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

Serodiversity, antibiotic resistance, and virulence genes of Vibrio parahaemolyticus in oysters collected in coastal areas of northwestern Mexico between 2012 and 2020

This study aimed to determine the prevalence of V. parahaemolyticus in oysters from the northwestern coast of Mexico and to identify the serotypes, virulence factors, and antibiotic resistance of the strains. Oyster samples were collected from 2012 to 2020 from the northwest coast of Mexico; biochemical and molecular methods were used to identify V. parahaemolyticus from oysters; antiserum reaction to determine V. parahaemolyticus serotypes, and PCR assays were performed to identify pathogenic (tdh and/or trh) or pandemic (toxRS/new, and/or orf8) strains and antibiotic resistance testing. A total of 441 oyster samples were collected and tested for V. parahaemolyticus. Forty-seven percent of oyster samples were positive for V. parahaemolyticus. Ten different O serogroups and 72 serovars were identified, predominantly serotype O1:KUT with 22.2% and OUT:KUT with 17.3%. Twenty new serotypes that had not been previously reported in our region were identified. We detected 4.3% of pathogenic clones but no pandemic strains. About 73.5% of strains were resistant to at least one antibiotic, mainly ampicillin and ciprofloxacin; 25% were multi-drug resistant. In conclusion, the pathogenic strains in oysters and antibiotic resistance are of public health concern, as the potential for outbreaks throughout northwestern Mexico is well established.

Advance typing of Vibrio parahaemolyticus through the mtlA and aer gene: A high-resolution, cost-effective approach

Vibrio parahaemolyticus is a significant cause of foodborne illness, and its incidence worldwide is on the rise. It is thus imperative to develop a straightforward and efficient method for typing strains of this pathogen. In this study, we conducted a pangenome analysis of 75 complete genomes of V. parahaemolyticus and identified the core gene mtlA with the highest degree of variation, which distinguished 44 strains and outperformed traditional seven-gene-based MLST when combined with aer, another core gene with high degree of variation. The mtlA gene had higher resolution to type strains with a close relationship compared to the traditional MLST genes in the phylogenetic tree built by core genomes. Strong positive selection was also detected in the gene mtlA (ω > 1), representing adaptive and evolution in response to the environment. Therefore, the panel of gene mtlA and aer may serve as a tool for the typing of V. parahaemolyticus, potentially contributing to the prevention and control of this foodborne disease.

Molecular characterization of Vibrio species isolated from dairy and water samples

Vibrio species can cause foodborne infections and lead to serious gastrointestinal illnesses. The purpose of this research was to detect the Vibrio cholerae and Vibrio parahaemolyticus in raw milk, dairy products, and water samples. Also, it investigated the virulence factors, antibiotic resistance and biofilm formation in isolated bacteria. Conventional and molecular approaches were used to identify the isolates in this study. Vibrio species were detected in 5% of the samples. Vibrio cholerae and Vibrio parahaemolyticus were isolated from 1.25 and 1.5%, respectively, of the total samples. Penicillin resistance was detected in all strains of Vibrio cholerae and Vibrio parahaemolyticus, with a MAR index ranging from 0.16 to 0.5. Four isolates were moderate biofilm producer and three of them were MDR. When Vibrio cholerae was screened for virulence genes, ctxAB, hlyA, and tcpA were found in 80, 60, and 80% of isolates, respectively. However, tdh + /trh + associated-virulence genes were found in 33.3% of Vibrio parahaemolyticus isolates.

A lanthanide-based high-sensitivity fluorescence method for the on-site rapid detection of thermostable direct hemolysin of Vibrio parahaemolyticus

Vibrio parahaemolyticus is a common foodborne pathogen in seafood, which often causes seafood borne bacterial gastroenteritis or food poisoning. Thermostable direct hemolysin (TDH) is considered to be one of the main virulence factors involved in this pathogen. The most clinical V. parahaemolyticus isolates produce TDH. Therefore, high sensitivity and specificity detection of TDH are of great significance for food safety and early diagnosis of diseases caused by V. parahaemolyticus. In this study, we developed a rapid, sensitive immunochromatographic test paper assay for the quantitative detection of TDH in seafood samples using time-resolved fluorescence techniques. First, we completed the preparation of fluorescent detection antibodies by coupling lanthanide fluorescent nanospheres with homemade high-affinity polyclonal antibodies based on the principle of the double-antibody sandwich. The lanthanide fluorescent nanospheres used in this study are characterized by a large stokes shift and a long fluorescence lifetime, which effectively reduces background noise and improves detection sensitivity. In addition, the method can be completed within 15 min for the detection of TDH, has a detection limit below 50 ng/mL and good linearity in the range of 50-5000 ng/mL. Moreover, it has good specificity and no cross-reactivity with Vibrio vulnificus hemolysin (VVH), Clostridium perfringens α toxin (CPA) or C. perfringens ε toxin (ETX). Finally, the sensitivity of this method was unchanged when the three simulated samples of Patinopecten yessoensis, Ruditapes philippinarum, and Scapharca broughtonii tested, indicating that the method is not affected by samples in a complex matrix. In conclusion, this study establishes a practical new method for on-site rapid detection of TDH, which is easy to operate, fast response, easy to carry and can be implemented under the field conditions without expensive equipment and professional person.

Emergence and predominance of a new serotype of Vibrio parahaemolyticus in Huzhou, China

BACKGROUND

During our surveillance period, we found a new type of Vibrio parahaemolyticus (V. parahaemolyticus) with serotype O10:K4, which had increased over the past 2 years in Huzhou and became the second most common serotype after O3:K6.

METHODS

Strains were isolated from stool samples of diarrhea patients in the First People's Hospital in Huzhou. The serotypes, virulence-associated genes, antimicrobial susceptibility, and pulsed field gel electrophoresis (PFGE) of these strains were analyzed.

RESULTS

Between January 2017 and December 2021, there were 598 (5.36%) V. parahaemolyticus-positive samples of 11,166 stool specimens. The V. parahaemolyticus detection rate was high in summer months. The O3:K6 was the dominant serotype in 2017-2020 and a new serotype, O10:K4, was the predominant serotype in 2021. The majority of isolates tested were resistant to ampicillin (86.8%). We randomly chose the strains with serotype O3:K6 and O10:K4 for PFGE to compare the genetic relationship between these two serotypes. The results showed that the PFGE profiles of V. parahaemolyticus O3:K6 and O10:K4 were genetically similar. The strains showed a tendency to cluster on the basis of their serotype profiles. However, some O3:K6 strains showed 100% similarity with O10:K4 strains.

