

Comparison of V. parahaemolyticus isolated from seafoods and cases of gastrointestinal disease in the UK

In this study the prevalence of Vibrio parahaemolyticus in shellfish and estuarine waters from the UK was examined using cultural and nucleic acid hybridisation approaches. Forty-nine isolates derived from environmental sources were characterised using serotyping, PCR, nucleic acid hybridisation and pulsed field gel electrophoresis (PFGE). The serotypic and molecular profiles of these isolates were compared to 20 clinical isolates, including representatives of the pandemic O3:K6 clone. Thirty percent of environmental samples were positive for V. parahaemolyticus. The tdh gene was identified in 12% of samples tested. Environmentally derived tdh+ strains were highly heterogeneous with neither association between isolates from similar origins nor seafood type. Previously uncharacterised clinical strains from UK patients with travel related V. parahaemolyticus associated gastroenteritis, were unrelated to tdh+ or tdh- environmental isolates but 2 were clonally indistinguishable from the pandemic O3:K6 strain responsible for outbreaks in Spain, Korea, Japan and Laos.

Molecular analysis of the emergence of pandemic Vibrio parahaemolyticus

Background

Vibrio parahaemolyticus is abundant in the aquatic environment particularly in warmer waters and is the leading cause of seafood borne gastroenteritis worldwide. Prior to 1995, numerous V. parahaemolyticus serogroups were associated with disease, however, in that year an O3:K6 serogroup emerged in Southeast Asia causing large outbreaks and rapid hospitalizations. This new highly virulent strain is now globally disseminated.

Results

We performed a four-way BLAST analysis on the genome sequence of V. parahaemolyticus RIMD2210633, an O3:K6 isolate from Japan recovered in 1996, versus the genomes of four published Vibrio species and constructed genome BLAST atlases. We identified 24 regions, gaps in the genome atlas, of greater than 10 kb that were unique to RIMD2210633. These 24 regions included an integron, f237 phage, 2 type III secretion systems (T3SS), a type VI secretion system (T6SS) and 7 Vibrio parahaemolyticus genomic islands (VPaI-1 to VPaI-7). Comparative genomic analysis of our fifth genome, V. parahaemolyticus AQ3810, an O3:K6 isolate recovered in 1983, identified four regions unique to each V. parahaemolyticus strain. Interestingly, AQ3810 did not encode 8 of the 24 regions unique to RMID, including a T6SS, which suggests an additional virulence mechanism in RIMD2210633. The distribution of only the VPaI regions was highly variable among a collection of 42 isolates and phylogenetic analysis of these isolates show that these regions are confined to a pathogenic clade.

Conclusion

Our data show that there is considerable genomic flux in this species and that the new highly virulent clone arose from an O3:K6 isolate that acquired at least seven novel regions, which included both a T3SS and a T6SS.

Type III secretion system 1 genes in Vibrio parahaemolyticus are positively regulated by ExsA and negatively regulated by ExsD

Vibrio parahaemolyticus harbours two distinct type III secretion systems (T3SS1 and T3SS2). A subset of 10 T3SS1 genes are transcribed when V. parahaemolyticus is grown in tissue culture medium [Dulbecco's modified Eagle's medium (DMEM)], while transcription of these genes (except exsD) is minimal upon growth in Luria-Bertani-Salt (LB-S). Transcription of T3SS1 genes and cytotoxicity towards HeLa cells was prevented by deletion of exsA while complementation with exsA restored these traits. Overexpression of ExsA in the wild-type strain, NY-4, activated the transcription of T3SS1 genes when bacteria were grown in LB-S. Thus, ExsA is necessary and sufficient to induce the transcription of T3SS1 genes. Deletion of the exsD permitted the transcription of T3SS1 genes when bacteria were grown in the LB-S medium and complementation with the wild-type exsD gene-blocked transcription of T3SS1 genes. Overexpression of ExsD in NY-4 prevented the transcription of T3SS1 gene when bacteria were grown in DMEM. A gel mobility shift assay demonstrated that purified ExsA protein binds a novel motif in the upstream region of vp1668 and vp1687, indicating that ExsA interacts directly with the promoter sequences of T3SS1 genes. ExsA positively regulates the expression and secretion of Vp1656 while ExsD negatively regulates the expression and secretion of Vp1656.

Identification of two translocon proteins of Vibrio parahaemolyticus type III secretion system 2

The type III secretion system (T3SS) translocon complex is composed of several associated proteins, which form a translocation channel through the host cell plasma membrane. These proteins are key molecules that are involved in the pathogenicity of many T3SS-positive bacteria, because they are necessary to deliver effector proteins into host cells. A T3SS designated T3SS2 of Vibrio parahaemolyticus is thought to be related to the enterotoxicity of this bacterium in humans, but the effector translocation mechanism of T3SS2 is unclear because there is only one gene (the VPA1362 gene) in the T3SS2 region that is homologous to other translocon protein genes. It is also not known whether the VPA1362 protein is functional in the translocon of T3SS2 or whether it is sufficient to form the translocation channel of T3SS2. In this study, we identified both VPA1362 (designated VopB2) and VPA1361 (designated VopD2) as T3SS2-dependent secretion proteins. Functional analysis of these proteins showed that they are essential for T3SS2-dependent cytotoxicity, for the translocation of one of the T3SS2 effector proteins (VopT), and for the contact-dependent activity of pore formation in infected cells in vitro. Their targeting to the host cell membrane depends on T3SS2, and furthermore, they are necessary for T3SS2-dependent enterotoxicity in vivo. These results indicate that VopB2 and VopD2 act as translocon proteins of V. parahaemolyticus T3SS2 and hence have a critical role in the T3SS2-dependent enterotoxicity of this bacterium.

