PlzD modifies Vibrio vulnificus foraging behavior and virulence in response to elevated c-di-GMP

IMPORTANCE

Many free-swimming bacteria propel themselves through liquid using rotary flagella, and mounting evidence suggests that the inhibition of flagellar rotation initiates biofilm formation, a sessile lifestyle that is a nearly universal surface colonization paradigm in bacteria. In general, motility and biofilm formation are inversely regulated by the intracellular second messenger bis-(3´-5´)-cyclic dimeric guanosine monophosphate (c-di-GMP). Here, we identify a protein, PlzD, bearing a conserved c-di-GMP binding PilZ domain that localizes to the flagellar pole in a c-di-GMP-dependent manner and alters the foraging behavior, biofilm, and virulence characteristics of the opportunistic human pathogen, Vibrio vulnificus. Our data suggest that PlzD interacts with components of the flagellar stator to decrease bacterial swimming speed and changes in swimming direction, and these activities are enhanced when cellular c-di-GMP levels are elevated. These results reveal a physical link between a second messenger (c-di-GMP) and an effector (PlzD) that promotes transition from a motile to a sessile state in V. vulnificus.

Sequence analysis of hepcidin in barbel steed (Hemibarbus labeo): QSHLS motif confers hepcidin iron-regulatory activity but limits its antibacterial activity

Fish hepcidin genes are generally classified into two groups: hamp1-and hamp2-type isoforms. Hamp1-type hepcidin exhibits iron regulatory and antimicrobial activity, while hamp2-type shows a unique role in the immune response against various pathogens. An iron-regulatory motif exists at the N-terminus of hamp1-type hepcidin; however, the functional effect of this motif in fish is not well understood. Here, cDNA of the barbel steed (Hemibarbus labeo) hepcidin gene was cloned and sequenced. The predicted amino acid sequence comprised a signal peptide, a prodomain, and a mature peptide. Phylogenetic tree analysis revealed that barbel steed hepcidin belongs to the fish HAMP1 cluster and is closely related to Chinese rare minnow (Gobiocypris rarus) hepcidin. Barbel steed hepcidin is constitutively expressed in healthy fish tissues, predominantly in the liver. Following iron dextran treatment or Aeromonas hydrophila infection, expression of barbel steed hepcidin increased significantly in tested tissues. In vivo administration of intact hepcidin mature peptide (hep25) significantly and dose-dependently reduced ferroportin 1 expression, while truncated hepcidin mature peptide (hep20) lacking a QSHLS motif had no such effect. In vitro treatment of barbel steed monocytes/macrophages with hep25, but not hep20, increased the labile iron pool levels. Hep25 and hep20 conferred antibacterial activity only against A. hydrophila and Vibrio vulnificus, with greater activity of the latter at low concentrations. Neither hep25 nor hep20 impaired the cell membrane integrity of A. hydrophila, but could hydrolyze its genomic DNA; lack of a QSHLS motif enables hep20 to have a better hydrolytic effect. In summary, we identified an iron-regulatory motif in a fish species and demonstrated that this motif confers hamp1-type hepcidin iron-regulatory activity, but attenuates its antibacterial activity.

rpoB mutations conferring rifampicin-resistance affect growth, stress response and motility in Vibrio vulnificus

Rifampicin is a broad-spectrum antibiotic that binds to the bacterial RNA polymerase (RNAP), compromising DNA transcription. Rifampicin resistance is common in several microorganisms and it is typically caused by point mutations in the gene encoding the β subunit of RNA polymerase, rpoB. Different rpoB mutations are responsible for various levels of rifampicin resistance and for a range of secondary effects. rpoB mutations conferring rifampicin resistance have been shown to be responsible for severe effects on transcription, cell fitness, bacterial stress response and virulence. Such effects have never been investigated in the marine pathogen Vibrio vulnificus, even though rifampicin-resistant strains of V. vulnificus have been isolated previously. Moreover, spontaneous rifampicin-resistant strains of V. vulnificus have an important role in conjugation and mutagenesis protocols, with poor consideration of the effects of rpoB mutations. In this work, effects on growth, stress response and virulence of V. vulnificus were investigated using a set of nine spontaneous rifampicin-resistant derivatives of V. vulnificus CMCP6. Three different mutations (Q513K, S522L and H526Y) were identified with varying incidence rates. These three mutant types each showed high resistance to rifampicin [minimal inhibitory concentration (MIC) >800 µg ml-1], but different secondary effects. The strains carrying the mutation H526Y had a growth advantage in rich medium but had severely reduced salt stress tolerance in the presence of high NaCl concentrations as well as a significant reduction in ethanol stress resistance. Strains possessing the S522L mutation had reduced growth rate and overall biomass accumulation in rich medium. Furthermore, investigation of virulence characteristics demonstrated that all the rifampicin-resistant strains showed compromised motility when compared with the wild-type, but no major effects on exoenzyme production were observed. These findings reveal a wide range of secondary effects of rpoB mutations and indicate that rifampicin resistance is not an appropriate selectable marker for studies that aim to investigate phenotypic behaviour in this organism.

Bacteriophages Against Pathogenic Vibrios in Delaware Bay Oysters (Crassostrea virginica) During a Period of High Levels of Pathogenic Vibrio parahaemolyticus

Eastern oysters (Crassostrea virginica) from three locations along the Delaware Bay were surveyed monthly from May to October 2017 for levels of total Vibrio parahaemolyticus, pathogenic strains of V. parahaemolyticus and Vibrio vulnificus, and for strain-specific bacteriophages against vibrios (vibriophages). The objectives were to determine (a) whether vibriophages against known strains or serotypes of clinical and environmental vibrios were detectable in oysters from the Delaware Bay and (b) whether vibriophage presence or absence corresponded with Vibrio abundances in oysters. Host cells for phage assays included pathogenic V. parahaemolyticus serotypes O3:K6, O1:KUT (untypable) and O1:K1, as well as clinical and environmental strains of V. vulnificus. Vibriophages against some, but not all, pathogenic V. parahaemolyticus serotypes were readily detected in Delaware Bay oysters. In July, abundances of total and pathogenic V. parahaemolyticus at one site spiked to levels exceeding regulatory guidelines. Phages against three V. parahaemolyticus host serotypes were detected in these same oysters, but also in oysters with low V. parahaemolyticus levels. Serotype-specific vibriophage presence or absence did not correspond with abundances of total or pathogenic V. parahaemolyticus. Vibriophages were not detected against three V. vulnificus host strains, even though V. vulnificus were readily detectable in oyster tissues. Selected phage isolates against V. parahaemolyticus showed high host specificity. Transmission electron micrographs revealed that most isolates were ~ 60-nm diameter, non-tailed phages. In conclusion, vibriophages were detected against pandemic V. parahaemolyticus O3:K6 and O1:KUT, suggesting that phage monitoring in specific host cells may be a useful technique to assess public health risks from oyster consumption.

Molecular identification and expression analysis of four Lysin motif (LysM) domain-containing proteins from turbot (Scophthalmus maximus)

Lysin motif (LysM) is involved in chitin, peptidoglycan and other structurally-related oligosaccharides recognition and binding, and it is important for the biological processes of responsing to bacterial and viral infections and pathogen defense. LysM is also a widely spread protein, ranging from prokaryotes to eukaryotes, including bacteria, plants and mammals. However, research of LysM in teleosts especially in marine fish was rarely scarce. In the present study, four novel LysM domain-containing proteins in turbot (Scophthalmus maximus), named as SmLysMd1, SmLysMd2, SmLysMd3, and SmLysMd4, were cloned and identified firstly. The full-length cDNA of SmLysMd1 was 1235 bp with a 678 bp ORF, capable of encoding a peptide of 225 amino acids. The complete cDNA sequence of SmLysMd2 was 1273 bp, and contained a 675 bp ORF, encoding a predicted protein of 224 amino acids. The full-length of SmLysMd3 cDNA was 2132 bp, containing a ORF of 987 bp, with a ORF of encoding 328 amino acids. The full-length SmLysMd4 cDNA was 1115 bp contained a 888 bp ORF, encoding 295 amino acids. And all the four predicated proteins contained a specific LYSM domain. Moreover, SmLysMd1 and SmLysMd2 belong to the intracellular non-secretory types, and SmLysMd3 and SmLysMd4 belong to the anchored transmembrane types. In addition, the four SmLysMd were ubiquitously expressed in all the examined tissues. Moreover, the SmLysMds levels were up-regulated in muscle and liver, and had a reduce tendency immediately in different degree following Vibrio vulnificus challenge, indicating that the turbot LysM could be participant in the immune responses to bacterial infections. The present result of LysM in turbot for the first time in a marine fish will provide foundation knowledge for the functions studies of LysM in immune responses. Further studies should be carried out to better understand their immune mechanism in turbot and other teleosts.

