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

Development of Multienzyme Isothermal Rapid Amplification (MIRA) Combined with Lateral-Flow Dipstick (LFD) Assay to Detect Species-Specific tlh and Pathogenic trh and tdh Genes of Vibrio parahaemolyticus

Vibrio parahaemolyticus causes severe gastroenteritis in humans after consuming contaminated raw or undercooked seafood. A species-specific marker, the thermolabile hemolysin (tlh) gene, and two pathogenic markers, thermostable-related hemolysin (trh) and thermostable-direct hemolysin (tdh) genes, have been used to identify V. parahaemolyticus and determine its pathogenicity using both PCR and qPCR assays. To enable testing in field conditions with limited resources, this study aimed to develop a simple and rapid method to detect the species-specific (tlh) and pathogenic (trh and tdh) genes of V. parahaemolyticus using multienzyme isothermal rapid amplification (MIRA) combined with a lateral-flow dipstick (LFD). The amplification of the tlh, trh, and tdh genes could be completed within 20 min at temperatures ranging from 30 to 45 °C (p < 0.05). The test yielded positive results for V. parahaemolyticus but produced negative results for nine Vibrio species and eighteen foodborne pathogenic bacterial species. MIRA-LFD could detect 10 fg of DNA and 2 colony-forming units (CFU) of V. parahaemolyticus per reaction, demonstrating a sensitivity level comparable to that of qPCR, which can detect 10 fg of DNA and 2 CFU per reaction. Both MIRA-LFD and qPCR detected seven tlh-positive results from thirty-six oyster samples, whereas one positive result was obtained using the PCR assay. No positive results for the trh and tdh genes were obtained from any oyster samples using MIRA-LFD, PCR, and qPCR. This study suggests that MIRA-LFD is a simple and rapid method to detect species-specific and pathogenic genes of V. parahaemolyticus with high sensitivity.

Vibrio pathogenicity island and phage CTX genes in Vibrio alginolyticus isolated from different aquatic environments

In the present study, we investigated the presence of four Vibrio cholerae virulence genes (ctxA, VPI, Zot and ace) in 36 Vibrio alginolyticus isolates obtained from different seawater, sediments and aquatic organisms. We tested the virulence of 13 V. alginolyticus strains against juveniles of Sparus aurata and this virulence was correlated with the presence of V. cholerae virulence genes. A positive amplification for the virulence pathogenicity island was produced by five V. alginolyticus strains and four for cholerae toxin. Some of the V. alginolyticus strains are pathogenic to aquatic animals and might have derived their virulence genes from V. cholerae. V. alginolyticus strains can be considered as a possible reservoir of V. cholerae virulence genes.

Distribution of Vibrio parahaemolyticus in Farmed Shrimp Penaeus vannamei, Farm Water and Sediment

The halophilic marine bacterium Vibrio parahaemolyticus is a zoonotic pathogen associated with wild-caught and farmed shrimp. The bacterium is an important cause of gastroenteritis associated with the consumption of raw or undercooked seafood. In the present study, the prevalence and human pathogenic potential of Vibrio parahaemolyticus in Penaeus vannamei (tissue and hepatopancreas) and the farm environment (water and sediment) was investigated by conventional culture and molecular techniques. The total Vibrio counts of P. vannamei ranged from <1 CFU/mL in hemolymph to 7.61 log CFU/g in the hepatopancreas. The sediment samples consistently showed the counts of 6-7 log CFU/g, while the pond water had Vibrio counts in the range of 2-3 log CFU/ml. Of 120 Vibrio isolates identified, 87 were confirmed as V. parahaemolyticus based on the toxR and tlh gene-specific PCR. The virulence marker gene tdh was not detected in any of the isolates, while the trh gene was detected in 3 (3.6%) isolates. Although the incidence of pathogenic V. parahaemolyticus in farmed P. vannamei is low, the high numbers of total vibrios and V. parahaemolyticus demand constant monitoring of animals and the farm environment for human pathogenic strains of V. parahaemolyticus.

Genetic and serological characterization of capsular antigen untypeable Vibrio parahaemolyticus strains reveal novel K serotypes and epidemiological characteristics in Shandong, China