Lysine decarboxylase of Vibrio parahaemolyticus: kinetics of transcription and role in acid resistance

AIM

The aim of this study was to investigate the detailed mechanisms of acid resistance in Vibrio parahaemolyticus.

METHODS AND RESULTS

All 11 strains of V. parahaemolyticus survived lethal acidic conditions following acid adaptation, and accumulation of cadaverine was detected. The addition of lysine improved survival, suggesting that lysine decarboxylase plays a role in the adaptive acid tolerance response. Two open reading frames (ORF) in V. parahaemolyticus, which are separated by a noncoding region, were found to be highly homologous to bacterial lysine decarboxylase (cadA) and lysine/cadaverine antiporter (cadB) genes. Transcriptional analyses of this operon revealed acid induction and enhanced induction by external lysine. The relative expression ratio of each transcript was found to follow the trend of cadA mRNA > cadB mRNA > cadBA bi-cistronic mRNA. A mutated strain, with a disrupted cadA gene, showed attenuated acid survival.

CONCLUSIONS

We identified the lysine decarboxylase gene operon of V. parahaemolyticus. Expression of this operon was induced under acidic conditions. The cadA-mutated strain constructed in this study showed weaker tolerance to acidic conditions than the wild-type strain.

SIGNIFICANCE AND IMPACT OF THE STUDY

Vibrio parahaemolyticus utilizes the lysine decarboxylation pathway for survival in acidic conditions.

Environmental determinants of the occurrence and distribution of Vibrio parahaemolyticus in the rias of Galicia, Spain

Infections associated with Vibrio parahaemolyticus on the coast of Galicia (in northwestern Spain) were reported to be linked to large outbreaks of illness during 1999 and 2000. Little information is available about the ecological factors that influence the emergence of V. parahaemolyticus infections in this temperate region. We carried out a 3-year study to investigate the occurrence and distribution of V. parahaemolyticus at 26 sites located in the four main rias of Galicia in association with environmental and oceanographic variables. V. parahaemolyticus was detected in all the areas investigated and throughout the complete period of study with an overall incidence of 12.5%. Salinity was the primary factor governing the temporal and spatial distribution of V. parahaemolyticus, whereas seawater temperature had a secondary effect and only modulated the abundance in periods and areas of reduced salinities. Higher occurrence of V. parahaemolyticus was observed during periods of lower salinity in autumn, with a total of 61 positive samples (18%) and a mean density of 1,234 most probable number/100 g. V. parahaemolyticus was primarily detected in areas of reduced salinity close to freshwater discharge points, where it was found in up to 45% of the samples. Characterization of the isolates obtained from the study resulted in the first identification of two pathogenic tdh-positive strains of V. parahaemolyticus recovered from the marine environment in Galicia. These isolates showed serotypes identical to and DNA profiles indistinguishable from those of the clinical clone of V. parahaemolyticus dominant in infections in Spain in the last 10 years.

Molecular characterization of Vibrio parahaemolyticus strains associated with foodborne illness in Florida

Vibrio parahaemolyticus is the leading cause of bacterial seafood-based illness in the United States. Real-time PCR, pandemic group-specific PCR, ribotyping, and multilocus sequence typing were used to characterize 30 strains of V. parahaemolyticus including 11 strains associated with foodborne outbreaks in Florida and 6 known pandemic strains. Thirteen strains were positive for four pandemic group-specific PCR markers, including 5 strains associated with outbreaks in Florida. Molecular typing methods were used to further define the pandemic status of these strains because the current PCR markers are not sufficient to identify pandemic isolates. Nine of the Florida strains clustered with a majority of the known pandemic strains, based on ribotyping patterns using PvuII, but no isolated pandemic branch was formed. Using multilocus sequence typing, it was determined that 14 strains possess a previously determined pandemic sequence type. This study identified 13 novel sequence types and seven to nine novel alleles for each locus. Furthermore, the results indicate that seven of the strains from recent foodborne outbreaks in Florida are pandemic strains, and that multilocus sequence typing was the most accurate molecular method to identify these strains.

Seaweeds as a reservoir for diverse Vibrio parahaemolyticus populations in Japan

Gastroenteritis caused by Vibrio parahaemolyticus has recently been associated with foods prepared with seaweeds, but little is known about the bacterium's abundance and diversity among seaweeds in coastal environment. Therefore, we determined its phenotypic and genotypic diversity in relation to its seasonal abundance in seawater and seaweed samples from three areas of Kii Channel, Japan during June 2003 to May 2004. Isolates were obtained by selective enrichment of samples and detection of V. parahaemolyticus by colony hybridization with a species-specific probe. A total of 128 isolates comprising 16 from each source in each season were characterized by serotyping and ribotyping. V. parahaemolyticus was more abundant in seaweeds (3,762 isolates) than in water samples (2,238 isolates). Twenty and 17 serotypes were found among the selected seaweed and seawater isolates, respectively. Cluster analysis revealed 19, 11, 7 and 9 ribotypes during summer, autumn, winter and spring, respectively. Seaweeds supported a diverse V. parahaemolyticus population throughout the year and thus seaweeds are a reservoir for the organism. However, V. parahaemolyticus occurrence had positive correlation with water temperature and its abundance in seaweeds was at least 50 times higher during summer than in winter.

