The thermostable direct hemolysin gene (tdh) of Vibrio hollisae is dissimilar in prevalence to and phylogenetically distant from the tdh genes of other vibrios: implications in the horizontal transfer of the tdh gene

Public health aspects of Vibrio spp. related to the consumption of seafood in the EU

Vibrio parahaemolyticus, Vibrio vulnificus and non-O1/non-O139 Vibrio cholerae are the Vibrio spp. of highest relevance for public health in the EU through seafood consumption. Infection with V. parahaemolyticus is associated with the haemolysins thermostable direct haemolysin (TDH) and TDH-related haemolysin (TRH) and mainly leads to acute gastroenteritis. V. vulnificus infections can lead to sepsis and death in susceptible individuals. V. cholerae non-O1/non-O139 can cause mild gastroenteritis or lead to severe infections, including sepsis, in susceptible individuals. The pooled prevalence estimate in seafood is 19.6% (95% CI 13.7-27.4), 6.1% (95% CI 3.0-11.8) and 4.1% (95% CI 2.4-6.9) for V. parahaemolyticus, V. vulnificus and non-choleragenic V. cholerae, respectively. Approximately one out of five V. parahaemolyticus-positive samples contain pathogenic strains. A large spectrum of antimicrobial resistances, some of which are intrinsic, has been found in vibrios isolated from seafood or food-borne infections in Europe. Genes conferring resistance to medically important antimicrobials and associated with mobile genetic elements are increasingly detected in vibrios. Temperature and salinity are the most relevant drivers for Vibrio abundance in the aquatic environment. It is anticipated that the occurrence and levels of the relevant Vibrio spp. in seafood will increase in response to coastal warming and extreme weather events, especially in low-salinity/brackish waters. While some measures, like high-pressure processing, irradiation or depuration reduce the levels of Vibrio spp. in seafood, maintaining the cold chain is important to prevent their growth. Available risk assessments addressed V. parahaemolyticus in various types of seafood and V. vulnificus in raw oysters and octopus. A quantitative microbiological risk assessment relevant in an EU context would be V. parahaemolyticus in bivalve molluscs (oysters), evaluating the effect of mitigations, especially in a climate change scenario. Knowledge gaps related to Vibrio spp. in seafood and aquatic environments are identified and future research needs are prioritised.

Antimicrobial Drug-resistance Profile of Vibrio Parahaemolyticus isolated from Japanese Horse Mackerel (Trachurus Japonicus)

This study aimed at investigating antimicrobial resistance (AMR) profile of Vibrio parahaemolyticus (V. parahaemolyticus). The bacteria were isolated from wild-caught and farmed Japanese horse mackerel (Trachurus japonicus), and examined for the antimicrobial drug resistance. Furthermore, the serotype, and the genes of thermostable direct hemolysin (tdh) and cholera toxin transcriptional activator (toxR) of the isolates were investigated by using a serotype testing kit and PCR method. Eighty-eight and 126 V. parahaemolyticus strains were isolated from wild-caught and farmed Japanese horse mackerel, respectively. Ten and 18 distinct serotypes were detected from wild-caught and farmed Japanese horse mackerel. All strains were negative for tdh genes but positive for toxR genes. Resistances to ampicillin (ABP) and to both ABP and fosfomycin (FOM) were observed in 54 and 23 strains from the wild-caught fish, while those resistant strains from farm fish were 112 and 7 strains. Multidrug-resistance to three or four drugs including ABP was observed in one or two strains from the wild-caught fish.

These results strongly suggest that the environmental exposure of antimicrobial drugs results in the spread of resistant genes in Japanese horse mackerel. This study highlights the need for monitoring the spread of resistance genes to the human intestinal flora as well as to other bacteria in the environment.

Continuous Genomic Surveillance Monitored the In Vivo Evolutionary Trajectories of Vibrio parahaemolyticus and Identified a New Virulent Genotype

