Characterization of Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease in southern Thailand

Determination of Whole Molecular of Thermostable Direct Hemolysins in Milk Powder by HPLC-ESI-TOF

Although Vibrio parahaemolyticus (V. parahaemolyticus) is a pathogen frequently found in seafood, there is a possibility of its presence in other foods, such as dairy products. The main virulence factors of V. parahaemolyticus are thermostable direct hemolysins (TDHs) which are lethal toxins, so it is necessary to establish qualitative and quantitative methods for determining TDHs. HPLC-ESI-TOF was employed to establish a method for identifying TDHs. The identification and quantification ions of TDHs were confirmed by HPLC-ESI-TOF. The method was developed for detecting TDHs in milk powder using HPLC-ESI-TOF in this paper, and limits of detection (were between 0.20 and 0.40 mg/kg, limits of quantitation were between 0.5 and 1.0 mg/kg and recoveries of all TDHs were between from 78% to 94% with relative standard deviation lower than 10%. This research will provide a reference for developing methods of HPLC-MS/MS to detect TDHs in food samples, which can provide a tool for the government to monitor TDHs contamination in foods.

Characterization and Preliminary Application of a Novel Lytic Vibrio parahaemolyticus Bacteriophage vB_VpaP_SJSY21

Litopenaeus vannamei is one of the most economically significant aquatic species globally. However, the emergence of acute hepatopancreatic necrosis disease (AHPND) in recent years has resulted in substantial losses within the L. vannamei farming industry. Phage therapy holds promise as an effective strategy for preventing and controlling bacterial infections like AHPND, thereby promoting the healthy and sustainable growth of the shrimp aquaculture sector. In this study, a novel and unique Vibrio parahaemolyticus bacteriophage, named vB_VpaP_SJSY21, was successfully isolated from sewage samples. Using transmission electron microscopy, it was observed that phage SJSY21 has an elongated shell. Notably, phage SJSY21 exhibited high infection efficiency, with an optimal multiplicity of infection (MOI) of only 0.01 and a remarkably short latent period of 10 min, resulting in a lysis quantity of 508. Furthermore, phage SJSY21 demonstrated notable heat resistance and the capacity to withstand high temperatures during preservation, thus holding potential for application in phage therapy. Whole-genome sequencing and analysis confirmed that phage SJSY21 has a genome size of 110,776 bp, classifying it as a new member of the short-tailed bacteriophage family. Additionally, cultivation experiments indicated that phage SJSY21 has the potential to enhance the survival of L. vannamei in culture systems, thereby offering innovative prospects for the application of phage therapy in aquaculture.

Construction of L-type lectin displaying Saccharomyces cerevisiae for Vibrio parahaemolyticus agglutination

The utilization of Aga1P anchor protein in the display system for expressing heterologous proteins on the surface of Saccharomyces cerevisiae has been shown to be an ideal approach. This system has the ability to improve the expression of target proteins beyond the cell surface, resulting in increased activity and stability of the expression system. Recent studies have demonstrated that a new L-type lectin from Litopenaeus vannamei (LvLTLC1) has been found to possess the capability of agglutinating Vibrio parahaemolyticus, a pathogen responsible for causing acute hepatopancreatic necrosis disease (AHPND) in shrimp. In this study, LvLTLC1 protein was designed to be expressed on the surface of S. cerevisiae via Aga1P anchor. The expression of LvLTLC1 protein on the surface of S. cerevisiae::pYIP-LvLTLC1-Aga1P was confirmed through the use of analytical techniques including SDS-PAGE, dot blot, and fluorescent immunoassay with LvLTC1-specific antibody. Subsequently, the newly generated yeast strain was evaluated for its ability to agglutinate V. parahaemolyticus and A. hydrophila. The obtained results indicated that S. cerevisiae expressing LvLTLC1 protein on its surface had the ability to agglutinate both AHPND-causing V. parahaemolyticus and A. hydrophila. This newly generated yeast strain could be served as a feed supplement for controlling bacteria in general and AHPND in particular.