CONCLUSION

A new serotype with pandemic potential of V. parahaemolyticus, O10:K4, was detected in 2020 and became dominant in 2021 in Huzhou.

Virulence factor genes and comparative pathogenicity study of tdh, trh and tlh positive Vibrio parahaemolyticus strains isolated from Whiteleg shrimp, Litopenaeus vannamei (Boone, 1931) in India

Vibrio parahaemolyticus is a gram-negative halophilic bacterium responsible for gastrointestinal infection in human and vibriosis in aquatic animals. The thermostable direct hemolysin (tdh), tdh-related hemolysin (trh) and thermolabile hemolysin (tlh) positive strains of V. parahaemolyticus were identified from brackishwater aquaculture farms of West Bengal and Andhra Pradesh, India. Moreover, the presence of other virulent genes like vcrD1, vopD, vp1680 under type three secretion system 1 (T3SS1) and vcrD2 vopD2, vopB2, vopC2 under type three secretion system 2 (T3SS2) were detected in tdh positive strain of V. parahaemolyticus. Furthermore, the study revealed that the tdh and trh positive isolates were resistant to β-lactam antibiotics and were able to lyse more than 95% of human Red Blood Cells (RBCs). In addition, both the isolates showed high cytotoxicity in Human Embryonic Kidney (HEK) cell line compared to tlh positive strain. Additionally, intraperitoneal and oral administration of tdh and trh positive strain of V. parahaemolyticus in Indian Major Carp, Labeo rohita caused 100% mortality at the level of 2.0 × 10⁸ CFU ml^-1 and 1.6 × 10⁸ CFU ml^-1, respectively. In contrast, only 10% mortality was observed in the case of tlh positive strain at the level of 2.5× 10⁸ CFU ml^-1. The histopathological changes like infiltration of blood cells and degenerated hepatic tissue in the liver of L. rohita were observed after the experimental challenge. The changes like degeneration of glomeruli, necrosis of renal tubules and Bowman's capsule were observed in the kidney section. Ragged, irregular shaped villi and necrosis of the villus were observed in the intestinal lumen. Overall, the study demonstrates that isolated V. parahaemolyticus is a potent aquatic microbial pathogen. Additionally, as V. parahaemolyticus is also a human pathogen and might pose a threat to the human population, proper management strategies are required to prevent the possible occurrence of disease.

Vibrio parahaemolyticus CadC regulates acid tolerance response to enhance bacterial motility and cytotoxicity

Pathogens adapted to sub-lethal acidic conditions could increase the virulence and survival ability under lethal conditions. In the aquaculture industry, feed acidifiers have been used to increase the growth of aquatic animals. However, there is limited study on the effects of acidic condition on the virulence and survival of pathogens in aquaculture. In this study, we investigated the survival ability of Vibrio parahaemolyticus at lethal acidic pH (4.0) after adapted the bacteria to sub-lethal acidic pH (5.5) for 1 hr. Our results indicated that the adapted strain increased the survival ability at lethal acidic pH invoked by an inorganic (HCl) or organic (citric) acid. RNA-sequencing (RNA-seq) results revealed that 321 genes were differentially expressed at the sub-lethal acidic pH including cadC, cadBA and groES/groEL relating to acid tolerance response (ATR), as well as genes relating to outer membrane, heat-shock proteins, phosphotransferase system and flagella system. Quantitative real-time polymerase chain reaction (qRT-PCR) confirmed that cadC and cadBA were upregulated under sub-lethal acidic conditions. The CadC protein could directly regulate the expression of cadBA to modulate the ATR in V. parahaemolyticus. RNA-seq data also indicated that 113 genes in the CadC-dependent way and 208 genes in the CadC-independent way were differentially expressed, which were related to the regulation of ATR. Finally, the motility and cytotoxicity of the sub-lethal acidic adapted wild type (WT) were significantly increased compared with the unadapted strain. Our results demonstrated that the dietary acidifiers may increase the virulence and survival of V. parahaemolyticus in aquaculture.

Occurrence and Abundance of Pathogenic Vibrio Species in Raw Oysters at Retail Seafood Markets in Northwestern Mexico

Seafood has frequently been associated with foodborne illness because pathogens are easily introduced during seafood cultivation, handling, and processing. Vibrio parahaemolyticus and Vibrio cholerae are human pathogens that cause gastroenteritis and cholera, respectively, and Vibrio vulnificus can cause fatal wound infections and septicemia. However, information about the occurrence of these pathogens in oysters from the Pacific coast of Mexico is limited to V. parahaemolyticus. In the present study, we evaluated the presence and abundance of these three Vibrio species in 68 raw oysters (Crassostrea corteziensis) obtained from retail seafood markets in Sinaloa, Mexico. The most probable number (MPN)-PCR assay was used for amplification of the tlh (thermolabile hemolysin), ompW (outer membrane protein), and vvhA (hemolytic cytolysin) genes that are specific to V. parahaemolyticus, V. cholerae, and V. vulnificus, respectively. All oyster samples were positive for at least one Vibrio species. V. parahaemolyticus, V. cholerae, and V. vulnificus prevalences were 77.9, 8.8, and 32.3% overall, respectively, and most species were present in all sample periods with increased prevalence in period 3. The tdh (thermostable direct hemolysin) gene was detected in 30.1%, trh (TDH-related hemolysin) was detected in 3.7%, and tdh/trh was detected in 7.5% of the total tlh-positive samples (53 of 68), whereas the pandemic serotype O3:K6 (orf8 positive) was detected in only 1 sample (1.8%). The total prevalence of tdh and/or trh was 41.5%. In none of the samples positive for V. cholerae were the cholera toxin (ctxA) and cholix (chxA) toxigenic genes or the rfb gene encoding the O1 and O139 antigens amplified, suggesting the presence of non-O1 non-O139 V. cholerae strains. Our results clearly indicated a high prevalence of pathogenic Vibrio species in raw oysters from retail seafood markets in Mexico. Consumption of these raw oysters carries the potential risk of foodborne illness, which can be limited by cooking.