Our ability to predict evolutionary trajectories of pathogens is one of the promising leverages to fight against the pandemic disease, yet few studies have addressed this question in situ, due to the difficulty in monitoring the milestone evolutionary events for a given pathogen and in understanding the evolutionary strategies. In this study, we monitored the real-time evolution of Vibrio parahaemolyticus in response to successive antibiotic treatment in three shrimp farms in North China from 2011 to 2018 by whole-genome sequencing. Results showed that the stepwise emergence of resistance was associated with the antibiotic usage. Genomic analysis of resistant isolates showed that the acquisition of the resistant mobile genetic elements flanked by an insertion sequence (ISVal1) closely mirrored the antibiotics used in shrimp farms since 2014. Next, we also identified 50 insertion sites of ISVal1 in the chromosome, which facilitated the formation of pathogenicity islands (PAIs) and fitness islands in the following years. Further, horizontal transfers of a virulent trh-nik-ure genomic island (GI) and two GIs improving the fitness have been observed in two farms since 2016. In this case study, we proposed that the insertion sequence triggered four major evolutionary events during the outbreaks of shrimp disease in three farms, including horizontal transfer of transposon (HTT) (stage 1), the formation of resistance islands (stage 2) and the PAIs (stage 3), and horizontal transfer of the PAIs (stage 4). This study presented the first in vivo evolutionary trajectories for a given bacterial pathogen, which helps us to understand the emergence mechanisms of new genotypes.IMPORTANCE Most human infectious diseases originate from animals. Thus, how to reduce or prevent pandemic zoonoses before they emerge in people is becoming a critical issue. Continuous genomic surveillance of the evolutionary trajectories of potential human pathogens on farms is a promising strategy to realize early warning. Here, we conducted an 8-year surveillance of Vibrio parahaemolyticus in three shrimp farms. The results showed that the use of antibiotics and horizontal transfer of transposons (HTT) drove the evolution of V. parahaemolyticus, which could be divided into four stages: HTT, formation of resistance islands, formation of pathogenicity islands (PAIs), and horizontal transfer of PAIs. This study presented the first in vivo monitoring of evolutionary trajectories for a given bacterial pathogen, providing valuable information for the prevention of pandemic zoonoses.

Rapid subtyping of pathogenic and nonpathogenic Vibrio parahaemolyticus by fourier transform infrared spectroscopy with chemometric analysis

Vibrio parahaemolyticus which naturally inhabits marine and estuarine environment represents pathogenic strains (virulence genes tdh or trh positive) and non-pathogenic strains (virulence genes negative). In this study, a rapid method for subtyping pathogenic and non-pathogenic V. parahaemolyticus was established using fourier transform infrared (FTIR) spectroscopy with chemometric analysis. This method targeted three strains of genotypes of V. parahaemolyticus including tdh positive, trh positive and virulence gene-negative (nonpathogenic) V. parahaemolyticus. The FTIR absorption spectra between 1800 and 900 cm^-1 highlighted the most distinctive variations and were the most useful for characterizing the three bacteria. The successful differentiation and identification of the three bacteria could be accomplished in less than 1 h by FTIR using principal component analysis (PCA), or another cluster model of hierarchical cluster analysis (HCA). The method was verified by analyzing spiked V. parahaemolyticus fish samples. Furthermore, all of ten clinical isolates of V. parahaemolyticus were identified as tdh-positive, none of the clinical isolates were trh-positive, and all of ten environmental isolates were identified as non-pathogenic by the subtyping method, which were confirmed by PCR assays. All data demonstrated that the newly established subtyping method by FTIR is practical, time-saving, labor-saving, specific and cost-effective, especially suitable for the basic laboratories of CDC and port quarantine departments to perform suiveillance and epidemiological traceability of pathogenic V. parahaemolyticus.

Detection and differentiation of Vibrio parahaemolyticus by multiplexed real-time PCR

Vibrio parahaemolyticus is a common and important pathogen that causes human gastroenteritis worldwide. A rapid, sensitive, and specific assay is urgently required for detection and differentiation of V. parahaemolyticus strains. We designed three sets of primers and probes using groEL and two virulence genes (tdh and trh) from V. parahaemolyticus, and developed a multiplex real-time PCR protocol. The sensitivity and specificity of the multiplex assay was evaluated by environmental and clinical specimens of V. parahaemolyticus. The multiplex PCR response system and annealing temperature were optimized. The detection limits of the multiplex real-time PCR were 10⁴ and 10⁵ CFU/mL (or CFU/g) in pure cultures and spiked oysters, respectively. The multiplex real-time PCR specifically detected and differentiated V. parahaemolyticus from 35 Vibrio strains and 11 other bacterial strains. Moreover, this method can detect and distinguish virulent from nonvirulent strains, with no cross-reactivity observed in the bacteria tested. This newly established multiplex real-time PCR assay offers rapid, specific, and reliable detection of the total and pathogenic V. parahaemolyticus strains, which is very useful during outbreaks and sporadic cases caused by V. parahaemolyticus infection.

