Distribution of virulent and pandemic strains of Vibrio parahaemolyticus in three molluscan shellfish species (Meretrix meretrix, Perna viridis, and Anadara granosa) and their association with foodborne disease in southern Thailand

Incidence, genetic diversity, and antimicrobial resistance profiles of Vibrio parahaemolyticus in seafood in Bangkok and eastern Thailand

Background

Emergence of Vibrio parahaemolyticus pandemic strain O3:K6 was first documented in 1996. Since then it has been accounted for large outbreaks of diarrhea globally. In Thailand, prior studies on pandemic and non-pandemic V. parahaemolyticus had mostly been done in the south. The incidence and molecular characterization of pandemic and non-pandemic strains in other parts of Thailand have not been fully characterized. This study examined the incidence of V. parahaemolyticus in seafood samples purchased in Bangkok and collected in eastern Thailand and characterized V. parahaemolyticus isolates. Potential virulence genes, VPaI-7, T3SS2, and biofilm were examined. Antimicrobial resistance (AMR) profiles and AMR genes (ARGs) were determined.

Methods

V. parahaemolyticus was isolated from 190 marketed and farmed seafood samples by a culture method and confirmed by polymerase chain reaction (PCR). The incidence of pandemic and non-pandemic V. parahaemolyticus and VPaI-7, T3SS2, and biofilm genes was examined by PCR. AMR profiles were verified by a broth microdilution technique. The presence of ARGs was verified by genome analysis. V. parahaemolyticus characterization was done by multilocus sequence typing (MLST). A phylogenomic tree was built from nucleotide sequences by UBCG2.0 and RAxML softwares.

Results

All 50 V. parahaemolyticus isolates including 21 pathogenic and 29 non-pathogenic strains from 190 samples had the toxRS/old sequence, indicating non-pandemic strains. All isolates had biofilm genes (VP0950, VP0952, and VP0962). None carried T3SS2 genes (VP1346 and VP1367), while VPaI-7 gene (VP1321) was seen in two isolates. Antimicrobial susceptibility profiles obtained from 36 V. parahaemolyticus isolates revealed high frequency of resistance to colistin (100%, 36/36) and ampicillin (83%, 30/36), but susceptibility to amoxicillin/clavulanic acid and piperacillin/tazobactam (100%, 36/36). Multidrug resistance (MDR) was seen in 11 isolates (31%, 11/36). Genome analysis revealed ARGs including blaCARB (100%, 36/36), tet(34) (83%, 30/36), tet(35) (42%, 15/36), qnrC (6%, 2/36), dfrA6 (3%, 1/36), and blaCTX-M-55 (3%, 1/36). Phylogenomic and MLST analyses classified 36 V. parahaemolyticus isolates into 5 clades, with 12 known and 13 novel sequence types (STs), suggesting high genetic variation among the isolates.

Conclusions

Although none V. parahaemolyticus strains isolated from seafood samples purchased in Bangkok and collected in eastern Thailand were pandemic strains, around one third of isolates were MDR V. parahaemolyticus strains. The presence of resistance genes of the first-line antibiotics for V. parahaemolyticus infection raises a major concern for clinical treatment outcome since these resistance genes could be highly expressed under suitable circumstances.

De novo transcriptome analysis of stressed blood clam (Anadara broughtonii) and identification of genes associated with hemoglobin

BACKGROUND

Blood clam (Anadara broughtonii) is a commercially important marine bivalve characterised by the red blood. Recently, the clams have been subjected to severe resource recession. Multiple environmental stressors are indispensable for the recession.

OBJECTIVE

We aimed to investigate the transcriptome information of blood clam under environmental stressors.

METHODS

Paired-end Illumina HiSeq™ 2500 sequencing technology was employed for cDNA library construction and Illumina sequencing. Several public databases were introduced for gene annotation, and Kyoto Encyclopedia of Genes and Genomes (KEGG) database was used for pathways analyses. The Open Reading Frame of annotated hemoglobin (Hb) was predicted and validated by DNAMAN 6.0 and NCBI BLASTx, respectively.