Vibrionaceae, a versatile bacterial family with evolutionarily conserved variability

Despite the broad diversity of Vibrionaceae, they display a surprising number of conserved features, most striking of which may be the ubiquitous presence of two chromosomes. Based on complete genome sequences and the findings generated therefrom, we discuss the origin, evolution and stability of this unusual chromosomal arrangement as well as its possible benefits.

The dominance of pandemic serovars of Vibrio parahaemolyticus in expatriates and sporadic cases of diarrhoea in Thailand, and a new emergent serovar (O3 : K46) with pandemic traits

Vibrio parahaemolyticus is a major cause of gastroenteritis worldwide. A total of 95 V. parahaemolyticus isolates belonging to 23 different serovars were identified in a case–control study of expatriates and Thai adults from 2001 to 2002 in Thailand. Fifty-two per cent of isolates (49/95) were resistant to ampicillin and sulfisoxazole, but all isolates were susceptible to ciprofloxacin and trimethoprim–sulfamethoxazole, two antibiotics commonly used to treat traveller’s diarrhoea. All isolates were positive for the species-specific toxR gene, and 91 and 5 were positive for the thermostable direct haemolysin (tdh) gene and the tdh-related (trh) gene, respectively. Sixty-five isolates were assigned to the pandemic group of V. parahaemolyticus by a group-specific PCR and the presence of the orf8 gene. The pandemic isolates belonged to three recognized serovars (O3 : K6, O1 : K25, O1 : KUT) and a new serovar, O3 : K46. This new serovar harboured pandemic traits. PFGE analysis revealed that all pandemic isolates including serovar O3 : K46 were closely related and clearly distinct from the non-pandemic isolates. In summary, three well-known serovars of pandemic V. parahaemolyticus isolates were identified as a major cause of diarrhoea in Thailand and a new V. parahaemolyticus isolate, serovar O3 : K46, with pandemic traits was detected.

Global dissemination of Vibrio parahaemolyticus serotype O3:K6 and its serovariants

Vibrio parahaemolyticus is recognized as a cause of food-borne gastroenteritis, particularly in the Far East, where raw seafood consumption is high. An unusual increase in admissions of V. parahaemolyticus cases was observed at the Infectious Diseases Hospital in Calcutta, a city in the northeastern part of India, beginning February 1996. Analysis of the strains revealed that a unique serotype, O3:K6, not previously isolated during the surveillance in Calcutta accounted for 50 to 80% of the infections in the following months. After this report, O3:K6 isolates identical to those isolated in Calcutta were reported from food-borne outbreaks and from sporadic cases in Bangladesh, Chile, France, Japan, Korea, Laos, Mozambique, Peru, Russia, Spain, Taiwan, Thailand, and the United States. Other serotypes, such as O4:K68, O1:K25, and O1:KUT (untypeable), that had molecular characteristics identical to that of the O3:K6 serotype were subsequently documented. These serotypes appeared to have diverged from the O3:K6 serotype by alteration of the O:K antigens and were defined as "serovariants" of the O3:K6 isolate. O3:K6 and its serovariants have now spread into Asia, America, Africa, and Europe. This review traces the genesis, virulence features, molecular characteristics, serotype variants, environmental occurrence, and global spread of this unique clone of V. parahaemolyticus.

Vibrio parahaemolyticus: a concern of seafood safety

Vibrio parahaemolyticus is a human pathogen that is widely distributed in the marine environments. This organism is frequently isolated from a variety of raw seafoods, particularly shellfish. Consumption of raw or undercooked seafood contaminated with V. parahaemolyticus may lead to development of acute gastroenteritis characterized by diarrhea, headache, vomiting, nausea, and abdominal cramps. This pathogen is a common cause of foodborne illnesses in many Asian countries, including China, Japan and Taiwan, and is recognized as the leading cause of human gastroenteritis associated with seafood consumption in the United States. This review gives an overview of V. parahaemolyticus food poisoning and provides information on recent development in methods for detecting V. parahaemolyticus and strategies for reducing risk of V. parahaemolyticus infections associated with seafood consumption.

Pore formation of thermostable direct hemolysin secreted from Vibrio parahaemolyticus in lipid bilayers

Vibrio parahaemolyticus secretes thermostable direct hemolysin (TDH), a major virulence factor. Earlier studies report that TDH is a pore-forming toxin. However, the characteristics of pores formed by TDH in the lipid bilayer, which is permeable to small ions, remain to be elucidated. Ion channel-like activities were observed in lipid bilayers containing TDH. Three types of conductance were identified. All the channels displayed relatively low ion selectivity, and similar ion permeability. The Cl- channel inhibitors, DIDS, glybenclamide, and NPPB, did not affect the channel activity of pores formed by TDH. R7, a mutant toxin of TDH, also forms pores with channel-like activity in lipid bilayers. The ion permeability of these channels is similar to that of TDH. R7 binds cultured cells and liposomes to a lower extent, compared to TDH. R7 does not display significant hemolytic activity and cell cytotoxicity, possibly owing to the difficulty of insertion into lipid membranes. Once R7 is assembled within lipid membranes, it may assume the same structure as TDH. The authors propose that the single glycine at position 62, substituted with serine in the R7 mutant toxin, plays an important role in TDH insertion into the lipid bilayer.

