Vibrio vulnificus: From Oyster Colonist to Human Pathogen

Epidemiological and genetic charateristics of Vibrio vulnificus from diverse sources in China during 2012-2023

Vibrio vulnificus is a significant zoonotic pathogen that causes severe vibriosis in humans and fish. The lack of a national annual surveillance program in China has hindered understanding of its epidemiological characteristics and genetic diversity. This study characterized 150 V. vulnificus isolates collected from diverse sources in China during 2012-2023, including seafood, aquaculture water, migratory birds, marine animals, and clinical patients. Most seafood-derived isolates and all 15 clinical isolates harbored the virulence-related gene vcgC and 16S rRNA type B. The isolates exhibited diverse virulence factors (VFs), including flagella, outer membrane components, RTX toxins, and multiple secretion systems. Genes associated with the Type III secretion system were identified in migratory bird isolates, while a unique Type VI secretion system (T6SS1) were identified exclusively within a specific phylogenetic sub-lineage. T6SS1-positive strains demonstrated an increased number of genomic islands (GIs) and VFs compared to T6SS1-negative strains. Enrichment of genes related to secretion systems and biofilm formation likely facilitated the expansion of the T6SS1-positive population. The novel association between T6SS1 and a specific sub-lineage underscores potential ecological and adaptive advantages. These findings provide new insights into the ecological and evolutionary dynamics of V. vulnificus.

Climate change and Vibrio vulnificus dynamics: A blueprint for infectious diseases

Climate change is having increasingly profound effects on human health, notably those associated with the occurrence, distribution, and transmission of infectious diseases. The number of disparate ecological parameters and pathogens affected by climate change are vast and expansive. Disentangling the complex relationship between these variables is critical for the development of effective countermeasures against its effects. The pathogen Vibrio vulnificus, a naturally occurring aquatic bacterium that causes fulminant septicemia, represents a quintessential climate-sensitive organism. In this review, we use V. vulnificus as a model organism to elucidate the intricate network of interactions between climatic factors and pathogens, with the objective of identifying common patterns by which climate change is affecting their disease burden. Recent findings indicate that in regions native to V. vulnificus or related pathogens, climate-driven natural disasters are the chief contributors to their disease outbreaks. Concurrently, climate change is increasing the environmental suitability of areas non-endemic to their diseases, promoting a surge in their natural populations and transmission dynamics, thus elevating the risk of new outbreaks. We highlight potential risk factors and climatic drivers aggravating the threat of V. vulnificus transmission under both scenarios and propose potential measures for mitigating its impact. By defining the mechanisms by which climate change influences V. vulnificus disease burden, we aim to shed light on the transmission dynamics of related disease-causing agents, thereby laying the groundwork for early warning systems and broadly applicable control measures.

Virulent properties and genomic diversity of Vibrio vulnificus isolated from environment, human, diseased fish

The incidence of Vibrio vulnificus infections, with high mortality rates in humans and aquatic animals, has escalated, highlighting a significant public health challenge. Currently, reliable markers to identify strains with high virulence potential are lacking, and the understanding of evolutionary drivers behind the emergence of pathogenic strains is limited. In this study, we analyzed the distribution of virulent genotypes and phenotypes to discern the infectious potential of V. vulnificus strains isolated from three distinct sources. Most isolates, traditionally classified as biotype 1, possessed the virulence-correlated gene-C type. Environmental isolates predominantly exhibited YJ-like alleles, while clinical and diseased fish isolates were significantly associated with the nanA gene and pathogenicity region XII. Hemolytic activity was primarily observed in the culture supernatants of clinical and diseased fish isolates. Genetic relationships, as determined by multiple-locus variable-number tandem repeat analysis, suggested that strains originating from the same source tended to cluster together. However, multilocus sequence typing revealed considerable genetic diversity across clusters and sources. A phylogenetic analysis using single nucleotide polymorphisms of diseased fish strains alongside publicly available genomes demonstrated a high degree of evolutionary relatedness within and across different isolation sources. Notably, our findings reveal no direct correlation between phylogenetic patterns, isolation sources, and virulence capabilities. This underscores the necessity for proactive risk management strategies to address pathogenic V. vulnificus strains emerging from environmental reservoirs.IMPORTANCEAs the global incidence of Vibrio vulnificus infections rises, impacting human health and marine aquacultures, understanding the pathogenicity of environmental strains remains critical yet underexplored. This study addresses this gap by evaluating the virulence potential and genetic relatedness of V. vulnificus strains, focusing on environmental origins. We conduct an extensive genotypic analysis and phenotypic assessment, including virulence testing in a wax moth model. Our findings aim to uncover genetic and evolutionary factors that drive pathogenic strain emergence in the environment. This research advances our ability to identify reliable virulence markers and understand the distribution of pathogenic strains, offering significant insights for public health and environmental risk management.

Wildfire Ashes from the Wildland-Urban Interface Alter Vibrio vulnificus Growth and Gene Expression

Climate change-induced stressors are contributing to the emergence of infectious diseases, including those caused by marine bacterial pathogens such as Vibrio spp. These stressors alter Vibrio temporal and geographical distribution, resulting in increased spread, exposure, and infection rates, thus facilitating greater Vibrio-human interactions. Concurrently, wildfires are increasing in size, severity, frequency, and spread in the built environment due to climate change, resulting in the emission of contaminants of emerging concern. This study aimed to understand the potential effects of urban interface wildfire ashes on Vibrio vulnificus (V. vulnificus) growth and gene expression using transcriptomic approaches. V. vulnificus was exposed to structural and vegetation ashes and analyzed to identify differentially expressed genes using the HTSeq-DESeq2 strategy. Exposure to wildfire ash altered V. vulnificus growth and gene expression, depending on the trace metal composition of the ash. The high Fe content of the vegetation ash enhanced bacterial growth, while the high Cu, As, and Cr content of the structural ash suppressed growth. Additionally, the overall pattern of upregulated genes and pathways suggests increased virulence potential due to the selection of metal- and antibiotic-resistant strains. Therefore, mixed fire ashes transported and deposited into coastal zones may lead to the selection of environmental reservoirs of Vibrio strains with enhanced antibiotic resistance profiles, increasing public health risk.

Structural determination and kinetic analysis of the transketolase from Vibrio vulnificus reveal unexpected cooperative behavior

Vibrio vulnificus (vv) is a multidrug-resistant human bacterial pathogen whose prevalence is expected to increase over the years. Transketolases (TK), transferases catalyzing two reactions of the nonoxidative branch of the pentose-phosphate pathway and therefore linked to several crucial metabolic pathways, are potential targets for new drugs against this pathogen. Here, the vvTK is crystallized and its structure is solved at 2.1 Å. A crown of 6 histidyl residues is observed in the active site and expected to participate in the thiamine pyrophosphate (cofactor) activation. Docking of fructose-6-phosphate and ferricyanide used in the activity assay, suggests that both substrates can bind vvTK simultaneously. This is confirmed by steady-state kinetics showing a sequential mechanism, on the contrary to the natural transferase reaction which follows a substituted mechanism. Inhibition by the I38-49 inhibitor (2-(4-ethoxyphenyl)-1-(pyrimidin-2-yl)-1H-pyrrolo[2,3-b]pyridine) reveals for the first time a cooperative behavior of a TK and docking experiments suggest a previously undescribed binding site at the interface between the pyrophosphate and pyridinium domains.