Expression patterns and influence of the two-component system in Vibrio parahaemolyticus of different genotypes

Vibrio parahaemolyticus is a foodborne pathogen that threatens global food security and human health. The two-component system (TCS) is a primary method for bacteria self-regulate and adapt to the environment. Previous studies have shown that V. parahaemolyticus has four hemolytic genotypes with diverse biological phenotypes and environmental adaptability, but the mechanism is unclear. In this study, we investigated TCS expression patterns in V. parahaemolyticus with different genotypes for the first time and explored the differences in TCS between strains. The results showed similarities in the TCS expression pattern between VPC17 (tdh+/trh-) and VPC44 (tdh-/trh-), while VPC85(tdh-/trh+) had the least similar TCS expression pattern to the other three strains. Analysis of biological information revealed that different regulations of C4 dicarboxylate transport, tetrathionate uptake, antibiotic resistance, and flagellar synthesis involved in the TCS might influence strains' growth, antibiotic resistance, biofilm, and virulence. The different TCS regulatory abilities of strains might be one of the reasons for diverse biological characteristics and different environmental adaptations. This work provides a theoretical basis and a new research direction for the strain variability of V. parahaemolyticus.

Draft Genome Sequence of Vibrio parahaemolyticus PSU5579, Isolated during an Outbreak of Acute Hepatopancreatic Necrosis Disease in Thailand

Here, we announce the draft genome sequence of Vibrio parahaemolyticus strain PSU5579, isolated from a shrimp hatchery in southern Thailand during an outbreak of acute hepatopancreatic necrosis disease (AHPND). The genome contains 44 contigs with a sequence length of 5,229,426 bp, 4,861 coding sequences, and a G+C content of 45.3%.

Characterization and Genome Analysis of Vibrio campbellii Lytic Bacteriophage OPA17

Vibrio campbellii is a marine bacterium that is associated with luminous vibriosis, especially in the hatchery and nursery stages of penaeid shrimp cultivation worldwide, which has led to low survival rates of shrimp during aquaculture. Phage therapy has been reported as an alternative biocontrol agent which can reduce or replace the use of antibiotics and other chemicals. This study characterized a lytic V. campbellii bacteriophage, OPA17, originally isolated from bloody clams and investigated its biocontrol efficacy against V. campbellii infection in a model system, Artemia franciscana. Phage OPA17 lysed 83.89% of V. campbellii strains tested (n = 118) with clear plaque morphology. Some strains of Vibrio parahaemolyticus and Vibrio vulnificus were also infected by phage OPA17. Transmission electron microscopy and genetic features indicated that OPA17 belongs to the Siphoviridae family. The latent period and burst size of OPA17 were approximately 50 min and 123 PFU/cell, respectively. Moreover, it survived in artificial seawater throughout the 2-month study period and effectively destroyed Vibrio campbellii biofilms after 4 h of incubation. The addition of OPA17 significantly increased the survival of A. franciscana nauplii infected with V. campbellii. The genome sequence of OPA17 showed that it does not carry genes unsuitable for phage therapy. The phylogenetic tree analysis showed that OPA17 was closely related to the V. vulnificus lytic phage SSP002 (98.90% similarity), which was previously reported as a potential biocontrol agent. Accordingly, the results of this study provide valuable information regarding the potential biocontrol application of phage OPA17 against V. campbellii. IMPORTANCE V. campbellii is an emerging luminous pathogen associated with vibriosis, especially in marine shrimp hatcheries. Several strategies, including pond management and use of natural antimicrobials and probiotics, have been studied for control of this organism. Phage therapy is considered one of the effective biocontrol strategies against bacterial infections in aquaculture. However, there has been limited study of V. campbellii bacteriophages. In this study, V. campbellii-specific bacteriophage OPA17 was isolated, characterized, and investigated for its biocontrol efficacy against V. campbellii infection in an Artemia nauplii model. Phage OPA17 belongs to the Siphoviridae family and shares significant genome similarity to phage SSP002, a potential biocontrol agent against V. vulnificus infection in a murine model. However, the host range of OPA17 was broader than that of SSP002. Overall, we discuss the potential of OPA17 for phage therapy application in shrimp hatcheries.