Ecological fitness and virulence features of Vibrio parahaemolyticus in estuarine environments

Vibrio parahaemolyticus is a commonly encountered and highly successful organism in marine ecosystems. It is a fast-growing, extremely versatile copiotroph that is active over a very broad range of conditions. It frequently occurs suspended in the water column (often attached to particles or zooplankton), and is a proficient colonist of submerged surfaces. This organism is an important pathogen of animals ranging from microcrustaceans to humans and is a causative agent of seafood-associated food poisoning. This review examines specific ecological adaptations of V. parahaemolyticus, including its broad tolerances to temperature and salinity, its utilization of a wide variety of organic carbon and energy sources, and its pervasive colonization of suspended and stationary materials that contribute to its success and ubiquity in temperate and tropical estuarine ecosystems. Several virulence-related features are examined, in particular the thermostable direct hemolysin (TDH), the TDH-related hemolysin (TRH), and the type 3 secretion system, and the possible importance of these features in V. parahaemolyticus pathogenicity is explored. The impact of new and much more effective PCR primers on V. parahaemolyticus detection and our views of virulent strain abundance are also described. It is clear that strains carrying the canonical virulence genes are far more common than previously thought, which opens questions regarding the role of these genes in pathogenesis. It is also clear that virulence is an evolving feature of V. parahaemolyticus and that novel combinations of virulence factors can lead to emergent virulence in which a strain that is markedly more pathogenic evolves and propagates to produce an outbreak. The effects of global climate change on the frequency of epidemic disease, the geographic distribution of outbreaks, and the human impacts of V. parahaemolyticus are increasing and this review provides information on why this ubiquitous human pathogen has increased its footprint and its significance so dramatically.

Potential antitumor therapeutic application of Grimontia hollisae thermostable direct hemolysin mutants

We report on the preparation of a new type of immunotoxin by conjugation of an epidermal growth factor receptor (EGFR)-binding peptide and an R46E mutation of thermostable direct hemolysin from Grimontia hollisae, (Gh-TDH^R46E/EB). The hybrid immunotoxin was purified to homogeneity and showed a single band with slight slower mobility than that of Gh-TDH^R46E. Cytotoxicity assay of Gh-TDH^R46E/EB on EGFR highly, moderately, low, and non-expressed cells, A431, MDA-MB-231, HeLa, and HEK293 cells, respectively, showed apparent cytotoxicity on A431 and MDA-MB-231 cells but not on HeLa or HEK293 cells. In contrast, no cytotoxicity was observed for these cells treated with either Gh-TDH^R46E or EB alone, indicating enhanced cytotoxic efficacy of Gh-TDH^R46E by the EGFR binding moiety. Further antitumor activity assay of Gh-TDH^R46E/EB in a xenograft model of athymic nude mice showed obvious shrinkage of tumor size and degeneration, necrosis, and lesions of tumor tissues compared to the normal tissues. Therefore, the combination of Gh-TDH^R46E with target affinity agents opens new possibilities for pharmacological treatment of cancers and potentiates the anticancer drug's effect.

Occurrence of virulence genes among Vibrio cholerae and Vibrio parahaemolyticus strains from treated wastewaters

Pathogenic Vibrio species are an important cause of foodborne illnesses. The aim of this study was to describe the occurrence of potentially pathogenic Vibrio species in the final effluents of a wastewater treatment plant and the risk that they may pose to public health. During the 1-year monitoring, a total of 43 Vibrio strains were isolated: 23 Vibrio alginolyticus, 1 Vibrio cholerae, 4 Vibrio vulnificus, and 15 Vibrio parahaemolyticus. The PCR investigation of V. parahaemolyticus and V. cholerae virulence genes (tlh, trh, tdh, toxR, toxS, toxRS, toxT, zot, ctxAB, tcp, ace, vpi, nanH) revealed the presence of some of these genes in a significant number of strains. Intraspecies variability and genetic relationships among the environmental isolates were analyzed by random amplified polymorphic DNA-PCR (RAPD-PCR). We report the results of the first isolation and characterization of an environmental V. cholerae non-O1 non-O139 and of a toxigenic V. parahaemolyticus strain in Tunisia. We suggest that non-pathogenic Vibrio might represent a marine reservoir of virulence genes that can be transmitted between strains by horizontal transfer.

