Detection of the thermostable direct hemolysin gene and related DNA sequences in Vibrio parahaemolyticus and other vibrio species by the DNA colony hybridization test

Prevalence, virulence characteristics, and antimicrobial resistance of Vibrio parahaemolyticus isolates from raw seafood in a province in Northern Thailand

Vibrio parahaemolyticus (V. parahaemolyticus) is commonly found in seawater and seafood products, but evidence is limited of its presence in seafood marketed in locations very distant from coastal sources. This study determined the prevalence and characterization of V. parahaemolyticus in seafood from markets in landlocked Phayao province, Northern Thailand. Among 120 samples, 26 (21.7%) were positive for V. parahaemolyticus, being highest in shrimp (43.3%), followed by shellfish (36.7%), and squid (6.7%), but was not found in fish. V. parahaemolyticus comprised 33 isolates that were non-pathogenic and non-pandemic. Almost all isolates from shrimp and shellfish samples were positive for T3SS1. Only five isolates (15.2%) showed two antimicrobial resistance patterns, namely, kanamycin-streptomycin (1) carrying sul2 and ampicillin-kanamycin-streptomycin (4) that carried tetA (2), tetA-sul2 (1), as well as one negative. Antimicrobial susceptible V. parahaemolyticus isolates possessing tetA (67.9%) and sul2 (3.5%) were also found. Six isolates positive for integron class 1 and/or class 2 were detected in 4 antimicrobial susceptible and 2 resistant isolates. While pathogenic V. parahaemolyticus was not detected, contamination of antimicrobial resistance V. parahaemolyticus in seafood in locations distant from coastal areas requires ongoing monitoring to improve food safety in the seafood supply chain.

Dynamics of efflux pumps in antimicrobial resistance, persistence, and community living of Vibrionaceae

The marine bacteria of the Vibrionaceae family are significant from the point of view of their role in the marine geochemical cycle, as well as symbionts and opportunistic pathogens of aquatic animals and humans. The well-known pathogens of this group, Vibrio cholerae, V. parahaemolyticus, and V. vulnificus, are responsible for significant morbidity and mortality associated with a range of infections from gastroenteritis to bacteremia acquired through the consumption of raw or undercooked seafood and exposure to seawater containing these pathogens. Although generally regarded as susceptible to commonly employed antibiotics, the antimicrobial resistance of Vibrio spp. has been on the rise in the last two decades, which has raised concern about future infections by these bacteria becoming increasingly challenging to treat. Diverse mechanisms of antimicrobial resistance have been discovered in pathogenic vibrios, the most important being the membrane efflux pumps, which contribute to antimicrobial resistance and their virulence, environmental fitness, and persistence through biofilm formation and quorum sensing. In this review, we discuss the evolution of antimicrobial resistance in pathogenic vibrios and some of the well-characterized efflux pumps' contributions to the physiology of antimicrobial resistance, host and environment survival, and their pathogenicity.

Multilocus Sequence Typing and Virulence Potential of Vibrio parahaemolyticus Strains Isolated from Aquatic Bird Feces

Vibrio parahaemolyticus is a Gram-negative, foodborne pathogenic bacterium that causes human gastroenteritis. This organism is ubiquitously present in the marine environment. Detection of V. parahaemolyticus in aquatic birds has been previously reported; however, the characterization of isolates of this bacterium recovered from these birds remains limited. The present study isolated and characterized V. parahaemolyticus from aquatic bird feces at the Bangpu Recreation Center (Samut Prakan province, Thailand) from 2016 to 2017, using multilocus sequence typing (MLST) and genome analysis. The results showed that V. parahaemolyticus was present in 34.9% (76/218) of the collected bird fecal samples. Among the ldh-positive V. parahaemolyticus isolates (n = 308), 1% (3/308) were positive for tdh, 1.3% (4/308) were positive for trh, and 0.3% (1/308) were positive for both tdh and trh. In turn, the MLST analysis revealed that 49 selected V. parahaemolyticus isolates resolved to 36 STs, 26 of which were novel (72.2%). Moreover, a total of 10 identified STs were identical to globally reported pathogenic strains (ST1309, ST1919, ST491, ST799, and ST2516) and environmental strains (ST1879, ST985, ST288, ST1925, and ST260). The genome analysis of isolates possessing tdh and/or trh (ST985, ST1923, ST1924, ST1929 and ST2516) demonstrated that the organization of the T3SS2α and T3SS2β genes in bird fecal isolates were almost identical to those of human clinical strains posing public health concerns of pathogen dissemination in the recreational area. The results of this study suggest that aquatic birds are natural reservoirs of new strains with high genetic diversity and are alternative sources of potentially pathogenic V. parahaemolyticus in the marine environment.