Strain variability and pathogenic potential of tdhcarrying Vibrio parahaemolyticus isolated from diseased Penaeus monodon

A disease outbreak in 42-d-old black tiger shrimp Penaeus monodon juveniles from a commercial aquaculture farm in Kerala, India, was investigated. The cause of the disease outbreak was confirmed as Vibrio parahaemolyticus by biochemical tests, PCR targeting the toxR gene and pathogenicity testing of the isolates. All of the isolates tested negative by PCR specific for V. parahaemolyticus associated with acute hepatopancreatic necrosis disease (AHPND), implicating vibriosis unrelated to AHPND as the cause of mortality. Among the 19 isolates obtained, 2 possessed the tdh gene (coding for thermo-stable hemolysin), whereas none of the isolates possessed trh. The LD50 value of 8 isolates of V. parahaemolyticus from diseased and apparently healthy shrimp ranged from 2.7 × 104 to 4.9 × 105 CFU ml-1 by immersion challenge of P. monodon postlarvae. BOX-PCR and dendrogram analysis of the bacterial isolates revealed that the isolates from moribund and apparently healthy shrimp formed separate clusters, indicating that these isolates originate from separate clones. The isolates from moribund shrimp including tdh-positive V. parahaemolyticus clustered together. The present study represents the first report of tdh-positive V. parahaemolyticus causing disease in a shrimp farm.

Simultaneous Identification of Clinically Common Vibrio parahaemolyticus Serotypes Using Probe Melting Curve Analysis

The dynamic nature of Vibrio parahaemolyticus epidemiology has presented a unique challenge for disease intervention strategies. Despite the continued rise of disease incidence and outbreaks of vibriosis, as well as the global emergence of pandemic clones and serovariants with enhanced virulence, there is a paucity of molecular methods for the serotyping of V. parahaemolyticus strains to improve disease surveillance and outbreak investigations. We describe the development of a multiplex ligation reaction based on probe melting curve analysis (MLMA) for the simultaneous identification of 11 clinically most common V. parahaemolyticus serotypes spanning a 10-year period. Through extensive sequence analyses using 418 genomes, specific primers and probes were designed for a total of 22 antigen gene targets for the O- and K- serogroups. Additionally, the toxR gene was incorporated into the assay for the confirmation of V. parahaemolyticus. All gene targets were detected by the assay and gave expected Tm values, without any cross reactions between the 11 clinically common serotypes or with 38 other serotypes. The limit of identification for all gene targets ranged from 0.1 to 1 ng/μL. The intra- and inter-assay standard deviations and the coefficients of variation were no more than 1°C and <1% respectively, indicating a highly reproducible assay. A multicenter double-blind clinical study was conducted using the traditional V. parahaemolyticus identification workflow and the MLMA assay workflow in parallel. From consecutive diarrheal stool specimens (n = 6118) collected over a year at 10 sentinel hospitals, a total of 153 V. parahaemolyticus isolates (2.5%) were identified by both workflows. A total agreement (kappa = 1.0) between the serotypes identified by the MLMA assay and conventional serological method was demonstrated. This is the first molecular assay to simultaneously identify multiple clinically important V. parahaemolyticus serotypes, which satisfies the acute need for a practical, rapid and robust identification of V. parahaemolyticus serotypes to facilitate the timely detection of vibriosis outbreaks and surveillance.

Toxigenic V. cholerae, V. parahaemolyticus, and V. vulnificus in oysters from the Gulf of Mexico and sold in Mexico City

Oysters can accumulate potentially pathogenic bacteria, such as Vibrio cholerae, V. parahaemolyticus, and V. vulnificus. The aim of this study was to detect the presence of these Vibrio species and their toxigenic variants in oysters from the Gulf of Mexico sold in Mexico City. Oyster samples were studied using traditional culture and molecular polymerase chain reaction analysis. V. cholerae was present in 30.4% of the samples and its toxigenic variant chxA+ in 26.1%. It was isolated only in deshelled oysters, mainly in the dry season. V. parahaemolyticus was present in 95.7% of the samples and the toxigenic variant was found in 17.4%. V. vulnificus was identified in 60.9% of the samples, 38% of which corresponded to the environmental genotype and 21.7% to the clinical genotype, mainly in the cold season. Consumption of the oysters analyzed poses health risks due to the presence of Vibrio species, especially in deshelled oysters.

Pathogenic Vibrio parahaemolyticus indiarrhoeal patients, fish and aquatic environments and their potential for inter-source transmission

The role of Vibrio parahaemolyticus in causing diarrhoeal disease is well known. However, phenotypic and genetic traits of this pathogen isolated from diverse sources have not been investigated in detail. In this study, we have screened samples from diarrhoeal cases (2603), brackish water fish (301) and aquatic environments (115) and identified V. parahaemolyticus in 29 (1.1%), 171 (56.8%) and 43 (37.4%) samples, respectively. Incidence of pathogenic V. parahaemolyticuswith virulence encoding thermostable-direct haemolysin gene (tdh) was detected mostly in fishes (19.3%) and waters (15.6%) than clinical samples (1.04%). The pandemic strain marker genes (toxRS and PGS-sequences) have been detected relatively more in water (6%) and fish (5%) samples than in clinical samples (0.7%). Majority of the V. parahaemolyticus isolates from clinical cases and fish samples (26.3%) belonged to classical pandemic serovars (O3:K6). In addition, several newly recognised pandemic serovars have also been identified. Pulsed field-gel electrophoresis (PFGE) analysis showed clonal relatedness (60-85%) of V. parahaemolyticus from different sources. The study observation revealed that the brackish water fishes and water bodies may act as a reservoir of pathogenic V. parahaemolyticus. Emergence of several new serovars of pandemic V. parahaemolyticussignifies the changing phenotypic characteristics of the pathogen.

Genetic and population analyses of Vibrio parahaemolyticus isolates from three major coastal regions in China

AIM

This study aims to evaluate the genetic and population structure of Vibrio parahaemolyticus in the major coastal regions of China.

MATERIALS & METHODS

Multilocus sequence typing was performed.

RESULTS

Insertion of large sequence into recA happened in nearly 30 strains, which were untypeable by multilocus sequence typing. A collection of 307 V. parahaemolyticus isolates were typed into 160 sequence types, including 117 novel ones. eBURST analysis revealed five clonal complexes, 11 doublets, and 108 singletons. The 160 sequence types formed two main lineages in the phylogenetic analysis.