Genes similar to the Vibrio parahaemolyticus virulence-related genes tdh, tlh, and vscC2 occur in other vibrionaceae species isolated from a pristine estuary

Detection of the human pathogen Vibrio parahaemolyticus often relies on molecular biological analysis of species-specific virulence factor genes. These genes have been employed in determinations of V. parahaemolyticus population numbers and the prevalence of pathogenic V. parahaemolyticus strains. Strains of the Vibrionaceae species Photobacterium damselae, Vibrio diabolicus, Vibrio harveyi, and Vibrio natriegens, as well as strains similar to Vibrio tubiashii, were isolated from a pristine salt marsh estuary. These strains were examined for the V. parahaemolyticus hemolysin genes tdh, trh, and tlh and for the V. parahaemolyticus type III secretion system 2α gene vscC2 using established PCR primers and protocols. Virulence-related genes occurred at high frequencies in non-V. parahaemolyticus Vibrionaceae species. V. diabolicus was of particular interest, as several strains were recovered, and the large majority (>83%) contained virulence-related genes. It is clear that detection of these genes does not ensure correct identification of virulent V. parahaemolyticus. Further, the occurrence of V. parahaemolyticus-like virulence factors in other vibrios potentially complicates tracking of outbreaks of V. parahaemolyticus infections.

Multiplex PCR for the detection and differentiation of Vibrio parahaemolyticus strains using the groEL, tdh and trh genes

Vibrio parahaemolyticus is a significant cause of human gastrointestinal disorders worldwide, transmitted primarily by ingestion of raw or undercooked contaminated seafood. In this study, a multiplex PCR assay for the detection and differentiation of V. parahaemolyticus strains was developed using primer sets for a species-specific marker, groEL, and two virulence markers, tdh and trh. Multiplex PCR conditions were standardised, and extracted genomic DNA of 70 V. parahaemolyticus strains was used for identification. The sensitivity and efficacy of this method were validated using artificially inoculated shellfish and seawater. The expected sizes of amplicons were 510 bp, 382 bp, and 171 bp for groEL, tdh and trh, respectively. PCR products were sufficiently different in size, and the detection limits of the multiplex PCR for groEL, tdh and trh were each 200 pg DNA. Specific detection and differentiation of virulent from non-virulent strains in shellfish homogenates and seawater was also possible after artificial inoculation with various V. parahaemolyticus strains. This newly developed multiplex PCR is a rapid assay for detection and differentiation of pathogenic V. parahaemolyticus strains, and could be used to prevent disease outbreaks and protect public health by helping the seafood industry maintain a safe shellfish supply.

The thermostable direct hemolysin from Grimontia hollisae causes acute hepatotoxicity in vitro and in vivo

Background

G. hollisae thermostable direct hemolysin (Gh-TDH) is produced by most strains of G. hollisae. This toxin has been reported to be absorbed in the intestines in humans. Secondary liver injury might be caused by venous return of the toxin through the portal system. We aimed to firstly analyze the in vitro and in vivo hepatotoxicity of Gh-TDH.

Methods

Liver cells (primary human non-cancer cell and FL83B mouse cells) were treated and mice (BALB/c) were fed with this toxin to investigate its hepatotoxicity. Morphological examination and cytotoxicity assays using liver cells were also performed. Fluorescein isothiocyanate-conjugated toxin was used to analyze the localization of this protein in liver cells. Mice were subjected to liver function measurements and liver biopsies following toxin treatment and wild-type bacterial infection. PET (positron emission tomography)/CT (computed tomography) images were taken to assess liver metabolism during acute injury and recovery.

Results

The effect of hepatotoxicity was dose and time dependent. Cellular localization showed that the toxin was initially located around the cellular margins and subsequently entered the nucleus. Liver function measurements and liver biopsies of the mice following treatment with toxin or infection with wild-type Grimontia hollisae showed elevated levels of transaminases and damage to the periportal area, respectively. The PET/CT images revealed that the reconstruction of the liver continued for at least one week after exposure to a single dose of the toxin or bacterial infection.

Conclusions

The hepatotoxicity of Gh-TDH was firstly demonstrated. The damage was located in the periportal area of the liver, and the liver became functionally insufficient.