CarRS Two-Component System Essential for Polymyxin B Resistance of Vibrio vulnificus Responds to Multiple Host Environmental Signals

Enteropathogenic bacteria express two-component systems (TCSs) to sense and respond to host environments, developing resistance to host innate immune systems like cationic antimicrobial peptides (CAMPs). Although an opportunistic human pathogen Vibrio vulnificus shows intrinsic resistance to the CAMP-like polymyxin B (PMB), its TCSs responsible for resistance have barely been investigated. Here, a mutant exhibiting a reduced growth rate in the presence of PMB was screened from a random transposon mutant library of V. vulnificus, and response regulator CarR of the CarRS TCS was identified as essential for its PMB resistance. Transcriptome analysis revealed that CarR strongly activates the expression of the eptA, tolCV2, and carRS operons. In particular, the eptA operon plays a major role in developing the CarR-mediated PMB resistance. Phosphorylation of CarR by the sensor kinase CarS is required for the regulation of its downstream genes, leading to the PMB resistance. Nevertheless, CarR directly binds to specific sequences in the upstream regions of the eptA and carRS operons, regardless of its phosphorylation. Notably, the CarRS TCS alters its own activation state by responding to several environmental stresses, including PMB, divalent cations, bile salts, and pH change. Furthermore, CarR modulates the resistance of V. vulnificus to bile salts and acidic pH among the stresses, as well as PMB. Altogether, this study suggests that the CarRS TCS, in responding to multiple host environmental signals, could provide V. vulnificus with the benefit of surviving within the host by enhancing its optimal fitness during infection. IMPORTANCE Enteropathogenic bacteria have evolved multiple TCSs to recognize and appropriately respond to host environments. CAMP is one of the inherent host barriers that the pathogens encounter during the course of infection. In this study, the CarRS TCS of V. vulnificus was found to develop resistance to PMB, a CAMP-like antimicrobial peptide, by directly activating the expression of the eptA operon. Although CarR binds to the upstream regions of the eptA and carRS operons regardless of phosphorylation, phosphorylation of CarR is required for the regulation of the operons, resulting in the PMB resistance. Furthermore, the CarRS TCS determines the resistance of V. vulnificus to bile salts and acidic pH by differentially regulating its own activation state in response to these environmental stresses. Altogether, the CarRS TCS responds to multiple host-related signals, and thus could enhance the survival of V. vulnificus within the host, leading to successful infection.

Searching pathogenic bacteria in the rare biosphere of the ocean

Harmful marine bacteria, such as Vibrio or Aeromonas species, typically exist at low abundance in ocean environments but represent a reservoir from which epidemics can arise. Particularly, Vibrio strains and their associated infections are on the rise globally due to increasing sea surface temperature representing an emergent threat for human and animal health also being responsible for large economic losses in the aquaculture industry worldwide. New technological approaches are needed to improve strategies targeting these pathogens. This review discusses new approaches based on improved sampling strategies and novel analytical methods offering increased accuracy, high throughput, and informativeness to study and detect microbial pathogens in the marine environment. Detecting and characterizing ultra-low-abundance pathogenic strains can serve as a critical tool in risk management and outbreak prevention of diseases caused by emerging marine pathogens.

Vibrio Infections and the Twenty-First Century

The Vibrionaceae is a highly diverse family of aquatic bacteria. Some members of this ubiquitous group can cause a variety of diseases in humans ranging from cholera caused by Vibrio cholerae, severe septicemia caused by Vibrio vulnificus, to acute gastroenteritis by Vibrio parahaemolyticus. Planet Earth is experiencing unprecedented changes of planetary scale associated with climate change. These environmental perturbations paired with overpopulation and pollution are increasing the distribution of pathogenic Vibrios and exacerbating the risk of causing infections. In this chapter, we discuss various aspects of Vibrio infections within the context of the twenty-first century with a major emphasis on the aforementioned pathogenic species. Overall, we believe that the twenty-first century is posed to be both one full of challenges due to the rise of these pathogens, and also a catalyst for innovative and groundbreaking discoveries.

A systematic review, meta-analysis and meta-regression of the global prevalence of foodborne Vibrio spp. infection in fishes: A persistent public health concern

Human vibriosis, caused by pathogenic Vibrio spp., such as Vibrio parahaemolyticus, Vibrio cholerae and Vibrio vulnificus, has been increasing worldwide, mediated by increasing consumption of seafood. The present study was conducted to examine the global prevalence of V. vulnificus, V. parahaemolyticus and V. cholerae in fishes. We searched PubMed, Web of Science, Scopus, and CNKI for peer-reviewed articles and dissertations prior to December 31, 2021. A total of 24,831 articles were retrieved, and 82 articles contained 61 fish families were included. The global pooled prevalence of V. cholerae, V. parahaemolyticus and V. vulnificus in fishes was 9.56 % (95 % CI: 2.12-20.92), 24.77 % (95 % CI: 17.40-32.93) and 5.29 % (95 % CI: 0.38-13.61), respectively. Subgroup and meta-regression analyses showed that study-level covariates, including temperature, country, continent, origin and detection methods partly explained the between-study heterogeneity. These heterogeneities were underpinned by differences of the three Vibrio spp. in fishes at geographical and climatic scales. These results reveal a high global prevalence of pathogenic Vibrio spp. in fishes and highlight the need for implementation of more effective prevention and control measures to reduce food-borne infection in humans.

Vibrio floridensis sp. nov., a novel species closely related to the human pathogen Vibrio vulnificus isolated from a cyanobacterial bloom

A Gram-stain-negative, rod-shaped bacterial strain, designated Vibrio floridensis IRLE0018 (=NRRL B-65642=NCTC 14661), was isolated from a cyanobacterial bloom along the Indian River Lagoon (IRL), a large and highly biodiverse estuary in eastern Florida (USA). The results of phylogenetic, biochemical, and phenotypic analyses indicate that this isolate is distinct from species of the genus Vibrio with validly published names and is the closest relative to the emergent human pathogen, Vibrio vulnificus. Here, we present the complete genome sequence of V. floridensis strain IRLE0018 (4 535 135 bp). On the basis of the established average nucleotide identity (ANI) values for the determination of different species (ANI <95 %), strain IRLE0018, with an ANI of approximately 92 % compared with its closest relative, V. vulnificus, represents a novel species within the genus Vibrio. To our knowledge, this represents the first time this species has been described. The results of genomic analyses of V. floridensis IRLE0018 indicate the presence of antibiotic resistance genes and several known virulence factors, however, its pathogenicity profile (e.g. survival in serum, phagocytosis avoidance) reveals limited virulence potential of this species in contrast to V. vulnificus.

Vibrio vulnificus and Vibrio parahaemolyticus in Oysters under Low Tidal Range Conditions: Is Seawater Analysis Useful for Risk Assessment?