Vibrio parahaemolyticus, which is commonly found in marine and estuarine environments worldwide and isolated from aquatic products, is one of the most important food-borne pathogens. Among the various typing methods, serotyping is widely accepted and utilized by infectious disease specialists and infection control agencies for the detection and epidemiological investigation of this pathogen. Thus far, 13 O serotypes and 71 K serotypes have been defined; however, untypeable strains are frequently isolated during routine detection, and some new O and/or K antigens have been identified and characterized. During a serotyping survey in Shandong province, China from 2016 to 2018, we collected 411 clinical V. parahaemolyticus strains and found that nine of them are untypeable K antigen strains. In this study, we identified three K serotypes of V. parahaemolyticus through in-depth genetic analysis of the K antigen gene cluster, serological tests, and the production of antisera. Among the nine strains, seven possess K untypeable 2 (KUT2) antigens, which have been reported recently by another group. However, two new O and K combinations (O3:KUT2 and O11:KUT2) were first characterized by us, with the remaining two each representing a novel K serotype. Moreover, through comparative genomic analysis, we showed that the Shandong KUT2 strains exhibit different virulence profiles compared to their identical K serotype partners from Zhejiang province, another Chinese coastal province; however, strains from these two regions are clustered into the same linage and may have evolved from a recent common ancestor. Additionally, one isolate, SD2016062, was phylogenetically similar to the strains associated with several local gastroenteritis outbreaks, with similar toxin patterns, suggesting its potential to cause sporadic occurrences of disease or even local pandemics. Finally, we developed a sero-specific PCR assay targeting the three novel K serotypes, which can monitor the V. parahaemolyticus spectrum for clinical and epidemiological purposes. Thus, we identified and characterized novel strains of V. parahaemolyticus and proposed a new technique for tracking the diversity of strains, which can help manage this food-borne pathogen.

Diversity of Vibrio parahaemolyticus in marine fishes of Bangladesh

AIMS

To determine the occurrence, diversity, antibiotic resistance and biofilm formation of Vibrio parahaemolyticus isolated from marine fishes in Bangladesh.

METHODS AND RESULTS

A total of 80 marine fishes were obtained from the local markets and examined for the presence of V. parahaemolyticus. All the isolated V. parahaemolyticus were characterized for the presence of virulence markers, thermostable direct hemolysin (TDH) or thermostable direct hemolysin related hemolysin (TRH). Isolates were serotyped and further characterized by enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR) typing to analyse the genetic diversity. Moreover, biofilm formation and antibiotic resistance patterns were also determined. About 63·75% (51/80) of the tested marine fishes were contaminated with V. parahaemolyticus. From the contaminated fishes, 71 representatives V. parahaemolyticus were isolated and none of them harboured tdh and trh virulence genes. Nine different O-groups and seven different K-types were found by serological analysis and the dominant serotype was O5:KUT. In ERIC-PCR analysis, eight clusters (A-H) were found and the most common pattern was A (46·5%). All of the isolates were resistant to ampicillin and 78·9% of isolates were resistant to streptomycin. The highest biofilm formation was found at 37°C compared to 25°C and 4°C.

CONCLUSION

Diverse V. parahaemolyticus are present in marine fishes in the local market of Bangladesh with antibiotic-resistant properties and biofilm formation capacity.

SIGNIFICANCE AND IMPACT OF THE STUDY

The widespread prevalence of diverse V. parahaemolyticus in marine fishes is an issue of serious concern, and it entails careful monitoring to ascertain the safety of seafood consumers.

Occurrence of antibiotic resistance among Gram negative bacteria isolated from effluents of fish processing plants in and around Mangalore

The presence of antibiotic-resistant bacteria in seafood not only poses a serious health risk for the consumers but also contributes to the spread of these antibiotic-resistant bacteria in the natural environments through the effluents discharged from the fish processing plants. The aims of this study were to isolate Gram-negative bacteria from the effluents of fish processing plants in and around Mangalore, India and to profile their antibiotic resistance pattern. Maximum resistance was seen for ampicillin (40.78%) followed by tetracycline (40.22%) and nitrofurantoin (29.05%). Further, the detection of genes that contribute to antibiotic resistance revealed the presence of sulfonamide resistance genes (sul1 and sul2) and extended spectrum β-lactamase genes (bla _CTX-M, bla _TEM) in a few isolates. The presence of such bacteria in fish processing effluents is a matter of great concern because they can contribute significantly to the antibiotic resistance in the natural environment. It is imperative that seafood processing plants follow the safe disposal of effluents in order to reduce or eliminate the antibiotic resistance menace.

Prevalence, Virulence Characterization, AMR Pattern and Genetic Relatedness of Vibrio parahaemolyticus Isolates From Retail Seafood of Kerala, India