Cloning of a novel collagenase gene from the gram-negative bacterium Grimontia (Vibrio) hollisae 1706B and its efficient expression in Brevibacillus choshinensis

The collagenase gene was cloned from Grimontia (Vibrio) hollisae 1706B, and its complete nucleotide sequence was determined. Nucleotide sequencing showed that the open reading frame was 2,301 bp in length and encoded an 84-kDa protein of 767 amino acid residues. The deduced amino acid sequence contains a putative signal sequence and a zinc metalloprotease consensus sequence, the HEXXH motif. G. hollisae collagenase showed 60 and 59% amino acid sequence identities to Vibrio parahaemolyticus and Vibrio alginolyticus collagenase, respectively. In contrast, this enzyme showed < 20% sequence identity with Clostridium histolyticum collagenase. When the recombinant mature collagenase, which consisted of 680 amino acids with a calculated molecular mass of 74 kDa, was produced by the Brevibacillus expression system, a major gelatinolytic protein band of ~ 60 kDa was determined by zymographic analysis. This result suggested that cloned collagenase might undergo processing after secretion. Moreover, the purified recombinant enzyme was shown to possess a specific activity of 5,314 U/mg, an ~ 4-fold greater activity than that of C. histolyticum collagenase.

Site-directed mutations of thermostable direct hemolysin from Grimontia hollisae alter its arrhenius effect and biophysical properties

Recombinant thermostable direct hemolysin from Grimontia hollisae (Gh-rTDH) exhibits paradoxical Arrhenius effect, where the hemolytic activity is inactivated by heating at 60 °C but is reactivated by additional heating above 80 °C. This study investigated individual or collective mutational effect of Tyr53, Thr59, and Ser63 positions of Gh-rTDH on hemolytic activity, Arrhenius effect, and biophysical properties. In contrast to the Gh-rTDH wild-type (Gh-rTDH(WT)) protein, a 2-fold decrease of hemolytic activity and alteration of Arrhenius effect could be detected from the Gh-rTDH(Y53H/T59I) and Gh-rTDH(T59I/S63T) double-mutants and the Gh-rTDH(Y53H/T59I/S63T) triple-mutant. Differential scanning calorimetry results showed that the Arrhenius effect-loss and -retaining mutants consistently exhibited higher and lower endothermic transition temperatures, respectively, than that of the Gh-rTDH(WT). Circular dichroism measurements of Gh-rTDH(WT) and Gh-rTDH(mut) showed a conspicuous change from a β-sheet to α-helix structure around the endothermic transition temperature. Consistent with the observation is the conformational change of the proteins from native globular form into fibrillar form, as determined by Congo red experiments and transmission electron microscopy.

Antimicrobial resistance of Vibrio parahaemolyticus and Vibrio alginolyticus strains isolated from farmed fish in Korea from 2005 through 2007

The antimicrobial resistance patterns to 15 antimicrobial agents of Vibrio parahaemolyticus and Vibrio alginolyticus isolated from farmed fishes, including olive flounder (Paralichthys olivaceus), black rockfish (Sebastes schlegeli), red sea bream (Pagrus major), and sea bass (Lateolabrax japonicus), were investigated from 2005 through 2007. A total of 218 V. parahaemolyticus isolates and 153 V. alginolyticus isolates were obtained from the 180 fish samples collected from fish farms located along the southern coast of Korea. We found that 65.1% of V. parahaemolyticus and 85.6% of V. alginolyticus isolates showed antimicrobial resistance against more than one antimicrobial agent. The prevalence of resistance in V. parahaemolyticus isolates to ampicillin was highest (57.8%), followed by resistance to rifampin (11.9%), streptomycin (8.7%), and trimethoprim (6.4%). V. alginolyticus isolates were also most resistant to ampicillin (75.2%), followed by tetracycline (15.0%), trimethoprim (12.4%), and rifampin (9.8%). The prevalence of multiresistance to four or more antimicrobials was higher in V. alginolyticus (11.1%) than in V. parahaemolyticus (5%). Antimicrobial resistance rates per isolate of V. parahaemolyticus and V. alginolyticus possessing virulence genes were not different from those of the rest of the isolates.