Inhibition of Vibrio parahaemolyticus by a bacteriocin-like inhibitory substance (BLIS) produced by Vibrio mediterranei 1

AIMS

The aim of this research was to identify and partially purify new bacteriocin-like substances from strains of halophilic 'non-cholera' vibrios isolated from food sources.

METHODS AND RESULTS

Forty-five halophilic Vibrio spp. strains were screened for antimicrobial production. Vibrio mediterranei 1, a nonpathogenic strain, showed antimicrobial activity towards Vibrio parahaemolyticus spp. and related species. The bacteriocin-like inhibitory substance (BLIS), released by the bacteria into growth media, was concentrated by ultrafiltration and characterized. BLIS was sensitive to proteinase K, was stable in the pH range 5-9, was resistant to organic solvents and was heat stable up to 75 degrees C. Initial purification of BLIS by size exclusion chromatography showed an apparent molecular mass of 63-65 kDa.

CONCLUSIONS

This study reports the ability of V. mediterranei 1 to produce a bacteriocin-like substance inhibiting growth of V. parahaemolyticus spp. and other closely related bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

The strong activity of BLIS towards the human and fish pathogen V. parahaemolyticus and the persistence of antimicrobial properties under a variety of different conditions suggest its potential application in food microbiology.

Three new regulators of swarming in Vibrio parahaemolyticus

Movement on surfaces, or swarming motility, is effectively mediated by the lateral flagellar (laf) system in Vibrio parahaemolyticus. Expression of laf is induced by conditions inhibiting rotation of the polar flagellum, which is used for swimming in liquid. However, not all V. parahaemolyticus isolates swarm proficiently. The organism undergoes phase variation between opaque (OP) and translucent (TR) cell types. The OP cell produces copious capsular polysaccharide and swarms poorly, whereas the TR type produces minimal capsule and swarms readily. OP<-->TR switching is often the result of genetic alterations in the opaR locus. Previously, OpaR, a Vibrio harveyi LuxR homolog, was shown to activate expression of the cpsA locus, encoding capsular polysaccharide biosynthetic genes. Here, we show that OpaR also regulates swarming by repressing laf gene expression. However, in the absence of OpaR, the swarming phenotype remains tightly surface regulated. To further investigate the genetic controls governing swarming, transposon mutagenesis of a TR (DeltaopaR1) strain was performed, and SwrT, a TetR-type regulator, was identified. Loss of swrT, a homolog of V. harveyi luxT, created a profound defect in swarming. This defect could be rescued upon isolation of suppressor mutations that restored swarming. One class of suppressors mapped in swrZ, encoding a GntR-type transcriptional regulator. Overexpression of swrZ repressed laf expression. Using reporter fusions and quantitative reverse transcription-PCR, SwrT was demonstrated to repress swrZ transcription. Thus, we have identified the regulatory link that inhibits swarming of OP strains and have begun to elucidate a regulatory circuit that modulates swarming in TR strains.

Vibrio parahaemolyticus in shellfish and clinical samples during two large epidemics of diarrhoea in southern Chile

Large epidemics of diarrhoea associated with seafood consumption and Vibrio parahaemolyticus occurred during the austral summers of 2004 and 2005 in the environs of Puerto Montt, Chile (41 degrees 29'S 72 degrees 24'W). There are no reports of V. parahaemolyticus infections before 2004 in this region, their absence being explained by the low ocean temperatures which seldom reach 16 degrees C. We analysed V. parahaemolyticus obtained from shellfish and clinical samples during epidemics. Isolates were examined using conventional protocols and an improved method for restriction enzyme analysis using total bacterial DNA which permits direct genome restriction enzyme analysis by conventional gel electrophoresis (DGREA) with a similar discrimination index as restriction fragment length polymorphism-pulsed field gel electrophoresis (RFLP-PFGE). Analysis of clinical samples showed that the epidemics were caused by the V. parahaemolyticus O3:K6 pandemic clonal group. On the other hand, analysis of shellfish samples during both epidemics showed that 53% contained V. parahaemolyticus (3-93 g(-1)). Detailed analysis of 50 positive shellfish samples showed that only three contained detectable levels of the pandemic clone. Most V. parahaemolyticus isolates obtained from shellfish corresponded to non-pandemic clones differentiated into 14 groups by DGREA. In summary, the causative agent during epidemics was only a minor component of a small but diverse population of V. parahaemolyticus in shellfish.

Biochemical fingerprinting of Vibrio parahaemolyticus by the PhenePlate system: comparison between pandemic and non-pandemic serotypes

During recent years a pandemic clone of Vibrio parahaemolyticus has emerged. Isolates of this clone are distributed among several serotypes, but are genotypically related. In the present study, a phenotyping method (biochemical fingerprinting) was used to characterize pandemic and non-pandemic isolates belonging to V. parahaemolyticus. It was found that the pandemic isolates showed a high level of phenotypic homogeneity and a majority of the pandemic isolates belonged to the same biochemical phenotype, whereas non-pandemic V. parahemolyticus isolates were more heterogeneous. In conclusion, biochemical fingerprinting of V. parahaemolyticus can be used as a first screening method to differentiate between pandemic and non-pandemic isolates of V. parahaemolyticus.