Microneedle Patch-Mediated Treatment of Bacterial Biofilms

Current treatments of bacterial biofilms are limited by the poor penetration of antibiotics through their physical barrier as well as significant off-target toxicity of antibiotics and the induction of antibiotic resistance. Here we report a microneedle patch-mediated treatment for the effective elimination of biofilms by penetrating the biofilm and specifically delivering antibiotics to regions of active growth. We fabricated patches with self-dissolvable microneedles and needle tips loaded with chloramphenicol (CAM)-bearing and gelatinase-sensitive gelatin nanoparticles (CAM@GNPs). During the microneedle patch-mediated treatment, arrays of 225 microneedles simultaneously penetrate the biofilm matrix. Once inside, the microneedles dissolve and uniformly release CAM@GNPs into the surrounding area. In response to the gelatinase produced by the active bacterial community, the CAM@GNPs disassemble and release CAM into these active regions of the biofilm. Moreover, CAM@GNPs exhibited minimal off-target toxicity compared to direct CAM administration, which in turn favors wound healing. Importantly, we found that our microneedle-mediated treatment is more effective in treating Vibrio vulnificus biofilms than drug in free solution. We believe this new treatment strategy can be used to improve the delivery of a wide range of antimicrobial agents to biofilm-contaminated sites.

Molecular identification and function analysis of bactericidal permeability-increasing protein/LPS-binding protein 1 (BPI/LBP1) from turbot (Scophthalmus maximus)

Bactericidal permeability-increasing protein (BPI) and lipopolysaccharide-binding protein (LBP) play important roles in host antimicrobial defense. In the present study, we identified one isoform of BPI/LBP gene from turbot (Scophthalmus maximus), designated as SmBPI/LBP1. The full-length cDNA sequence of SmBPI/LBP1 was 1826 bp, which encoding one secreted protein with 480 amino acid residues. Structurally, the SmBPI/LBP1 showed high similarity to its homologs from other vertebrates or invertebrates, which all contained a signal peptide, a BPI/LBP/CETP N-terminal with a LPS-binding domain, and a BPI/LBP/CETP C-terminal domain. The deduced amino acid sequences of SmBPI/LBP1 shared significant similarity to BPI/LBP of Seriola lalandi dorsalis (71%) and Paralichthys olivaceus (69%). Phylogentic analysis further supported that SmBPI/LBP1 act as a new member of vertebrate BPI/LBP family. SmBPI/LBP1 was ubiquitously expressed in all tested tissues, with the highest expression level in spleen tissue. The mRNA expression of SmBPI/LBP1 in spleen and kidney were significantly up-regulated after Vibrio vulnificus challenge. Finally, the recombinant SmBPI/LBP1 showed high affinity to lipopolysaccharide, followed by peptidoglycan and lipoteichoic acid, which is the ubiquitous component of Gram-negative or Gram-positive bacteria. These results indicated that SmBPI/LBP1 probably played important roles in immune response against bacteria infection.

Identification of 2',4'-Dihydroxychalcone as an Antivirulence Agent Targeting HlyU, a Master Virulence Regulator in Vibrio vulnificus

The emergence of antimicrobial resistance and rapid acclimation allows Vibrio vulnificus to rapidly propagate in the host. This problematic pathological scenario can be circumvented by employing an antivirulence strategy, treating Vibrio infections without hindering the bacterial growth. We developed a genome-integrated orthogonal inhibitor screening platform in E. coli to identify antivirulence agents targeting a master virulence regulator of V. vulnificus. We identified 2′,4′-dihydroxychalcone (DHC) from the natural compound library and verified that it decreases the expression of the major toxin network which is equivalent to the ∆hlyU deletion mutant. 2′,4′-DHC also reduced the hemolytic activity of V. vulnificus which was tested as an example of virulence phenotype. The electrophoretic mobility shift assay confirmed that 2′,4′-DHC specifically targeted HlyU and inhibited its binding to PrtxA1 promoter. Under in vivo conditions, a single dose of 2′,4′-DHC protected ~50% wax-worm larvae from V. vulnificus infection at a non-toxic concentration to both V. vulnificus and wax-worm larvae. In the current study, we demonstrated that an orthogonal reporter system is suitable for the identification of antivirulence compounds with accuracy, and identified 2′,4′-DHC as a potent antivirulence agent that specifically targets the HlyU virulence transcriptional regulator and significantly reduces the virulence and infection potential of V. vulnificus.

A potent tilapia secreted granulin peptide enhances the survival of transgenic zebrafish infected by Vibrio vulnificus via modulation of innate immunity

Progranulin (PGRN) is a multi-functional growth factor that mediates cell proliferation, survival, migration, tumorigenesis, wound healing, development, and anti-inflammation activity. A novel alternatively spliced transcript from the short-form PGRN1 gene encoding a novel, secreted GRN peptide composed of 20-a.a. signal peptide and 41-a.a. GRN named GRN-41 was identified to be abundantly expressed in immune-related organs including spleen, head kidney, and intestine of Mozambique tilapia. The expression of GRN-41 and PGRN1 were further induced in the spleen of tilapia challenged with Vibrio vulnificus at 3 h post infection (hpi) and 6 hpi, respectively. In this study, we established three transgenic zebrafish lines expressing the secreted GRN-41, GRN-A and PGRN1 of Mozambique tilapia specifically in muscle. The relative percent of survival (RPS) was enhanced in adult transgenic zebrafish expressing tilapia GRN-41 (68%), GRN-A (32%) and PGRN1 (36%) compared with control transgenic zebrafish expressing AcGFP after challenge with V. vulnificus. It indicates tilapia GRN-41 is a potent peptide against V. vulnificus infection. The secreted tilapia GRN-41 can induce the expression of innate immune response-related genes, such as TNFa, TNFb, IL-8, IL-1β, IL-6, IL-26, IL-21, IL-10, complement C3, lysozyme (Lyz) and the hepatic antimicrobial peptide hepcidin (HAMP), in adult transgenic zebrafish without V. vulnificus infection. The tilapia GRN-41 peptide can enhance the innate immune response by further elevating TNFb, IL-1β, IL-8, IL-6, and HAMP expression in early responsive time to the V. vulnificus challenge in transgenic zebrafish. Our results suggest that the novel GRN-41 peptide generated from alternative splicing of the tilapia PGRN1 gene is a potent peptide that defends against V. vulnificus in the transgenic zebrafish model by modulation of innate immunity.

Effects of temperature and salinity on prevalence and intensity of infection of blue crabs, Callinectes sapidus, by Vibrio cholerae, V. parahaemolyticus, and V. vulnificus in Louisiana

Coastal marine and estuarine environments are experiencing higher average temperatures, greater frequency of extreme temperature events, and altered salinities. These changes are expected to stress organisms and increase their susceptibility to infectious diseases. However, beyond these generalities, little is known about how environmental factors influence host-pathogen relationships in the marine realm. We investigated the prevalence and intensity of infections by Vibrio cholerae, V. parahaemolyticus, and V. vulnificus in blue crabs, Callinectes sapidus, from Louisiana saltmarshes in relation to temperature and salinity. We evaluated relationships for single measurements taken at the time of collection and for more complex measurements representing accumulated exposure to physiologically-stressful environmental conditions for up to 31 days prior to collection. We found that: (1) prevalence of infection varied across the Louisiana coast, (2) prevalence of all three Vibrio species was influenced by temperature and salinity, and (3) measurements that represent accumulated exposure to extreme conditions are useful predictors of infection prevalence and can provide insights into underlying biological mechanisms.

Vibrio vulnificus induces mTOR activation and inflammatory responses in macrophages

Vibrio vulnificus (V. vulnificus), a Gram-negative marine bacterium, can cause life-threatening primary septicemia, especially in patients with liver diseases. How V. vulnificus affects the liver and how it acts on macrophages are not well understood. In this report, we demonstrated that V. vulnificus infection causes a strong inflammatory response, marked expansion of liver-resident macrophages, and liver damage in mice. We demonstrated further that V. vulnificus activates mTOR in macrophages and inhibition of mTOR differentially regulates V. vulnificus induced inflammatory responses, suggesting the possibility of targeting mTOR as a strategy to modulate V. vulnificus induced inflammatory responses.