Rugosity in Grimontia hollisae

Grimontia hollisae, formerly Vibrio hollisae, produces both smooth and rugose colonial variants. The rugose colony phenotype is characterized by wrinkled colonies producing copious amounts of exopolysaccharide. Cells from a rugose colony grown at 30 degrees C form rugose colonies, while the same cells grown at 37 degrees C form smooth colonies, which are characterized by a nonwrinkled, uncrannied appearance. Stress response studies revealed that after exposure to bleach for 30 min, rugose survivors outnumbered smooth survivors. Light scatter information obtained by flow cytometry indicated that rugose cells clumped into clusters of three or more cells (average, five cells) and formed two major clusters, while smooth cells formed only one cluster of single cells or doublets. Fluorescent lectin-binding flow cytometry studies revealed that the percentages of rugose cells that bound either wheat germ agglutinin (WGA) or Galanthus nivalis lectin (GNL) were greater than the percentages of smooth cells that bound the same lectins (WGA, 35% versus 3.5%; GNL, 67% versus 0.21%). These results indicate that the rugose exopolysaccharide consists partially of N-acetylglucosamine and mannose. Rugose colonies produced significantly more biofilm material than did smooth colonies, and rugose colonies grown at 30 degrees C produced more biofilm material than rugose colonies grown at 37 degrees C. Ultrastructurally, rugose colonies show regional cellular differentiation, with apical and lateral colonial regions containing cells embedded in a matrix stained by Alcian Blue. The cells touching the agar surface are packed tightly together in a palisade-like manner. The central region of the colony contains irregularly arranged, fluid-filled spaces and loosely packed chains or arrays of coccoid and vibrioid cells. Smooth colonies, in contrast, are flattened, composed of vibrioid cells, and lack distinct regional cellular differences. Results from suckling mouse studies showed that both orally fed rugose and smooth variants elicited significant, but similar, amounts of fluid accumulated in the stomach and intestines. These observations comprise the first report of expression and characterization of rugosity by G. hollisae and raise the possibility that expression of rugose exopolysaccharide in this organism is regulated at least in part by growth temperature.

Levels of Vibrio parahaemolyticus and thermostable direct hemolysin gene-positive organisms in retail seafood determined by the most probable number-polymerase chain reaction (MPN-PCR) method

The incidence and levels of Vibrio parahaemolyticus and thermostable direct hemolysin gene (tdh)-positive organisms in retail seafood were determined. The most probable number-polymerase chain reaction (MPN-PCR) method using a PCR procedure targeting the species-specific thermolabile hemolysin gene (tlh) and tdh was used to determine the levels of V. parahaemolyticus and tdh-positive organisms, respectively. In seafood for raw consumption, V. parahaemolyticus was found in four (13.3%) of 30 fish samples, 11 (55.0%) of 20 crustacean samples, and 29 (96.7%) of 30 mollusc samples. Levels of V. parahaemolyticus were below 10(4) MPN/100 g in all fish and crustacean samples tested. However, they were above 10(4) MPN/100 g in 11 (36.7%) of the 30 mollusc samples. In all seafood for raw consumption, the level of tdh-positive organisms was below the limit of detection (< 30 MPN/100 g). In seafood for cooking, V. parahaemolyticus was found in 15 (75.0%) of 20 fish samples, nine (45.0%) of 20 crustacean sample, and 20 (100%) of 20 mollusc samples. Levels of V. parahaemolyticus were above 10(4) MPN/100 g in only three (15.0%) and one (5.0%) of the 20 fish and 20 crustacean samples, respectively. However, they were above 10(4) MPN/100 g in 18 (90.0%) of the 20 mollusc samples. In seven (35.0%) of the 20 mollusc samples, tdh-positive organisms were found and their levels ranged from 3.6x10 to 1.1 x 103 MPN/100 g. From four of seven tdhpositive samples, tdh-positive V. parahaemolyticus was isolated.

Rapid phenotypic characterization of Vibrio isolates by pyrolysis metastable atom bombardment mass spectrometry

Pyrolysis mass spectrometry was investigated for rapid characterization of food-borne bacterial pathogens. Nine isolates of Vibrio parahaemolyticus and one isolate each of Vibrio fluvialis, Vibrio hollisae, and Vibrio vulnificus were analyzed. Pyrolysis mass spectra, generated via an alternative ionization method, metastable atom bombardment, were subject to principal component-discriminant analysis. The spectral patterns were used to distinguish Vibrio isolates differing in species, serotype and expression of the thermostable direct hemolysin gene. The patterns of similarity and dissimilarity amongst spectra in the Vibrio test set generally reflected those associated with species, serotype or hemolysin-producing genes, though the combined influence of these and other variables in the multi-dimensional data did not produce a simple clustering with respect to any one of these characteristics. These results suggested that with enough examples to model the most common combinations, the method should be able to characterize Vibrio isolates according to their phenotypic characteristics. Pyrolysis-mass spectrometry with metastable atom bombardment and pattern recognition appeared suitable for rapid infraspecific comparison of Vibrio isolates. This integrated analytical, pattern-recognition system should be examined further for potential utility in clinical and public health diagnostic contexts.