IMPORTANCE To our knowledge, infection of foodborne bacterium V. parahamolyticus occurs via the consumption of undercooked seafood contaminated with pathogenic strains. Aquatic bird is a neglectable source that can transmit V. parahaemolyticus along coastal areas. This study reported the detection of potentially pathogenic V. parahamolyticus harboring virulence genes from aquatic bird feces at the recreational center situated near the Gulf of Thailand. These strains shared identical genetic profile to the clinical isolates that previously reported in many countries. Furthermore, the strains from aquatic birds showed extremely high genetic diversity. Our research pointed out that the aquatic bird is possibly involved in the evolution of novel strains of V. parahaemolyticus and play a role in dissimilation of the potentially pathogenic strains across geographical distance.

Characterization of Vibrio parahaemolyticus strains isolated from clinically asymptomatic seafood workers

Vibrio parahaemolyticus (VP) is a major cause of gastroenteritis outbreaks in Thailand and other countries due to the consumption of contaminated and undercooked seafood. However, there have been few reports of the molecular epidemiology of VP isolates from asymptomatic seafood handlers. Here, we report the phenotypic and genetic characterization of 61 VP isolates obtained from asymptomatic workers in two seafood-processing plants. We found 24 O:K serotypes, of which O11:KUT, O1:KUT and O3:KUT were the dominant serotypes. Analysis by PCR showed that 12 isolates harbored either tdh or trh genes with the potential to be pathogenic VP strains. The presence of T3SS2α and T3SS2β genes was correlated with the presence of tdh and trh, respectively. Four tdh+ isolates were positive for pandemic marker. In this study, VP isolates were commonly resistant to ampicillin, cephazolin, fosfomycin and novobiocin. Phylogenetic analysis of VP1680 loci in 35 isolates from 17 asymptomatic workers, 6 gastroenteritis patients, 7 environmental samples and 5 genomes from a database showed 22 different alleles. Gene VP1680 was conserved in tdh+ isolates and pandemic strains, while that of trh + isolates was diverse. Asymptomatic workers carrying VP were the most likely source of contamination, which raises concerns over food safety in seafood-processing plants.

Isolation of Harveyi clade Vibrio spp. collected in aquaculture farms: How can the identification issue be addressed?

Aquaculture is a fast growing industry with its development hampered by bacterial diseases. Vibriosis caused by Harveyi clade strains is known for causing heavy loss especially in shrimp aquaculture farms. For farm treatment and pathogen spread management, veterinarians and researchers need reliable bacterial identification tools. A range of identification methods have been presented for Vibrio spp. in recent literature but little feedback on their performance have been made available to this day. This study aims at comparing Vibrio spp. identification methods and providing guidance on their use. Fifty farms were sampled and bacterial colonies were isolated using specific culture media before microscopic analysis and genomic profiling using ERIC-PCR. A preliminary identification step was carried out using MALDI-ToF mass spectrometry. Four methods were compared for strain identification on 14 newly isolated Harveyi clade Vibrio spp. strains: whole genome sequencing (digital DNA DNA Hybridization (dDDH)), 5 MLSA schemes, ferric uptake regulation (fur) and lecithin-dependent haemolysin (ldh) single gene based identification methods. Apart from dDDH which is a reference method, no technique could identify all the isolates to the species level. The other tested techniques allowed a faster, cheaper but sub genus clade identification which can be interesting when absolute precision is not required. In this regard, MALDI-ToF and fur based identification seemed especially promising.

Occurrence, virulence, and antimicrobial resistance of Vibrio parahaemolyticus isolated from bivalve shellfish farms along the southern coast of Korea

Vibrio parahaemolyticus is the most common pathogen causing seafood-borne illnesses in Korea. The present study evaluated the occurrence, virulence, and antimicrobial resistance of V. parahaemolyticus in seawater and bivalves obtained in 2016 from the southern coast of Korea, an important region for commercial aquaculture industries, especially the Korean raw seafood culture. V. parahaemolyticus was detected in 87 of 160 (54.4%) bivalve samples and in 32 of 130 (24.5%) seawater samples. Especially high levels were detected during summer to early autumn. All the seawater and bivalves contained less than 2 and 5% of the tdh and trh genes of the isolates, respectively, and seawater isolates possessed two fewer genes than the bivalve isolates. Of 23 antimicrobials tested, three agents (ofloxacin, norfloxacin, and trimethoprim/sulfamethoxazole) effectively treated V. parahaemolyticus illness due to the sensitivity of the isolates. The isolates were highly resistant to ampicillin, however, excluding it as a treatment option. More than half of the isolates exhibited resistance to at least three antimicrobials. These findings indicate the importance of an integrated monitoring and surveillance program noting the occurrence, virulence, and antimicrobial resistance patterns of V. parahaemolyticus in various aquatic sources for preventing human health risks from seafood consumption.