Vibrio parahaemolyticus, a halophilic bacterium often found in the marine or estuarine environment is a well-known enteropathogen responsible for foodborne outbreaks associated with seafood. The pathogenic strains of V. parahaemolyticus are marked by the presence of thermostable direct hemoylsin (tdh) and/or TDH related hemolysin (trh) genes. This study aimed to investigate the prevalence and characteristics of potentially pathogenic V. parahaemolyticus in selected retail markets of Cochin, Kerala, along the south-western coast of the Indian subcontinent. One hundred samples collected from 10 retail markets were analyzed for the presence of pathogenic isolates of V. parahaemolyticus. Out of the 721 presumptive isolates, 648 were confirmed to be V. parahaemolyticus by toxR gene amplification, among which 29 were Kanagawa phenomenon (KP) positive. Among these potentially pathogenic isolates, 17 possessed the tdh gene whereas none of them had the trh gene. The faint amplification bands produced during the amplification of tdh gene from two isolates was confirmed by sequencing. Multiplex O serotyping identified O1 serotype as the most prevalent serotype among the 29 potentially pathogenic isolates. Further, studies on the pandemic nature of these isolates revealed that 14 of the 29 were positive for the PGS-PCR, whereas all the isolates were negative for GS-PCR and HU-α PCR. The antibiogram of the isolates revealed that three isolates had significant Multiple Antibiotic Resistance (MAR) index of 0.2 or above. Pathogenic isolates resistant to second, third and fourth generation Cephalosporins were found to be present in the seafood studied. The molecular fingerprinting studies using ERIC-PCR, and PFGE revealed that three of these isolates shared close genetic similarities with the clinical strains. The environmental and seafood isolates that produced faint amplification bands during the amplification of tdh gene suggests that the tdh gene often goes undetected in environmental isolates. The conventional methods used to identify the pathogenic V. parahaemolyticus would be good for clinical isolates, but a more elaborate method is recommended for the detection of tdh gene in environmental isolates. This is the first comprehensive study on pathogenic V. parahaemolyticus in Kerala, India and demonstrates for the first time, the isolation of potentially pathogenic V. parahaemolyticus, carrying tdh gene from seafood collected from retail markets in Kerala.

Review of Electrochemical DNA Biosensors for Detecting Food Borne Pathogens

The vital importance of rapid and accurate detection of food borne pathogens has driven the development of biosensor to prevent food borne illness outbreaks. Electrochemical DNA biosensors offer such merits as rapid response, high sensitivity, low cost, and ease of use. This review covers the following three aspects: food borne pathogens and conventional detection methods, the design and fabrication of electrochemical DNA biosensors and several techniques for improving sensitivity of biosensors. We highlight the main bioreceptors and immobilizing methods on sensing interface, electrochemical techniques, electrochemical indicators, nanotechnology, and nucleic acid-based amplification. Finally, in view of the existing shortcomings of electrochemical DNA biosensors in the field of food borne pathogen detection, we also predict and prospect future research focuses from the following five aspects: specific bioreceptors (improving specificity), nanomaterials (enhancing sensitivity), microfluidic chip technology (realizing automate operation), paper-based biosensors (reducing detection cost), and smartphones or other mobile devices (simplifying signal reading devices).

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.

Exposure Assessment and Sensitivity Analysis for Chilled Shrimp During Distribution: A Case Study of Home Delivery Services in Taiwan

In this study, we evaluated the temperature requirements for home delivery in Taiwan by considering food safety risks of chilled shrimp that may be contaminated with Vibrio parahaemolyticus. Pathogenic V. parahaemolyticus was chosen because it was the main cause of foodborne outbreaks originating from contaminated seafood in Taiwan. The risk of becoming ill due to consumption of raw shrimp was estimated to be 7.3 × 10^-3 per serving, estimated based on the real-time temperature profile. Lowering the maximum temperature to 7 °C during transit and cooking shrimps at 100 °C for 5 min could reduce the risk by more than 94%. These interventions, therefore, were suggested to be used as an integral part of temperature management control in the home delivery cold chain. These findings can help food authorities to institute temperature management policies and regulations to prevent broken cold chains and reduce food safety risks. PRACTICAL APPLICATION: This research may be applicable to home delivery services that deliver low-temperature food products, such as seafood products.

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.

Discovery on Antibiotic Resistance Patterns of Vibrio parahaemolyticus in Selangor Reveals Carbapenemase Producing Vibrio parahaemolyticus in Marine and Freshwater Fish

Vibrio parahaemolyticus, a Gram-negative halophilic bacterium is often associated with fish and fishery products, thus causing gastroenteritis in humans upon ingestion of contaminated food. V. parahaemolyticus has become a globally well-known pathogen with yearly reported cases in many countries. This study aimed to discover the antibiotic resistance patterns of V. parahaemolyticus as well as detect Carbapenem resistant isolates from marine and freshwater fish in Selangor. A total of 240 freshwater and marine fish samples collected from wet market and supermarket in Selangor were tested for the presence of V. parahaemolyticus. All the fish samples were determined positive for V. parahaemolyticus using conventional microbiological culture-based method. The toxR gene were detected via polymerase chain reaction (PCR) in 165/240 (69%) isolates. The two-virulence factor of V. parahaemolyticus, thermostable direct hemolysin (tdh) and TDH-related hemolysin (trh) was screened via PCR. As such, four isolates were trh+and none were tdh+. Majority of the isolates presented high resistance to ampicillin (88%), amikacin (64%), and kanamycin (50%). In addition, this study identified 19-imipenem resistant isolates isolated from freshwater and marine fish samples. Further analysis of these 19-imipenem resistant isolates revealed that the resistance toward imipenem was plasmid mediated after plasmid curing assay. The multiple antibiotics resistance index was >0.2 for 70% of the isolates. In summary, the results confirm the presence of V. parahaemolyticus in freshwater and marine fish samples in Selangor, Malaysia. To our best knowledge, this is the first report discovering the antibiotic resistant patterns and Carbapenem-resistant isolates of V. parahaemolyticus isolated from marine and freshwater fish samples in Selangor.