Responses of Mytilus galloprovincialis hemocytes to environmental strains of Vibrio parahaemolyticus, Vibrio alginolyticus, Vibrio vulnificus

Marine bivalves are exposed to different types of bacteria in the surrounding waters, in particular of the Vibrio genus. In the hemocytes of the mussel Mytilus spp. immune responses to different vibrios have been largely characterized. However, little information is available on the hemocyte responses to human pathogenic vibrios commonly detected in coastal waters and bivalve tissues that are involved in seafood-borne diseases. In this work, functional parameters of the hemocytes from the Mediterranean mussel M. galloprovincialis were evaluated in response to in vitro challenge with different vibrios isolated from environmental samples of the Adriatic sea (Italy): V. parahaemolyticus Conero, V. alginolyticus 1513 and V. vulnificus 509. V. parahaemolyticus ATCC 43996 was used for comparison. At the 50:1 bacteria hemocyte ratio, only V. parahaemolyticus strains induced significant lysosomal membrane destabilisation. Stimulation of extracellular lysozyme release, total ROS, O₂^- and NO production were observed, although to different extents and with distinct time courses for different vibrios, V. vulnificus 509 in particular. Further comparisons between V. parahaemolyticus Conero and V. vulnificus 509 showed that only the latter induced dysregulation of the phosphorylation state of p38 MAP Kinase and apoptotic processes. The results indicate that mussel hemocytes can mount an efficient immune response towards V. parahaemolyticus and V. alginolyticus strains, whereas V. vulnificus 509 may affect the hemocyte function. This is the first report on immune responses of mussels to local environmental isolates of human pathogenic vibrios. These data reinforce the hypothesis that Mytilus hemocytes show specific responses to different vibrio species and strains.

Transcriptome analysis of the effect of polyunsaturated fatty acids against Vibrio vulnificus infection in Oreochromis niloticus

Vibrio vulnificus infection causes severe economic losses in Oreochromis niloticus aquaculture by inducing pro-inflammatory cytokines, that lead to inflammation and mortality. Omega-3 fatty acids, such as Docosahexaenoic acid (DHA) and Eicosapentaenoic acid (EPA), have been reported for their anti-inflammatory and antibacterial abilities in murine and zebrafish models. However, the anti-inflammatory and antibacterial functions of DHA and EPA in commercial aquaculture organisms such as Oreochromis niloticus remain unknown. The present study demonstrates antibacterial function and transcriptional modulation of inflammation-associated genes by DHA and EPA in Vibrio vulnificus infection in Oreochromis niloticus fish models. The administration of EPA or DHA improved the Oreochromis niloticus survival rate against Vibrio vulnificus infection. The induction of proinflammatory cytokines, Interleukin (IL)-1β, IL-6, Tumor necrosis factor (TNF)-α, and Toll-like receptor (TLR)-2 by Vibrio vulnificus was suppressed in fish that were administered DHA. Bacterial membrane disruption and the killing of Vibrio vulnificus by EPA and DHA was observed using SEM, TEM, and cytoplasm leakage studies. In silico analysis of the transcription profile in Ingenuity Pathway Analysis software showed that DHA may enhance anti-Vibrio vulnificus activity in Oreochromis niloticus via the activation of peroxisome proliferator-activated receptor α (PPARα) to inhibit nuclear factor kappa B and suppress hepatocyte nuclear factor 4 α (HNF4α). In summary, the results of the present study demonstrated that DHA and EPA reduce the severity of Vibrio vulnificus infection and increase the survival rate of Oreochromis niloticus.

Electrotransfer of the tilapia piscidin 3 and tilapia piscidin 4 genes into skeletal muscle enhances the antibacterial and immunomodulatory functions of Oreochromis niloticus

Tilapia piscidin 3 (TP3) and tilapia piscidin 4 (TP4) are antimicrobial peptides recently isolated from Oreochromis niloticus. We previously showed that synthetic TP3 and TP4 possessed antimicrobial activities. Here, we analyzed the bactericidal abilities and immunomodulatory properties of these AMPs following the electroporation of pCMV-GFP-TP3 or pCMV-GFP-TP4 plasmid into tilapia (O. niloticus) muscle and subsequent infection with Vibrio vulnificus or Streptococcus agalactiae. Prior overexpression of TP3 or TP4 in tilapia muscle tissues efficiently reduced bacterial numbers at 24 and 48 h after V. vulnificus infection and reduced bacterial numbers at 24 h after S. agalactiae infection compared to numbers in controls expressing pCMV-GFP (EGFP). Electroporation of pCMV-EGFP-TP3 (TP3) or pCMV-EGFP-TP4 (TP4) significantly increased expression of several immune-related genes in muscle (IL-1β (12 h, TP3), IL-8 (12 h, TP3), TGFβ (3 h, TP4), and IκB (48 h, TP3, TP4)) and decreased the expression of TLR5 (12 h and 24 h, TP3) after V. vulnificus infection. Following S. agalactiae infection, expression of the following genes was significantly decreased in muscle: IL-1β (12 h, TP3), IL-8 (12 h, TP3, TP4), TLR5 (3 h-24 h, TP3, TP4), TGFβ (3 h, TP4; 24 h, TP3, TP4), and IκB (3 h, TP3). These data suggest that TP3 and TP4 exert antimicrobial effects after overexpression in the O. niloticus muscle, and also play important roles in the regulation of immune-related gene expression.

The cabABC Operon Essential for Biofilm and Rugose Colony Development in Vibrio vulnificus

A transcriptome analysis identified Vibrio vulnificus cabABC genes which were preferentially expressed in biofilms. The cabABC genes were transcribed as a single operon. The cabA gene was induced by elevated 3′,5′-cyclic diguanylic acid (c-di-GMP) and encoded a calcium-binding protein CabA. Comparison of the biofilms produced by the cabA mutant and its parent strain JN111 in microtiter plates using crystal-violet staining demonstrated that CabA contributed to biofilm formation in a calcium-dependent manner under elevated c-di-GMP conditions. Genetic and biochemical analyses revealed that CabA was secreted to the cell exterior through functional CabB and CabC, distributed throughout the biofilm matrix, and produced as the biofilm matured. These results, together with the observation that CabA also contributes to the development of rugose colony morphology, indicated that CabA is a matrix-associated protein required for maturation, rather than adhesion involved in the initial attachment, of biofilms. Microscopic comparison of the structure of biofilms produced by JN111 and the cabA mutant demonstrated that CabA is an extracellular matrix component essential for the development of the mature biofilm structures in flow cells and on oyster shells. Exogenously providing purified CabA restored the biofilm- and rugose colony-forming abilities of the cabA mutant when calcium was available. Circular dichroism and size exclusion analyses revealed that calcium binding induces CabA conformational changes which may lead to multimerization. Extracellular complementation experiments revealed that CabA can assemble a functional matrix only when exopolysaccharides coexist. Consequently, the combined results suggested that CabA is a structural protein of the extracellular matrix and multimerizes to a conformation functional in building robust biofilms, which may render V. vulnificus to survive in hostile environments and reach a concentrated infective dose.

Biofilms are specialized and highly differentiated three-dimensional communities of bacteria encased in an extracellular polymeric matrix (EPM), and the bacteria’s mechanisms to form biofilm are closely linked to their virulence. The EPM often consists of polysaccharides, proteins, nucleic acids, and lipids. Compared to extracellular polysaccharides, little is known about the protein components in the biofilm matrix of Vibrio vulnificus, a foodborne pathogen. In this study, we identified and characterized cabABC genes which were preferentially expressed in biofilms. CabA is a calcium-binding protein and is secreted through functional CabB and CabC. Our results indicated that CabA contributes to the development of biofilm and rugose colony morphology under elevated c-di-GMP conditions. CabA is an extracellular matrix protein crucial for the structural integrity of robust biofilm in flow cells and on oyster shells. Calcium binding induces conformational changes and multimerization of CabA that may render the protein functional to build a well-structured matrix. CabA can assemble a functional matrix extracellularly only when exopolysaccharides (EPS) coexist, indicating that both CabA and EPS are required for the scaffold of V. vulnificus biofilm matrix. This is the first report on a non-polysaccharide matrix component that is essential for the development of the V. vulnificus biofilm structure.

Early steps in the European eel (Anguilla anguilla)-Vibrio vulnificus interaction in the gills: role of the RtxA13 toxin

Vibrio vulnificus is an aquatic gram-negative bacterium that causes a systemic disease in eels called warm-water vibriosis. Natural disease occurs via water born infection; bacteria attach to the gills (the main portal of entry) and spread to the internal organs through the bloodstream, provoking host death by haemorrhagic septicaemia. V. vulnificus produces a toxin called RtxA13 that hypothetically interferes with the eel immune system facilitating bacterial invasion and subsequent death by septic shock. The aim of this work was to study the early steps of warm-water vibriosis by analysing the expression of three marker mRNA transcripts related to pathogen recognition (tlr2 and tlr5) and inflammation (il-8) in the gills of eels infected by immersion with either the pathogen or a mutant deficient in rtxA13. Results indicate a differential response that is linked to the rtx toxin in the expression levels of the three measured mRNA transcripts. The results suggest that eels are able to distinguish innocuous from harmful microorganisms by the local action of their toxins rather than by surface antigens. Finally, the cells that express these transcripts in the gills are migratory cells primarily located in the second lamellae that re-locate during infection suggesting the activation of a specific immune response to pathogen invasion in the gill.