Differences in the API 20E biochemical patterns of clinical and environmentalVibrio parahaemolyticusisolates

Genetic differences in clinical and environmental strains of Vibrio parahaemolyticus have been widely used as criteria in identifying pathogenic isolates. However, few studies have been carried out to assess the differences in biochemical characteristics of V. parahaemolyticus isolates from human and environmental sources. We compared the biochemical profiles obtained by the characterization of V. parahaemolyticus isolates from human infections and the marine environment using the API 20E system. Environmental and clinical isolates showed significant differences in the gelatin and arabinose tests. Additionally, clinical isolates were correctly identified according to the API 20E profile using 0.85% NaCl diluent, but they presented nonspecific profiles with 2% NaCl diluent. In contrast, use of 2% NaCl diluent facilitated correct identification of the environmental isolates. Clinical isolates showed significant differences in up to five biochemical tests with respect to the API 20E database. The API 20E system is widely used in routine identification of bacteria in clinical laboratories, and this discrepancy in an important number of biochemical tests may lead to misidentification of V. parahaemolyticus infection.

Isolation and molecular characterization of toxigenic Vibrio parahaemolyticus from the Kii Channel, Japan

Studies were conducted on the ecology of potentially pathogenic Vibrio parahaemolyticus in three coastal areas of Kii Channel, Tokushima, Japan. Seawater and seaweed samples were collected seasonally between June 2003 and May 2004. Total and toxigenic strains of V. parahaemolyticus were isolated using most probable number culture and colony blot hybridization. Toxigenic strains were serotyped and further characterized by random amplified polymorphic DNA (RAPD) and ribotyping. Six thousand strains of V. parahaemolyticus were isolated and 18 were found positive for tdh. V. parahaemolyticus were detected in all samples during summer and autumn, and from some samples during winter and spring. Among the toxigenic strains seven serotypes, five ribotypes and RAPD patterns were observed. Seven strains belonged to O3:K6 clone with identical ribotypes and RAPD patterns to that of a pandemic reference strain. The presence of toxigenic V. parahaemolyticus with pandemic potential might indicate a human health risk due to consumption of marine food sources.

Outbreak of Vibrio parahaemolyticus gastroenteritis associated with Alaskan oysters

BACKGROUND

Vibrio parahaemolyticus, the leading cause of seafood-associated gastroenteritis in the United States, typically is associated with the consumption of raw oysters gathered from warm-water estuaries. We describe a recognized outbreak of V. parahaemolyticus infection associated with the consumption of seafood from Alaska.

METHODS

After we received reports of the occurrence of gastroenteritis on a cruise ship, we conducted a retrospective cohort study among passengers, as well as active surveillance throughout Alaska to identify additional cases, and an environmental study to identify sources of V. parahaemolyticus and contributors to the outbreak.

RESULTS

Of 189 passengers, 132 (70 percent) were interviewed; 22 of the interviewees (17 percent) met our case definition of gastroenteritis. In our multiple logistic-regression analysis, consumption of raw oysters was the only significant predictor of illness; the attack rate among people who consumed oysters was 29 percent. Active surveillance identified a total of 62 patients with gastroenteritis. V. parahaemolyticus serotype O6:K18 was isolated from the majority of patients tested and from environmental samples of oysters. Patterns on pulsed-field gel electrophoresis were highly related across clinical and oyster isolates. All oysters associated with the outbreak were harvested when mean daily water temperatures exceeded 15.0 degrees C (the theorized threshold for the risk of V. parahaemolyticus illness from the consumption of raw oysters). Since 1997, mean water temperatures in July and August at the implicated oyster farm increased 0.21 degrees C per year (P<0.001 by linear regression); 2004 was the only year during which mean daily temperatures in July and August at the shellfish farm did not drop below 15.0 degrees C.

CONCLUSIONS

This investigation extends by 1000 km the northernmost documented source of oysters that caused illness due to V. parahaemolyticus. Rising temperatures of ocean water seem to have contributed to one of the largest known outbreaks of V. parahaemolyticus in the United States.

Seasonal variation in abundance of total and pathogenic Vibrio parahaemolyticus bacteria in oysters along the southwest coast of India

The seasonal abundance of Vibrio parahaemolyticus in oysters from two estuaries along the southwest coast of India was studied by colony hybridization using nonradioactive labeled oligonucleotide probes. The density of total V. parahaemolyticus bacteria was determined using a probe binding to the tlh (thermolabile hemolysin) gene, and the density of pathogenic V. parahaemolyticus bacteria was determined by using a probe binding to the tdh (thermostable direct hemolysin) gene. Furthermore, the prevalence of V. parahaemolyticus was studied by PCR amplification of the toxR, tdh, and trh genes. PCR was performed directly with oyster homogenates and also following enrichment in alkaline peptone water for 6 and 18 h. V. parahaemolyticus was detected in 93.87% of the samples, and the densities ranged from <10 to 10(4) organisms per g. Pathogenic V. parahaemolyticus could be detected in 5 of 49 samples (10.2%) by colony hybridization using the tdh probe and in 3 of 49 samples (6.1%) by PCR. Isolates from one of the samples belonged to the pandemic serotype O3:K6. Twenty-nine of the 49 samples analyzed (59.3%) were positive as determined by PCR for the presence of the trh gene in the enrichment broth media. trh-positive V. parahaemolyticus was frequently found in oysters from India.