QsvR integrates into quorum sensing circuit to control Vibrio parahaemolyticus virulence

Vibrio parahaemolyticus, the leading cause of seafood-associated gastroenteritis worldwide, requires the two type-III secretion systems (T3SS1 and T3SS2) and a thermostable direct hemolysin (encoded by tdh1 and tdh2) for full virulence. The tdh genes and the T3SS2 gene cluster constitute an 80 kb pathogenicity island known as Vp-PAI located on the chromosome II. Expression of T3SS1 and Vp-PAI is regulated in a quorum sensing (QS)-dependent manner but its detailed mechanisms remain unknown. Herein, we show that three factors (QS regulators AphA and OpaR and an AraC-type transcriptional regulator QsvR) form a complex regulatory network to control the expression of T3SS1 and Vp-PAI genes. At low cell density (LCD), whereas Vp-PAI expression is repressed, T3SS1 genes are induced by AphA, which directly binds (an operator region of) the exsBAD-vscBCD operon. At high cell density (HCD), the bacterium turns off T3SS1 expression by replacing AphA with OpaR, triggering the induction of Vp-PAI. Furthermore, QsvR binds to the regulatory regions of all the tested T3SS1 and Vp-PAI genes to activate their transcription at HCD. Taken together, our data highlight how multiple QS regulators contribute to the pathogenicity of V. parahaemolyticus by precisely controlling the expression of major virulence determinants during different stages of growth.

Comparative performance of TCBS and TSA for the enumeration of trh+ Vibrio parahaemolyticus by direct colony hybridization

Vibrio parahaemolyticus is one of the important foodborne pathogens is of public health concern due to the emergence of pandemic strains causing disease outbreaks worldwide. We evaluated the DNA based colony hybridization technique for the detection and enumeration of total and pathogenic V. parahaemolyticus from the bivalve shellfish, clam using non-radioactive, enzyme-labeled probe targeting the tlh and trh genes, respectively. The digoxigenin (DIG) labeled probes designed in this study showed 100% specificity by dot blot assay. Colony hybridization using DIG probes was performed using both non-selective, trypticase soy agar (TSA) and the selective medium, thiosulfate citrate bile salts sucrose (TCBS) agar. Of 32 clam samples analyzed, 71.88% had>10,000 V. parahaemolyticus cells/g in TSA whereas it was 18.75% in case of TCBS. All the samples showed the presence of total V. parahaemolyticus in TSA and 97% in the case of TCBS. Interestingly, results of the trh⁺V. parahaemolyticus samples were quite high while using TCBS plates (62.5%) as compared to TSA (43.75%). However, the cell numbers obtained from TSA were higher than from TCBS. Several yellow colonies on TCBS turned out to be V. parahaemolyticus using colony hybridization, which was further confirmed by PCR and sucrose utilization test. Colony hybridization using DIG-labeled probe was found to be highly sensitive and could differentiate and enumerate pathogenic and non-pathogenic strains of V. parahaemolyticus. Since traditional methods are not only labor-intensive and time-consuming but also less sensitive, colony hybridization using DIG-labeled probes would be a useful alternative for the enumeration of V. parahaemolyticus in naturally contaminated seafood.

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.

Electronic Properties of Synthetic Shrimp Pathogens-derived DNA Schottky Diodes

The exciting discovery of the semiconducting-like properties of deoxyribonucleic acid (DNA) and its potential applications in molecular genetics and diagnostics in recent times has resulted in a paradigm shift in biophysics research. Recent studies in our laboratory provide a platform towards detecting charge transfer mechanism and understanding the electronic properties of DNA based on the sequence-specific electronic response, which can be applied as an alternative to identify or detect DNA. In this study, we demonstrate a novel method for identification of DNA from different shrimp viruses and bacteria using electronic properties of DNA obtained from both negative and positive bias regions in current-voltage (I–V) profiles. Characteristic electronic properties were calculated and used for quantification and further understanding in the identification process. Aquaculture in shrimp industry is a fast-growing food sector throughout the world. However, shrimp culture in many Asian countries faced a huge economic loss due to disease outbreaks. Scientists have been using specific established methods for detecting shrimp infection, but those methods do have their significant drawbacks due to many inherent factors. As such, we believe that this simple, rapid, sensitive and cost-effective tool can be used for detection and identification of DNA from different shrimp viruses and bacteria.