RESULTS

A total of 242,919 transcripts were generated, 116,264 unigenes were subsequently assembled with an average length of 747 base pairs, and 33,776 unigenes were successfully annotated. Gene Ontology (GO) categories indicated that the terms of cellular processes, metabolic processes, cell, cell part, binding, and catalytic activity were dominant. KEGG pathway analyses suggested ribosome, oxytocin, focal adhesion, Ras, and PI3K-Akt were the largest signaling pathway groups, and many presented pathways (Ras, Rap1, and MAPK, etc.) were related to apoptosis, immune and stress response. In addition, a total of 19,306 potential simple sequence repeats (SSRs) were detected in 15,852 sequences. Six hemoglobin-related genes with complete conserved domain sequences were identified and 3 of them were predicted as HbI, HbIIα, and HbIIβ.

CONCLUSION

This study provides transcriptome responses to multiple environmental stressors in blood clams and would provide interesting hints for further studies.

Molecular cloning, characterization and functional analysis of a putative mitogen-activated protein kinase kinase kinase 4 (MEKK4) from blood clam Tegillarca granosa

The mitogen-activated protein kinase (MAPK) cascades stand for one of the most important signaling mechanisms in response to environmental stimuli. In the present study, we cloned and identified for the first time the full-length cDNA of MAPK kinase kinase 4 (TgMEKK4) from Blood clam Tegillarca granosa using rapid amplification of cDNA ends method. The full-length cDNA of TgMEKK4 was of 1605 bp in length, encoding a polypeptide of 364 amino acids with a predicted molecular mass of 41.22 kDa and theoretical isoelectric point of 6.29. The conserved MEKK4-domain was identified in TgMEKK4 by SMART program analysis. Homology analysis of the deduced amino acid sequence of TgMEKK4 with other known sequences revealed that TgMEKK4 shared 58%-80% identity to MEKK4s from other species. TgMEKK4 mRNA transcripts could be detected in all tissues examined with the highest expression level in the gill by qRT-PCR. The mRNA expression of TgMEKK4 was up-regulated significantly in hemocytes after Vibrio parahaemolyticus, Vibrio alginolyticus and Lipopolysaccharide (LPS) challenges. Overexpression of TgMEKK4 in HEK 293T cells resulted in the activation of JNK and ERK, but not p38. Consistently, In vivo study indicated that LPS stimulation enhanced JNK, ERK and p38 phosphorylation in blood clams. These results suggest that TgMEKK4 is a powerful factor in the regulation of genes that may be involved in innate immune response of blood clam.

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.

Improvement of the quantitation method for the tdh (+) Vibrio parahaemolyticus in molluscan shellfish based on most-probable- number, immunomagnetic separation, and loop-mediated isothermal amplification

Vibrio parahaemolyticus is a marine microorganism that can cause seafood-borne gastroenteritis in humans. The infection can be spread and has become a pandemic through the international trade of contaminated seafood. Strains carrying the tdh gene encoding the thermostable direct hemolysin (TDH) and/or the trh gene encoding the TDH-related hemolysin (TRH) are considered to be pathogenic with the former gene being the most frequently found in clinical strains. However, their distribution frequency in environmental isolates is below 1%. Thus, very sensitive methods are required for detection and quantitation of tdh⁺ strains in seafood. We previously reported a method to detect and quantify tdh⁺V. parahaemolyticus in seafood. This method consists of three components: the most-probable-number (MPN), the immunomagnetic separation (IMS) targeting all established K antigens, and the loop-mediated isothermal amplification (LAMP) targeting the tdh gene. However, this method faces regional issues in tropical zones of the world. Technicians have difficulties in securing dependable reagents in high-temperature climates where we found MPN underestimation in samples having tdh⁺ strains as well as other microorganisms present at high concentrations. In the present study, we solved the underestimation problem associated with the salt polymyxin broth enrichment for the MPN component and with the immunomagnetic bead-target association for the IMS component. We also improved the supply and maintenance of the dependable reagents by introducing a dried reagent system to the LAMP component. The modified method is specific, sensitive, quick and easy and applicable regardless of the concentrations of tdh⁺V. parahaemolyticus. Therefore, we conclude this modified method is useful in world tropical, sub-tropical, and temperate zones.