Human-pathogenic Vibrio bacteria are acquired by oysters through filtering seawater, however, the relationships between levels of these bacteria in measured in oysters and overlying waters are inconsistent across regions. The reasons for these discrepancies are unclear hindering our ability to assess if -or when- seawater samples can be used as a proxy for oysters to assess risk. We investigated whether concentrations of total and human pathogenic Vibrio vulnificus (vvhA and pilF genes) and Vibrio parahaemolyticus (tlh, tdh and trh genes) measured in seawater reflect concentrations of these bacteria in oysters (Crassostrea virginica) cultured within the US lower Chesapeake Bay region. We measured Vibrio spp. concentrations using an MPN-qPCR approach and analyzed the data using structural equation modeling (SEM). We found seawater concentrations of these bacteria to predictably respond to temperature and salinity over chlorophyll a, pheophytin or turbidity. We also inferred from the SEM results that Vibrio concentrations in seawater strongly predict their respective concentrations in oysters. We hypothesize that such seawater-oyster coupling can be observed in regions of low tidal range. Due to the ease of sampling and processing of seawater samples compared to oyster samples, we suggest that under low tidal range conditions, seawater samples can foster increased spatial and temporal coverage and complement data associated with oyster samples.

Fine-Scale Structuring of Planktonic Vibrio spp. in the Chinese Marginal Seas

Vibrio is ubiquitous in marine environments with high metabolism flexibility and genome plasticity. Studies have investigated the ecological distribution of Vibrio spp. in several narrow zones, but a broad scale pattern of distribution and community assembly is still lacking. Here, we elucidated the distribution of Vibrio spp. in seawater along the Chinese marginal seas with a high spatial range. Comparison of Vibrio abundance between 3- and 0.2-μm-pore-size membranes showed distinction in preferential lifestyle. Vibrio spp. in the Yellow Sea (YS) was low in abundance and adopted a particle-associated lifestyle, whereas that in the East China Sea (ECS) and South China Sea (SCS) was more abundant and was likely in a temporary free-living state as a strategy to cope with nutrient limitation. Vibrio community compositions were also separated by sampling area, with different dominant groups in YS (Vibrio chagasii and Vibrio harveyi), ECS and SCS (Vibrio japonicus and V. chagasii). The community niche breadth was significantly wider in ECS and SCS than that of YS. Among species, V. chagasii and V. harveyi had the largest niche breadths likely reflecting strong competitive positions. Stochastic processes played important roles in shaping the geographical pattern of the vibrionic community. Environmental selection (e.g., temperature, salinity, and dissolved oxygen) had a much greater impact on the community in surface than in bottom water. The large proportions of unexplained variations (78.9%) imply complex mechanisms in their community assembly. Our study provides insights into the spatial distribution patterns and underlying assembly mechanisms of Vibrio at a broad spatial scale. IMPORTANCE Vibrio spp. may exert large impacts on biogeochemical cycling in coastal habitats, and their ecological importance has drawn increasing attention. Here, we investigated the spatial distribution pattern and community assembly of Vibrio populations along the Chinese marginal seas, spanning a wide spatial scale. Our results showed that the abundances of the Vibrio population increased with decreasing latitude and their preferential lifestyle differed among adjacent coastal areas. The compositions of Vibrio spp. were also separated by geographical location, which was mainly attributable to stochastic processes. Overall, this work contributes to the understanding of the ecological distribution patterns and the community assembly mechanisms of marine vibrios at a high spatial range. The large proportion of unexplained variations indicates the existence of complex mechanisms in the assembly of vibrionic community which should be considered comprehensively in future.

Genetic Divergence of Vibrio vulnificus Clinical Isolates with Mild to Severe Outcomes

The marine bacterium Vibrio vulnificus infects humans via food or water contamination, leading to serious manifestations, including gastroenteritis, wound infections, and septic shock. Previous studies suggest phylogenetic Lineage 1 isolates with the vcgC allele of the vcg gene cause human infections, whereas Lineage 2 isolates with the vcgE allele are less pathogenic. Mouse studies suggest that some variants of the primary toxin could drive more serious infections. A collection of 109 V. vulnificus United States human clinical isolates from 2001 to 2019 with paired clinical outcome data were assembled. The isolates underwent whole-genome sequencing, multilocus-sequence phylogenetic analysis, and toxinotype analysis of the multifunctional autoprocessing repeats-in-toxin (MARTX) toxin. In contrast to prior reports, clinical isolates were equally distributed between lineages. We found no correlation between phylogenetic lineage or MARTX toxinotype and disease severity. Infections caused by isolates in Lineage 1 demonstrated a borderline statistically significant higher mortality. Lineage 1 isolates had a trend toward a higher proportion of M-type MARTX toxins compared with Lineage 2, although this was not statistically significant. IMPORTANCE Vibrio vulnificus is an aquatic pathogen that is capable of causing severe disease in humans. Previous studies have suggested that pathogenic isolates were restricted to certain phylogenetic lineages and possibly toxinotype. Our study demonstrated that phylogenetic lineage and multifunctional autoprocessing repeats-in-toxin (MARTX) toxinotype do not predict severity of infection. V. vulnificus strains capable of causing severe human disease are not concentrated in Lineage 1 but are genetically diverse. Thus, food surveillance based on lineage type or toxinotype may not be an appropriate intervention measure to control this rare but serious infection.

Antibacterial Effect of Oregano Essential Oil against Vibrio vulnificus and Its Mechanism

Oregano essential oil (OEO) is an effective natural antibacterial agent, but its antibacterial activity against Vibrio vulnificus has not been widely studied. The aim of this study was to investigate the inhibitory effect and germicidal activity of OEO on V. vulnificus and its possible inhibition mechanism. The minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of OEO against four V. vulnificus strains (ATCC 27562 and three isolates from seafoods) were from 0.06 to 0.15 μL/mL. Compared with untreated bacteria, OEO reduced the concentration of intracellular adenosine triphosphate (ATP), hyperpolarized the cell membrane, increased the level of reactive oxygen species (ROS), and increased the concentration of intracellular malondialdehyde (MDA), but there was no obvious DNA damage at the OEO test concentration. It was indicated that OEO inactivated V. vulnificus by generating ROS which caused lipid peroxidation of cell membranes, thereby reducing the permeability and integrity of cell membranes and causing morphological changes to cells, but there was no obvious damage to DNA. In addition, OEO could effectively kill V. vulnificus in oysters at 25 °C, and the number of bacteria decreased by 48.2% after 0.09% OEO treatment for 10 h. The good inhibitory effect and bactericidal activity of OEO showed in this study, and the economy and security of OEO make it possible to apply OEO to control V. vulnificus contamination in oysters and other seafoods.

The ecological impact of a bacterial weapon: microbial interactions and the Type VI secretion system

Bacteria inhabit all known ecological niches and establish interactions with organisms from all kingdoms of life. These interactions are mediated by a wide variety of mechanisms and very often involve the secretion of diverse molecules from the bacterial cells. The Type VI secretion system (T6SS) is a bacterial protein secretion system that uses a bacteriophage-like machinery to secrete a diverse array of effectors, usually translocating them directly into neighbouring cells. These effectors display toxic activity in the recipient cell, making the T6SS an effective weapon during inter-bacterial competition and interactions with eukaryotic cells. Over the last two decades, microbiology research has experienced a shift towards using systems-based approaches to study the interactions between diverse organisms and their communities in an ecological context. Here, we focus on this aspect of the T6SS. We consider how our perspective of the T6SS has developed and examine what is currently known about the impact that bacteria deploying the T6SS can have in diverse environments, including niches associated with plants, insects and mammals. We consider how T6SS-mediated interactions can affect host organisms by shaping their microbiota, as well as the diverse interactions that can be established between different microorganisms through the deployment of this versatile secretion system.