Prevalence and antimicrobial susceptibility of Vibrio parahaemolyticus isolated from oysters in Korea

Vibrio parahaemolyticus is the most prevalent gastroenteritis-causing pathogen in Korea and in some other Asian countries. It is frequently found in oysters and other seafood. This study monitored changes in the prevalence of V. parahaemolyticus and environmental parameters in oyster aquaculture environments in Korea. From June to October 2014, we tested oysters (Crassostrea gigas) from shellfish-harvesting areas off the west coast of Korea. These 71 isolates were the sum of 16 (22.5%), 19 (26.8%), 23 (32.4%), and 13 (18.3%) isolates collected in July, August, September, and October, respectively. These 71 isolates had the following profiles of resistance against 16 antibiotics: all isolates were resistant to ampicillin and vancomycin, and 52.2, 50.7, and 50.7% of isolates exhibited resistance to cephalothin, rifampin, and streptomycin, respectively. PCR analysis for the presence of the species-specific toxR gene confirmed that 38 (53.5%) of the total 71 isolated strains were positive for V. parahaemolyticus. In PCR analysis for virulence of V. parahaemolyticus, of the 71 isolates tested in the present study, only 38 (53.5%) were positive for the trh virulence gene and 71 (100%) was negative for the tdh virulence gene.

The First Report of Vibrio parahaemolyticus Strain O10:K60 in Japan, a New Combination of O and K Serotypes Isolated from a Patient with Gastroenteritis

Vibrio parahaemolyticus is an important pathogen that causes gastroenteritis in humans, generally associated with the consumption of contaminated seafood, particularly raw shellfish. There are many serotypes in V. parahaemolyticus resulting from a combination of O and K antigens. Among them, O3:K6 and their variants, which represent the pandemic clone, are the most widespread strains worldwide. In this study, we examined V. parahaemolyticus isolated from a gastroenteritis patient's stool at a hospital in Saitama City, Japan in 2013. Serotyping of the O and K antigens identified the strain as O10:K60. To our knowledge, this is the first reported case of a V. parahaemolyticus strain with this antigen combination in Japan. Subsequently, we used PCR to assay for pathogenicity-associated genes, and found that it was positive for tdh, T3SS1, and T3SS2α genes. Antibiotic susceptibility tests showed that the strain was susceptible to all selected antibiotics except ampicillin. Moreover, we detected specific marker genes for the pandemic clone with two kinds of PCR assay. Our results suggest that the isolate O10:K60 is a newly emerging serotype that belongs to the pandemic clone.

Development of a colony hybridization method for the enumeration of total and potentially enteropathogenic Vibrio parahaemolyticus in shellfish

Vibrio parahaemolyticus is a marine microorganism, recognized as cause of gastroenteritis outbreaks associated with seafood consumption. In this study the development and the in-house validation of a colony hybridization method for the enumeration of total and potentially pathogenic V. parahaemolyticus is reported. The method included a set of three controls (process, hybridization and detection control) for the full monitoring of the analytical procedure. Four digoxigenin-labeled probes were designed for pathogenic strains enumeration (tdh1, tdh2, trh1 and trh2 probes) and one for total V. parahaemolyticus count (toxR probe). Probes were tested on a panel of 70 reference strains and 356 environmental, food and clinical isolates, determining the inclusivity (tdh: 96.7%, trh: 97.8%, toxR: 99.4%) and the exclusivity (100% for all probes). Accuracy and linearity of the enumeration were evaluated on pure and mixed cultures: slopes of the regression lines ranged from 0.957 to 1.058 depending on the target gene and R(2) was greater than or equal to 0.989 for all reactions. Evaluation was also carried on using four experimentally contaminated seafood matrices (shellfish, finfish, crustaceans and cephalopods) and the slopes of the curves varied from 0.895 (finfish) to 0.987 (cephalopods) for the counts of potentially pathogenic V. parahaemolyticus (R(2)≥0.965) and from 0.965 to 1.073 for total V. parahaemolyticus enumeration (R(2)≥0.981). Validation was performed on 104 naturally contaminated shellfish samples, analyzed in parallel by colony hybridization, ISO/TS 21872-1 and MPN enumeration. Colony hybridization and ISO method showed a relative accuracy of 86.7%, and a statistically significant correlation was present between colony hybridization enumeration and MPN results (r=0.744, p<0.001). The proposed colony hybridization can be a suitable alternative method for the enumeration of total and potentially pathogenic V. parahaemolyticus in seafood.