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.

Most-probable-number loop-mediated isothermal amplification-based procedure enhanced with K antigen-specific immunomagnetic separation for quantifying tdh(+) Vibrio parahaemolyticus in molluscan Shellfish

Although thermostable direct hemolysin-producing (tdh(+)) Vibrio parahaemolyticus is the leading cause of seafood-borne gastroenteritis, the enumeration of tdh(+) V. parahaemolyticus remains challenging due to its low densities in the environment. In this study, we developed a most-probable-number (MPN)-based procedure designated A-IS(1)-LAMP, in which an immunomagnetic separation (IMS) technique targeting as many as 69 established K antigens and a loop-mediated isothermal amplification (LAMP) assay targeting the thermostable direct hemolysin (tdh) gene were applied in an MPN format. Our IMS employed PickPen, an eight-channel intrasolution magnetic particle separation device, which enabled a straightforward microtiter plate-based IMS procedure (designated as PickPen-IMS). The ability of the procedure to quantify a wide range of tdh(+) V. parahaemolyticus levels was evaluated by testing shellfish samples in Japan and southern Thailand, where shellfish products are known to contain relatively low and high levels of total V. parahaemolyticus, respectively. The Japanese and Thai shellfish samples showed, respectively, relatively low (< 3 to 11 MPN/10 g) and considerably higher (930 to 110,000 MPN/10 g) levels of tdh(+) V. parahaemolyticus, raising concern about the safety of Thai shellfish products sold to domestic consumers at local morning markets. LAMP showed similar or higher performance than conventional PCR in the detection and quantification of a wide range of tdh(+) V. parahaemolyticus levels in shellfish products. Whereas a positive effect of PickPen-IMS was not observed in MPN determination, PickPen-IMS was able to concentrate tdh(+) V. parahaemolyticus 32-fold on average from the Japanese shellfish samples at an individual tube level, suggesting a possibility of using PickPen-IMS as an optional tool for specific shellfish samples. The A-IS(1)-LAMP procedure can be used by any health authority in the world to measure the tdh(+) V. parahaemolyticus levels in shellfish products.

Vibrio parahaemolyticus and its specific bacteriophages as an indicator in cockles (Anadara granosa) for the risk of V. parahaemolyticus infection in Southern Thailand

Correlation between the numbers of Vibrio parahaemolyticus and its specific bacteriophages in cockles was investigated from June 2009 to May 2010 in Hat Yai, Songkhla, Thailand. Cockles obtained monthly from a local market were sampled to determine the numbers of V. parahaemolyticus and bacteriophages that could form plaques on ten strains of pandemic and nonpandemic V. parahaemolyticus. In addition, V. parahaemolyticus isolates from clinical samples from Hat Yai hospital over the same period were investigated. All 139 cockles sampled were positive for V. parahaemolyticus. However, only 76 of them were positive for bacteriophages. During the testing period, the number of bacteriophages was not significantly correlated with the incidence of V. parahaemolyticus-infected patients, but the numbers of V. parahaemolyticus isolates from the cockle samples were closely related to the number of infected patients. The bacteriophages isolated from V. parahaemolyticus also infected Vibrio alginolyticus and Vibrio mimicus, suggesting that the broad host range of phages may be a factor of providing the possibility of their participation in the processes of genetic exchange between V. parahaemolyticus and closely related Vibrio spp. In conclusion, this study indicated that the number of V. parahaemolyticus in cockles may be a useful tool for predicting the relative risk of infection by V. parahaemolyticus in this area of Thailand.