FORMAÇÃO DE BIOFILME APÓS ESTRESSE SUBLETAL POR Vibrio parahaemolyticus ISOLADOS DE CAMARÃO-ROSA (Farfantepenaeus paulensis)

Resumo O consumo de frutos do mar, como o camarão-rosa, contaminados com V. parahaemolyticus pode causar gastrenterite aguda. O objetivo deste trabalho foi verificar a capacidade de V. parahaemolyticus isolados de camarões provenientes do estuário da Lagoa dos Patos formarem biofilme após exposição a diferentes tipos de estresse subletal. Para obtenção das amostras, foram realizadas 12 coletas de Farfantepenaeus paulensis, durante o período de safra de 2016. As amostras foram analisadas quanto à presença de V. parahaemolyticus. As cepas foram avaliadas quanto à capacidade de produção de biofilme em placas de microtitulação, tanto antes como após serem submetidas a diferentes tipos de estresse subletal. V. parahaemolyticus foi isolado de 16,66% (2/12) das amostras. Uma das duas cepas isoladas foi capaz de formar biofilme, sendo classificada como fraca formadora de biofilme, a outra foi classificada como não formadora de biofilme. Nenhuma das cepas alterou sua capacidade de formar biofilme quando submetida aos estresses de 4 ºC e 20 ºC; contudo, com relação aos estresses de 42 ºC e pH ácido, cada cepa respondeu de uma maneira diferente.

Direct bacterial loop-mediated isothermal amplification detection on the pathogenic features of the nosocomial pathogen - Methicillin resistant Staphylococcus aureus strains with respiratory origins

Loop-mediated isothermal amplification based detection assays using bacterial culture or colony for direct detection of methicillin resistant Staphylococcus aureus(MRSA) had been developed and evaluated, followed by its extensive application on a large scale of clinical MRSA isolated from respiratory origins, including nasal swabs and sputums. Six primers, including outer primers, inner primers and loop primers, were specifically designed for recognizing eight distinct sequences on four targets: 16SrRNA, femA, mecA and orfX. Twenty-seven reference strains were used to develop, evaluate and optimize this assay. Then, a total of 532 clinical MRSA isolates were employed for each detected targets. And the results were determined through both visual observation of the color change by naked eye and electrophoresis. The specific of each primer had been confirmed, and the optimal amplification was obtained under 65 °C for 40 min. The limit of detections (LOD) of bacteria culture LAMP assays were determined to be 10⁴ CFU/ml for 16S rRNA, femA, as well as orfX and 10⁵ CFU/ml for mecA, respectively. The established novel assays on MRSA detection may provide new strategies for rapid detection of foodborne pathogens.

Loop-mediated isothermal amplification (LAMP): A novel rapid detection platform for pathogens

Foodborne bacterial infections and diseases have been considered to be a major threat for public health in the worldwide. Increased incidence of human diseases caused by foodborne pathogens have been correlated with growing world population and mobility. Loop-mediated isothermal amplification (LAMP) has been regarded as an innovative gene amplification technology and emerged as an alternative to PCR-based methodologies in both clinical laboratory and food safety testing. Nowadays, LAMP has been applied to detection and identification on pathogens from microbial diseases, as it showed significant advantage in high sensitivity, specificity and rapidity. The high sensitivity of LAMP enables detection of the pathogens in sample materials even without time consuming sample preparation. An overview of LAMP mainly containing the development history, reaction principle and its application to four kind of foodborne pathogens detection are presented in this paper. As concluded, with the advantages of rapidity, simplicity, sensitivity, specificity and robustness, LAMP is capable of applications for clinical diagnosis as well as surveillance of infection diseases. Moreover, the main purpose of this paper is to provide theoretical basis for the clinical application of LAMP technology.

Incidence and prevalence of Vibrio parahaemolyticus in seafood: a systematic review and meta-analysis