Biochemical, serological, and virulence characterization of clinical and oyster Vibrio parahaemolyticus isolates

In this study, 77 clinical and 67 oyster Vibrio parahaemolyticus isolates from North America were examined for biochemical profiles, serotype, and the presence of potential virulence factors (tdh, trh, and type III secretion system [T3SS] genes). All isolates were positive for oxidase, indole, and glucose fermentation, consistent with previous reports. The isolates represented 35 different serotypes, 9 of which were shared by clinical and oyster isolates. Serotypes associated with pandemic strains (O1:KUT, O1:K25, O3:K6, and O4:K68) were observed for clinical isolates, and 7 (9%) oyster isolates belonged to serotype O1:KUT. Of the clinical isolates, 27% were negative for tdh and trh, while 45% contained both genes. Oyster isolates were preferentially selected for the presence of tdh and/or trh; 34% contained both genes, 42% had trh but not tdh, and 3% had tdh but not trh. All but 1 isolate (143/144) had at least three of the four T3SS1 genes examined. The isolates lacking both tdh and trh contained no T3SS2α or T3SS2β genes. All clinical isolates positive for tdh and negative for trh possessed all T3SS2α genes, and all isolates negative for tdh and positive for trh possessed all T3SS2β genes. The two oyster isolates containing tdh but not trh possessed all but the vopB2 gene of T3SS2α, as reported previously. In contrast to the findings of previous studies, all strains examined that were positive for both tdh and trh also carried T3SS2β genes. This report identifies the serotype as the most distinguishing feature between clinical and oyster isolates. Our findings raise concerns about the reliability of the tdh, trh, and T3SS genes as virulence markers and highlight the need for more-detailed pathogenicity investigations of V. parahaemolyticus.

Inflammation and disintegration of intestinal villi in an experimental model for Vibrio parahaemolyticus-induced diarrhea

Vibrio parahaemolyticus is a leading cause of seafood-borne gastroenteritis in many parts of the world, but there is limited knowledge of the pathogenesis of V. parahaemolyticus-induced diarrhea. The absence of an oral infection-based small animal model to study V. parahaemolyticus intestinal colonization and disease has constrained analyses of the course of infection and the factors that mediate it. Here, we demonstrate that infant rabbits oro-gastrically inoculated with V. parahaemolyticus develop severe diarrhea and enteritis, the main clinical and pathologic manifestations of disease in infected individuals. The pathogen principally colonizes the distal small intestine, and this colonization is dependent upon type III secretion system 2. The distal small intestine is also the major site of V. parahaemolyticus-induced tissue damage, reduced epithelial barrier function, and inflammation, suggesting that disease in this region of the gastrointestinal tract accounts for most of the diarrhea that accompanies V. parahaemolyticus infection. Infection appears to proceed through a characteristic sequence of steps that includes remarkable elongation of microvilli and the formation of V. parahaemolyticus-filled cavities within the epithelial surface, and culminates in villus disruption. Both depletion of epithelial cell cytoplasm and epithelial cell extrusion contribute to formation of the cavities in the epithelial surface. V. parahaemolyticus also induces proliferation of epithelial cells and recruitment of inflammatory cells, both of which occur before wide-spread damage to the epithelium is evident. Collectively, our findings suggest that V. parahaemolyticus damages the host intestine and elicits disease via previously undescribed processes and mechanisms.

The marine bacterium Vibrio parahaemolyticus is a leading cause worldwide of gastroenteritis linked to the consumption of contaminated seafood. Despite the prevalence of V. parahaemolyticus-induced gastroenteritis, there is limited understanding of how this pathogen causes disease in the intestine. In part, the paucity of knowledge results from the absence of an oral infection-based animal model of the human disease. We developed a simple oral infection-based infant rabbit model of V. parahaemolyticus-induced intestinal pathology and diarrhea. This experimental model enabled us to define several previously unknown but key features of the pathology elicited by this organism. We found that V. parahaemolyticus chiefly colonizes the distal small intestine and that the organism's second type III secretion system is essential for colonization. The epithelial surface of the distal small intestine is also the major site of V. parahaemolyticus-induced damage, which arises via a characteristic sequence of events culminating in the formation of V. parahaemolyticus-filled cavities in the epithelial surface. This experimental model will transform future studies aimed at deciphering the bacterial and host factors/processes that contribute to disease, as well as enable testing of new therapeutics to prevent and/or combat infection.