Evaluation of Selenoprotein Supplementation on Digestibility, Growth, and Health Performance of Pacific White Shrimp Litopenaeus vannamei

Selenoprotein is a feed additive that can overcome oxidative stress in intensive Pacific white shrimp (Litopenaeus vannamei) culture. This study evaluated the effects of selenoprotein supplementation at various doses on Pacific white shrimp's digestibility, growth, and health performance. The experimental design used was a completely randomized design consisting of four feed treatments, namely, control and treatments with selenoprotein supplementation of 2.5, 5, and 7.5 g kg feed^-1 with four replications. Shrimps (1.5 g) were reared for 70 days and challenged for 14 days by the bacteria Vibrio parahaemolyticus (10⁷ CFU mL^-1). Shrimps used in the digestibility performance evaluation (6.1 g) were reared until sufficient quantities of feces were collected for analysis. Shrimp supplemented with selenoprotein exhibited superior digestibility, growth, and health performance compared to the control (P < 0.05). The use of selenoprotein at a dose of 7.5 g kg of feed^-1 (2.72 mg Se kg of feed^-1) was considered the most effective for increasing productivity and preventing disease attacks in intensive shrimp culture.

Culture optimization to enhance carotenoid production of a selected purple nonsulfur bacterium and its activity against acute hepatopancreatic necrosis disease-causing Vibrio parahaemolyticus

Purple nonsulfur bacteria (PNSB) were investigated for their carotenoid production and anti-vibrio activity against acute hepatopancreatic necrosis disease (AHPND)-causing Vibrio parahaemolyticus. To test carotenoid production, selected strains were cultivated in basic isolation medium (BIM), glutamate acetate medium, G5 medium and artificial acetic acid wastewater (AAW) medium. From 144 PNSB, Rhodopseudomonas palustris KTSSG46 was selected to produce carotenoids under microaerobic light conditions in BIM. When the culture medium was optimized, strain KTSSG46 grown in BIM modified with l-glutamate at 1 g/L more effectively inhibited AHPND-causing V. parahaemolyticus strains than standard BIM with 1 g/L (NH₄ )₂ SO₄ . BIM was further modified with 1.23 g/L MgSO₄ ·7H₂ O and carotenoid production increased 40.22%. Carotenoid production at day 2 by strain KTSSG46 grown in BIM modified with l-glutamate at 1 and 1.23 g/L MgSO₄ ·7H₂ O was the same as production in BIM modified with monosodium glutamate (MSG). Culture supernatants from all BIM formulations showed similar activity against the resistant AHPND strain SR2. Based on high-performance liquid chromatography, carotenoids of strain KTSSG46 might be canthaxanthin. Grown in BIM modified with MSG, strain KTSSG46 could produce inexpensive carotenoids and release anti-vibrio compounds that, applied as shrimp feed additive, would prevent AHPND strains.

Isolation and Characterization of Mannanase-Producing Bacteria for Potential Synbiotic Application in Shrimp Farming

Prebiotics such as mannan-oligosaccharides (MOS) are a promising approach to improve performance and disease resistance in shrimp. To improve prebiotic utilization, we investigated the potential probiotics and their feasibility of synbiotic use in vitro. Two bacterial isolates, Man26 and Man122, were isolated from shrimp intestines and screened for mannanase, the enzyme for mannan digestion. The crude mannanase from both isolates showed optimal activities at pH 8 with optimum temperatures at 60 °C and 50 °C, respectively. The enzymes remained stable at pH 8−10 for 3 h (>70% relative activity). The thermostability range of Man26 was 20−40 °C for 20 min (>50%), while that of Man122 was 20−60 °C for 30 min (>50%). The Vmax of Man122 against locust bean gum substrate was 41.15 ± 12.33 U·mg−1, six times higher than that of Man26. The Km of Man26 and Man122 were 18.92 ± 4.36 mg·mL−1 and 34.53 ± 14.46 mg·mL−1, respectively. With the addition of crude enzymes, reducing sugars of copra meal, palm kernel cake, and soybean meal were significantly increased (p < 0.05), as well as protein release. The results suggest that Man26 and Man122 could potentially be used in animal feeds and synbiotically with copra meal to improve absorption and utilization of feedstuffs.