Genetic characterization of Vibrio vulnificus strains isolated from oyster samples in Mexico

Vibrio vulnificus strains were isolated from oysters that were collected at the main seafood market in Mexico City. Strains were characterized with regard to vvhA, vcg genotype, PFGE, multilocus sequence typing (MLST), and rtxA1. Analyses included a comparison with rtxA1 reference sequences. Environmental (vcgE) and clinical (vcgC) genotypes were isolated at nearly equal percentages. PFGE had high heterogeneity, but the strains clustered by vcgE or vcgC genotype. Select housekeeping genes for MLST and primers that were designed for rtxA1 domains divided the strains into two clusters according to the E or C genotype. Reference rtxA1 sequences and those from this study were also clustered according to genotype. These results confirm that this genetic dimorphism is not limited to vcg genotyping, as other studies have reported. Some environmental C genotype strains had high similarity to reference strains, which have been reported to be virulent, indicating a potential risk for oyster consumers in Mexico City.

Factors affecting the uptake and retention of Vibrio vulnificus in oysters

Vibrio vulnificus, a bacterium ubiquitous in oysters and coastal water, is capable of causing ailments ranging from gastroenteritis to grievous wound infections or septicemia. The uptake of these bacteria into oysters is often examined in vitro by placing oysters in seawater amended with V. vulnificus. Multiple teams have obtained similar results in studies where laboratory-grown bacteria were observed to be rapidly taken up by oysters but quickly eliminated. This technique, along with suggested modifications, is reviewed here. In contrast, the natural microflora within oysters is notoriously difficult to eliminate via depuration. The reason for the transiency of exogenous bacteria is that those bacteria are competitively excluded by the oyster's preexisting microflora. Evidence of this phenomenon is shown using in vitro oyster studies and a multiyear in situ case study. Depuration of the endogenous oyster bacteria occurs naturally and can also be artificially induced, but both of these events require extreme conditions, natural or otherwise, as explained here. Finally, the "viable but nonculturable" (VBNC) state of Vibrio is discussed. This bacterial torpor can easily be confused with a reduction in bacterial abundance, as bacteria in this state fail to grow on culture media. Thus, oysters collected from colder months may appear to be relatively free of Vibrio but in reality harbor VBNC cells that respond to exogenous bacteria and prevent colonization of oyster matrices. Bacterial-uptake experiments combined with studies involving cell-free spent media are detailed that demonstrate this occurrence, which could explain why the microbial community in oysters does not always mirror that of the surrounding water.

Starvation induces phenotypic diversification and convergent evolution in Vibrio vulnificus

Starvation is a common stress experienced by bacteria living in natural environments and the ability to adapt to and survive intense stress is of paramount importance for any bacterial population. A series of starvation experiments were conducted using V. vulnificus 93U204 in phosphate-buffered saline and seawater. The starved population entered the death phase during the first week and approximately 1% of cells survived. After that the population entered a long-term stationary phase, and could survive for years. Starvation-induced diversification (SID) of phenotypes was observed in starved populations and phenotypic variants (PVs) appeared in less than 8 days. The cell density, rather than the population size, had a major effect on the extent of SID. SID was also observed in strain YJ016, where it evolved at a faster pace. PVs appeared to emerge in a fixed order: PV with reduced motility, PV with reduced proteolytic activity, and PV with reduced hemolytic activity. All of the tested PVs had growth advantages in the stationary phase phenotypes and increased fitness compared with 93U204 cells in co-culture competition experiments, which indicates that they had adapted to starvation. We also found that SID occurred in natural seawater with a salinity of 1%–3%, so this mechanism may facilitate bacterial adaptation in natural environments.

Identification and expression analysis of Dicer2 in black tiger shrimp (Penaeus monodon) responses to immune challenges

Dicer is a key initiative protein of the RNA interference (RNAi) pathway that produces small interfering RNAs (siRNAs) or micro RNAs (miRNA), which then leads to RNA-directed gene regulation or viral immunity. In the present study, we identified and characterized a Dicer2 cDNA from black tiger shrimp Penaeus monodon (designated as PmDcr2). The full length cDNA of PmDcr2 contains a 5' untranslated region (UTR) of 109 bp, an open reading frame (ORF) of 4509 bp and a 3' UTR of 842 bp. The molecular weight (MW) of predicted PmDcr2 protein is 171.7 KDa with the theoretical isoelectric point of 6.23. PmDcr2 amino acid shared the highest similarity of 91.8% and 90.7% with Dicer2 of Litopenaeus vannamei and Marsupenaeus japonicas, respectively. Phylogenic analysis showed PmDcr2 was clustering with shrimp Dicer2, and closed to the insect group including Tribolium castaneum Dicer2. Real-time quantitative PCR showed that PmDcr2 was widely expressed in almost all examined tissues except muscle, with high expression in gill, hemocyte and lymph. The expression of PmDcr2 in hepatopancreas was up-regulated by Vibrio vulnificus and White Spot Syndrome Virus (WSSV), but not by Staphylococcus aureus. Furthermore, the viral nucleotide homologue dsRNA poly (I:C) and ssRNA R484 also remarkably induced PmDcr2 mRNA expression more efficient and stronger. These data reflect that PmDcr2 is not only response to the gram negative bacteria infection, but also specially to the viral infection in black tiger shrimp.

The interactions of Vibrio vulnificus and the oyster Crassostrea virginica

The human bacterial pathogen, Vibrio vulnificus, is found in brackish waters and is concentrated by filter-feeding molluscan shellfish, especially oysters, which inhabit those waters. Ingestion of raw or undercooked oysters containing virulent strains of V. vulnificus can result in rapid septicemia and death in 50 % of victims. This review summarizes the current knowledge of the environmental interactions between these two organisms, including the effects of salinity and temperature on colonization, uptake, and depuration rates of various phenotypes and genotypes of the bacterium, and host-microbe immunological interactions.

The antifouling potentiality of galactosamine characterized from Vibrio vulnificus exopolysaccharide

To gain a better insight into biofilm composition, the exopolysaccharide (EPS) of the Gram-negative bacterium Vibrio vulnificus was studied. Monosaccharide composition analysis of the wild-type and mutant V. vulnificus EPS carried out with Bio-liquid chromatography revealed the presence of D-glucosamine, D-galactose, D-glucose and D-xylose in both strains. D-galactosamine was found only in the mutant that formed less biofilm compared to its wild-type. The influence of galactosamine on biofilm formation was then studied by adding this substance gradually to six different Gram-negative/positive bacteria associated with various autoinducers. Four bacterial species known to use the autoinducer type-2 signaling system produced less biofilm in the presence of galactosamine. No significant inhibition of biofilm formation was observed in bacteria that produce autoinducer type-1 signal molecules. Galactosamine was also immobilized on polymeric nanofibers to determine its re-usability for the study of biofilm inhibition. The immobilized galactosamine retained >65% of its initial antifouling activity after 10 repeated uses. The results of this study suggest the antifouling role of galactosamine for bacteria that produce AI-2.

Identification and functional characterization of an interferon regulatory factor 7-like (IRF7-like) gene from orange-spotted grouper, Epinephelus coioides

Interferon regulatory factor (IRF) 7 plays a crucial role in modulating cellular responses to viral infection and cytokines, including interferons (IFNs). In the present study, a novel IRF7 gene (designated as EcIRF7) was cloned and characterized from orange-spotted grouper, Epinephelus coioides. The full-length EcIRF7 cDNA is composed of 2089 bp and encodes a polypeptide of 433 amino acids with 81% identity to IRF7 of Siniperca chuatsi, and the genomic DNA of EcIRF7 consists of 9 exons and 8 introns, with a length of approximately 5629 bp. EcIRF7 contains three conserved domains including a DNA-binding domain (DBD), an IRF associated domain (IAD) and a serine-rich domain, all of which are highly conserved across species. Recombinant EcIRF7 was expressed in Escherichia coli BL21 (DE3) and purified for mouse anti-EcIRF7 serum preparation. Realtime quantitative PCR (RT-qPCR) analysis revealed a broad expression of EcIRF7, with a relative strong expression in spleen, kidney, skin and intestine. The expression of EcIRF7 was differentially up-regulated after stimulation with Vibrio vulnificus, Staphylococcus aureus and Singapore grouper iridovirus (SGIV). EcIRF7 showed similar intracellular localization pattern to those of mammalian and chicken, and translocated into nucleus after SGIV infection. Further more, EcIRF7 was proved to be capable of activating zebrafish type I IFN promoter and inhibiting the replication of SGIV in grouper spleen (GS) cells. These results suggest that EcIRF7 is potentially involved in grouper immune responses to invasion of viral and bacterial pathogens.