Insufficiency of the Kanagawa hemolytic test for detecting pathogenic Vibrio parahaemolyticus in Shanghai, China

We evaluated the Kanagawa hemolytic test and tdh gene test for accuracy in identifying pathogenic Vibrio parahaemolyticus isolates in Shanghai. One hundred and seventy-two V. parahaemolyticus isolates were collected from diarrhea patients, freshly harvested sea fish, or fresh water samples. Statistical data for the Kanagawa hemolytic test and tdh gene test were compared. There were 83.51% isolates (81/97) from patients and 22.22% isolates (10/45) from sea-fish positive for the tdh gene. However, none of 30 isolates from fresh water samples were tdh-positive. Positive Kanagawa hemolytic tests were obtained in 88.66%, 46.67%, and 76.67% of isolates, which were from patients, sea fish, and fresh water samples, respectively. Positive rates of the Kanagawa hemolytic tests and the tdh gene tests were significantly different in isolates from those 3 sources (P < 0.001). The tdh gene test showed higher specificity than the Kanagawa hemolytic test on identifying pathogenic V. parahaemolyticus isolates in Shanghai, China.

Precise region and the character of the pathogenicity island in clinical Vibrio parahaemolyticus strains

In this study, we determined the borders of the pathogenicity island in V. parahaemolyticus RIMD2210633 (Vp-PAI). Vp-PAI has features in common with Tn7 and other related elements at both terminal ends. Our findings indicate that the mobile element with a transposase which contains the DDE motif may have been involved in Vp-PAI formation.

Rapid detection and enumeration of trh-carrying Vibrio parahaemolyticus with the alkaline phosphatase-labelled oligonucleotide probe

An alkaline phosphatase (AP)-labelled oligonucleotide probe was developed to detect and enumerate trh(+)Vibrio parahaemolyticus in seafood. The probe was evaluated using 40 isolates of V. parahaemolyticus, 45 isolates of other vibrios and 55 non-vibrio isolates. The probe reacted specifically with V. parahaemolyticus possessing either the trh1 or trh2 variant of the trh gene and was found to be 100% specific for trh(+)V. parahaemolyticus. Using the trh probe, V. parahaemolyticus carrying trh gene was targeted in 34 seafood samples by direct plating and colony hybridization procedure. The trh(+)V. parahaemolyticus could be detected in five of 34 (14.7%) samples and the levels ranged from 5.0 x 10(2) to 3.4 x 10(3) cfu g(-1). Colonies of trh(+)V.parahaemolyticus were isolated from the five positive samples. Forty seafood samples were analysed for trh(+)V. parahaemolyticus by colony hybridization following enrichment in alkaline peptone water. 16 samples (40%) were positive for trh gene and trh(+)V. parahaemolyticus was isolated from 15 samples (37.5%). To assess the sensitivity of the trh probe, seafood homogenates spiked with known concentrations of trh-positive V. parahaemolyticus were plated and hybridized. Counts obtained using the probe were similar to those of inocula. The results suggest that the AP-labelled trh probe is useful for the detection and enumeration of trh(+)V. parahaemolyticus in seafood.

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.

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.

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.

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.

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 oftdh-positiveVibrio parahaemolyticusfrom an outbreak associated with raw oyster consumption in Spain

Between August and September 1999, a total of 64 cases of illness were identified in three episodes of acute gastroenteritis associated with the consumption of live oysters from a typical outdoor street market in Galicia (northwest Spain). Nine case patients were hospitalized and analysis of their stool samples revealed the presence of Vibrio parahaemolyticus. The strains isolated from two stool samples were studied for antibiotic susceptibility, biochemical characteristics and presence of virulence factors. Both isolates were Kanagawa phenomenon positive and produced thermostable direct hemolysin, which is related to pathogenicity in humans. These results show the presence of pathogenic V. parahaemolyticus in mollusks harvested in Europe and reveal the risk of illness associated with their consumption, suggesting the revision of V. parahaemolyticus risk assessment associated with consumption of raw live shellfish.