Identification of an iron-regulated hemin-binding outer membrane protein, HupO, in Vibrio fluvialis: effects on hemolytic activity and the oxidative stress response

In pathogenic bacteria, iron acquisition is important for colonization and proliferation in the host under iron-limited conditions. The ability of Vibrio spp. to acquire iron is often critical to their virulence, causing gastroenteritis or excessive watery diarrhea in humans. In the study described here, we cloned the 2,100-bp heme utilization protein gene hupO in Vibrio fluvialis. HupO had high homology to iron-regulated outer membrane receptor proteins in Vibrio sp. and contained motifs that are common to bacterial heme receptors, including a consensus TonB box, a FRAP domain, and an NPNL domain. To characterize the hemin-binding activity of HupO, we purified the recombinant HupO protein (rHupO) from Escherichia coli by using an overexpression system. HupO was found to bind to hemin but not to hemoglobin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting demonstrated that the 77-kDa outer membrane protein HupO of V. fluvialis was induced under iron-restricted conditions. We constructed a hupO mutant, HP1, to investigate the biochemical function of HupO in V. fluvialis. The hemolytic activity of HP1 was reduced compared to that of wild-type cells and, when exposed to hydrogen peroxide, significantly lower numbers of HP1 survived than was the case in the wild type. These results suggest that HupO is associated with virulence expression in V. fluvialis through stimulation of hemolysin production and resistance to oxidative stress. In experimentally infected mice, the 50% lethal dose value of the wild-type was lower than that of the mutant, HP1.

Serologic and molecular characterization of Vibrio parahaemolyticus strains isolated from seawater and fish products of the Gulf of Mexico

The thermostable direct hemolysin (TDH) and TDH-related hemolysin (TRH) are the main virulence factors of Vibrio parahaemolyticus. We isolated V. parahaemolyticus from seawater, fish, and oysters obtained from the Pueblo Viejo Lagoon in Veracruz, determined the serogroups, phenotypically and genotypically characterized TDH and TRH, and investigated the presence of the toxR gene. A total of 46 V. parahaemolyticus strains were isolated, and all of them amplified the 368-bp toxR gene fragment. The trh gene was not identified in any of the strains; 4 of the 46 strains were Kanagawa phenomenon (KP) positive and amplified the 251-bp tdh gene fragment. The most frequent serogroup was serogroup O3. This is the first report of the presence of KP-positive tdh-positive environmental V. parahaemolyticus strains in Mexico.

Characterization of pathogenic Vibrio parahaemolyticus isolates from clinical sources in Spain and comparison with Asian and North American pandemic isolates

In spite of the potential risk involved with contamination of seafood with Vibrio parahaemolyticus, there is a lack of information on the occurrence of pathogenic V. parahaemolyticus in Europe. This organism was isolated in 1999 from a large outbreak (64 cases admitted to a single hospital) associated with raw oyster consumption in Galicia, Spain, one of the most important regions in shellfish production worldwide. Two V. parahaemolyticus isolates from the 1999 Galicia outbreak, three additional clinical isolates obtained in the same period from hospitals in Spain, two reference strains from clinical sources, and five Spanish environmental isolates were examined. Seventeen isolates belonging to the pandemic clone isolated in Asia and North America were included in the study for comparison. All isolates were characterized by serotyping, PCR for virulence-related genes, pulsed-field gel electrophoresis (PFGE), and plasmid analysis. Four of the five clinical isolates from hospitals in Spain belonged to serotype O4:K11; the remaining isolate was O4:K untypeable (KUT). All five isolates were positive for V. parahaemolyticus toxR and tlh (species-specific genes) and tdh and negative for trh and group-specific PCR (a PCR method for detection of the pandemic clone). PFGE analysis with NotI and SfiI discriminated the European isolates in two closely related PFGE types included in a homogeneous cluster, clearly differentiated from the Asian and North American isolates. The five environmental isolates belonged to serotypes O2:K28, O2:KUT, O3:K53, O4:KUT, and O8:K22 and were negative for all virulence genes. The five isolates were discriminated into five different PFGE types unrelated to any other isolate included in the study. While the virulence characteristics (tdh positive, trh negative) of the Spanish clinical isolates matched those of the O3:K6 clone from Asia and North America, they were clearly excluded from this clone by group-specific PCR, PFGE, and serotyping. The results of this study suggest that a unique and specific clone could be related to the V. parahaemolyticus infections in Europe.