Mechanism of the Potential Therapeutic Candidate Bacillus subtilis BSXE-1601 Against Shrimp Pathogenic Vibrios and Multifunctional Metabolites Biosynthetic Capability of the Strain as Predicted by Genome Analysis

The global shrimp industry has suffered bacterial diseases caused mainly by Vibrio species. The typical vibriosis, acute hepatopancreatic necrosis disease (AHPND), has resulted in mass mortality and devastating economic losses. Thus, therapeutic strategies are highly needed to decrease the risk of vibriosis outbreaks. Herein, we initially identified that the growth of the causative agent of AHPND, Vibrio parahaemolyticus (VP AHPND ) and other vibrios in Pacific white shrimp (Litopenaeus vannamei) was inhibited by a Bacillus subtilis strain BSXE-1601. The natural products amicoumacins A, B, and C were purified from the cell-free supernatant from the strain BSXE-1601, but only amicoumacin A was demonstrated to be responsible for this anti-Vibrio activity. Our discovery provided the first evidence that amicoumacin A was highly active against shrimp pathogens, including the representative strain VP AHPND . Furthermore, we elucidated the amicoumacin A biosynthetic gene cluster by whole genome sequencing of the B. subtilis strain BSXE-1601. In addition to amicoumacin A, the strain BSXE-1601 genome harbored other genes encoding bacillibactin, fengycin, surfactin, bacilysin, and subtilosin A, all of which have previously reported antagonistic activities against pathogenic strains. The whole-genome analysis provided unequivocal evidence in support of the huge potential of the strain BSXE-1601 to produce diverse biologically antagonistic natural products, which may facilitate further studies on the effective therapeutics for detrimental diseases in shrimp.

Prevalence of Vibrio parahaemolyticus Causing Acute Hepatopancreatic Necrosis Disease of Shrimp in Shrimp, Molluscan Shellfish and Water Samples in the Mekong Delta, Vietnam

Simple Summary

Recently, Vibrio parahaemolyticus has been identified as an important agent of acute hepatopancreatic necrosis disease in shrimp. In Vietnam, this disease has appeared since 2010 and caused a big economic loss for shrimp farming. However, the information of this agent in Vietnam has been not fully understood. This study aims to investigate the prevalence of shrimp pathogenic Vibrio parahaemolyticus and several it’s characteristics in the Mekong Delta of Vietnam. A total of 481 shrimp and molluscan shellfish samples from retail shops and farms and 64 water samples from shrimp and molluscan shellfish farms were examined for the presence of pathogenic strains. The pathogenic strains were isolated in 0.7% of molluscan shellfish samples from retail shops, 9.9% of shrimp samples from shrimp ponds, and 4.8% of water samples from shrimp ponds. These strains were classified into two types of O antigen (O1 and O3), in which O1 was the predominant. They showed resistance to several antimicrobial agents, multidrug resistance and pathogenicity to experimental shrimp. These results indicate that shrimp pathogenic Vibrio parahaemolyticus is widely prevalent in environment in the Mekong Delta, Vietnam. These findings can be used for understanding the risk of shrimp pathogenic Vibrio parahaemolyticus in the Mekong Delta.