Application of polymerase chain reaction for detection of Vibrio parahaemolyticus associated with tropical seafoods and coastal environment

AIMS

To study the incidence of Vibrio parahaemolyticus in seafoods, water and sediment by molecular techniques vs conventional microbiological methods.

METHODS AND RESULTS

Of 86 samples analysed, 28 recorded positive for V. parahaemolyticus by conventional microbiological method, while 53 were positive by the toxR-targeted PCR, performed directly on enrichment broth lysates. While one sample of molluscan shellfish was positive for tdh gene, trh gene was detected in three enrichment broths of molluscan shellfish.

CONCLUSIONS

Direct application of PCR to enrichment broths will be useful for the rapid and sensitive detection of potentially pathogenic strains of V. parahemolyticus in seafoods.

SIGNIFICANCE AND IMPACT OF THE STUDY

Vibrio parahaemolyticus is an important human pathogen responsible for food-borne gastroenteritis world-wide. As, both pathogenic and non-pathogenic strains of V. parahaemolyticus exist in the seafood, application of PCR specific for the virulence genes (tdh & trh) will help in detection of pathogenic strains of V. parahaemolyticus and consequently reduce the risk of food-borne illness.

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.

Molecular analysis of Vibrio parahaemolyticus isolated from human patients and shellfish during US Pacific north-west outbreaks

AIMS

The objective of this study was to investigate the occurrence and distribution of haemolysin genes, plasmid profile, serogroup analysis and cellular urease activity for Vibrio parahaemolyticus isolates from infected human patients and oysters from the Pacific north-western United States between 1988 and 1997.

METHODS AND RESULTS

All of the clinical and environmental isolates tested in this study exhibited the presence of the thermolabile haemolysin gene, tl, confirming that all of the isolates were V. parahaemolyticus. Furthermore, the V. parahaemolyticus isolates that contained either the thermostable direct haemolysin gene, tdh, or the thermostable direct haemolysin-related gene, trh, or both, were also positive for urease. Isolates from infected human patients belong to serogroups O1 and O4, whereas, the isolates from oysters belong to serogroups O1, O4 and O5. These results suggest that the presence of a V. parahaemolyticus serogroup O1 and O4 could indicate the presence of a virulent strain of this pathogen. In this study, the presence of the haemolysin genes, serogroup profiles and urease production in V. parahaemolyticus isolated from human patients correlated with the oysters collected during the outbreaks. However, no significant correlation of the plasmid profiles was detected, based on their distribution and molecular weights, between V. parahaemolyticus isolated from infected human patients and from oysters collected during this outbreak.

CONCLUSIONS, SIGNIFICANCE AND IMPACT OF STUDY

It is apparent from this study that the identification of the haemolysin genes by multiplex PCR amplification, in conjunction with serogroup analysis and urease production, can be used to monitor shellfish for the presence of potentially pathogenic strains of V. parahaemolyticus.

Cloning and characterization of a novel haemolysin in Vibrio cholerae O1 that does not directly contribute to the virulence of the organism

A previously undescribed haemolysin, distinct from the major Vibrio cholerae O1 El Tor haemolysin, HlyA, was cloned from the O1 classical biotype strain Z17561. This novel haemolysin showed 71.5% overall similarity to the delta-thermostable direct haemolysin of Vibrio parahaemolyticus, and so it has been termed V. cholerae delta-thermostable haemolysin (Vc-deltaTH, encoded by the dth gene). An ORF found immediately downstream, which appears to be transcriptionally and translationally linked to dth, displayed strong homology to the family of acyl-CoA synthetases. When expressed from an inducible promoter in Escherichia coli, Vc-deltaTH was shown to be a 22.8 kDa protein active on sheep red blood cells. Co-expression of acs with dth had no effect on the haemolytic activity or cytoplasmic localization of Vc-deltaTH. A V. cholerae Z17561 dth::Km(R) mutant showed unaltered behaviour in the infant mouse cholera model.

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.

Isolation of a pandemic O3:K6 clone of a Vibrio parahaemolyticus strain from environmental and clinical sources in Thailand

Application of an immunomagnetic enrichment method selective for Vibrio parahaemolyticus serovar K6 allowed isolation of a strain belonging to the pandemic O3:K6 clone of V. parahaemolyticus from fresh shellfish not implicated in a clinical case in southern Thailand. Arbitrarily primed PCR profiles of this strain, clinical O3:K6 strains isolated from sporadic diarrhea cases in the same area, and a standard pandemic O3:K6 strain were indistinguishable.