Contamination by Vibrio parahaemolyticus and Its Virulent Strains in Seafood Marketed in Thailand, Vietnam, Malaysia, and Indonesia

Infections by virulent strains of Vibrio parahaemolyticus are frequently reported in Southeast Asia. This is due to the frequent seafood contamination by virulent strains. In this study conducted from 2008 to 2011, seafood like fish, shrimp, squid, crab, and molluscan shellfish were purchased from provinces in Thailand and three Southeast Asian countries and examined for the prevalence of three genetic markers of V. parahaemolyticus (species-specific gene: toxR gene, virulence genes: tdh and trh genes). An enrichment culture of seafood was examined for these markers using PCR methods. Molluscan shellfish showed a high frequency of contamination in Thailand. The shellfish harvested from the Gulf of Thailand were significantly more contaminated with virulence genes than those from the Andaman Sea. The seafood purchased from three Southeast Asian countries was positive for the three markers of V. parahaemolytcus at differing frequencies. The virulence markers (tdh and trh markers) were frequently detected in molluscan shellfish from Vietnam (17.9 and 8.0%, respectively), Malaysia (11.1 and 16.7%), and Indonesia (9.1 and 13.6%). These data suggest that the molluscan shellfish sold in Southeast Asian markets are highly contaminated with virulent strains of V. parahaemolyticus.

Hemoglobin of the bloody clam Tegillarca granosa (Tg-HbI) is involved in the immune response against bacterial infection

Hemoglobins (Hb) are the major protein components of erythrocytes circulating in the red blood, but can serve additional functions besides the transport of oxygen. Here, the cDNA of the bloody clam (Tegillarca granosa) Hb dimer (designated Tg-HbI) was cloned and was found to be 748 bp in length, consisting of an open reading frame of 441 bp encoding a polypeptide of 147 amino acids. The deduced amino acid sequence of Tg-HbI shared 81.6% similarity with HbI from two species of the genus Scapharca and 46-51% similarity with the Hb proteins from other mollusks. The 3D structure of bloody clam Tg-HbI was predicted by the SWISS-MODEL Protein Modelling Server and compared with that of Scapharca kagoshimensis. The mRNA transcript of Tg-HbI was detected in all of the clam cells/tissues examined, including haemocytes, the adductor muscle, foot, hepatopancreas, gill and mantle. The mRNA expression of Tg-HbI was significantly up-regulated after Vibrio parahaemolyticus, lipopolysaccharide and peptidoglycan challenge, indicating that Tg-HbI was involved in the immune defence responses against bacterial infection and exposure to bacterial pathogenic factors. As the first functional research on the Hb protein in bloody clam, our findings provide new insight into the innate immune defence mechanisms of T. granosa and other mollusks.

A small HSP gene of bloody clam (Tegillarca granosa) involved in the immune response against Vibrio parahaemolyticus and lipopolysaccharide

Small heat shock proteins (sHSPs) associate with nuclei, cytoskeleton and membranes, and as molecular chaperones they bind partially denatured proteins, thereby preventing irreversible protein aggregation during stress. In the present study, the small heat shock proteins of Tegillarca granosa (Tg-sHSP) were identified from hemocytes by 3' and 5' rapid amplification of cDNA ends (RACE) PCR. The full-length cDNA consisted of 1005 bp with a 594 bp open reading frame encoding 197 amino acids. Sequence comparison showed that Tg-sHSP had low degree of homology to sHSP of other organisms, such as 47.8% similarity with sHSP from Zhikong scallop Chlamys farreri (AAR11780), 34.8% similarity with silkworm Bombyx mori (NP_001036941). A sHSP feature domain Alpha-crystallin domain (ACD) and V/IXI/V motif in the C-terminal extension were identified in Tg-sHSP, indicating that Tg-sHSP should be a new member of sHSP family. Quantitative RT-PCR assay was developed to detect the mRNA expression of Tg-sHSP in five different tissues. Higher-level mRNA expression of Tg-sHSP was detected in the tissues of hemocytes and mantle. The up-regulation of Tg-sHSP after bacteria Vibrio parahaemolyticus and lipopolysaccharide (LPS) challenge showed that sHSPs play a pivotal role in anti-bacterial immunity. These results together indicated that Tg-sHSP would provide candidate promising therapeutic or prophylactic agents in health management and diseases control of clam aquaculture.

Vibrio parahaemolyticus-associated gastroenteritis in Italy: persistent occurrence of O3:K6 pandemic clone and emergence of O1:KUT serotype

We report 2 cases of O3:K6 and O1:KUT Vibrio parahaemolyticus gastroenteritis associated with consumption of local mussels in Italy in 2008. Serotypic, antibiogram, toxigenic, and pulsed-field gel electrophoresis patterns of these strains were compared to those of other isolates collected from local clinical and seafood samples in 2007 to 2008. We underline the recurrent presence of O3:K6 pandemic clone and the emergence of trh-positive O1:KUT serotype in Italy.