Biodiversity of vibrios

Vibrios are ubiquitous and abundant in the aquatic environment. A high abundance of vibrios is also detected in tissues and/or organs of various marine algae and animals, e.g., abalones, bivalves, corals, fish, shrimp, sponges, squid, and zooplankton. Vibrios harbour a wealth of diverse genomes as revealed by different genomic techniques including amplified fragment length polymorphism, multilocus sequence typing, repetetive extragenic palindrome PCR, ribotyping, and whole-genome sequencing. The 74 species of this group are distributed among four different families, i.e., Enterovibrionaceae, Photobacteriaceae, Salinivibrionaceae, and Vibrionaceae. Two new genera, i.e., Enterovibrio norvegicus and Grimontia hollisae, and 20 novel species, i.e., Enterovibrio coralii, Photobacterium eurosenbergii, V. brasiliensis, V. chagasii, V. coralliillyticus, V. crassostreae, V. fortis, V. gallicus, V. hepatarius, V. hispanicus, V. kanaloaei, V. neonatus, V. neptunius, V. pomeroyi, V. pacinii, V. rotiferianus, V. superstes, V. tasmaniensis, V. ezurae, and V. xuii, have been described in the last few years. Comparative genome analyses have already revealed a variety of genomic events, including mutations, chromosomal rearrangements, loss of genes by decay or deletion, and gene acquisitions through duplication or horizontal transfer (e.g., in the acquisition of bacteriophages, pathogenicity islands, and super-integrons), that are probably important driving forces in the evolution and speciation of vibrios. Whole-genome sequencing and comparative genomics through the application of, e.g., microarrays will facilitate the investigation of the gene repertoire at the species level. Based on such new genomic information, the taxonomy and the species concept for vibrios will be reviewed in the next years.

Bacteriological examination of ballast water in Singapore Harbour by flow cytometry with FISH

In this study the concentrations of total bacteria, enterobacteria, Vibrio spp., and E. coli have been compared for ballast water samples taken from ships in Singapore Harbour. The cell concentrations were enumerated using FISH and flow cytometry. The data were highly variable, reflecting the many influences upon ballast water as it is utilized in the shipping industry. The concentration of bacterial species was determined as a proportion of the total concentration of cells for the ballast water sampled. For the ballast water sampled these concentrations were 0.67-39.55% for eubacteria, 0-2.46% for enterobacteria, 0.18-35.82% for Vibrio spp., and 0-2.46% for E. coli. Using FISH and flow cytometry, an informative determination of the bacterial hazards of ship ballast water can be made.

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.

Dual flagellar systems enable motility under different circumstances

Flagella are extremely effective organelles of locomotion used by a variety of bacteria and archaea. Some bacteria, including Aeromonas, Azospirillum, Rhodospirillum, and Vibrio species, possess dual flagellar systems that are suited for movement under different circumstances. Swimming in liquid is promoted by a single polar flagellum. Swarming over surfaces or in viscous environments is enabled by the production of numerous peritrichous, or lateral, flagella. The polar flagellum is produced continuously, while the lateral flagella are produced under conditions that disable polar flagellar function. Thus at times, two types of flagellar organelles are assembled simultaneously. This review focuses on the polar and lateral flagellar systems of Vibrio parahaemolyticus. Approximately 50 polar and 40 lateral flagellar genes have been identified encoding distinct structural, motor, export/assembly, and regulatory elements. The sodium motive force drives polar flagellar rotation, and the proton motive force powers lateral translocation. Polar genes are found exclusively on the large chromosome, and lateral genes reside entirely on the small chromosome of the organism. The timing of gene expression corresponds to the temporal demand for components during assembly of the organelle: RpoN and lateral- and polar-specific sigma(54)-dependent transcription factors control early/intermediate gene transcription; lateral- and polar-specific sigma(28) factors direct late flagellar gene expression. Although a different gene set encodes each flagellar system, the constituents of a central navigation system (i.e., chemotaxis signal transduction) are shared.

Induction of viable but nonculturable state in Vibrio parahaemolyticus and its susceptibility to environmental stresses

AIMS

This work analysed factors that influence the induction of viable but nonculturable (VBNC) state in the common enteric pathogen, Vibrio parahaemolyticus. The susceptibility of the VBNC cells to environmental stresses was investigated.

METHODS AND RESULTS

Bacterium was cultured in tryptic soy broth-3% NaCl medium, shifted to a nutrient-free Morita mineral salt-0.5% NaCl medium (pH 7.8) and further incubated at 4 degrees C in a static state to induce the VBNC state in 28-35 days. The culturability and viability of the cells were monitored by the plate count method and the Bac Light viable count method, respectively. Cells grown at the optimum growth temperature and in the exponential phase better induced the VBNC state than those grown at low temperature and in the stationary phase. Low salinity of the medium crucially and markedly shortened the induction period. The VBNC cells were highly resistant to thermal (42, 47 degrees C), low salinity (0% NaCl), or acid (pH 4.0) inactivation.

CONCLUSIONS

Optimal conditions for inducing VBNC V. parahaemolyticus were reported. The increase in resistance of VBNC V. parahaemolyticus to thermal, low salinity and acidic inactivation verified that this state is entered as part of a survival strategy in an adverse environment.

SIGNIFICANCE AND IMPACT OF THE STUDY

The methods for inducing VBNC V. parahaemolyticus in a markedly short time will facilitate further physiological and pathological study. The enhanced stress resistance of the VBNC cells should attract attention to the increased risk presented by this pathogen in food.

Real-time PCR detection of the thermostable direct hemolysin and thermolabile hemolysin genes in a Vibrio parahaemolyticus cultured from mussels and mussel homogenate associated with a foodborne outbreak

Molecular methods have become vital epidemiological tools in the detection and characterization of bacteria associated with a foodborne outbreak. We used both culture and real-time PCR to detect a Vibrio parahaemolyticus isolate associated with a foodborne outbreak. The outbreak occurred in July 2002 in Polk County, Florida, and originated at a Chinese buffet, with one person being hospitalized. The hospital isolated V. parahaemolyticus from the patient but destroyed the sample after diagnosis. From an onsite visit of the restaurant, food samples that possibly contributed to the outbreak were collected and sent to the Florida Department of Health, Tampa Branch Laboratory. Crab legs, crabsticks, and mussel samples were homogenized and incubated according to the Food and Drug Administration Bacteriological Analytical Manual culture protocol. Three sets of primers and a TaqMan probe were designed to target the tdh, trh, and tlh genes and used for real-time PCR. This study was successful in isolating V. parahaemolyticus from a mussel sample and detecting two of its genes (tdh and tlh) in food and pure culture by real-time PCR.