Ecological diversification reveals routes of pathogen emergence in endemic Vibrio vulnificus populations

Pathogen emergence is a complex phenomenon that, despite its public health relevance, remains poorly understood. Vibrio vulnificus, an emergent human pathogen, can cause a deadly septicaemia with over 50% mortality rate. To date, the ecological drivers that lead to the emergence of clinical strains and the unique genetic traits that allow these clones to colonize the human host remain mostly unknown. We recently surveyed a large estuary in eastern Florida, where outbreaks of the disease frequently occur, and found endemic populations of the bacterium. We established two sampling sites and observed strong correlations between location and pathogenic potential. One site is significantly enriched with strains that belong to one phylogenomic cluster (C1) in which the majority of clinical strains belong. Interestingly, strains isolated from this site exhibit phenotypic traits associated with clinical outcomes, whereas strains from the second site belong to a cluster that rarely causes disease in humans (C2). Analyses of C1 genomes indicate unique genetic markers in the form of clinical-associated alleles with a potential role in virulence. Finally, metagenomic and physicochemical analyses of the sampling sites indicate that this marked cluster distribution and genetic traits are strongly associated with distinct biotic and abiotic factors (e.g., salinity, nutrients, or biodiversity), revealing how ecosystems generate selective pressures that facilitate the emergence of specific strains with pathogenic potential in a population. This knowledge can be applied to assess the risk of pathogen emergence from environmental sources and integrated toward the development of novel strategies for the prevention of future outbreaks.

Presence, Seasonal Distribution, and Biomolecular Characterization of Vibrio parahaemolyticus and Vibrio vulnificus in Shellfish Harvested and Marketed in Sardinia (Italy) between 2017 and 2018

ABSTRACT

In the present study, we investigated the presence, seasonal distribution, and biomolecular characteristics of Vibrio parahaemolyticus and Vibrio vulnificus in samples of bivalve mollusks (Mytilus galloprovincialis, Crassostrea gigas, and Ruditapes decussatus) harvested and marketed in Sardinia (Italy) between 2017 and 2018. A total of 435 samples were submitted for qualitative determination of Vibrio spp., V. parahaemolyticus, and V. vulnificus. Potentially enteropathogenic isolates were detected with biomolecular methods. The overall prevalence of Vibrio spp. was 7.6%. The highest Vibrio prevalence was found in R. decussatus (8.3%). The prevalences of V. parahaemolyticus and V. vulnificus were 2.7 and 4.8%, respectively. Higher prevalences of V. parahaemolyticus and V. vulnificus were found in R. decussatus (4.2%) and C. gigas (6.2%), respectively. Only two pathogenic V. parahaemolyticus strains were recovered (genotypes: tdh- and trh+; tdh+ and trh-), both from M. galloprovincialis. None of the isolates were tdh+ and trh+. Pathogenic Vibrio infections are often underestimated, and human infections are increasing in Europe. European data on the true distribution of Vibrionaceae are scarce, and the results of the present study highlight the need of constant monitoring to update the distribution of pathogenic vibrios.

HIGHLIGHTS

Disentangling the abundance and structure of Vibrio communities in a semi-enclosed Bay with mariculture (Dongshan Bay, Southern China)

The genus Vibrio contains a diverse group of heterotrophic bacteria, which are members of ubiquitous and abundant microbial communities in coastal ecosystems. Vibrio has been frequently found in a wide range of marine environments either by employing Vibrio-specific 16S rRNA sequencing or culturing methods. A combination of molecular and cultivation-dependent methods was developed to more precisely discriminate between different members of the genus Vibrio in seawater. This newly developed assay was subsequently applied to characterize Vibrio community composition in surface water at 18 mariculture sites. It Substantially improved the taxonomic resolution of Vibrio species when compared to traditional 16S rRNA analysis. Our qPCR and cultivation analyses revealed that average Vibrio abundance (Vibrio 16S rRNA gene copy numbers: 3.46 × 10⁶ to 6.70 × 10⁶ copies L⁻¹) and live cell numbers (5.65 × 10⁴–5.75 × 10⁵ cfu mL⁻¹) are significantly related to pH. Total bacteria and Vibrio-specific 16S rRNA metabarcode sequenceing resulted in a total of 10 and 32 operational taxonomic units (OTUs), respectively, and 15 Vibrio species were identified by targeted cultivation of Vibrio strains, with Vibrio fortis and V. brasiliensis dominating in the mariculture areas. The purpose of this study was to combine several analytical methods to improve current sequence-based Vibrio community surveys, and to prove for the effectiveness of this methodological approach comprehensively testing for Vibrio dynamics in different coastal environments.

Analysis of Gene Expression Profiles, Cytokines, and Bacterial Loads Relevant to Alcoholic Liver Disease Mice Infected With V. vulnificus

Patients with liver disease are susceptible to infection with Vibrio vulnificus (V. vulnificus), but the specific reasons remain elusive. Through RNA-seq, we found that when mice with alcoholic liver disease (ALD) were infected with V. vulnificus by gavage, compared with the Pair group, the small intestinal genes affecting intestinal permeability were upregulated; and the number of differentially expressed genes related to immune functions (e.g., such as cell chemotaxis, leukocyte differentiation, and neutrophil degranulation) decreased in the liver, spleen, and blood. Further analysis showed that the number of white blood cells decreased in the Pair group, whereas those in the ALD mice did not change significantly. Interestingly, the blood bacterial load in the ALD mice was about 100 times higher than that of the Pair group. After the ALD mice were infected with V. vulnificus, the concentrations of T cell proliferation-promoting cytokines (IL-2, IL-23) decreased. Therefore, unlike the Pair group, ALD mice had weaker immune responses, lower T cell proliferation-promoting cytokines, and higher bacterial loads post-infection, possibly increasing their susceptibility to V. vulnificus infection. These new findings we presented here may help to advance the current understanding of the reasons why patients with liver disease are susceptible to V. vulnificus infection and provides potential targets for further investigation in the context of treatment options for V. vulnificus sepsis in liver disease patient.

Vibrio vulnificus induces the death of a major bacterial species in the mouse gut via cyclo-Phe-Pro

BACKGROUND

A foodborne pathogen, Vibrio vulnificus, encounters normal microflora inhabiting the gut environments prior to causing fatal septicemia or gastroenteritis and should overcome the barriers derived from the gut commensals for successful infection. Its interactions with gut commensals during the infection process, however, have not yet been understood. In the present study, the effect of V. vulnificus on the community structures of gut microbiota in mice was examined.