CONCLUSION

V. parahaemolyticus along the Chinese coastal regions exhibits high levels of genetic diversity and has undergone significant purifying selection and frequent recombination. A deeper understanding of V. parahaemolyticus genetic diversity could be obtained at the level of genome sequences.

Inactivation of Vibrio parahaemolyticus by antimicrobial photodynamic technology using methylene blue

BACKGROUND

Vibrio parahaemolyticus is the leading causative pathogen of gastroenteritis often related to contaminated seafood. Photodynamic inactivation has been recently proposed as a strategy for killing cells and viruses. The objective of this study was to verify the bactericidal effects caused by photodynamic inactivation using methylene blue (MB) over V. parahaemolyticus via flow cytometry, agarose gel electrophoresis and sodium dodecyl sulfate polyacrylamide gel electrophoresis. Vibrio parahaemolyticus counts were determined using the most probable number method. A scanning electron microscope and a transmission electron microscope were employed to intuitively analyze internal and external cell structure.

RESULTS

Combination of MB and laser treatment significantly inhibited the growth of V. parahaemolyticus. The inactivation rate of V. parahaemolyticus was >99.99% and its counts were reduced by 5 log10 in the presence of 0.05 mg mL(-1) MB when illuminated with visible light (power density 200 mW cm(-2)) for 25 min. All inactivated cells showed morphological changes, leakage of cytoplasm and degradation of protein and DNA.

CONCLUSION

Results from this study indicated that photodynamic technology using MB produced significant inactivation of V. parahaemolyticus mainly brought about by the degradation of protein and DNA.

iTRAQ-based proteomic profiling of Vibrio parahaemolyticus under various culture conditions

Background

Vibrio parahaemolyticus is a common pathogen infecting humans and marine animals; this pathogen has become a major concern of marine food products and trade. In this study, V. parahaemolyticus isolated from sewage was exposed to different culture conditions and analyzed by isobaric tag for relative and absolute quantitation (iTRAQ) based reversed-phase liquid chromatography-tandem mass spectrometry (LC-MS/MS) technique. Our goal is to gain further insights into the proteomics of V. parahaemolyticus, particularly differentially expressed proteins closely correlated with growth conditions and pathogenicity associated proteins.

Results

In this study, a total of 2,717 proteins including numerous membrane proteins were significantly identified, and 616 proteins displayed significant differential expression under different conditions. Of them, 12 proteins mainly participating in metabolism showed the most elastic expression differentiation between different culture conditions. Some membrane proteins such as type I secretion outer membrane protein, TolC, lipoprotein, efflux system proteins iron-regulated protein A and putaive Fe-regulated protein B, ferric siderophore receptor homolog and several V. parahaemolyticus virulence-associated proteins were differentially regulated under different conditions. Some differentially regulated proteins were analyzed and confirmed at gene expression level by quantitative real time polymerase chain reaction (qRT-PCR).

Conclusions

Proteomics analysis results revealed the characteristics of V. parahaemolyticus proteome expression, provided some promising biomarkers related with growth conditions, the results likely advance insights into the mechanism involved in the response of V. parahaemolyticus to different conditions. Some virulence-associated proteins were discovered to be differentially expressed under different conditions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-015-0075-4) contains supplementary material, which is available to authorized users.

A pandemic Vibrio parahaemolyticus O3:K6 clone causing most associated diarrhea cases in the Pacific Northwest coast of Mexico

Between September and October of 2004, more than 1230 cases of gastroenteritis due to pandemic O3:K6 strains of Vibrio parahaemolyticus (V. parahaemolyticus) were reported in the relatively small geographical area of Southern Sinaloa, a state located in Northwest Mexico. Since then, V. parahaemolyticus-associated gastroenteritis cases have gradually increased in prevalence spreading from south to north. The present study conducted an epidemiological surveillance of V. parahaemolyticus strains in both environmental and clinical samples along the Pacific coast of Sinaloa from 2011 to 2013. The genetic relatedness, serotype dominance and antibiotic resistance of isolates were investigated. A total of 46 strains were isolated from environmental samples (e.g., sediment, seawater and shrimp), whereas 249 strains were obtained from stools of patients with gastroenteritis. Nine different O serogroups and 16 serovars were identified. Serovars O3:K6 and O6:K46 were identified in both environmental and clinical strains. Whereas most environmental isolates carried the tdh gene (71.74%, 33/46), only three (6.52%) belonged to pandemic clones (O3:K6, O3:KUT and OUT:KUT). In contrast, 81.1% (202/249) of clinical isolates belonged to pandemic serotypes, with O3:K6 (tdh, toxRS/new, and/or orf8) representing the predominant serovar (97%, 196/202). This prevalence of pathogenic (tdh and/or trh positive) and O3:K6 pandemic V. parahaemolyticus isolates in this study were similar to those found from 2004 to 2010. As investigated by REP-PCR, genetic lineages of selected O3:K6 strains isolated in this study and some isolated earlier were nearly identical. Antimicrobial susceptibility testing showed that most strains (93.8%) were resistant to ampicillin but sensitive to chloramphenicol (98.8%). Multidrug resistance significantly increased from 8.6% (2004-2010) to 22.93% (2011-2013; p < 0.05). Our data indicate that pandemic O3:K6 clone has endemically established in the Pacific Coast of Mexico.

Environmental parameters influence on the dynamics of total and pathogenic Vibrio parahaemolyticus densities in Crassostrea virginica harvested from Mexico's Gulf coast

The influence of environmental parameters on the total and pathogenic Vibrio parahaemolyticus seasonal densities in American oysters (Crassostrea virginica) was evaluated for 1 year. Harvesting site A yielded the highest mean densities of V. parahaemolyticus tlh+, tdh+/trh-, tdh-/trh+ and tdh+/trh+ during spring season at 2.57, 1.74, 0.36, and -0.40 log10 MPN/g, respectively, and tdh+/orf8+ during winter season (0.90 log10 MPN/g). V. parahaemolyticus tlh+ densities were associated to salinity (R(2)=0.372, P<0.022), tdh+/trh+ to turbidity (R(2)=0.597, P<0.035), and orf8+ to temperature, salinity, and pH (R(2)=0.964, P<0.001). The exposure to salinity and temperature conditions during winter and spring seasons regulated the dynamics of V. parahaemolyticus harboring potentially pathogenic genotypes within the oyster. The adaptive response of V. parahaemolyticus to seasonal environmental changes may lead to an increase in survival and virulence, threatening the seafood safety and increasing the risk of illness.