Abstract

A total of 481 samples, including 417 shrimp and molluscan shellfish samples from retail shops and farms and 64 water samples from shrimp and molluscan shellfish farms in the Mekong Delta located the southern part of Vietnam, were examined for the presence of Vibrio parahaemolyticus (Vp_AHPND) caused acute haepatopancreatic necrosic disease (AHPND) in shrimp. Vp_AHPND strains were isolated in two of 298 (0.7%) molluscan shellfish samples from retail shops, seven of 71 (9.9%) shrimp samples from shrimp ponds, and two of 42 (4.8%) water samples from shrimp ponds. Vp_AHPND strains were classified into two types of O antigen, including O1 and O3, in which O1 was the predominant. Vp_AHPND strains isolated showed high resistance rates to colistin (100%), ampicillin (93.8%), and streptomycin (87.5%). These results indicate that Vp_AHPND is widely prevalent in environment in the Mekong Delta, Vietnam.

Determination of the Infectious Agent of Translucent Post-Larva Disease (TPD) in Penaeus vannamei

A new emerging disease called “translucent post-larvae disease” (TPD) or “glass post-larvae disease” (GPD) of Penaeus vannamei, characterized by pale or colorless hepatopancreas and digestive tract, has become an urgent threat to the shrimp farming industry. Following this clue that treatment of an antibacterial agent could alleviate the disease, systematic investigation of the potential infectious agent of TPD was conducted using bacterial identification and artificial challenge tests to fulfill Koch’s postulates. A dominant bacterial isolate, Vp-JS20200428004-2, from the moribund individuals was isolated and identified as Vibrio parahaemolyticus based on multi-locus sequence analysis. However, Vp-JS20200428004-2 differed from the V. parahaemolyticus that caused typical acute hepatopancreatic necrosis disease. Immersion challenge tests revealed that Vp-JS20200428004-2 could cause 100% mortality within 40 h at a dose of 1.83 × 10⁶ CFU/mL, and experimental infected shrimp showed similar clinical signs of TPD. The Vp-JS20200428004-2 could be re-isolated and identified from the experimental infected individuals. Moreover, histopathological analysis of diseased samples indicated that Vp-JS20200428004-2 caused severe necrosis and sloughing of epithelial cells of the hepatopancreas and midgut in shrimp individuals both naturally and experimentally infected. Our present results indicated that Vp-JS20200428004-2 is a highly virulent infectious agent associated with the TPD and deserves further attention.

A novel vibriophage exhibits inhibitory activity against host protein synthesis machinery

Since the emergence of deadly pathogens and multidrug-resistant bacteria at an alarmingly increased rate, bacteriophages have been developed as a controlling bioagent to prevent the spread of pathogenic bacteria. One of these pathogens, disease-causing Vibrio parahaemolyticus (VPAHPND) which induces acute hepatopancreatic necrosis, is considered one of the deadliest shrimp pathogens, and has recently become resistant to various classes of antibiotics. Here, we discovered a novel vibriophage that specifically targets the vibrio host, VPAHPND. The vibriophage, designated Seahorse, was classified in the family Siphoviridae because of its icosahedral capsid surrounded by head fibers and a non-contractile long tail. Phage Seahorse was able to infect the host in a broad range of pH and temperatures, and it had a relatively short latent period (nearly 30 minutes) in which it produced progeny at 72 particles per cell at the end of its lytic cycle. Upon phage infection, the host nucleoid condensed and became toroidal, similar to the bacterial DNA morphology seen during tetracycline treatment, suggesting that phage Seahorse hijacked host biosynthesis pathways through protein translation. As phage Seahorse genome encodes 48 open reading frames with many hypothetical proteins, this genome could be a potential untapped resource for the discovery of phage-derived therapeutic proteins.

Genomic basis of antibiotic resistance in Vibrio parahaemolyticus strain JPA1

A multi-resistant strain of Vibrio parahaemolyticus was isolated from a tropical estuary in Rio de Janeiro, Brazil. Genome sequencing was conducted to establish the molecular basis of antibiotic resistance in this organism. The genetic content of this strain revealed it to be a non-virulent lineage that nevertheless possesses several antibiotic resistance determinants.