RESULTS

Analyses of microbiota in the fecal samples of mice that died due to V. vulnificus infection revealed the decreased abundance of bacteria belonged to Bacteroidetes, notably, the species Bacteroides vulgatus. In vitro coculturing of the two bacterial species resulted in the decreased survival of B. vulgatus. The antagonistic effect of V. vulnificus against B. vulgatus was found to be mediated by cyclo-Phe-Pro (cFP), one of the major compounds secreted by V. vulnificus. cFP-treated B. vulgatus showed collapsed cellular morphology with an undulated cell surface, enlarged periplasmic space, and lysed membranes, suggesting the occurrence of membrane disruption. The degree of membrane disruption caused by cFP was dependent upon the cellular levels of ObgE in B. vulgatus. Recombinant ObgE exhibited a high affinity to cFP at a 1:1 ratio. When mice were orally injected with cFP, their feces contained significantly reduced B. vulgatus levels, and their susceptibility to V. vulnificus infection was considerably increased.

CONCLUSIONS

This study demonstrates that V. vulnificus-derived cFP modulates the abundance of the predominant species among gut commensals, which made V. vulnificus increase its pathogenicity in the hosts. Video abstract.

Detection of Vibrio vulnificus in Seafood With a DNAzyme-Based Biosensor

Vibrio vulnificus is an important pathogenic bacterium that is often associated with seafood-borne illnesses. Therefore, to detect this pathogen in aquatic products, a DNAzyme-based fluorescent sensor was developed for the in vitro detection of V. vulnificus. After screening and mutation, a DNAzyme that we denominated “RFD-VV-M2” exhibited the highest activity, specificity, and sensitivity. The limit of detection was 2.2 × 10³ CFU/ml, and results could be obtained within 5–10 min. Our findings suggested that the target of DNAzyme RFD-VV-M2 was a protein with a molecular weight between 50 and 100 kDa. The proposed biosensor exhibited an excellent capacity to detect marine products contaminated with V. vulnificus. Therefore, our study established a rapid, simple, sensitive, and highly specific detection method for V. vulnificus in aquatic products.

Improved Method for Transformation of Vibrio vulnificus by Electroporation

Vibrio vulnificus, an emergent human pathogen, causes fulminant septicemia with a mortality rate of over 50%. Unlike for other pathogenic Vibrio species, the factors to conclusively indicate the virulence potential of V. vulnificus strains remain largely unknown. Understanding the pathogenesis of this bacterium at a molecular level is severely hindered by inefficiencies in transformation, for instance, due to the presence of a periplasmic nuclease, Vvn. Currently, successful transformation of V. vulnificus is nearly impossible due to lack of mobilizable plasmids for the bacterium, requiring (i) very high DNA concentrations, (ii) plasmid linearization, (iii) development of novel V. vulnificus-derived plasmids, or (iv) time-consuming conjugation-based methods. To overcome these limitations, we describe a rapid, efficient, and reproducible electroporation protocol to effectively transform widely available plasmids, with different copy numbers and antibiotic resistances, into phylogenetically distant strains of V. vulnificus. Cells are made competent in high concentrations of sucrose devoid of cations and recovered from electroporation using a high-salinity recovery medium. Compared to existing methods for transformation of V. vulnificus, significantly higher efficiencies are obtained using this improved protocol. Rapid and effective transformations can markedly improve molecular analyses of V. vulnificus leading to a greater understanding of its virulence potential. This is crucial to develop rapid detection methods which have the potential to prevent future outbreaks. The electroporation protocol described here may be particularly useful for optimizing transformation of other nuclease-producing bacteria. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Preparation of competent cells Basic Protocol 2: Transformation of cells by electroporation.

Analyzing Possible Native Functions of the Quinolone Resistance Gene qnr in Vibrio vulnificus

The worldwide distribution of qnr genes found on plasmids and their presence on the chromosomes of aquatic bacteria, such as Vibrio vulnificus, one of the suspected sources, suggests an origin before the development of synthetic quinolones. However, their native function remains unknown. Previous work indicated that expression of qnrVv in V. vulnificus was induced by cold shock. To investigate its role further, we constructed single in-frame deletion mutants in qnrVv and cspA (the gene for cold shock protein) and a double mutant in qnrVv and cspA in V. vulnificus ATCC 17562 to evaluate the response to different environmental conditions and stresses and to exposure to various DNA-damaging agents. We found that qnrVv is involved in resistance to ciprofloxacin, levofloxacin, and mitomycin C and in the cold shock response in V. vulnificus Moreover, ΔqnrVv and ΔcspA mutants showed slower growth when they were treated with bile salts at 37°C and then shifted to 15°C (cold shock) without bile salts in the medium, with the effect being stronger in the double mutant. This transition may mimic what happens when V. vulnificus is ingested into the gastrointestinal tract and released in its natural environment. Cold shock and bile salts induced the expression of cspA and DNA gyrase and topoisomerase IV genes. However, no induction was found in the ΔqnrVv mutant, suggesting that the qnrVv gene is involved in the response to DNA damage and nucleic acid secondary structure.

New atypical manifestations and prognostic factors of Vibrio vulnificus infection: A 10-year retrospective study

Vibrio vulnificus (V. vulnificus) infection is rare but potentially fatal. This study explored the new atypical manifestations and prognostic factors of V. vulnificus-infected patients throughout hospitalization. we retrospectively reviewed 33 patients diagnosed as having V. vulnificus infection in Guangdong Province, China between 2010 and 2020. Medical records were analyzed. Multiple logistic regression and receiver operating characteristic (ROC) curve analyses were performed. New atypical manifestations were found, including cholangitis, urinary tract infection, and suppurative otitis media. Eleven of thirty-three (33.3%) V. vulnificus-infected patients died eventually. By univariate analysis, patients with cardio-cerebro-vascular diseases, lower platelet counts, higher levels of C-reactive protein and procalcitonin (PCT) had a statistically higher mortality. However, multivariate analysis showed that only PCT (P = 0.036) reached statistical significance. Also, the area under the ROC value estimate for PCT was 0.8816 (95% CI, 0.759-1.000; P = 0.0009). More than half of patients with V. vulnificus infection would die when PCT ＞20 ng/ml, while no patient dies when PCT ≤ 20 ng/ml. This study found new atypical manifestations of V. vulnificus infection. Also, PCT is an effective and independent predictor of mortality of V. vulnificus infection, and is suitable for clinicians to make early risk stratification and best therapeutic strategies.

Is the Rattus norvegicus Population Playing a Role in the Transmission of Zoonotic Diseases to Children? A Pilot Study in Tehran, Iran

Background: Due to frequent exposure to surface water and contact with animals, children represent a group susceptible to zoonotic diseases. Objectives: The present study aims to determine the presence and prevalence of the main zoonotic agents in R. norvegicus populations in Tehran, Iran. Methods: In the present study, 100 R. norvegicus were captured within a time span of one year from five districts of Tehran, Iran. Fecal and blood samples were collected from rodents and serum was recovered after centrifugation. The presence of specific IgG antibodies against Leptospira spp. and Rabies virus was detected using a commercial qualitative rat ELISA kit. A conventional PCR assay was employed to detect the presence of Vibrio vulnificus in the commensal R. norvegicus population. Results: In general, 80% (n = 80/100) and 20% (n = 20/100) of rats were males and females, respectively. The results of the ELSA assay showed that of the 100 R. norvegicus captured in Tehran, 7% (n = 7/100) and 1% (n = 1/100) were positive for Leptospira spp. and Rabies virus, respectively. Leptospira spp. revealed the highest frequency (20%; 4/20) among R. norvegicus collected from the eastern part of Tehran. Rabies virus was detected only from the southern (5%; 1/20) part of Tehran. Results of the PCR method showed that the percentage of the rats tested positive for V. vulnificus was 5%. Overall, the surveyed zoonotic microorganisms had the highest (n = 5/20; 25%) and lowest (n = 1/20; 5%) frequency rates in the eastern and northern parts of Tehran, respectively. Conclusions: The results accentuate the necessity of implementing rodent control programs and regular disinfection as well as avoiding contact with rodent populations in urban environments.