Vibrio parahaemolyticus is an important seafood borne human pathogen worldwide due to it occurrence, prevalence and ability to cause gastrointestinal infections. This current study aim at investigating the incidence and prevalence of V. parahaemolyticus in seafood using systematic review-meta-analysis by exploring heterogeneity among primary studies. A comprehensive systematic review and meta-analysis of peer reviewed primary studies reported between 2003 and 2015 for the occurrence and prevalence of V. parahaemolyticus in seafood was conducted using “isolation”, “detection”, “prevalence”, “incidence”, “occurrence” or “enumeration” and V. parahaemolyticus as search algorithms in Web of Science (Science Direct) and ProQuest of electronic bibliographic databases. Data extracted from the primary studies were then analyzed with fixed effect meta-analysis model for effect rate to explore heterogeneity between the primary studies. Publication bias was evaluated using funnel plot. A total of 10,819 articles were retrieved from the data bases of which 48 studies met inclusion criteria. V. parahaemolyticus could only be isolated from 2761 (47.5 %) samples of 5811 seafood investigated. The result of this study shows that incidence of V. parahaemolyticus was more prevalent in oysters with overall prevalence rate of 63.4 % (95 % CI 0.592–0.674) than other seafood. Overall prevalence rate of clams was 52.9 % (95 % CI 0.490–0.568); fish 51.0 % (95 % CI 0.476–0.544); shrimps 48.3 % (95 % CI 0.454–0.512) and mussels, scallop and periwinkle: 28.0 % (95 % CI 0.255–0.307). High heterogeneity (p value <0.001; I² = 95.291) was observed mussel compared to oysters (I² = 91.024). It could be observed from this study that oysters harbor V. parahaemolyticus based on the prevalence rate than other seafood investigated. The occurrence and prevalence of V. parahaemolyticus is of public health importance, hence, more studies involving seafood such as mussels need to be investigated.

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.

Impact of seafood regulations for Vibrio parahaemolyticus infection and verification by analyses of seafood contamination and infection

Consumption of seafood contaminated with Vibrio parahaemolyticus causes foodborne infections, which are on the rise owing to increased consumption of raw seafood in Asia, Europe, North America, and other regions. V. parahaemolyticus infections have been common in Japan since the 1960s. Following an epidemic in 1997, the Japanese Ministry of Health, Labour, and Welfare instituted regulations for seafood in 1999, which appear to be reducing V. parahaemolyticus infections. In this review, we describe the scientific findings for these regulations. Analyses of the V. parahaemolyticus serotypes and isolate characteristics in samples from infected patients and contaminated seafood are discussed. In addition, based on the results of a survey, we show that new food safety regulations have led to improvements in food hygiene at many seafood retail shops, food service facilities, and restaurants. This example from Japan could be of immense help to control foodborne infections in other countries.

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.

Presence of T3SS2β genes in trh⁺ Vibrio parahaemolyticus isolated from seafood harvested along Mangalore coast, India

Vibrio parahaemolyticus is a seafood-borne pathogen autochthonous to the marine and estuarine ecosystem, responsible for gastroenteritis when contaminated raw seafood is consumed. The pathogenicity has been associated with thermostable direct haemolysin (TDH) and TDH-related haemolysin (TRH). Of late, the presence of T3SS2α and T3SS2β gene clusters has been well documented in clinical isolates of Vibrio parahaemolyticus and known to play an essential role in pathogenesis. However, reports on the presence of T3SSβ genes in V. parahaemolyticus isolated from the seafood and/or environmental samples are scanty. In this study, we have identified and analysed the distribution of the T3SS2β genes in V. parahaemolyticus isolated from seafood harvested along southwest coast of India. Results showed that T3SS2β genes are solely associated with trh⁺ and tdh⁺ /trh⁺ strains of V. parahaemolyticus. Reverse transcriptase PCR (RT-PCR) showed that the T3SS2β genes identified in trh⁺ V. parahaemolyticus were transcriptionally active. To our knowledge, this study appears to be the first description on the presence of T3SS2β-positive V. parahaemolyticus isolated from seafood in India. The study of T3SS2 along with other virulence factors will help in better understanding of the risk of seafood-borne illness due to V. parahaemolyticus.

SIGNIFICANCE AND IMPACT OF THE STUDY

T3SSs (α or β) are the important virulence factors of Vibrio parahaemolyticus that contribute to their pathogenicity in humans. This study demonstrated the presence of T3SS2β genes in V. parahaemolyticus isolated from the seafood harvested along Mangalore coast. RT-PCR showed that the T3SS2β genes identified in seafood isolates of V. parahaemolyticus were found to be functional. To the best of our knowledge, this is the first description of T3SS2β genes in trh⁺ V. parahaemolyticus isolated from seafood in India. The presence of T3SS2 along with other virulence factors such as TDH and/or TRH highlights a potential health risk for seafood consumers.

Defining the niche of Vibrio parahaemolyticus during pre- and post-monsoon seasons in the coastal Arabian Sea

The bacteria Vibrio parahaemolyticus is an important component of coastal ecosystems worldwide, and in recent years, V. parahaemolyticus has caused several cases of food-borne gastroenteritis. However, research investigating which parameters are important in regulating V. parahaemolyticus abundance in tropical areas with relatively stable temperatures and salinity are largely lacking. The objective here was to investigate which environmental forces are driving elevated abundances of V. parahaemolyticus in a tropical oligotrophic coastal area in the Arabian Sea. We analysed a large number of environmental parameters in parallel with cell densities of V. parahaemolyticus and Vibrio spp. Abundance data was obtained using real-time PCR, during two different sampling periods, representative for two distinct seasons. Water temperature and salinity were stable during and between sampling periods, but V. parahaemolyticus abundances were on average six times higher during the first sampling period in December, compared to the second period in February-March. V. parahaemolyticus abundance was found to be positively correlated to inorganic phosphate concentration and copepod abundance. We thus hypothesise that these are important factors regulating V. parahaemolyticus abundance in coastal tropical areas during these periods.