FmLC6: An ultimate dual-CRD C-type lectin from Fenneropenaeus merguiensis mediated its roles in shrimp defense immunity towards bacteria and virus

C-type lectins are a member of pattern recognition receptors (PRRs) that can interact with pathogen-associated molecular patterns of invading microorganisms by using their conserved motifs in carbohydrate recognition domain (CRD). The binding can trigger various immune responses in both direct and indirect mechanisms. Hereby, an ultimate C-type lectin with dual CRDs each of which containing a different motif was identified from hepatopancreas of Fenneropenaeus merguiensis (mentioned as FmLC6). The full-length cDNA of FmLC6 consisted of 1148 bp comprising one 1005 bp open reading frame (ORF) encoding a signal peptide and a mature protein of 317 residues. FmLC6 was composed of two CRDs with a highly conserved QPD (Gln-Pro-Asp) motif and one variant EPQ (Glu-Pro-Gln) motif for illustrating the carbohydrate binding affinity. The transcription of FmLC6 was detected only in hepatopancreas of normal shrimp. After injection with pathogens or immunostimulants, the expression of FmLC6 was significantly up-regulated and reached the highest level at 12 h post-injection except with lipoteichoic acid challenge. The FmLC6 expression was severely suppressed by knockdown based-silencing. This gene silencing with co-injection by Vibrio parahaemolyticus caused increasing in cumulative mortality and reduction of the median lethal time. Purified recombinant proteins of an entire ORF and two individual CRDs of FmLC6 produced in Escherichia coli could induce a broad spectrum of microbial agglutination with calcium dependence. The agglutination induced by rFmLC6, rCRD1 and rCRD2 was suppressed by galactose plus mannose, galactose and mannose, respectively which this event was confirmed by the inhibition of hemagglutination. All three recombinant proteins possessed ability to inhibit the bacterial growth with a dose-response. Purified rFmLC6 could bind directly to white spot syndrome virus particles and also its recombinant proteins including VP15, VP39A and VP28 with different affinity. Altogether, these results indicate that FmLC6 acts as a PRR to recognize invading microorganisms and leads to mediating the immune response to cooperation in pathogenic elimination via the binding, agglutination and antimicrobial activity.

A Natural Vibrio parahaemolyticus ΔpirA Vp pirB Vp+ Mutant Kills Shrimp but Produces neither Pir Vp Toxins nor Acute Hepatopancreatic Necrosis Disease Lesions

Acute hepatopancreatic necrosis disease (AHPND) of shrimp is caused by Vibrio parahaemolyticus isolates (VP_AHPND isolates) that harbor a pVA plasmid encoding toxins PirA ^Vp and PirB ^Vp These are released from VP_AHPND isolates that colonize the shrimp stomach and produce pathognomonic AHPND lesions (massive sloughing of hepatopancreatic tubule epithelial cells). PCR results indicated that V. parahaemolyticus isolate XN87 lacked pirA ^Vp but carried pirB ^Vp Unexpectedly, Western blot analysis of proteins from the culture broth of XN87 revealed the absence of both toxins, and the lack of PirB ^Vp was further confirmed by enzyme-linked immunosorbent assay. However, shrimp immersion challenge with XN87 resulted in 47% mortality without AHPND lesions. Instead, lesions consisted of collapsed hepatopancreatic tubule epithelia. In contrast, control shrimp challenged with typical VP_AHPND isolate 5HP gave 90% mortality, accompanied by AHPND lesions. Sequence analysis revealed that the pVA plasmid of XN87 contained a mutated pirA ^Vp gene interrupted by the out-of-frame insertion of a transposon gene fragment. The upstream region and the beginning of the original pirA ^Vp gene remained intact, but the insertion caused a 2-base reading frameshift in the remainder of the pirA ^Vp gene sequence and in the downstream pirB ^Vp gene sequence. Reverse transcription-PCR and sequencing of 5HP revealed a bicistronic pirAB ^Vp mRNA transcript that was not produced by XN87, explaining the absence of both toxins in its culture broth. However, the virulence of XN87 revealed that some V. parahaemolyticus isolates carrying mutant pVA plasmids that produce no Pir ^Vp toxins can cause mortality in shrimp in ponds experiencing an outbreak of early mortality syndrome (EMS) but may not have been previously recognized to be AHPND related because they did not cause pathognomonic AHPND lesions.IMPORTANCE Shrimp acute hepatopancreatic necrosis disease (AHPND) is caused by Vibrio parahaemolyticus isolates (VP_AHPND isolates) that harbor the pVA1 plasmid encoding toxins PirA ^Vp and PirB ^Vp The toxins are produced in the shrimp stomach but cause death by massive sloughing of hepatopancreatic tubule epithelial cells (pathognomonic AHPND lesions). V. parahaemolyticus isolate XN87 harbors a mutant pVA plasmid that produces no Pir toxins and does not cause AHPND lesions but still causes ∼50% shrimp mortality. Such isolates may cause a portion of the mortality in ponds experiencing an outbreak of EMS that is not ascribed to VP_AHPND Thus, they pose to shrimp farmers an additional threat that would be missed by current testing for VP_AHPND Moribund shrimp from ponds experiencing an outbreak of EMS that exhibit collapsed hepatopancreatic tubule epithelial cells can serve as indicators for the possible presence of such isolates, which can then be confirmed by additional PCR tests for the presence of a pVA plasmid.