Chemotactic invasion in deep soft tissue by Vibrio vulnificus is essential for the progression of necrotic lesions

Necrotizing soft tissue infections (NSTI) progress to severe necrosis and result in fatal sepsis within a short time. Vibrio vulnificus is a causative agent and can spread from the initial infection site through soft tissue finally to the systemic circulation of the host. The motility and chemotaxis of this bacterium are essential for proliferation and lethality in a murine model of the infection, but their role in pathogenicity has not been characterized. In this study, we revealed the roles of motility and chemotaxis during the process of V. vulnificus infection. We compared a nonmotile mutant and two nonchemotactic mutants with their parent strain (WT) with regard to bacterial spread using an in vivo imaging system (IVIS) and invasion by detection of bacteria from the muscle and spleen of a murine infection model. WT rapidly spread throughout the infected thigh and invaded deep muscle causing severe tissue damage. The detection rate in the systemic circulation and the lethality were high. On the other hand, the nonmotile mutant stayed at the inoculation site, and the nonchemotactic mutants spread only slowly through the soft tissue of the infected thigh. Detection in the systemic circulation, the degree of tissue damage, and the lethality of nonchemotactic mutants were significantly reduced in mice compared with WT. This study demonstrated that chemotaxis is essential for invasion from the infection site to the deep and distant tissues and the main pathogenic factor for the rapid progression leading to sepsis in V. vulnificus NSTI.

A Secreted NlpC/P60 Endopeptidase from Photobacterium damselae subsp. piscicida Cleaves the Peptidoglycan of Potentially Competing Bacteria

Peptidoglycan (PG) is a major component of the bacterial cell wall, forming a mesh-like structure enwrapping the bacteria that is essential for maintaining structural integrity and providing support for anchoring other components of the cell envelope. PG biogenesis is highly dynamic and requires multiple enzymes, including several hydrolases that cleave glycosidic or amide bonds in the PG. This work describes the structural and functional characterization of an NlpC/P60-containing peptidase from Photobacterium damselae subsp. piscicida (Phdp), a Gram-negative bacterium that causes high mortality of warm-water marine fish with great impact for the aquaculture industry. PnpA ( PhotobacteriumNlpC-like protein A) has a four-domain structure with a hydrophobic and narrow access to the catalytic center and specificity for the γ-d-glutamyl-meso-diaminopimelic acid bond. However, PnpA does not cleave the PG of Phdp or PG of several Gram-negative and Gram-positive bacterial species. Interestingly, it is secreted by the Phdp type II secretion system and degrades the PG of Vibrio anguillarum and Vibrio vulnificus This suggests that PnpA is used by Phdp to gain an advantage over bacteria that compete for the same resources or to obtain nutrients in nutrient-scarce environments. Comparison of the muropeptide composition of PG susceptible and resistant to the catalytic activity of PnpA showed that the global content of muropeptides is similar, suggesting that susceptibility to PnpA is determined by the three-dimensional organization of the muropeptides in the PG.IMPORTANCE Peptidoglycan (PG) is a major component of the bacterial cell wall formed by long chains of two alternating sugars interconnected by short peptides, generating a mesh-like structure that enwraps the bacterial cell. Although PG provides structural integrity and support for anchoring other components of the cell envelope, it is constantly being remodeled through the action of specific enzymes that cleave or join its components. Here, it is shown that Photobacterium damselae subsp. piscicida, a bacterium that causes high mortality in warm-water marine fish, produces PnpA, an enzyme that is secreted into the environment and is able to cleave the PG of potentially competing bacteria, either to gain a competitive advantage and/or to obtain nutrients. The specificity of PnpA for the PG of some bacteria and its inability to cleave others may be explained by differences in the structure of the PG mesh and not by different muropeptide composition.

Characteristics of Vibrio vulnificus isolates from clinical and environmental sources

Researchers have developed multiple methods to characterize clinical and environmental strains of Vibrio vulnificus. The aim of our study was to use four assays to detect virulence factors in strains from infected patients and those from surface waters/sediments/oysters of South Carolina and the Gulf of Mexico. Vibrio vulnificus strains from clinical (n = 81) and environmental (n = 171) sources were tested using three real-time PCR methods designed to detect polymorphisms in the 16S rRNA, vcg and pilF genes and a phenotypic method, the ability to ferment D-mannitol. Although none of the tests correctly categorized all isolates, the differentiation between clinical and environmental isolates was similar for the pilF, vcgC/E and 16S rRNA assays, with sensitivities of 74.1-79.2% and specificities of 77.4-82.7%. The pilF and vcgC/E assays are comparable in efficacy to the widely used 16S rRNA method, while the D-mannitol fermentation test is less discriminatory (sensitivity = 77.8%, specificity = 61.4%). Overall percent agreement for the D-mannitol fermentation method was also lower (66.7%) than overall percent agreement for the 3 molecular assays (78.0%-80.2%). This study demonstrated, using a large, diverse group of Vibrio vulnificus isolates, that three assays could be used to distinguish most clinical vs environmental isolates; however, additional assays are needed to increase accuracy.

Genome- and Proteome-Wide Analysis of Lysine Acetylation in Vibrio vulnificus Vv180806 Reveals Its Regulatory Roles in Virulence and Antibiotic Resistance

Infection with Vibrio vulnificus is notorious for its atypical clinical manifestations and irreversible disease progression. Lysine acetylation is a conserved post-translational modification (PTM) that plays a critical regulatory role in diverse cellular processes. However, little is known about the role of lysine acetylation on the pathogenesis of V. vulnificus. Here, we report the complete genome sequence and a global profile for protein lysine acetylation of V. vulnificus Vv180806, a highly cefoxitin resistant strain isolated from a mortality case. The assembled genome comprised two circular chromosomes and one circular plasmid; it contained 4,770 protein-coding genes and 153 RNA genes. Phylogenetic analysis revealed genetic homology of this strain with other V. vulnificus strains from food sources. Of all the proteins in this strain, 1,924 (40.34%) were identified to be acetylated at 6,626 sites. The acetylated proteins were enriched in metabolic processes, binding functions, cytoplasm, and multiple central metabolic pathways. Moreover, the acetylation was found in most identified virulence factors of this strain, suggesting its potentially important role in bacterial virulence. Our work provides insights into the genomic and acetylomic features responsible for the virulence and antibiotic resistance of V. vulnificus, which will facilitate future investigations on the pathogenesis of this bacterium.