A modified molecular beacons-based multiplex real-time PCR assay for simultaneous detection of eight foodborne pathogens in a single reaction and its application

Foodborne disease outbreaks are often caused by one of the major pathogens. Early identification of the causal pathogen is crucial for disease control and prevention. We describe a real-time polymerase chain reaction (rtPCR) assay that can identify, in a single reaction, up to eight common foodborne bacterial pathogens, including Salmonella enterica subsp. enterica, Listeria monocytogenes, Escherichia coli O157, Vibrio parahaemolyticus, V. vulnificus, Campylobacter jejuni, Enterobacter sakazakii, and Shigella spp. This multiplex rtPCR assay takes advantage of modified molecular beacons and the multicolor combinational probe coding strategy to discriminate each pathogen and the homo-tag assisted non-dimer (HAND) system to prevent dimer formation. The detection limits of the assay ranged from 1.3×10(3) colony-forming units (CFU)/g stool (L. monocytogenes) to 1.6×10(4) CFU/g stool (Shigella spp.). The target genes were 100% specific as assessed on 986 reference strains covering 41 species since no cross-reactions were observed. The assay was applied to the detection of foodborne pathogens in 11,167 clinical samples and the results were compared with culture methods for further validation. The sensitivity and specificity of the rtPCR were 100% and 99%, respectively. When performed in a 96-well rtPCR system, more than 90 samples could be analyzed within 3 h. Given the high accuracy, sensitivity, specificity, and short turn-around time, the established assay could be used for the rapid and reliable identification of the causative pathogens responsible for a certain foodborne disease outbreak and rapid screening of these major foodborne pathogens in laboratory-based surveillance of outpatient clinical samples or even food samples.

Predictive models for the effect of storage temperature on Vibrio parahaemolyticus viability and counts of total viable bacteria in Pacific oysters (Crassostrea gigas)

Vibrio parahaemolyticus is an indigenous bacterium of marine environments. It accumulates in oysters and may reach levels that cause human illness when postharvest temperatures are not properly controlled and oysters are consumed raw or undercooked. Predictive models were produced by injecting Pacific oysters (Crassostrea gigas) with a cocktail of V. parahaemolyticus strains, measuring viability rates at storage temperatures from 3.6 to 30.4°C, and fitting the data to a model to obtain parameter estimates. The models were evaluated with Pacific and Sydney Rock oysters (Saccostrea glomerata) containing natural populations of V. parahaemolyticus. V. parahaemolyticus viability was measured by direct plating samples on thiosulfate-citrate-bile salts-sucrose (TCBS) agar for injected oysters and by most probable number (MPN)-PCR for oysters containing natural populations. In parallel, total viable bacterial counts (TVC) were measured by direct plating on marine agar. Growth/inactivation rates for V. parahaemolyticus were -0.006, -0.004, -0.005, -0.003, 0.030, 0.075, 0.095, and 0.282 log₁₀ CFU/h at 3.6, 6.2, 9.6, 12.6, 18.4, 20.0, 25.7, and 30.4°C, respectively. The growth rates for TVC were 0.015, 0.023, 0.016, 0.048, 0.055, 0.071, 0.133, and 0.135 log₁₀ CFU/h at 3.6, 6.2, 9.3, 14.9, 18.4, 20.0, 25.7, and 30.4°C, respectively. Square root and Arrhenius-type secondary models were generated for V. parahaemolyticus growth and inactivation kinetic data, respectively. A square root model was produced for TVC growth. Evaluation studies showed that predictive growth for V. parahaemolyticus and TVC were "fail safe." The models can assist oyster companies and regulators in implementing management strategies to minimize V. parahaemolyticus risk and enhancing product quality in supply chains.

Serological and molecular characterization of Vibrio parahaemolyticus marine strains carrying pandemic genetic markers

In 2005, pandemic Vibrio parahaemolyticus was reported to have been introduced in Europe: O3:K6 strains were isolated from clinical cases in France and Spain, and were found to be associated with consumption of contaminated seafood. On the contrary, pandemic strains were not isolated from seafood or from the environment itself. Analysis of two V. parahaemolyticus strains isolated in May 2007 from Northern Italy seawater and plankton samples revealed the presence of the virulence gene tdh and the pandemic-specific markers orf8 and toxRS/new sequence (group-specific PCR). The two strains showed serotypes not included in the 'pandemic group', but their molecular typing proved that they represent a single clone showing a genetic profile very similar to that of pandemic O3:K6 reference isolates. Moreover, the two marine strains carried three virulence-related genes associated with clinical strains and, to date, hardly ever or never detected in environmental strains. The presence, in strains isolated from the marine environment, of genetic pandemic markers and virulence genes normally associated with clinical isolates proves that marine strains might constitute a public health concern.