Tilapia hepcidin (TH)2-3 as a transgene in transgenic fish enhances resistance to Vibrio vulnificus infection and causes variations in immune-related genes after infection by different bacterial species

Hepcidin is an antimicrobial peptide (AMP) secreted by the liver during inflammation that plays a central role in mammalian iron homeostasis. But the function of hepcidin in fish is still not completely understood. We recently described three different hepcidins (named tilapia hepcidin (TH)1-5, TH2-2, and TH2-3) from tilapia Oreochromis mossambicus, the cDNA sequences were determined, the predicted peptides were synthesized, and the TH2-3 peptide showed antimicrobial activity against several bacteria. We hypothesized that TH2-3 may have a biological function like an AMP in fishes and can be used as a transgene to boost resistance against bacterial infection. To examine the antimicrobial effects of TH2-3, we produced and engineered the overexpression of TH2-3 in zebrafish (Danio rerio) and the convict cichlid (Archocentrus nigrofasciatus). The microinjected plasmid also contained a green fluorescent protein (GFP) which was used as an indicator to trace germline transmission. In vivo, transgenic TH2-3 fish (of the F3 generation) were challenged with Vibrio vulnificus (204) and Streptococcus agalactiae (SA). Results showed significant clearance of bacterial numbers of V. vulnificus (204) but not of S. agalactiae in transgenic TH2-3 fish. A gene expression study using a real-time RT-PCR revealed that transgenic TH2-3 zebrafish showed increased endogenous expressions of Myd88, tumor necrosis factor-alpha, and TRAM1 in vivo. After transgenic TH2-3 zebrafish were infected with V. vulnificus (204), interleukin (IL)-10, IL-26, lysozyme, toll-like receptor (TLR)-4a, and Myd88 were upregulated, but IL-1beta (at 12-24 h) and IL-15 (at 1-12 h) were downregulated post-infection. After transgenic TH2-3 zebrafish were infected with S. agalactiae, IL-1beta (at 1-24 h), IL-15 (at 6 h), IL-22 (at 1-6 h), and TLR3 (at 1-24 h) were downregulated, but TLR4a (at 6-12 h) and c3b (at 12 h) were upregulated post-infection. Our findings identify the TH2-3 transgene in transgenic fish as an active component of the host response to bacterial pathogens. These results suggest that using TH2-3 as a transgene in zebrafish can effectively inhibit bacterial growth, specifically the V. vulnificus (204) strain for up to 24 h.

Resveratrol modulates RTX toxin-induced cytotoxicity through interference in adhesion and toxin production

Host-parasite contact is a prerequisite for the acute cytotoxicity of Vibrio vulnificus, which is mediated primarily by RtxA1, a repeat in toxin (RTX) toxin. We found that resveratrol (at 10 or 30 microM), a natural polyphenol, protected HeLa cells from V. vulnificus cytotoxicity. To further characterize the underlying mechanism, the effect of resveratrol was investigated at the level of the host-microbe interactions. We studied the effects of resveratrol on adhesion, motility, cytotoxicity, and RtxA1 toxin expression of V. vulnificus. In addition, the effect of resveratrol on mouse mortality caused by V. vulnificus was investigated. Resveratrol inhibited V. vulnificus motility and the microbe adhesion to host cells, critical virulence traits for many bacteria. Resveratrol also down-regulated the expression of RtxA1 toxin at the transcriptional level and thereby protected the host cells from becoming rounded and damaged. In addition, resveratrol (20mg/kg) protected CD-1 mice from V. vulnificus infection. Taken together, these results suggest that resveratrol, a modulator of host-microbe interactions, has potential for development as a new paradigm drug to treat infectious diseases.

Using an improved Tol2 transposon system to produce transgenic zebrafish with epinecidin-1 which enhanced resistance to bacterial infection

In order to advance the application of antimicrobial peptides in aquaculture, transgenic zebrafish expressing the antimicrobial peptide, epinecidin-1, were developed and are reported on here. First, we cloned the zebrafish mylz2 promoter for this purpose. To characterize the activity of the mylz2 promoter, various fragments of it were analyzed using a firefly luciferase transient expression assay, in which maximum promoter activity was found with a 2.5-kb fragment. In addition, the 2.5-kb fragment also expressed considerable red fluorescent proteins in skeletal muscles of transgenic zebrafish. Second, in order to improve the translation efficiency of the Tol2 transposase, we constructed untranslated regions (UTRs) of zebrafish ba1 globin flanked by a transposase. A transient embryonic excision assay (TEEA) and in vivo fluorescent observations showed high transposition efficiency during embryonic development. After optimization of the promoter and transgene efficiencies, transgenic zebrafish with the Epi-1/DsRed plasmid (pTLR-m2.5 K-K.Epinecidin-1/DsRed vector) were developed, and expressions of Epi-1/DsRed in muscles and blood were demonstrated by immunohistochemical staining techniques. Moreover, we also found that the Epi-1/DsRed gene was efficiently and significantly expressed in vivo against Vibrio vulnificus and Streptococcus agalactiae after injecting the bacteria and determining bacterial counts. A gene expression study using real-time RT-PCR revealed that Epi-1/DsRed itself induced endogenous MyD88 expression in vivo. After Epi-1/DsRed transgenic zebrafish were infected with V. vulnificus 204, interleukin (IL)-10, IL-22, IL-26, lysozyme, toll-like receptor (TLR)1, TLR3, TLR4a, MyD88, and nuclear factor (NF)-kappaB activating protein-like were upregulated, but IL-1beta and tumor necrosis factor-alpha were downregulated at 12h post-infection; IL-21, complement component c3b, and NF-kappaB activating protein-like were downregulated, but MyD88 was upregulated at 24h post-infection. These results suggest that using epinecidin-1 as a transgene in zebrafish can effectively inhibit bacterial growth for up to 24h after infection.

Role of RpoS in the susceptibility of low salinity-adapted Vibrio vulnificus to environmental stresses

Vibrio vulnificus is an opportunistic pathogen commonly found in oyster and marine environments, which frequently encounters low salinity stress in its natural and food processing environment. In this study, the responses of a V. vulnificus wild-type strain C78140o and its rpoS isogenic mutant AH1 to sublethal low salinity were examined to investigate the role of rpoS in this response. Both strains, adapted in low salinity (0.4% NaCl), were protected against the lethal low salinity (0.1% NaCl), but were not protected against heat (45 degrees C) or acid stress (pH 3.5), and were sensitized against 5% bile. Protection of the adapted cells against the lethal low salinity was not inhibited by the addition of chloramphenicol. Hemolysis was detected only in the adapted C78140o cells and its spent medium, and was inhibited by chloramphenicol. Transcription of the mechanosensitive channels (VVl_1542 and VVl_2579) and an aquaporin gene (VVl_2010) was markedly increased in the wild-type cells adapted in low salinity medium, while transcription of these genes was slightly enhanced or inhibited in AH1 cells. Results of this study support the active role of rpoS in the low salinity adaptation of V. vulnificus by regulating the expression of virulence and low salinity-associated factors, although rpoS is not related to the immediate protection of the adapted cells against lethal low salinity.

Identification of the Vibrio vulnificus ahpCl gene and its influence on survival under oxidative stress and virulence

Pathogens have evolved sophisticated mechanisms to survive oxidative stresses imposed by host defense systems, and the mechanisms are closely linked to their virulence. In the present study, ahpCl, a homologue of Escherichia coli ahpC encoding a peroxiredoxin, was identified among the Vibrio vulnificus genes specifically induced by exposure to H(2)O(2). In order to analyze the role of AhpCl in the pathogenesis of V. vulnificus, a mutant, in which the ahpCl gene was disrupted, was constructed by allelic exchanges. The ahpCl mutant was hypersusceptable to killing by reactive oxygen species (ROS) such as H(2)O(2) and t-BOOH, which is one of the most commonly used hydroperoxides in vitro. The purified AhpCl reduced H(2)O(2) in the presence of AhpF and NADH as a hydrogen donor, indicating that V. vulnificus AhpCl is a NADH-dependent peroxiredoxin and constitutes a peroxide reductase system with AhpF. Compared to wild type, the ahpCl mutant exhibited less cytotoxicity toward INT-407 epithelial cells in vitro and reduced virulence in a mouse model. In addition, the ahpCl mutant was significantly diminished in growth with INT-407 epithelial cells, reflecting that the ability of the mutant to grow, survive, and persist during infection is also impaired. Consequently, the combined results suggest that AhpCl and the capability of resistance to oxidative stresses contribute to the virulence of V. vulnificus by assuring growth and survival during infection.