Vibrio parahaemolyticus: a review on the pathogenesis, prevalence, and advance molecular identification techniques

Vibrio parahaemolyticus is a Gram-negative halophilic bacterium that is found in estuarine, marine and coastal environments. V. parahaemolyticus is the leading causal agent of human acute gastroenteritis following the consumption of raw, undercooked, or mishandled marine products. In rare cases, V. parahaemolyticus causes wound infection, ear infection or septicaemia in individuals with pre-existing medical conditions. V. parahaemolyticus has two hemolysins virulence factors that are thermostable direct hemolysin (tdh)-a pore-forming protein that contributes to the invasiveness of the bacterium in humans, and TDH-related hemolysin (trh), which plays a similar role as tdh in the disease pathogenesis. In addition, the bacterium is also encodes for adhesions and type III secretion systems (T3SS1 and T3SS2) to ensure its survival in the environment. This review aims at discussing the V. parahaemolyticus growth and characteristics, pathogenesis, prevalence and advances in molecular identification techniques.

Phylogenetic and in silico functional analyses of thermostable-direct hemolysin and tdh-related encoding genes in Vibrio parahaemolyticus and other Gram-negative bacteria

Emergence and spread of pandemic strains of Vibrio parahaemolyticus have drawn attention to make detailed study on their genomes. The pathogenicity of V. parahaemolyticus has been associated with thermostable-direct hemolysin (TDH) and/or TDH-related hemolysin (TRH). The present study evaluated characteristics of tdh and trh genes, considering the phylogenetic and in silico functional features of V. parahaemolyticus and other bacteria. Fifty-two tdh and trh genes submitted to the GenBank were analyzed for sequence similarity. The promoter sequences of these genes were also analyzed from transcription start point to -35 regions and correlated with amino acid substitution within the coding regions. The phylogenetic analysis revealed that tdh and trh are highly distinct and also differ within the V. parahaemolyticus strains that were isolated from different geographical regions. Promoter sequence analysis revealed nucleotide substitutions and deletions at -18 and -19 positions among the pandemic, prepandemic, and nonpandemic tdh sequences. Many amino acid substitutions were also found within the signal peptide and also in the matured protein region of several TDH proteins as compared to TDH-S protein of pandemic V. parahaemolyticus. Experimental evidences are needed to recognize the importance of substitutions and deletions in the tdh and trh genes.

Seasonal abundance of total and pathogenic Vibrio parahaemolyticus isolated from American oysters harvested in the Mandinga Lagoon System, Veracruz, Mexico: implications for food safety

The abundance of total and pathogenic Vibrio parahaemolyticus (Vp) strains in American oysters (Crassostrea virginica) harvested in two different harvest sites from the Mandinga lagoon System was evaluated monthly for 1 year (January through December 2012). Frequencies of species-specific genes and pathogenic genes exhibited a seasonal distribution. The annual occurrence of Vp with the species-specific tlh gene (tlh(+)) was significantly higher during the winter windy season (32.50%) and spring dry season (15.0%), with the highest densities observed during spring dry season at 283.50 most probable number (MPN)/g (lagoon bank A, near human settlements), indicating the highest risk of infection during warmer months. Pathogenic Vp tlh(+)/tdh(+) frequency was significantly higher during the winter windy and the spring dry seasons at 22.50 and 10.00%, respectively, with highest densities of 16.22 and 41.05 MPN/g (bank A), respectively. The tlh/trh and tdh/trh gene combinations were also found in Vp isolates during the spring dry season at 1.25 and 1.3%, respectively, with densities of 1.79 and 0.4 MPN/g (bank A), respectively. The orf8 genes were detected during the winter windy season (1.25%) with highest densities of 5.96 MPN/g (bank A) and 3.21 MPN/g (bank B, near mangrove islands and a heron nesting area). Densities of Vp tdh(+) were correlated (R(2) = 0.245, P < 0.015) with those of Vp orf8(+). The seasonal dynamics of Vp harboring pathogenic genes varied with seasonal changes, with very high proportions of Vp tdh(+) and Vp orf8(+) isolates in the winter windy season at 46.2 and 17.0%, respectively, which suggests that environmental factors may differentially affect the abundance of pathogenic subpopulations. Although all densities of total Vp (Vp tlh(+)) were lower than 10(4) MPN/g, thus complying with Mexican regulations, the presence of pathogenic strains is a public health concern. Our results suggest that total Vp densities may not be appropriate for assessing oyster contamination and predicting the risk of infection. Evaluation of the presence of pathogenic strains would be a better approach to protecting public health.

A multiplex PCR assay for simultaneous detection of Escherichia coli O157:H7, Bacillus cereus, Vibrio parahaemolyticus, Salmonella spp., Listeria monocytogenes, and Staphylococcus aureus in Korean ready-to-eat food

A multiplex polymerase chain reaction (PCR) assay was developed for simultaneous detection of Escherichia coli O157:H7, Bacillus cereus, Vibrio parahaemolyticus, Salmonella spp., Listeria monocytogenes, and Staphylococcus aureus in various Korean ready-to-eat foods. The six specific primer pairs for multiplex PCR were selected based on the O157 antigen (rfbE) gene of E. coli O157:H7, the DNA gyrase subunit B (gyrB) gene of B. cereus, the toxin regulatory protein (toxR) gene of V. parahaemolyticus, the invasion protein A (invA) gene of Salmonella spp., the hemolysin (hly) gene of L. monocytogenes, and the thermonuclease (nuc) gene of S. aureus. The 16S rRNA gene was targeted as an internal control gene in the presence of bacterial DNA. The specificity and sensitivity assays for multiplex primer pairs were investigated by testing different strains. When this multiplex PCR assay was applied to evaluate the validity of detecting six foodborne pathogens in artificially inoculated several ready-to-eat food samples, the assay was able to specifically simultaneously detect as few as 1 colony-forming unit/mL of each pathogen after enrichment for 12 h. Their presence in naturally contaminated samples also indicates that the developed multiplex PCR assay is an effective and informative supplement for practical use.