Evaluation of RAPD-PCR and protein profile analysis to differentiate Vibrio harveyi strains prevalent along the southwest coast of India

Sixty five isolates of Vibrio harveyi were subjected to random amplified polymorphic DNA (RAPD)-PCR analysis and protein profiling to investigate the genetic variability among V. harveyi prevalent along the coast and also assess the discriminating ability of these two molecular methods. A total of 10 RAPD primers were assayed for their specificity in detecting V. harveyi, of which only two primers: PM3 and CRA25 were highly reproducible and found suitable for use in RAPD-PCR. The genetic diversity among V. harveyi isolates assessed by RAPD-PCR using PM3 primer yielded 35 different RAPD patterns which clustered the isolates into 15 groups at 72% similarity level. Similarly, RAPD-PCR with CRA25 clustered the 38 patterns into 10 groups at 74% similarity. The discriminatory index (D) value calculated for RAPD fingerprints generated with PM3 and CRA25 were 0.90 and 0.85, respectively. On the other hand, molecular typing of V. harveyi using whole cell proteins generated profiles that showed no major difference indicating the technique to be not useful in typing strains of this bacterium. However, a few of the isolates showed the presence of unique band of 28 kDa that needs to be further investigated to understand the role of the protein in disease process if any.

Species-specific PCR detection of the food-borne pathogen Vibrio parahaemolyticus using the irgB gene identified by comparative genomic analysis

Vibrio parahaemolyticus is an enteric pathogen, which can cause acute gastroenteritis in humans after consumption of raw or partially cooked seafood, and specific molecular markers are necessary for its accurate identification by PCR methods. In the present study, 23 protein-coding sequences were identified by the comparative genomics method as V. parahaemolyticus-specific candidate markers. We targeted the irgB gene (vp2603), coding for iron-regulated virulence regulatory protein IrgB, in order to develop a PCR method for the detection of V. parahaemolyticus. PCR specificity was identified by amplification of 293 V. parahaemolyticus templates and by the loss of a PCR product with 11 strains from other Vibrio species and 35 non-Vibrio bacterial strains. The PCR assay had the 369-bp fragment and the sensitivity of 0.17 pg purified genomic DNA from V. parahaemolyticus. Furthermore, a multiplex PCR assay for the detection of total and virulent strains of V. parahaemolyticus was developed by targeting irgB, tdh and trh genes. These data indicated that the irgB gene is a new and effective marker for the detection of V. parahaemolyticus. In addition, this study demonstrates that genome sequence comparison has a powerful application in identifying specific markers for the detection and identification of bacterial pathogens.

Detection of the tdh and trh genes in Vibrio parahaemolyticus isolates in fish and mussels from Middle Black Sea Coast of Turkey

AIM

The aim of this study was to demonstrate the occurrence of potential pathogenic Vibrio parahaemolyticus in seafoods using DNA-based techniques in comparison with bacteriological methods.

METHODS AND RESULTS

From 120 fresh and processed fish and mussel samples collected from Middle Black Sea, 32 isolates were identified as V. parahaemolyticus by bacteriological methods and confirmed by tl gene-based conventional PCR. Of them, 13 isolates were found positive for only tdh gene, six isolates for only trh gene and 13 isolates for both genes by multiplex PCR.

CONCLUSIONS

It is the first report demonstrating the presence of potential pathogenic V. parahaemolyticus isolates from the Black Sea seafoods by PCR detection of tl, trh and tdh genes that was found more rapid than bacteriological methods.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study confirmed the previous reports that characterization of potential pathogenic V. parahaemolyticus isolates based on the PCR techniques was reliable and cost-effective. These results suggest that molecular detection methods should be included in Turkish Standards of seafood control in addition to bacteriological methods.

Presence of T3SS2 and other virulence-related genes in tdh-negative Vibrio parahaemolyticus environmental strains isolated from marine samples in the area of the Venetian Lagoon, Italy

Vibrio parahaemolyticus-mediated disease has traditionally been associated with two virulence factors, thermostable direct haemolysin (TDH) and TDH-related haemolysin (TRH), which are present in most clinical isolates. Recently, it has been suggested that other virulence-related factors, such as some type III secretion system (T3SS) proteins, urease and DNA-methyltransferase, among others, might also play a role in disease caused by this bacterial species and have been shown to be carried by clinical, but not by environmental strains. Screening for a number of virulence and virulence-related genes in a collection of V. parahaemolyticus strains isolated from the Italian Adriatic coast indicates that in addition to the trh-positive strains isolated (6%), a significant percentage (18%) of these strains contain one or more genes with a possible role in pathogenicity. Specifically, some of the V. parahaemolyticus strains described in this study are the first environmental strains ever detected carrying T3SS2 genes. Data obtained by reverse transcription-PCR on environmental strain RNA indicate that at least some of these genes are functional. On the basis of the results obtained, it is suggested that such strains might constitute an environmental reservoir of genes possibly contributing to V. parahaemolyticus pathogenicity and to the spread, in the marine environment, of virulence-related genes usually found in clinical strains.