Knowledge of Vibrio vulnificus infection among Japanese patients with liver diseases: a prospective multicenter study

BACKGROUND

Vibrio vulnificus (V. vulnificus) is a seafood-borne infectious pathogen that can be lethal to humans. The infection has been correlated with pre-existing liver disease, particularly liver cirrhosis. Awareness of V. vulnificus infection among Japanese citizens is low, despite the increasing number of patients with hepatocellular carcinoma (HCC). The present study was conducted to assess the level of knowledge of patients with liver disease regarding V. vulnificus infection.

MATERIAL/METHODS

Questionnaires were sent to patients with chronic liver disease who had been treated by liver specialists at 14 medical institutes.

RESULTS

Of 1,336 patients, 304 (22.8%) had liver cirrhosis, and 732 (54.8%) had comorbidities of this disease. Only 14.5% (194/1,336) of patients had knowledge of V. vulnificus infection. Of 304 patients with liver cirrhosis, 17.4% (53/304) of the patients had knowledge of V. vulnificus infection. Of 60 patients with liver cirrhosis and diabetes mellitus, 11 (18.3%) patients had knowledge of V. vulnificus infections. Even when the patients with high risk factors such as liver cirrhosis and diabetes mellitus had knowledge of V. vulnificus infections, most ate raw seafood without regard to season.

CONCLUSIONS

Patients with chronic liver diseases and their physicians need to be better educated about V. vulnificus infection and its prevention.

Effect of antimicrobial agents on the toll-like receptors and inflammatory cytokines in liver tissue of the alcohol-induced liver disease in rats with Vibrio vulnificus sepsis

BACKGROUND

Septicemia and inflammation-mediated septic shock caused by Vibrio vulnificus (VV) is strongly associated with chronic liver disease. This study examined the effects of antimicrobial therapy on expression of hepatic toll-like receptors and inflammatory cytokines in rats with alcohol-induced liver disease complicated by VV sepsis.

METHODS

Male Sprague-Dawley rats were assigned to the following treatment groups: normal control (N), alcoholic liver disease control (A), antimicrobial-treated alcoholic liver disease control (AA), alcoholic liver disease with VV sepsis (AV), and antimicrobial-treated alcoholic liver disease with VV sepsis (AVA). Alcohol-induced liver disease was observed in all groups except N. Expression of mRNAs encoding hepatic toll-like receptors 2 and 4, myeloid differentiation protein-2, tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta, IL-6 and IL-10 was determined by RT-PCR.

RESULTS

mRNAs encoding toll-like receptors 2 and 4 and myeloid differentiation protein-2 were significantly up-regulated in group AV as compared to control groups at 2 - 24 hours of sepsis; peak expression occurred at 12 hours. These mRNAs were also up-regulated in group AVA but to lesser degrees than in group AV at comparable time post-infection. mRNAs encoding TNF-alpha, IL-1beta and IL-6 were significantly elevated in group AV as a function of infection. In group AVA as compared to AV, expression of TNF-alpha and IL-1beta mRNAs was lower at 12 - 24 hours post-infection and expression of IL-6 mRNA was lower at 24 hours post-infection. Compared with control groups, IL-10 mRNA expression in group AV was markedly higher at 12 - 24 hours of sepsis. Expression of IL-10 mRNA was lower in group AVA as compared to AV at 24 hours of sepsis.

CONCLUSIONS

Antimicrobial therapy reduces expression of toll-like receptors and cytokines in rats with alcohol-induced liver disease complicated by VV sepsis. Monitoring hepatic toll-like receptor and cytokine expression during antibiotic therapy may be valuable for determining the course of VV sepsis in subjects with liver disease.

Immune response and inhibition of bacterial growth by electrotransfer of plasmid DNA containing the antimicrobial peptide, epinecidin-1, into zebrafish muscle

Bacterial infections represent serious diseases in aquaculture, rapidly leading to fish death by septicemia. We investigated whether the electrotransfer of green fluorescent protein gene fusion epinecidin-1 (CMV-gfp-epi) DNA into zebrafish muscle could regulate the fish immune response and inhibit bacterial growth. Electroporation parameters such as the number of pulses, voltage, and amount of plasmid DNA were analyzed, and results demonstrated the greatest mRNA expression level of gfp-epi relative to beta-actin was obtained with a pulse number of 4, a voltage strength of 100 V/cm, a concentration of DNA of 90 microg/fish, and electroporation for 96 h. In addition, the cytomegalovirus (CMV) promoter exhibited higher activity compared to the mylz promoter in muscle for electrotransfer in zebrafish. GFP fluorescence and gfp-epi mRNA expression in tissues after electroporation were also studied by a polymerase chain reaction, immunohistochemistry, and fluorescence microscopy. gfp-epi expression was significantly correlated with decreased bacterial numbers and immune-related gene expression. These data demonstrate that electroporation of epinecidin-1 might have provoked an inflammatory response that accounts for the improvement in bacterial clearance.

Studies on diseased freshwater prawn Macrobrachium rosenbergii infected with Vibrio vulnificus

The present study was aimed at isolation and characterization of the pathogenic bacterium from diseased freshwater prawn. The effect of the bacterial pathogen on hepatopancreas, gills and exoskeleton was also investigated. Diseased freshwater prawn, Macrobrachium rosenbergii were collected from commercial hatchery in Behera Governorate, Egypt. The diseased prawn showed dark brown focal lesions and necrosis of appendage tips. The causative bacterial pathogen was isolated from haemolymph and hepatopancreas of the diseased prawn. Based on the morphological, biochemical and physiological characteristics, in addition EPI 20E test, the isolated pathogen was characterized as Vibrio vulnificus. Histopathology, hepatopancreas showed haemocytic infiltration in the interstitial sinuses, thickening and ruptures of the basal lamina and necrosis of its tubules. Similarly, the accumulation of haemocytes in the haemocoelic space, swelling, fusion of lamellae and abnormal gill tips. Also, the cuticular layers of the exoskeleton of diseased prawn had a rough or wrinkled surface and were disrupted and separated from the epidermis. The pathogen, V. vulnificus showed different degrees of sensitivity to different antimicrobial agents. It was highly sensitive to each of the antibiotics rifadin, virbamycin, oflaxcin, garamycin, flummox and trimethoprim/sulfamethoxzole) and resistant to nalidixic acid, unasyn, velosef, claforan, negram and amoxicillin. The minimal inhibitory concentration of trimethoprin/sulfamethoxzole for the studied pathogen, V. vulnificus was 0.31/5.93 microg.

Identification of quorum sensing-related regulons in Vibrio vulnificus by two-dimensional gel electrophoresis and differentially displayed reverse transcriptase PCR

Vibrio vulnificus is thought to employ a quorum-sensing system to control the expression of a global gene. In this study, proteomes and transcriptomes of a lacZ null mutant, VvSR Delta Z, and a luxS-smcR double mutant, VvSR Delta ZSR, were compared with the parent strain, VvAR, by means of two-dimensional gel electrophoresis (2D-PAGE) and differentially displayed reverse transcriptase PCR (DDRT-PCR). 2D-PAGE analysis showed that 36 protein spots were differentially expressed, 14 of which have been identified by peptide-mass fingerprinting. The expression of eight cellular proteins was repressed by luxS and smcR mutation: Zn-dependent protease, 6-phosophofructokinase, periplasmic ABC-type Fe3(+) transport system, deoxyribose-phosphate aldolase, phosphomannomutase, orotidine-5'-phosphate decarboxylase, uridylate kinase, and an unidentified protein. These proteins are involved in virulence, adaptation to environmental stress, biosynthesis of LPS, and cell multiplication. Phage shock protein A, a chemotaxis signal transduction protein, and an uncharacterized low-complexity protein were activated in the cellular components of the luxS-smcR mutant. However, only three proteins, of unknown function, were identified in the extracellular components of the mutants. Analysis of transcriptomes with DDRT-PCR showed that two genes, phosphoribosylformylglycinamidine synthase and ATP-dependent protease HslVU protease were regulated at the transcriptional level by luxS and smcR gene mutation. The results from this study show conclusively that luxS/smcR quorum sensing endows a global change in gene expression to V. vulnificus.