Molecular, serological, and virulence characteristics of Vibrio parahaemolyticus isolated from environmental, food, and clinical sources in North America and Asia

Potential virulence attributes, serotypes, and ribotypes were determined for 178 pathogenic Vibrio parahaemolyticus isolates from clinical, environmental, and food sources on the Pacific, Atlantic, and Gulf Coasts of the United States and from clinical sources in Asia. The food and environmental isolates were generally from oysters, and they were defined as being pathogenic by using DNA probes to detect the presence of the thermostable direct hemolysin (tdh) gene. The clinical isolates from the United States were generally associated with oyster consumption, and most were obtained from outbreaks in Washington, Texas, and New York. Multiplex PCR was used to confirm the species identification and the presence of tdh and to test for the tdh-related hemolysin trh. Most of the environmental, food, and clinical isolates from the United States were positive for tdh, trh, and urease production. Outbreak-associated isolates from Texas, New York, and Asia were predominantly serotype O3:K6 and possessed only tdh. A total of 27 serotypes and 28 ribogroups were identified among the isolates, but the patterns of strain distribution differed between the serotypes and ribogroups. All but one of the O3:K6 isolates from Texas were in a different ribogroup from the O3:K6 isolates from New York or Asia. The O3:K6 serotype was not detected in any of the environmental and food isolates from the United States, and none of the food or environmental isolates belonged to any of the three ribogroups that contained all of the O3:K6 and related clinical isolates. The combination of serotyping and ribotyping showed that the Pacific Coast V. parahaemolyticus population appeared to be distinct from that of either the Atlantic Coast or Gulf Coast. The fact that certain serotypes and ribotypes contained both clinical and environmental isolates while many others contained only environmental isolates implies that certain serotypes or ribotypes are more relevant for human disease.

Vibrio parahaemolyticus infectious for both humans and edible mollusk abalone

The aims of this study are to report evidence of the first laboratory-acquired infection of Vibrio parahaemolyticus associated with handling experimentally infected abalones and to describe the virulence of the two bacterial strains tested in these animals. Two strains of V. parahaemolyticus, one from the stool of a patient with acute gastroenteritis (strain 880713) and the other from the hemolymph of a diseased small abalone Haliotis diversicolor supertexta (strain 880915), were identified and characterized. Both strains were lethal to small abalone, with similar LD(50) values (8.36-8.41 x 10(4) colony-forming units/g abalone). Laboratory-acquired infection resulted in one individual experiencing two episodes of acute gastroenteritis due to handling virulence tests during a 1-week interval. Our present results suggest that a V. parahaemolyticus strain isolated from the stool of a patient with gastroenteritis was infectious for small abalone, a major species of edible mollusk abalone cultured in Taiwan, while a similar strain isolated from hemolymph of a diseased small abalone was infectious for humans. This is the first report of V. parahaemolyticus virulent to small abalone as a zoonotic pathogen.

Genome sequence of Vibrio parahaemolyticus: a pathogenic mechanism distinct from that of V cholerae

BACKGROUND

Vibrio parahaemolyticus, a gram-negative marine bacterium, is a worldwide cause of food-borne gastroenteritis. V parahaemolyticus strains of a few specific serotypes, probably derived from a common clonal ancestor, have lately caused a pandemic of gastroenteritis. The organism is phylogenetically close to V cholerae, the causative agent of cholera.

METHODS

The whole genome sequence of a clinical V parahaemolyticus strain RIMD2210633 was established by shotgun sequencing. The coding sequences were identified by use of Gambler and Glimmer programs. Comparative analysis with the V cholerae genome was undertaken with MUMmer.

FINDINGS

The genome consisted of two circular chromosomes of 3288558 bp and 1877212 bp; it contained 4832 genes. Comparison of the V parahaemolyticus genome with that of V cholerae showed many rearrangements within and between the two chromosomes. Genes for the type III secretion system (TTSS) were identified in the genome of V parahaemolyticus; V cholerae does not have these genes.

INTERPRETATION

The TTSS is a central virulence factor of diarrhoea-causing bacteria such as shigella, salmonella, and enteropathogenic Escherichia coli, which cause gastroenteritis by invading or intimately interacting with intestinal epithelial cells. Our results suggest that V parahaemolyticus and V cholerae use distinct mechanisms to establish infection. This finding explains clinical features of V parahaemolyticus infections, which commonly include inflammatory diarrhoea and in some cases systemic manifestations such as septicaemia, distinct from those of V cholerae infections, which are generally associated with non-inflammatory diarrhoea.

Filamentous bacteriophages of vibrios are integrated into the dif-like site of the host chromosome

The dif site is located in the replication terminus region of bacterial chromosomes, having a function of resolving dimeric chromosomes formed during replication. We demonstrate that filamentous bacteriophages of vibrios, such as f237 (Vibrio parahaemolyticus) and CTXphi (V. cholerae), are integrated into the dif-like site of host chromosome.