Evaluation of the Compact Dry VP method for screening raw seafood for total Vibrio parahaemolyticus

Compact Dry VP (CDVP) is a ready-to-use method for enumerating Vibrio parahaemolyticus in food. The presterilized plates contain a culture medium comprising peptone, NaCl, bile salts, antibiotics, chromogenic substrates, and polysaccharide gum as a cold water-soluble gelling. After diluting raw seafood samples in a phosphate-buffered saline solution, a 1-ml aliquot was inoculated onto the center of the plate and allowed to diffuse by capillary action. Blue-green colonies forming on the plates were counted after 18 to 20 h of incubation at 35 degrees C. A total of 85 V. parahaemolyticus strains (62 tdh+ strains and 23 tdh- strains) were studied for inclusivity, 81 (95.3 %) of which produced blue-green colonies. When 97 strains (14 strains of Vibrio spp., 33 strains of coliform bacteria, and 50 strains of noncoliform bacteria) were assessed for exclusivity, 10 strains of Vibrio spp. produced non-blue-green colonies, and 87 strains failed to grow. The CDVP and U.S. Food and Drug Administration Bacteriological Analytical Manual (FDA-BAM) methods were compared with the use of four different types of raw seafood that were inoculated with four different V. parahaemolyticus strains. For raw tuna and oysters, the FDA-BAM colony lift method was used, whereas the FDA-BAM most-probable-number method was used for salmon and scallop. The linear correlation coefficients between the CDVP and FDA-BAM methods were 0.99 for fresh raw tuna, 0.95 for fresh raw oysters, 0.95 for frozen raw salmon, and 0.95 for frozen raw scallops. These results suggest that the CDVP method is useful for screening raw seafood for V. parahaemolyticus.

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

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

Rapid detection of pathogenic Vibrio parahaemolyticus by a sensitive and specific duplex PCR-hybridization probes assay using LightCycler

AIMS

To develop a real-time polymerase chain reaction (PCR) hybridization probe assay for rapid and specific detection of thermostable direct haemolysin-producing Vibrio parahaemolyticus.

METHODS AND RESULTS

Primers and hybridization probes were designed to target the toxR and tdh2 genes. Mismatches were introduced in the tdh2 primers for specific amplification of the target. The 3' ends of donor probes for both genes were labelled with fluorescein. The 5' ends of recipient probes for tdh2 and toxR were labelled with LC Red 640 and LC Red 705, respectively. The real-time assay was evaluated against conventional biochemical tests and the KAP-RPLA kit (Kanagawa phenomenon detection kit by reverse passive latex agglutination). toxR and tdh2 were detected in 100% and 91% of clinical V. parahaemolyticus isolates (n = 118), respectively. Specificity and sensitivity of the real-time assay for toxR and tdh2 were 100%, respectively. Dynamic range of detection for toxR was 10(7)-10(1) CFU ml(-1) and that for tdh2 was 10(7)-10(4) CFU ml(-1).

CONCLUSIONS

The LightCycler assay described is sensitive and highly specific for detection of pathogenic V. parahaemolyticus in a single reaction tube within 80 min.

SIGNIFICANCE AND IMPACT OF THE STUDY

The assay developed allows accurate detection of pathogenic V. parahaemolyticus, which is valuable for rapid tracing of infection source during outbreaks.

Comparison of different biochemical and molecular methods for the identification of Vibrio parahaemolyticus

AIMS

Multicentre evaluation of biochemical and molecular methods for the identification of Vibrio parahaemolyticus.

METHODS AND RESULTS

For the biochemical identification methods, API 20E and API 20NE and Alsina's scheme were evaluated in intra- and interlaboratory tests in order to determine the accuracy and concordance of each method. Both in intra- and interlaboratory tests, the Alsina's scheme showed the highest sensitivity (86% of correct identifications in the interlaboratory test). False-positive results were obtained by all methods (specificity was 95% for API 20E, 73% for API 20NE and 84% for Alsina's scheme) and concordance varied from 65% of API 20NE to 84% of API 20E. For the molecular identifications, polymerase chain reaction (PCR) for the detection of toxR gene, tl gene and pR72H fragment were tested on 30 strains by two laboratories. The PCR for toxR showed the highest inclusivity (96%), exclusivity (100%) and concordance (97%).

CONCLUSIONS

Among the biochemical identification methods tested, the Alsina's scheme gave more reliable results; however, in order to avoid false-positive results, all the biochemical identifications should be confirmed by means of molecular methods.

SIGNIFICANCE AND IMPACT OF THE STUDY

Availability of an efficient identification method of Vibrio parahaemolyticus to use in official control of fisheries products.