Role of type IV pilins in persistence of Vibrio vulnificus in Crassostrea virginica oysters

Vibrio vulnificus is part of the natural estuarine microflora and accumulates in shellfish through filter feeding. It is responsible for the majority of seafood-associated fatalities in the United States mainly through consumption of raw oysters. Previously we have shown that a V. vulnificus mutant unable to express PilD, the type IV prepilin peptidase, does not express pili on the surface of the bacterium and is defective in adherence to human epithelial cells (R. N. Paranjpye, J. C. Lara, J. C. Pepe, C. M. Pepe, and M. S. Strom, Infect. Immun. 66:5659-5668, 1998). A mutant unable to express one of the type IV pilins, PilA, is also defective in adherence to epithelial cells as well as biofilm formation on abiotic surfaces (R. N. Paranjpye and M. S. Strom, Infect. Immun. 73:1411-1422, 2005). In this study we report that the loss of PilD or PilA significantly reduces the ability of V. vulnificus to persist in Crassostrea virginica over a 66-h interval, strongly suggesting that pili expressed by this bacterium play a role in colonization or persistence in oysters.

Surface properties of Vibrio vulnificus

AIMS

Vibrio vulnificus adheres to a diverse range of surfaces, ranging from the chitinous exoskeleton of mollusks to human tissue. To determine whether environmental and human clinical isolates exhibit different adhesion traits, we studied the ability of 10 environmental isolates and 10 clinical isolates to adhere to human epithelial cells and hydrocarbons with log P values ranging from 3.1 to 8.2.

METHODS AND RESULTS

All isolates adhered to varying levels to epithelial cells, and were inhibited to various extents from adherence by mannose and fructose. There was a lack of correlation between adherence to either hydrocarbons or cells and colony opacity. Adherence to hydrocarbons was optimal for solvents with a log P < 8.2.

CONCLUSIONS

Vibrio vulnificus clinical and environmental isolates exhibit differential adherence to epithelial cells and hydrocarbons.

SIGNIFICANCE AND IMPACT OF THE STUDY

The differential adherence of organisms to hydrocarbons based on log P may have utility in drug design and enhancement of food safety.

Isolation and characterization of a cold-induced nonculturable suppression mutant of Vibrio vulnificus

The viable but nonculturable (VBNC) suppression mutant formed platable cells at low temperature stress after inoculation in artificial seawater (ASW). Suppression subtractive hybridization was used to identify differentially expressed genes among cDNAs of the VBNC suppression mutant and the wild-type Vibrio vulnificus strain. Glutathione S-transferase was identified as a responsive gene of the VBNC suppression mutant in our assay, and was highly expressed from the VBNC suppression mutant at low temperature stress. Culturability tests revealed that the wild-type cells were sensitive to oxidative stress in the hydrogen peroxide (H(2)O(2)) and to 1-chloro-2,4-dinitrobenzene (CDNB) compared with the VBNC suppression mutant cells. Adding glutathione showed that many wild-type V. vulnificus cells maintained culturability in cold ASW. These results suggest that non-nutritional growth inhibitors, such as peroxide that accumulates at low temperatures, influence VBNC in V. vulnificus cells.

The pyrH gene of Vibrio vulnificus is an essential in vivo survival factor

We have suggested an important role of the pyrH gene during the infectious process of Vibrio vulnificus. Previously, we have identified 12 genes expressed preferentially during human infections by using in vivo-induced antigen technology. Among the in vivo-expressed genes, pyrH encodes UMP kinase catalyzing UMP phosphorylation. Introduction of a deletion mutation to the pyrH gene was lethal to V. vulnificus, and an insertional mutant showed a high frequency of curing. We constructed a site-directed mutant strain (R62H/D77N) on Arg-62 and Asp-77, both predicted to be involved in UMP binding, and characterized the R62H/D77N strain compared with the previously reported insertional mutant. We further investigated the essential role of the pyrH gene in the establishment of infection using the R62H/D77N strain. Cytotoxicity was decreased in the R62H/D77N strain, and the defect was restored by an in trans complementation. The intraperitoneal 50% lethal dose of the R62H/D77N strain increased by 26- and 238,000-fold in normal and iron-overloaded mice, respectively. The growth of the R62H/D77N strain in 50% HeLa cell lysate, 100% human ascitic fluid, and 50% human serum was significantly retarded compared to that of the isogenic wild-type strain. The R62H/D77N mutant also had a critical defect in the ability to survive and replicate even in iron-overloaded mice. These results demonstrate that pyrH is essential for the in vivo survival and growth of V. vulnificus and should be an attractive new target for the development of antibacterial drugs and replication-controllable live attenuated vaccines.

Vibrio vulnificus metalloprotease VvpE is essentially required for swarming

Bacterial swarming constitutes a good in vitro model for surface adherence and colonization, and is accompanied by expressions of virulence factors related to invasiveness. In this study, it was determined that Vibrio vulnificus swarming was abolished by mutation of the vvpE gene encoding a metalloprotease VvpE and this swarming defect was recovered by complementation of the vvpE gene. Expression of the vvpE gene began simultaneously with the beginning of swarming and increased along with expression of the luxS gene encoding the synthase of the precursor of quorum-sensing signal molecule autoinducer 2, and this increased vvpE expression was decreased by mutation of the luxS gene. Moreover, VvpE destroyed IgA and lactoferrins, which are responsible for mucosal immunity. These results suggest that VvpE may play important roles in the surface adherence and colonization of V. vulnificus by facilitating swarming and in the mucosal invasion of V. vulnificus by destroying IgA and lactoferrin.

Susceptibility of the heat-, acid-, and bile-adapted Vibrio vulnificus to lethal low-salinity stress

As a marine pathogenic bacterium that inhabits seawater or seafood, Vibrio vulnificus encounters low salinity and other stresses in the natural environment and during food processing. This investigation explores the cross-protective response of sublethal heat-, acid-, or bile-adapted V. vulnificus YJ03 against lethal low-salinity stress. Experimental results reveal that the acid (pH 4.4)- and heat (41 degrees C)-adapted V. vulnificus were not cross-protected against the lethal low-salinity challenge (0.04% NaCl). The bile (0.05%)-adapted exponential- and stationary-phase cells were cross-protected against low salinity, whereas low-salinity (0.12% NaCl)-adapted stationary cells were sensitized against 12% bile stress. Results of this study provide further insight into the interaction between low salinity and other common stresses in V. vulnificus.

Role of NtrC in biofilm formation via controlling expression of the gene encoding an ADP-glycero-manno-heptose-6-epimerase in the pathogenic bacterium,Vibrio vulnificus

To identify the genetic elements required for biofilm formation, we screened a pool of random Vibrio vulnificus mutants for their ability to form biofilms. One mutant displaying significantly decreased biofilm-forming activity was found to contain a transposon insertion in the ntrC gene. The ntrC gene encodes a well-known transcriptional activator. We examined how this regulator modulates a biofilm-forming process in V. vulnificus by searching for NtrC target gene(s). Comparison of the proteomes of ntrC mutant and wild-type strains grown under planktonic and biofilm stages revealed that synthesis of the protein homologous to GmhD (ADP-glycero-manno-heptose-6-epimerase) was elevated during the growth period for biofilm formation and was strongly influenced by NtrC. A luxAB-transcriptional fusion with the gmhD promoter region indicated that gmhD expression was positively regulated by both NtrC and RpoN. The function of the gmhD gene product in V. vulnificus was assessed by constructing and phenotypic analyses of an isogenic mutant. The gmhD mutant was defective in production of mature lipopolysaccharide (LPS) and exopolysaccharides (EPS), and demonstrated an attenuated ability to form a biofilm. These results suggest that NtrC acts as a key regulator of both LPS and EPS biosyntheses and, thereby, modulates critical steps in biofilm development of V. vulnificus.

Lysine decarboxylase expression by Vibrio vulnificus is induced by SoxR in response to superoxide stress

Lysine decarboxylase expression by Vibrio vulnificus, which is up-regulated by CadC in response to acid stress, is also induced by SoxR in response to superoxide stress. SoxR binds to the promoter region of the cadBA operon, coding for a lysine-cadaverine antiporter (CadB) and a lysine decarboxylase (CadA). The induction of cadBA transcription by SoxR is independent of CadC. Cadaverine, which neutralizes the external medium, also appears to scavenge superoxide radicals, since increasing cellular cadaverine by elevating the gene dosage of cadBA significantly diminished the induction of Mn-containing superoxide dismutase under methyl viologen-induced oxidative stress. Consistently, a lack of cadaverine caused by mutation in cadA resulted in low tolerance to oxidative stress compared with that of the wild type.