Pandemic spread of an O3:K6 clone of Vibrio parahaemolyticus and emergence of related strains evidenced by arbitrarily primed PCR and toxRS sequence analyses

Vibrio parahaemolyticus O3:K6 strains responsible for the increase in the number of cases of diarrhea in Calcutta, India, beginning in February 1996 and those isolated from Southeast Asian travelers beginning in 1995 were shown to belong to a unique clone characterized by possession of the tdh gene but not the trh gene and by unique arbitrarily primed PCR (AP-PCR) profiles (J. Okuda, M. Ishibashi, E. Hayakawa, T. Nishino, Y. Takeda, A. K. Mukhopadhyay, S. Garg, S. K. Bhattacharya, G. B. Nair, and M. Nishibuchi, J. Clin. Microbiol. 35:3150-3155, 1997). Evidence supporting a hypothesis that this clone emerged only recently and is spreading to many countries was obtained in this study. Of 227 strains isolated in a hospital in Bangladesh between 1977 and 1998, only 22 strains isolated between 1996 and 1998 belonged to the new O3:K6 clone (defined by the serovar, the tdh and trh typing, and AP-PCR profiles). The O3:K6 strains isolated from clinical sources in Taiwan, Laos, Japan, Thailand, Korea, and the United States between 1997 and 1998 were also shown to belong to the new O3:K6 clone. The clonality of the new O3:K6 strains was also confirmed by analysis of the toxRS sequence, which has been shown to be useful for phylogenetic analysis of the members of the genus Vibrio. The toxRS sequences of the representative strains of the new O3:K6 clone differed from those of the O3:K6 strains isolated before 1995 at least at 7 base positions within a 1,346-bp region. A new PCR method targeted to 2 of the base positions unique to the new O3:K6 clone was developed. This PCR method could clearly differentiate all 172 strains belonging to the new O3:K6 clone from other O3:K6 strains isolated earlier. One hundred sixty-six strains belonging to 28 serovars other than O3:K6 were also examined by the new PCR method. The tdh-positive and trh-lacking strains that belonged to the O4:K68 and O1:K untypeable serovars and were isolated in three countries and from international travelers beginning in 1997 gave positive results. The AP-PCR profiles of these strains were nearly identical to those of the new O3:K6 clone, and their toxRS sequences were 100% identical to that of the new O3:K6 clone. The results suggest that these strains may have diverged from the new O3:K6 clone by alteration of the O:K antigens. In conclusion, this study presents strong evidence for the first pandemicity in the history of V. parahaemolyticus and reports a novel toxRS-targeted PCR method that will be useful in epidemiological investigation of the cases associated with the current pandemic spread.

Detection of total and hemolysin-producing Vibrio parahaemolyticus in shellfish using multiplex PCR amplification of tl, tdh and trh

Vibrio parahaemolyticus is an important human pathogen which can cause gastroenteritis when consumed in raw or partially-cooked seafood. A multiplex PCR amplification-based detection of total and virulent strains of V. parahaemolyticus was developed by targeting thermolabile hemolysin encoded by tl, thermostable direct hemolysin encoded by tdh, and thermostable direct hemolysin-related trh genes. Following optimization using oligonucleotide primers targeting tl, tdh and trh genes, the multiplex PCR was applied to V. parahaemolyticus from 27 clinical, 43 seafood, 15 environmental, 7 strains obtained from various laboratories and 19 from oyster plants. All 111 V. parahaemolyticus isolates showed PCR amplification of the tl gene; however, only 60 isolates showed amplification of tdh, and 43 isolates showed amplification of the trh gene. Also, 18 strains showed amplification of the tdh gene, but these strains did not show amplification of the trh gene. However, one strain exhibited amplification for the trh but not the tdh gene, suggesting both genes need to be targeted in a PCR amplification reaction to detect all hemolysin-producing strains of this pathogen. The multiplex PCR approach was successfully used to detect various strains of V parahaemolyticus in seeded oyster tissue homogenate. Sensitivity of detection for all three target gene segments was at least between 10(1)-10(2) cfu per 10 g of alkaline peptone water enriched seeded oyster tissue homogenate. This high level of sensitivity of detection of this pathogen within 8 h of pre-enrichment is well within the action level (10(4) cfu per 1 g of shell stock) suggested by the National Seafood Sanitation Program guideline. Compared to conventional microbiological culture methods, this multiplex PCR approach is rapid and reliable for accomplishing a comprehensive detection of V. parahaemolyticus in shellfish.