Characterization of bacteriophage VVP001 and its application for the inhibition of Vibrio vulnificus causing seafood-borne diseases

Vibrio vulnificus is a major food-borne pathogen that causes septicemia and cellulitis with a mortality rate of >50%. However, there are no efficient natural food preservatives or biocontrol agents to control V. vulnificus in seafood. In this study, we isolated and characterized a novel bacteriophage VVP001. Host range and transmission electron microscopy morphology observations revealed that VVP001 belongs to the family Siphoviridae and specifically infects V. vulnificus. Phage stability tests showed that VVP001 is stable at a broad temperature range of -20 °C to 65 °C and a pH range from 3 to 11, which are conditions for food applications (processing, distribution, and storage). In vitro challenge assays revealed that VVP001 inhibited V. vulnificus MO6-24/O (a clinical isolate) growth up to a 3.87 log reduction. In addition, complete genome analysis revealed that the 76 kb VVP001 contains 102 open reading frames with 49.64% G + C content and no gene encoding toxins or other virulence factors, which is essential for food applications. Application of VVP001 to fresh abalone samples contaminated with V. vulnificus demonstrated its ability to inhibit V. vulnificus growth, and an in vivo mouse survival test showed that VVP001 protects mice against high mortality (survival rate >70% at a multiplicity of infection of 1000 for up to 7 days). Therefore, the bacteriophage VVP001 can be used as a good natural food preservative and biocontrol agent for food applications.

Spatiotemporal dynamics of the total and active Vibrio spp. populations throughout the Changjiang estuary in China

Vibrio is ubiquitously distributed in marine environments and is the most extensively characterized group within Gammaproteobacteria. Studies have investigated Vibrio spp. worldwide, but mostly focused on pathogenic vibrios and based on cultivation methods. Here, using a combination of molecular and culturing methods, we investigated the dynamics of the total and active Vibrio spp. throughout the Changjiang estuary in China. The total Vibrio abundance was higher in summer (~6.59 × 10³ copies ml⁻¹) than in winter (~1.85 × 10³ copies ml⁻¹) and increased from freshwater to saltwater (e.g. 8.04 × 10¹ to 9.39 × 10³ copies ml⁻¹ in summer). The ratio of active to total Vibrio (Va/Vt) revealed a high activity of vibrios, with remarkable differences between freshwater and saltwater (p < 0.05). Based on the community compositions of the culturable, total and active Vibrio, Vibrio atlanticus and Vibrio owensii were the dominant and active species in winter and summer, respectively. The distribution of Vibrio was governed by the effects of diverse environmental factors, such as temperature, salinity, pH, dissolved oxygen and SiO₃²⁻. Our study clearly demonstrates the spatiotemporal dynamics of total and active Vibrio spp. and lays a foundation for fully understanding the ecological roles of marine Vibrio.

[Vibrio vulnificus, an increasing threat of sepsis in Germany?]

BACKGROUND

The prevalence of Vibrio vulnificus heavily depends on the temperature and salinity of the sea water. In the course of climate change an increase in cases of fatal sepsis caused by V. vulnificus at the German Baltic Sea coast could be detected.

OBJECTIVE

To generate awareness for a life-threatening infection with increasing incidence in Germany.

MATERIAL AND METHODS

This article presents an overview of the current state of the literature followed by an exemplary description of cases with V vulnificus sepsis caused by contact with water in the Baltic Sea, which were treated at the Medical University in Greifswald in summer 2018.

RESULTS

In the presence of risk factors, such as liver and kidney diseases, immunosuppression and male sex, there is a danger of severe sepsis if damaged skin comes into contact with contaminated sea water. A pronounced organ dysfunction can frequently be found on admission. In these cases the diagnosis must be made promptly and timely surgical cleansing and antibiotic treatment should be initiated (e.g. a combination of tetracyclines and third generation cephalosporins).

CONCLUSION

Sepsis due to V. vulnificus will probably increase over the coming years. Because there is a latency in some cases between infection and onset of sepsis, physicians beyond the coastal region must also be informed about this disease.

Faraday-Cage-Type Electrochemiluminescence Immunoassay: A Rise of Advanced Biosensing Strategy

Electrochemiluminescence immunoassays are usually carried out through "on-electrode" strategy, i.e., sandwich-type immunoassay format, the sensitivity of which is restricted by two key bottlenecks: (1) the number of signal labels is limited and (2) only a part of signal labels could participate in the electrode reaction. In this Perspective, we discuss the development of an "in-electrode" Faraday-cage-type concept-based immunocomplex immobilization strategy. The biggest difference from the traditional sandwich-type one is that the designed "in-electrode" Faraday-cage-type immunoassay uses a conductive two-dimensional (2-D) nanomaterial simultaneously coated with signal labels and a recognition component as the detection unit, which could directly overlap on the electrode surface. In such a case, electrons could flow freely from the electrode to the detection unit, the outer Helmholtz plane (OHP) of the electrode is extended, and thousands of signal labels coated on the 2-D nanomaterial are all electrochemically "effective." Thus, then, the above-mentioned bottlenecks obstructing the improvement of the sensitivity in sandwich-type immunoassay are eliminated, and as a result a much higher sensitivity of the Faraday-cage-type immunoassay can be obtained. And, the applications of the proposed versatile "in-electrode" Faraday-cage-type immunoassay have been explored in the detection of target polypeptide, protein, pathogen, and microRNA, with the detection sensitivity improved tens to hundreds of times. Finally, the outlook and challenges in the field are summarized. The rise of Faraday-cage-type electrochemiluminescence immunoassay (FCT-ECLIA)-based biosensing strategies opens new horizons for a wide range of early clinical identification and diagnostic applications.

Unveiling the acid stress response of clinical genotype Vibrio vulnificus isolated from the marine environments of Mangaluru coast, India

Gastric acidity is one of the earliest host defences faced by ingested organisms, and successful pathogens need to overcome this hurdle. The objective of this study was the systematic assessment of acid-stress response of Vibrio vulnificus isolated from coastal regions of Mangaluru. Acid-shock experiments were carried out at pH 4.0 and pH 4.5, with different experimental conditions expected to produce a varied acid response. Exposure to mild acid before the acid shock was favourable to the bacteria but was dependent on cell population and pH of the media and was independent of the strains tested. Lysine-dependent acid response was demonstrated with reference to the previously identified lysine decarboxylase system. Additionally, the results showed that inoculation into oysters provided some level of protection against acid stress. Increased expression of lysine/cadaverine genes was observed upon the addition of ground oyster and was confirmed by quantitative real-time PCR. The potential role of ornithine was analyzed with regard to acid stress, but no change in the survival pattern was observed. These findings highlight the physiology of bacteria in acid stress.