Isolation of Bdellovibrio and like organisms and potential to reduce acute hepatopancreatic necrosis disease caused by Vibrio parahaemolyticus

Acute hepatopancreatic necrosis disease, a severe disease of shrimp, is caused by Vibrio parahaemolyticus (AHPND Vp), a halophilic bacterium harboring a plasmid that contains toxin genes homologous to Photorhabdus insect-related toxins. We obtained 9 isolates of Bdellovibrio and like organisms (BALOs) from water and sediment samples in Thailand. Using 16S rRNA sequencing, all of the organisms were identified as Bacteriovorax spp. and were able to attack all tested AHPND Vp isolates. In addition, their various susceptible hosts, including Gram-positive and Gram-negative bacteria, were observed. The optimal ratio for interaction between the Bacteriovorax isolate BV-A and AHPND Vp was determined to be 1:10. The suitable conditions applied for co-culture between BV-A and AHPND Vp were 30°C, 2% NaCl, and pH 7.6. The capability of BV-A to reduce numbers of AHPND Vp in vitro was observed in co-culture after incubation for 2 d and continued until the end of the incubation period. In vivo, BV-A was able to reduce mortality of shrimp post-larvae infected with AHPND Vp. In addition, BV-A significantly decreased the formation of biofilm by AHPND Vp. These findings provide evidence for using Bacteriovorax as a biocontrol of AHPND Vp in shrimp aquaculture.

Vibrio Parahaemolyticus: A Review on Distribution, Pathogenesis, Virulence Determinants and Epidemiology

Vibrio parahaemolyticus is a Gram-negative, halophilic bacterium isolated from marine environments globally. After the consumption of contaminated seafood, V. parahaemolyticus causes acute gastroenteritis. To initiate infection, a wide range of virulence factors are required. A complex group of genes is known to participate in the pathogenicity of V. parahaemolyticus; however, to understand the full mechanism of infection, extensive research is yet required. V. parahaemolyticus has become the leading cause of seafood-related gastroenteritis in Japan, the United States and several other parts of the world. In addition, outbreaks caused by the pandemic clone of this organism are escalating and spreading universally. To minimize the risk of V. parahaemolyticus infection and warrant the safety of seafood, collaboration between governments and scientists is required. We herein provide an updated review of the pathogenicity determinants and distribution of V. parahaemolyticus to deliver a better understanding of the significance of V. parahaemolyticus and its host-pathogen interactions.