Epidemiology, pathogenesis, and prevention of foodborne Vibrio parahaemolyticus infections

Since its discovery about 50 years ago, Vibrio parahaemolyticus has been implicated as a major cause of foodborne illness around the globe. V. parahaemolyticus is a natural inhabitant of marine waters. Human infections are most commonly associated with the consumption of raw, undercooked or contaminated shellfish. A few individual V. parahaemolyticus virulence factors, including the thermostable direct hemolysin (TDH) and TDH-related hemolysin (TRH), have been investigated in depth, yet a comprehensive understanding of this organism's ability to cause disease remains unclear. Since 1996, serotype O3:K6 strains have been associated with an increased incidence of gastroenteritis in India and in Southeast Asia, and with large-scale foodborne outbreaks in the United States (US). In light of the emerging status of pathogenic V. parahaemolyticus, the US Food and Drug Administration conducted a microbial risk assessment to characterize the risk of contracting V. parahaemolyticus infections from consuming raw oysters. This review summarizes epidemiological findings, discusses recognized and putative V. parahaemolyticus virulence factors and pathogenicity mechanisms, and describes strategies for preventing V. parahaemolyticus infections.

Investigation of seven Vibrio virulence genes among Vibrio alginolyticus and Vibrio parahaemolyticus strains from the coastal mariculture systems in Guangdong, China

AIMS

To investigate the distribution of the virulence of two Vibrio species among different strains obtained from the mariculture systems on the coast of Guangdong in China and the correlation between the virulence strains and the virulence genes among Vibrio alginolyticus.

METHODS

Besides three strains, 72 V. alginolyticus strains and seven Vibrio parahaemolyticus strains were examined by PCR or semi-nested PCR for the virulence genes (tlh, trh, tdh, toxR, toxRS, ctxA, VPI). Additionally, the virulence of 18 V. alginolyticus strains was tested.

SIGNIFICANCE AND IMPACT OF THE STUDY

Virulence genes homologous to those in the V. parahaemolyticus and Vibrio cholerae are widely distributed among V. alginolyticus and V. parahaemolyticus in the coastal mariculture systems in Guangdong, China. Some of the V. alginolyticus strains are pathogenic to aquatic animals, and might have derived their virulence genes from V. parahaemolyticus or V. cholerae, representing a possible reservoir of these genes. However, there is no correlation between presence and absence of the virulence genes used to investigate V. alginolyticus and its virulent strains. In this report, we also show that tlh is distributed among V. alginolyticus.

Evaluation of nonisotopic DNA hybridization methods for detection of the tdh gene of vibrio parahaemolyticus

Production of the thermostable direct hemolysin (TDH) by Vibrio parahaemolyticus is associated with pathogenicity of the organism and is encoded by the tdh gene. The timely resolution of seafood-associated outbreaks requires rapid and accurate detection of pathogenic V. parahaemolyticus. The specificity of alkaline phosphatase- and digoxigenin-labeled tdh gene probes was evaluated against 61 strains of V. parahaemolyticus (including isolates from recent outbreaks involving oysters from the Pacific Northwest, Texas, and New York), 85 strains of other vibrios, and 7 strains of non-vibrio species from clinical and environmental sources. The probes were specific for detection of the V. parahaemolyticus tdh gene.

Analysis of gyrB and toxR gene sequences of Vibrio hollisae and development of gyrB- and toxR-targeted PCR methods for isolation of V. hollisae from the environment and its identification