Pandemic Vibrio parahaemolyticus O3:K6 on the American continent

Vibrio parahaemolyticus is one of the most important seafood-borne bacterial in recent years and is the leading causal agent of human acute gastroenteritis, primarily following the consumption of raw, undercooked or mishandled marine products. Until 1996, infections caused by V. parahaemolyticus were generally associated with diverse serovars. However, in February 1996, a unique serovar (O3:K6) of V. parahaemolyticus with specific genetic markers (tdh, toxRS/New and/or orf8) appeared abruptly in Kolkata, India. In subsequent years, O3:K6 isolates similar to those isolated in Kolkata have been reported from food borne outbreaks in Southeast Asia, as well as in the Atlantic and Gulf coasts of the United States (U.S). More recently, there have been reports in Europe, Africa and Central and South America. Specifically, in the American continent, some countries have reported cases of gastroenteritis due to the pandemic O3:K6 strain and its serovariants; the pandemic strain was first detected in Peru (1996, >100 cases), subsequently spreading to Chile in 1998 (>16,804 human cases), to the U.S. in 1998 (>700 cases), to Brazil in 2001 (>18 cases) and to Mexico in 2004 (>1200 cases). The arrival of the pandemic clone on the American continent may have resulted in a significant shift on the epidemic dynamics of V. parahaemolyticus. However, although O3:K6 is the predominant serovar of the recognized clinical strains in some countries in the Americas, a decrease in clinical cases caused by O3:K6 and an increase in cases associated with a new serotype (O3:K59, Chile) have been recently reported. The emergence and worldwide dissemination of O3:K6 and other pandemic strains since 1996 have come to represent a threat to public health and should concern health authorities. This review focuses on the presence, distribution and virulence factors of the V. parahaemolyticus O3:K6 pandemic clone and its serovariants in clinical and environmental strains on the American continent.

Isolation and identification of Vibrio parahaemolyticus from seawater and sediment samples in the southern coast of the Caspian Sea

The objectives of this study were to investigate the occurrence of Vibrio parahaemolyticus in the seawater and its sediment by molecular techniques and conventional microbiological methods. Of 300 samples analyzed, 20.3 % was recorded positive for V. parahaemolyticus. Of the 62 strains isolated, 26 (8.3 %) were obtained from the seawater samples, and 36 (12 %); from sediments. Only three strains (4.83 %) showed hemolytic activity in Wagatsuma agar. The results of this study demonstrated the presence of V. parahaemolyticus in the southern coast of the Caspian Sea (Northern Iran). Furthermore, the PCR approach proved useful for reliable confirmation of species identification. V. parahaemolyticus is an important human pathogen responsible for food-borne gastroenteritis worldwide. These findings indicated the potential sanitary risk associated with the presence of pathogenic V. parahaemolyticus in the Caspian Sea.

Ocurrence of Vibrio spp., positive coagulase staphylococci and enteric bacteria in oysters (Crassostrea gigas) harvested in the south bay of Santa Catarina island, Brazil

The aim of this study was to assess the contamination of oysters (Crassostrea gigas), harvested in six different regions of the South Bay of Santa Catarina Island, with Coliforms at 45 ºC, Escherichia coli, Vibrio spp., positive coagulase staphylococci, and Salmonella sp. over a period of one year. One hundred eighty oyster samples were collected directly from their culture sites and analyzed. Each sample consisted of a pool of 12 oysters. All of the samples analyzed showed absence of Salmonella, 18 (10%) samples showed presence of Escherichia coli, 15 (8.3%) samples were positive for V. alginolyticus, and Vibriocholerae was detected in 4 samples (2.2%). The counts of positive-coagulase staphylococci varied from <10 to 1.9 x 102 CFU.g-1, whereas the counts of Coliforms at 45 ºC and E. coli ranged from <3 to 1.5 x 102 MPN.g-1 and <3 and 4.3 x 10 MPN.g-1, respectively. Counts of V. parahaemolyticus and V. vulnificus ranged between <3 and 7 MPN.g-1, for both microorganisms. This suggests the need for monitoring these Vibrios contamination in oysters. Based on the results of the microbiological assays, the samples analyzed showed acceptable bacteriological quality, i.e., they were within the parameters established by Brazilian Legislation.

Genome-wide characterization of Vibrio phage φpp2 with unique arrangements of the mob-like genes

Background

Vibrio parahaemolyticus is associated with gastroenteritis, wound infections, and septicemia in human and animals. Phages can control the population of the pathogen. So far, the only one reported genome among giant vibriophages is KVP40: 244,835 bp with 26% coding regions that have T4 homologs. Putative homing endonucleases (HE) were found in Vibrio phage KVP40 bearing one segD and Vibrio cholerae phage ICP1 carrying one mobC/E and one segG.

Results

A newly isolated Vibrio phage ϕpp2, which was specific to the hosts of V. parahaemolyticus and V. alginolyticus, featured a long nonenveloped head of ~90 × 150 nm and tail of ~110 nm. The phage can survive at 50°C for more than one hour. The genome of the phage ϕpp2 was sequenced to be 246,421 bp, which is 1587 bp larger than KVP40. 383 protein-encoding genes (PEGs) and 30 tRNAs were found in the phage ϕpp2. Between the genomes of ϕpp2 and KVP40, 254 genes including 29 PEGs for viral structure were of high similarity, whereas 17 PEGs of KVP40 and 21 PEGs of ϕpp2 were unmatched. In both genomes, the capsid and tail genes have been identified, as well as the extensive representation of the DNA replication, recombination, and repair enzymes. In addition to the three giant indels of 1098, 1143 and 3330 nt, ϕpp2 possessed unique proteins involved in potassium channel, gp2 (DNA end protector), tRNA nucleotidyltransferase, and mob-type HEs, which were not reported in KVP40. The ϕpp2 PEG274, with strong promoters and translational initiation, was identified to be a mobE type, flanked by NrdA and NrdB/C homologs. Coincidently, several pairs of HE-flanking homologs with empty center were found in the phages of Vibrio phages ϕpp2 and KVP40, as well as in Aeromonas phages (Aeh1 and Ae65), and cyanophage P-SSM2.

Conclusions

Vibrio phage ϕpp2 was characterized by morphology, growth, and genomics with three giant indels and different types of HEs. The gene analysis on the required elements for transcription and translation suggested that the ϕpp2 PEG274 was an active mobE gene. The phage was signified to be a new species of T4-related, differing from KVP40.