Genetic diversity of Vibrio parahaemolyticus strains isolated from farmed Pacific white shrimp and ambient pond water affected by acute hepatopancreatic necrosis disease outbreak in Thailand

Acute hepatopancreatic necrosis disease (AHPND) is an emerging shrimp disease that causes massive die-offs in farmed shrimps. Recent outbreaks of AHPND in Asia have been causing great losses for shrimp culture and have become a serious socioeconomic problem. The causative agent of AHPND is Vibrio parahaemolyticus, which is typically known to cause food-borne gastroenteritis in humans. However, there have been few reports of the epidemiology of V. parahaemolyticus AHPND strains, and the genetic relationship among AHPND strains is unclear. Here, we report the genetic characterization of V. parahaemolyticus strains isolated from AHPND outbreaks in Thailand. We found eight isolates from AHPND-suspected shrimps and pond water that were positive for AHPND markers AP1 and AP2. PCR analysis confirmed that none of these eight AP-positive AHPND strains possesses the genes for the conventional virulence factors affecting to humans, such as thermostable direct hemolysin (TDH), TDH-related hemolysin (TRH) and type III secretion system 2. Phylogenetic analysis by multilocus sequence typing showed that the AHPND strains are genetically diverse, suggesting that AHPND strains were not derived from a single genetic lineage. Our study represents the first report of molecular epidemiology of AHPND-causing V. parahaemolyticus strains using multilocus sequence typing, and provides an insight into their evolutionary mechanisms.

Genotyping of virulence plasmid from Vibrio parahaemolyticus isolates causing acute hepatopancreatic necrosis disease in shrimp

Acute hepatopancreatic necrosis disease (AHPND) has caused severe mortalities in farmed penaeid shrimp throughout SE Asia and Mexico. The causative agent of AHPND is the marine bacterium Vibrio parahaemolyticus, which secretes PirA- and PirB-like binary toxin that caused deterioration in the hepatopancreas of infected shrimp. The genes responsible for the production of this toxin are located in a large plasmid residing within the bacterial cells. We analyzed the plasmid sequence from the whole genome sequences of AHPND-V. parahaemolyticus isolates and identified 2 regions that exhibit a clear geographical variation: a 4243-bp Tn3-like transposon and a 9-bp small sequence repeat (SSR). The Tn3-like transposon was only found in the isolates from Mexico and 2 unspecified Central American countries, but not in SE Asian isolates from China, Vietnam, and Thailand. We developed PCR methods to characterize AHPND-V. parahaemolyticus isolates as either Mexican-type or SE Asian-type based on the presence of the Tn3-like transposon. The SSR is found within the coding region of a hypothetical protein and has either 4, 5, or 6 repeat units. SSRs with 4 repeat units were found in isolates from Vietnam, China, and Thailand. SSRs with 5 repeat units were found in some Vietnamese isolates, and SSRs with 6 repeat units were only found in the Mexican isolates.

The opportunistic marine pathogen Vibrio parahaemolyticus becomes virulent by acquiring a plasmid that expresses a deadly toxin

Acute hepatopancreatic necrosis disease (AHPND) is a severe, newly emergent penaeid shrimp disease caused by Vibrio parahaemolyticus that has already led to tremendous losses in the cultured shrimp industry. Until now, its disease-causing mechanism has remained unclear. Here we show that an AHPND-causing strain of V. parahaemolyticus contains a 70-kbp plasmid (pVA1) with a postsegregational killing system, and that the ability to cause disease is abolished by the natural absence or experimental deletion of the plasmid-encoded homologs of the Photorhabdus insect-related (Pir) toxins PirA and PirB. We determined the crystal structure of the V. parahaemolyticus PirA and PirB (PirA(vp) and PirB(vp)) proteins and found that the overall structural topology of PirA(vp)/PirB(vp) is very similar to that of the Bacillus Cry insecticidal toxin-like proteins, despite the low sequence identity (<10%). This structural similarity suggests that the putative PirAB(vp) heterodimer might emulate the functional domains of the Cry protein, and in particular its pore-forming activity. The gene organization of pVA1 further suggested that pirAB(vp) may be lost or acquired by horizontal gene transfer via transposition or homologous recombination.