Vibrio vulnificus infection and metalloprotease

Vibrio vulnificus is ubiquitous in aquatic environments; however, it occasionally causes serious and often fatal infections in humans. These include invasive septicemia contracted through consumption of raw seafood, as well as wound infections acquired through contact with brackish or marine waters. In most cases of septicemia, the patients have underlying disease(s), such as liver dysfunction or alcoholic cirrhosis, and the secondary skin lesions including cellulitis, edema and hemorrhagic bulla appear on the limbs. Although V. Vul produces various virulent factors including polysaccharide capsule, type IV pili, hemolysin and proteolytic enzymes, the 45-kDa metalloprotease may be a causative factor of the skin lesions, because the purified protease enhances vascular permeability through generation of chemical mediators and also induces serious hemorrhagic damage through digestion of the vascular basement membrane. As well as other bacteria, V. Vul can regulate the protease production through the quorum-sensing system depending on bacterial cell density. However, this system operates efficiently at 25 degrees C, but not at 37 degrees C. Therefore, V. vulnificus may produce sufficient amounts of the protease only in the interstitial tissue of the limbs, in which temperature is lower than the internal temperature of the human body.

Capsular polysaccharide phase variation in Vibrio vulnificus

Commonly found in raw oysters, Vibrio vulnificus poses a serious health threat to immunocompromised individuals and those with serum iron overload, with a fatality rate of approximately 50%. An essential virulence factor is its capsular polysaccharide (CPS), which is responsible for a significant increase in virulence compared to nonencapsulated strains. However, this bacterium is known to vary the amount of CPS expressed on the cell surface, converting from an opaque (Op) colony phenotype to a translucent (Tr) colony phenotype. In this study, the consistency of CPS conversion was determined for four strains of V. vulnificus. Environmental conditions including variations in aeration, temperature, incubation time, oxidative stress, and media (heart infusion or modified maintenance medium agar) were investigated to determine their influence on CPS conversion. All conditions, with the exception of variations in media and oxidative stress, significantly affected the conversion of the population, with high ranges of CPS expression found even within cells from a single colony. The global quorum-sensing regulators RpoS and AI-2 were also examined. While RpoS was found to significantly mediate phenotypic conversion, quorum sensing was not. Finally, 12 strains that comprise the recently found clinical (C) and environmental (E) genotypes of V. vulnificus were examined to determine their rates of population conversion. C-genotype strains, which are most often associated with infection, had a significantly lower rate of population conversion from Op to Tr phenotypes than did E-genotype strains (ca. 38% versus ca. 14%, respectively). Biofilm capabilities of these strains, however, were not correlated with increased population conversion.

Caenorhabditis elegans as a simple model host for Vibrio vulnificus infection

Vibrio vulnificus is a human opportunistic pathogen which causes fatal septicemia and necrotic wound infection, resulting in a high mortality (over 50%). Caenorhabditis elegans has been studied as a model experimental host for V. vulnificus infection. V. vulnificus was shown to kill C. elegans effectively on different growth media and culture conditions. A marked reduction was observed in the life spans of worms when they were fed on V. vulnificus rather than on the ordinary laboratory food source, Escherichia coli OP50. The intestines of the C. elegans fed on V. vulnificus were grossly distended. In the C. elegans infection model, a V. vulnificus global virulence regulator CRP mutant and an exotoxin mutant exhibited significantly extended host killing duration. Here, we have shown that the virulence factors essential to mammalian V. vulnificus infections also play important roles in the killing of C. elegans, and thereby suggest that C. elegans is a favorable model for host-parasite interaction.

In situ gene expression by Vibrio vulnificus

Strains of Vibrio vulnificus incubated in situ in natural estuarine waters during warm months continued to express katG (periplasmic catalase), rpoS (stress sigma factor), tufA (elongation factor), wza, and wzb (capsule synthesis). vvhA (hemolysin) was differentially expressed between environmental and clinical isolates. These results paralleled our in vitro findings.

Detection and differentiation of Vibrio vulnificus in seawater and plankton of a coastal zone of the Mediterranean Sea

Vibrio vulnificus, a human and animal pathogen, is present in low numbers in the Mediterranean Sea. Seawater and plankton samples were collected from a marine coastal zone of the Straits of Messina in the Mediterranean Sea (Italy) in order to investigate V. vulnificus as free-living (>0.2 microm) and associated with small (>64 microm) and large plankton (>200 microm) utilizing cultural and molecular techniques. Characteristic colonies, grown on thiosulfate, citrate, bile salts and sucrose agar plates, were identified using a biochemical protocol system. A PCR assay was used to confirm isolates and to directly detect V. vulnificus in environmental concentrated samples. Specific primers were used to target the structural cytotoxin/hemolysin gene and the variable regions of 16S rRNA species-specific for V. vulnificus. In addition, a tri-primer PCR of 16S rRNA was used for the differentiation of V. vulnificus strains. Direct detection in marine samples was more frequent than isolation of culturable forms. All isolates were assigned to V. vulnificus biotype 1, 16S rRNA type B. These results confirm the low incidence of V. vulnificus in Mediterranean coastal waters. The isolation of cultivable forms is limited to the warmest months. 16S rRNA primers were the most sensitive molecular tool as they allowed detection of V. vulnificus in 79.1% of samples. Due to the low incidence of V. vulnificus in the Mediterranean coastal environment, its detection requires a molecular approach. The occurrence of V. vulnificus as plankton-associated confirms the role of plankton as a potential reservoir for this pathogen.

Quorum sensing in vibrios: complexity for diversification

N-acylhomoserine lactone-dependent quorum sensing was first discovered in two luminescent marine bacteria, Vibrio fischeri and Vibrio harveyi. The LuxI/R system of V. fischeri is the paradigm of Gram-negative quorum-sensing systems; however, it is not found in all vibrios. A more complex quorum-sensing regulation is found in V. harveyi. Three parallel systems transmit signals via phosphorelays that converge onto one regulatory protein LuxO. Components of the three systems are found only in vibrios. Of the five Vibrio strains analysed, the number and types of signal circuits found in each strain are diverse. The signalling systems have different regulatory responses depending on the type of association the Vibrio strains have with an animal host, which may reflect the diverse roles the vibrios have in structuring and maintaining microniches within the aquatic milieu. Further studies are likely to show that the diversity and complexity of the Vibrio quorum-sensing systems coordinate intraspecies behaviour, niche occupation, and possibly evolution.

The role of quorum sensing and the effect of environmental conditions on biofilm formation by strains of Vibrio vulnificus

It has been suggested that Vibrio vulnificus attaches to plankton and algae and is found in large numbers in the environment. Factors affecting attachment, biofilm formation and morphology of V. vulnificus have not been thoroughly investigated. This study evaluated the role of quorum sensing (QS) and environmental conditions on biofilm development of V. vulnificus. It was found that biofilm development by V. vulnificus was affected by nutrient and glucose concentration, but not by NaCl concentration or temperature under the conditions used here. Moreover, biofilm development of a QS mutant strain proceeded rapidly and sloughing occurred earlier than for the isogenic parent strain. There was a significant loss of viability for the QS mutant biofilm early in development. Hence, it is hypothesised that factors regulated by the QS system play a role in proper biofilm development and maintenance of V. vulnificus. Furthermore, it is shown that biofilm development varied among isolates.

Essential role of an adenylate cyclase in regulating Vibrio vulnificus virulence

Vibrio vulnificus, a halophilic estuarine bacterium, causes a fatal septicemia and necrotizing wound infection. To investigate the role of cAMP in V. vulnificus virulence regulation, an in-frame deletion mutant of the cya gene encoding adenylate cyclase was constructed. The cya null mutation resulted in a pleiotropic change of virulence phenotypes. The production of hemolysin and protease, the motility, and the cytotoxicity were decreased by the cya mutation. The defects in the cya mutant were functionally complemented in trans by a plasmid carrying the wild type cya allele. The V. vulnificus cya mutant exhibited a 100-fold increase in LD50 to mice. The result indicates that cAMP plays an essential role in the global regulation of V. vulnificus virulence.

Bactericidal effects of toluidine blue-mediated photodynamic action on Vibrio vulnificus

Vibrio vulnificus is a gram-negative, highly invasive bacterium responsible for human opportunistic infections. We studied the antibacterial effects of toluidine blue O (TBO)-mediated photodynamic therapy (PDT) for V. vulnificus wound infections in mice. Fifty-three percent (10 of 19) of mice treated with 100 microg of TBO per ml and exposed to broad-spectrum red light (150 J/cm(2) at 80 mW/cm(2)) survived, even though systemic septicemia had been established with a bacterial inoculum 100 times the 50% lethal dose. In vitro, the bacteria were killed after exposure to a lower light dose (100 J/cm(2) at 80 mW/cm(2)) in the presence of low-dose TBO (0.1 microg/ml). PDT severely damaged the cell wall and reduced cell motility and virulence. Cell-killing effects were dependent on the TBO concentration and light doses and were mediated partly through the reactive oxygen species generated during the photodynamic reaction. Our study has demonstrated that PDT can cure mice with otherwise fatal V. vulnificus wound infections. These promising results suggest the potential of this regimen as a possible alternative to antibiotics in future clinical applications.