Association of pandemic Vibrio parahaemolyticus O3:K6 present in the coastal environment of Northwest Mexico with cases of recurrent diarrhea between 2004 and 2010

In 2004, more than 1,230 cases of gastroenteritis due to pandemic O3:K6 strains of Vibrio parahaemolyticus were reported in southern Sinaloa, a state in Northwestern Mexico. Recurrent sporadic cases arose from 2004 to 2010, spreading from the south to the north. In the present study, Vibrio parahaemolyticus was detected in both environmental samples and clinical cases along the Pacific coast of Sinaloa during 2004 to 2010. An evaluation was made of the serotypes, distribution of virulence genes, and presence of pandemic O3:K6 strains. A total of 144 strains were isolated from environmental samples (from sediment, seawater, and shrimp), and 154 clinical strains were isolated. A total of 10 O serogroups and 30 serovars were identified in the strains. Environmental strains (n = 144) belonged to 10 O serogroups and 28 serovars, while clinical strains (n = 154) belonged to 8 O serogroups and 14 serovars. Ten serovars were shared by both environmental and clinical strains. Among 144 environmental isolates, 4.1% (6/144) belonged to the pandemic clone, with 83.3% containing the orf8 gene and with O3:K6 accounting for 67%. On the other hand, pathogenic strains (tdh and/or trh) accounted for 52% (75/144) of the environmental isolates. Interestingly, among 154 clinical isolates, 80.5% (124/154) were pandemic strains, with O3:K6 (tdh, toxRS(new), and orf8) representing the predominant serovar (99.2%, 123/124). Overall, our results indicate that in spite of a high serodiversity and prevalence of pathogenic Vibrio parahaemolyticus in the environment, the pandemic strain O3:K6 caused >79% of reported cases between 2004 and 2010 in Sinaloa, Mexico.

Ecological determinants of the occurrence and dynamics of Vibrio parahaemolyticus in offshore areas

The life cycle of Vibrio parahaemolyticus has been conventionally associated with estuarine areas characterized by moderate salinity and warm seawater temperatures. Recent evidence suggests that the distribution and population dynamics of V. parahaemolyticus may be shaped by the existence of an oceanic transport of communities of this organism mediated by zooplankton. To evaluate this possibility, the presence of V. parahaemolyticus in the water column of offshore areas of Galicia was investigated by PCR monthly over an 18-month period. Analysis of zooplankton and seawater showed that the occurrence of V. parahaemolyticus in offshore areas was almost exclusively associated with zooplankton and was present in 80% of the samples. The influence of environmental factors assessed by generalized additive models revealed that the abundance and seasonality of V. parahaemolyticus in zooplankton was favoured by the concurrence of downwelling periods that promoted the zooplankton patchiness. These results confirm that offshore waters may be common habitats for V. parahaemolyticus, including strains with virulent traits. Additionally, genetically related populations were found in offshore zooplankton and in estuaries dispersed along 1500 km. This finding suggests that zooplankton may operate as a vehicle for oceanic dispersal of V. parahaemolyticus populations, connecting distant regions and habitats, and thereby producing impacts on the local community demography and the spread of Vibrio-related diseases.

Development of a polymerase chain reaction (PCR) test for the detection of virulent forms of Vibrio parahaemolyticus

Vibrio parahaemolyticus is a marine bacterium and some strains cause gastroenteritis in humans. Clinical isolates are thought to possess virulence factors that are absent from the majority of environmental isolates. Use of randomly amplified polymorphic DNA (RAPD)-PCR produced a unique 600 bp amplicon (band Y) in the majority of clinical isolates and rarely in environmental isolates tested. The DNA from band Y was cloned and sequenced and found to code for an outer membrane protein (OMP). Two polymerase chain reaction (PCR) primers were designed to specifically amplify a 200 bp unique sequence from presumptive virulent strains (PCR-OMP). The virulence of 23 clinical and 32 environmental isolates was assessed in cytotoxicity tests by treatment of Caco-2 cells with extracellular products (ECPs). All but two of the clinical isolates (91%) were positive for the 200 bp PCR-OMP and their ECPs produced a significantly higher (p < 0.05) lactate dehydrogenase (LDH) release (mean 72.88%) than the ECPs of environmental isolates (mean 15.3%) with the exception of one environmental isolate that produced the 200 bp amplicon. A positive 200 bp PCR-OMP is strongly correlated with virulence, as determined by the cytotoxicity assay, and identified virulent forms better than current PCR tests for tdh, trh or T3SS2.

Serogroup, virulence, and genetic traits of Vibrio parahaemolyticus in the estuarine ecosystem of Bangladesh

Forty-two strains of Vibrio parahaemolyticus were isolated from Bay of Bengal estuaries and, with two clinical strains, analyzed for virulence, phenotypic, and molecular traits. Serological analysis indicated O8, O3, O1, and K21 to be the major O and K serogroups, respectively, and O8:K21, O1:KUT, and O3:KUT to be predominant. The K antigen(s) was untypeable, and pandemic serogroup O3:K6 was not detected. The presence of genes toxR and tlh were confirmed by PCR in all but two strains, which also lacked toxR. A total of 18 (41%) strains possessed the virulence gene encoding thermostable direct hemolysin (TDH), and one had the TDH-related hemolysin (trh) gene, but not tdh. Ten (23%) strains exhibited Kanagawa phenomenon that surrogates virulence, of which six, including the two clinical strains, possessed tdh. Of the 18 tdh-positive strains, 17 (94%), including the two clinical strains, had the seromarker O8:K21, one was O9:KUT, and the single trh-positive strain was O1:KUT. None had the group-specific or ORF8 pandemic marker gene. DNA fingerprinting employing pulsed-field gel electrophoresis (PFGE) of SfiI-digested DNA and cluster analysis showed divergence among the strains. Dendrograms constructed using PFGE (SfiI) images from a soft database, including those of pandemic and nonpandemic strains of diverse geographic origin, however, showed that local strains formed a cluster, i.e., "clonal cluster," as did pandemic strains of diverse origin. The demonstrated prevalence of tdh-positive and diarrheagenic serogroup O8:K21 strains in coastal villages of Bangladesh indicates a significant human health risk for inhabitants.