Survival and growth of Salmonella and Vibrio in som-fak, a Thai low-salt garlic containing fermented fish product

Fermentation of raw fish is a common process in Asia for improvement of shelf life and safety, however, little is known about the survival of pathogenic bacteria in these products. Raw fish may be contaminated with Salmonella and Vibrio species. The purpose of this study was to determine survival and potential growth of Salmonella enterica serovar Weltevreden, S. enterica serovar Enteritidis, Vibrio cholerae and V. parahaemolyticus as influenced by the preservation parameters (sodium chloride, garlic and lactic acid) present in the Thai fermented fish product som-fak. The inhibitory effects of sodium chloride (0-4%), garlic (0-10%) and lactic acid (pH levels as in som-fak) were measured in modified brain heart infusion (BHI) broth at 30 degrees C. All bacteria were inhibited by 8-10% sodium chloride. Salmonella grew in all concentrations of garlic whereas Vibrio spp. were inhibited by 1.0-1.5%. Lactic acid was inhibitory at levels above 1.5%. The combinations of sodium chloride, lactic acid and garlic showed a distinct hurdle effect in the broth system. Neither S. Enteritidis, V. cholerae nor V. parahaemolyticus grew in garlic (0.5-1%), regardless of the level of sodium chloride (0.5-4% (w/v)), when lactic acid (0.5-2%) was present. S. Weltevreden was the least inhibited of the four bacteria and grew in the combination of 0.5% garlic and 0.5% lactic acid regardless of the NaCl level (0.5-4% (w/v)). Som-fak with 0 to 10% garlic or 2% glucose was inoculated with either (i) 10(3) CFU/g Salmonella Weltevreden, (ii) 10(6) CFU/g garlic fermenting Lactobacillus plantarum strain 509 or (iii) a combination of the two strains and stored at 30 degrees C. The Salmonella count increased to >10(8) CFU/g (>10(6) CFU/g for 10% garlic) in all types of som-fak inoculated with S. Weltevreden within the first day. Only a combination of at least 6% garlic and L. plantarum 509 was enough to prevent growth of the inoculated Salmonella whereas adding the Lactobacillus strain alone or in combination with glucose was insufficient to prevent growth. Our results show that Salmonella Weltevreden can grow in som-fak independently of the inhibitory substances normally present in this type of product, emphasising the importance of preventing contamination. However, our results also suggest that the use of garlic fermenting starter cultures in combination with garlic could improve safety of fermented fish products.

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

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

Variability of properties of Vibrio parahaemolyticus strains isolated from individual patients

Infections by strains belonging to the O3:K6 pandemic clone of Vibrio parahaemolyticus are prevalent in southern Thailand, and serovariants of these strains have also been detected. V. parahaemolyticus strains lacking important virulence genes (tdh and trh) were isolated from 6.5 to 10.9% of clinical specimens during the period from 2000 to 2003. In order to understand whether changes to the characteristics of V. parahaemolyticus occur during infection, 10 isolates collected from each of 63 patients who presented with diarrhea at the Hat Yai hospital from 2003 to 2004 were examined for the presence of the tdh and trh genes, the O:K serotype, and genetic markers for the pandemic clone. A total of 42 patients (66.7%) yielded identical isolates (homogeneous populations), and 21 of the patients (33.3%) yielded isolates that differed in at least one character from the other isolates (heterogeneous populations). The DNA fingerprints (examined by arbitrarily primed PCR and pulsed-field gel electrophoresis) of some, but not all, of the heterogeneous populations from single patients were indistinguishable. The results indicated that some patients were infected with a unique strain and that in vivo changes (tdh deletion or serotype conversion) might have occurred in certain individuals. It is therefore important to bear in mind that epidemiological studies based on the analysis of a single colony from a single patient might lead to misleading conclusions. Finally, the present study did not rule out the possibility that isolates lacking tdh and trh have unknown virulence mechanisms other than the tdh and trh genes.