Isolation of Vibrio hollisae strains, particularly from the environment, is rare. This may be due, in part, to the difficulty encountered when using conventional biochemical tests to identify the microorganism. In this study, we evaluated whether two particular genes may be useful for the identification of V. hollisae. The two genes are presumed to be conserved among the bacterial species (gyrB) or among the species of the genus Vibrio (toxR). A portion of the gyrB sequence of V. hollisae was cloned by PCR using a set of degenerate primers. The sequence showed 80% identity with the corresponding Vibrio parahaemolyticus gyrB sequence. The toxR gene of V. hollisae was cloned utilizing a htpG gene probe derived from the V. parahaemolyticus htpG gene, which is known to be linked to the toxR gene in V. hollisae. The coding sequence of the cloned V. hollisae toxR gene had 59% identity with the V. parahaemolyticus toxR coding sequence. The results of DNA colony hybridization tests using the DNA probes derived from the two genes of V. hollisae indicated that these gene sequences could be utilized for differentiation of V. hollisae from other Vibrio species and from microorganisms found in marine fish. PCR methods targeting the two gene sequences were established. Both PCR methods were shown to specifically detect the respective target sequences of V. hollisae but not other organisms. A strain of V. hollisae added at a concentration of 1 to 10(2) CFU/ml to alkaline peptone water containing a seafood sample could be detected by a 4-h enrichment incubation in alkaline peptone water at 37 degrees C followed by quick DNA extraction with an extraction kit and 35-cycle PCR specific for the V. hollisae toxR gene. We conclude that screening of seafood samples by this 35-cycle, V. hollisae toxR-specific PCR, followed by isolation on a differential medium and identification by the above htpG- and toxR-targeted PCR methods, can be useful for isolation from the environment and identification of V. hollisae.

Manifestation of the Kanagawa phenomenon, the virulence-associated phenotype, of Vibrio parahaemolyticus depends on a particular single base change in the promoter of the thermostable direct haemolysin gene

Thermostable direct haemolysin of Vibrio parahaemolyticus has been shown to be a major virulence factor. The Kanagawa phenomenon (KP), haemolysis induced by this haemolysin on a special blood agar medium, is strongly associated with clinical strains. We have been studying the expressions of various tdh genes encoding this haemolysin to elucidate the significance of the tdh genes possessed by KP-negative strains isolated from patients. We examined the importance of the promoter sequence variation for expression level of the tdh gene in this study. Only the tdh2 gene, one of the two tdh genes (tdh1 and tdh2) present in a KP-positive strain, was previously shown to be responsible for the haemolytic activity of the KP-positive strain. The tdh1- and tdh2-lacZ fusions were used to determine and analyse the promoter sequence by primer extension and site-directed mutagenesis methods. Two bases (positions -24 and -34) within the determined tdh2 promoter sequence were shown to be mostly responsible for the difference in the promoter strength between the tdh2 and tdh1 genes both in Escherichia coli and in V. parahaemolyticus backgrounds. Representative tdh promoters of KP-negative strains are close to the tdh2 promoter; they differ at position -34 but have the same base at position -24 as the tdh2 promoter. We demonstrated that base substitution of the tdh promoters of KP-negative strains only at position -34 is sufficient to increase the expression of these genes to the KP-positive level. Therefore, the tdh genes of KP-negative strains are considered to be potentially important because they can generate a KP-positive subclone by a point mutation in their promoters.

Analysis of the thermostable direct hemolysin (tdh) gene and the tdh-related hemolysin (trh) genes in urease-positive strains of Vibrio parahaemolyticus isolated on the West Coast of the United States

Urease-positive (Ure+) and urease-negative (Ure-) strains of Vibrio parahaemolyticus isolated from patients on the West Coast of the United States between 1979 and 1995 were analyzed for the thermostable direct hemolysin (tdh) gene and the tdh-related hemolysin (trh) genes (trh1 and trh2). The DNA colony hybridization method with the polynucleotide probes was used to determine the distribution of the genes. Of 60 Ure+ strains, 59 strains (98%) had the trh (either trh1 or trh2) gene and 54 strains (90%) carried the tdh gene. The absence of the trh gene or a related sequence in an exceptional Ure+ strain was confirmed by Southern blot analyses. The stronger correlation with the trh gene than with the tdh gene was mostly attributable to strains possessing only the trh2 gene. Of 25 Ure- strains, 20 strains (80%) had the tdh gene but none had the trh gene. These results indicate a very strong correlation between the Ure+ phenotype and the trh gene and are consistent with those reported for strains isolated in Asia. The Ure+ strains carrying the trh genes were not restricted to a unique group of the strains. The O4:K12 strains carrying the trh1 gene have predominantly been isolated since 1979. However, strains of various non-O4:K12 serovars carrying either the trh1 or the trh2 gene became predominant after 1992. In addition, analysis by the arbitrarily primed PCR method revealed two subgroups within the selected Ure+ O4:K12 strains. Hybridization tests with oligonucleotide probes demonstrated that the trh1 sequences of the West Coast strains differ to some extent from those of Asian strains. Nevertheless, a PCR method previously established to detect both the trh1 and the trh2 genes in Asian strains could detect 98% of those genes in the West Coast strains.