Molecular analysis of the emergence of pandemic Vibrio parahaemolyticus

Background

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

Results

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

Conclusion

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

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

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

A novel multiplex PCR assay for rapid and simultaneous detection of five pathogenic bacteria: Escherichia coli O157:H7, Salmonella, Staphylococcus aureus, Listeria monocytogenes, and Vibrio parahaemolyticus

Rapid and sensitive detection techniques for foodborne pathogens are important to the food industry. However, traditional detection methods rely on bacterial culture in combination with biochemical tests, a process that typically takes 4 to 7 days to complete. Thus, this study was conducted to address the issue of time lag inherent in traditional methods by developing a novel PCR assay for each of five foodborne pathogenic bacteria. This new system consists of a simultaneous screening method using multiplex PCR in a single reaction tube for the rapid and sensitive detection of each of the five bacteria. Specific primers for multiplex PCR amplification of the Shiga-like toxin (verotoxin type II), femA (cytoplasmic protein), toxR (transmembrane DNA binding protein), iap (invasive associative protein), and invA (invasion protein A) genes were designed to allow simultaneous detection of Escherichia coli O157:H7, Staphylococcus aureus, Vibrio parahaemolyticus, Listeria monocytogenes, and Salmonella, respectively. To confirm the specificity of each primer pair for the respective target gene, three types of experiments were carried out using boiled cell lysates and their DNAs. In the multiplex PCR with mixed DNA samples, specific bands for corresponding genes were simultaneously detected from a single reaction. The detection of all five foodborne pathogenic bacteria could be completed in less than 24 h with this novel PCR method.

Vibrios patogênicos em ostras (Crassostrea rhizophorae) servidas em restaurantes no Rio de Janeiro: um alerta para a Saúde Pública

Avaliaram-se 40 amostras de ostras (Crassostrea rhizophorae) servidas in natura em 15 restaurantes da Cidade do Rio de Janeiro, a fim de investigar a presença de Vibrio spp. As amostras de ostras foram analisadas e submetidas a enriquecimento em água peptonada alcalina adicionada de 1 e 3% de NaCl, incubadas a 37°C por 24 horas. Em seguida, os cultivos foram semeados em agar tiossulfato citrato bile sacarose e as colônias suspeitas foram submetidas à caracterização bioquímica. Vibrio parahaemolyticus, Vibrio carchariae, Vibrio alginolyticus e Vibrio vulnificus representaram as principais espécies (> 60%) isoladas a partir das ostras in natura.

Outbreak of gastroenteritis caused by the pandemic Vibrio parahaemolyticus O3 : K6 in Mexico

During 2003 and during late September of 2004, more than 1230 cases of gastroenteritis were reported in the south of Sinaloa State, north-western Mexico. All cases were attributed to the consumption of raw or undercooked shrimp collected at the Huizache-Caimanero lagunary system. Vibrio parahaemolyticus was identified by standard biochemical methods, and many strains were positive for PCR amplifications of the tlh and tdh genes and negative for the trh gene. A representative strain belonged to the O3:K6 serogroup. This is the first outbreak of gastroenteritis caused by the pandemic strains of O3:K6 V. parahaemolyticus in México.

Evaluation of an alkaline phosphatase-labeled oligonucleotide probe for the detection and enumeration of the thermostable-related hemolysin (trh) gene of Vibrio parahaemolyticus

Reliable methods are needed to detect total and pathogenic Vibrio parahaemolyticus. One marker of V. parahaemolyticus virulence is the thermostable-related hemolysin. We developed an alkaline phosphatase-labeled DNA probe method for the specific detection and enumeration of trh-positive V. parahaemolyticus by colony hybridization. The probe was tested against a panel of 200 bacterial strains and determined to be specific for trh-positive V. parahaemolyticus. Additionally, the trh alkaline phosphatase probe colony hybridization was successfully used to detect and enumerate trh-positive V. parahaemolyticus in seafood and water samples collected from the United States and the United Kingdom.

Four genomic islands that mark post-1995 pandemic Vibrio parahaemolyticus isolates

Background

Vibrio parahaemolyticus is an aquatic, halophilic, Gram-negative bacterium, first discovered in 1950 in Japan during a food-poisoning outbreak. Infections resulting from consumption of V. parahaemolyticus have increased globally in the last 10 years leading to the bacterium's classification as a newly emerging pathogen. In 1996 the first appearance of a pandemic V. parahaemolyticus clone occurred, a new O3:K6 serotype strain that has now been identified worldwide as a major cause of seafood-borne gastroenteritis.

Results

We examined the sequenced genome of V. parahaemolyticus RIMD2210633, an O3:K6 serotype strain isolated in Japan in 1996, by bioinformatic analyses to uncover genomic islands (GIs) that may play a role in the emergence and pathogenesis of pandemic strains. We identified 7 regions ranging in size from 10 kb to 81 kb that had the characteristics of GIs such as aberrant base composition compared to the core genome, presence of phage-like integrases, flanked by direct repeats and the absence of these regions from closely related species. Molecular analysis of worldwide clinical isolates of V. parahaemolyticus recovered over the last 33 years demonstrated that a 24 kb region named V. parahaemolyticus island-1 (VPaI-1) encompassing ORFs VP0380 to VP0403 is only present in new O3:K6 and related strains recovered after 1995. We investigated the presence of 3 additional regions, VPaI-4 (VP2131 to VP2144), VPaI-5 (VP2900 to VP2910) and VPaI-6 (VPA1254 to VPA1270) by PCR assays and Southern blot analyses among the same set of V. parahaemolyticus isolates. These 3 VPaI regions also gave similar distribution patterns amongst the 41 strains examined.

Conclusion

The 4 VPaI regions examined may represent DNA acquired by the pandemic group of V. parahaemolyticus isolates that increased their fitness either in the aquatic environment or in their ability to infect humans.

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

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

Vibrio parahaemolyticus, Vibrio vulnificus and microorganisms of fecal origin in mussels (Mytilus galloprovincialis) sold in the Puglia region (Italy)

Mytilus galloprovincialis is one of the most commonly consumed of all bivalve molluscs. The consumption of raw bivalve molluscs has caused outbreaks of food poisoning due to Vibrio parahaemolyticus and Vibrio vulnificus. This paper reports the results of a survey on the presence of V. parahaemolyticus, V. vulnificus fecal coliform bacteria, Escherichia coli and Salmonella spp. in 600 M. galloprovincialis samples collected from retail outlets in the Puglia region. V. parahaemolyticus and V. vulnificus were found in 47 (7.83%) and 17 (2.83%) of the samples, respectively. One sample (0.16%) was contaminated with Salmonella spp. but no relationship was observed between vibrios and fecal coliforms and E. coli. There were no significant differences among vibrios present in bivalve molluscs during the 3-year survey.