Structure and assembly of pilotin-dependent and -independent secretins of the type II secretion system

The type II secretion system (T2SS) is a cell envelope-spanning macromolecular complex that is prevalent in Gram-negative bacterial species. It serves as the predominant virulence mechanism of many bacteria including those of the emerging human pathogens Vibrio vulnificus and Aeromonas hydrophila. The system is composed of a core set of highly conserved proteins that assemble an inner membrane platform, a periplasmic pseudopilus and an outer membrane complex termed the secretin. Localization and assembly of secretins in the outer membrane requires recognition of secretin monomers by two different partner systems: an inner membrane accessory complex or a highly sequence-diverse outer membrane lipoprotein, termed the pilotin. In this study, we addressed the question of differential secretin assembly mechanisms by using cryo-electron microscopy to determine the structures of the secretins from A. hydrophila (pilotin-independent ExeD) and V. vulnificus (pilotin-dependent EpsD). These structures, at approximately 3.5 Å resolution, reveal pentadecameric stoichiometries and C-terminal regions that carry a signature motif in the case of a pilotin-dependent assembly mechanism. We solved the crystal structure of the V. vulnificus EpsS pilotin and confirmed the importance of the signature motif for pilotin-dependent secretin assembly by performing modelling with the C-terminus of EpsD. We also show that secretin assembly is essential for membrane integrity and toxin secretion in V. vulnificus and establish that EpsD requires the coordinated activity of both the accessory complex EpsAB and the pilotin EpsS for full assembly and T2SS function. In contrast, mutation of the region of the S-domain that is normally the site of pilotin interactions has little effect on assembly or function of the ExeD secretin. Since secretins are essential outer membrane channels present in a variety of secretion systems, these results provide a structural and functional basis for understanding the key assembly steps for different members of this vast pore-forming family of proteins.

Potentially human-virulent Vibrio vulnificus isolates from diseased great pompano (Trachinotus goodei)

Vibrio vulnificus is an opportunistic human pathogen responsible for the majority of seafood-associated deaths worldwide and is also a relevant fish pathogen for the aquaculture industry. In addition to infections in aquatic livestock, V. vulnificus also represents a risk to aquarium animals. For the first time, this work describes an important mortality outbreak in Trachinotus goodei in a zoo aquarium, with the isolation of Vibrio vulnificus (Vv) from the internal organs of the diseased fish. The isolates were identified by MALDI-TOF MS, serotyped and characterized by pulsed-field gel electrophoresis (PFGE). Although the isolates from great pompanos did not belong to pathovar piscis (formerly biotype 2) or to any of the fish-related serovars, they all had identical phenotypes, antimicrobial susceptibility profiles and PFGE patterns, which together with their isolation in pure culture from internal organs is strongly indicative of their clinical significance. Moreover, Vv isolates harboured important genetic markers of human virulence potential: they had the clinical variant of the vcg gene, gave the 338 bp DNA amplification product of the pilF gene and resisted the bactericidal activity of human serum. All these results strongly suggest that these Vv isolates should be considered potentially virulent for humans. These results extend the range of fish species affected by V. vulnificus, confirm the threat that this pathogen represents to aquatic animals and highlight the risk that this bacterial pathogen poses to human health.

Evolutionary Model of Cluster Divergence of the Emergent Marine Pathogen Vibrio vulnificus: From Genotype to Ecotype

Vibrio vulnificus is an emergent marine pathogen and is the cause of a deadly septicemia. However, the genetic factors that differentiate its clinical and environmental strains and its several biotypes remain mostly enigmatic. In this work, we investigated the underlying genomic properties and population dynamics of the V. vulnificus species to elucidate the traits that make these strains emerge as a human pathogen. The acquisition of different ecological determinants could have allowed the development of highly divergent clusters with different lifestyles within the same environment. However, we identified strains from both clusters in the mucosa of aquaculture species, indicating that manmade niches are bringing strains from the two clusters together, posing a potential risk of recombination and of emergence of novel variants. We propose a new evolutionary model that provides a perspective that could be broadly applicable to other pathogenic vibrios and facultative bacterial pathogens to pursue strategies to prevent their infections.

Vibrio vulnificus, an opportunistic pathogen, is the causative agent of a life-threatening septicemia and a rising problem for aquaculture worldwide. The genetic factors that differentiate its clinical and environmental strains remain enigmatic. Furthermore, clinical strains have emerged from every clade of V. vulnificus. In this work, we investigated the underlying genomic properties and population dynamics of the V. vulnificus species from an evolutionary and ecological point of view. Genome comparisons and bioinformatic analyses of 113 V. vulnificus isolates indicate that the population of V. vulnificus is made up of four different clusters. We found evidence that recombination and gene flow between the two largest clusters (cluster 1 [C1] and C2) have drastically decreased to the point where they are diverging independently. Pangenome and phenotypic analyses showed two markedly different lifestyles for these two clusters, indicating commensal (C2) and bloomer (C1) ecotypes, with differences in carbohydrate utilization, defense systems, and chemotaxis, among other characteristics. Nonetheless, we identified frequent intra- and interspecies exchange of mobile genetic elements (e.g., antibiotic resistance plasmids, novel “chromids,” or two different and concurrent type VI secretion systems) that provide high levels of genetic diversity in the population. Surprisingly, we identified strains from both clusters in the mucosa of aquaculture species, indicating that manmade niches are bringing strains from the two clusters together. We propose an evolutionary model of V. vulnificus that could be broadly applicable to other pathogenic vibrios and facultative bacterial pathogens to pursue strategies to prevent their infections and emergence.

Uncovering the geographical and host impacts on the classification of Vibrio vulnificus

Vibrio vulnificus causes human sickness throughout the world via the consumption of undercooked seafood or exposure to contaminated water. Previous attempts at phylogenetic analyses of V. vulnificus have proven unsuccessful, mainly due to the poorly understood impact of factors on its divergence. In this study, we used advanced statistical and phylogenetic methods to strengthen the classification of V. vulnificus. This updated classification included the impact of geographical and host factors. The results demonstrate the existence of hierarchies and multidimensional effects in the classification of V. vulnificus, from the molecular level using biotypes, to the distributional level using geographical location, to the adaptational level through host immune response. These findings have implications for the classification of bacteria, bacterial evolution, and public health.

Eco-evolutionary Dynamics Linked to Horizontal Gene Transfer in Vibrios

Vibrio is a genus of ubiquitous heterotrophic bacteria found in aquatic environments. Although they are a small percentage of the bacteria in these environments, vibrios can predominate during blooms. Vibrios also play important roles in the degradation of polymeric substances, such as chitin, and in other biogeochemical processes. Vibrios can be found as free-living bacteria, attached to particles, or associated with other organisms in a mutualistic, commensal, or pathogenic relationship. This review focuses on vibrio ecology and genome plasticity, which confers an ability to adapt to new niches and is driven, at least in part, by horizontal gene transfer (HGT). The extent of HGT and its role in pathogen emergence are discussed based on genomic studies of environmental and pathogenic vibrios, mobile genetically encoded virulence factors, and mechanistic studies on the different modes of HGT.

Environmental role of pathogenic traits in Vibrio cholerae

Vibrio cholerae is a natural inhabitant of aquatic ecosystems. Some strains of V. cholerae can colonize the human host and cause cholera, a profuse watery diarrhea. The major pathogenicity factors and virulence regulators of V. cholerae are either encoded in mobile genetic elements acquired in the environment (e.g. pathogenicity islands or lysogenic phages) or in the core genome. Several lines of evidence indicate that the emergence of numerous virulence traits of V. cholerae occurred in its natural environment due to biotic and abiotic pressures. Here, we discuss the connection between the human host and the potential ecological role of these virulent traits. Unraveling these connections will help us understand the emergence of this organism and other facultative bacterial pathogens.

Identification and characterization of Vibrio vulnificus plpA encoding a phospholipase A2 essential for pathogenesis

The marine bacterium Vibrio vulnificus causes food-borne diseases, which may lead to life-threatening septicemia in some individuals. Therefore, identifying virulence factors in V. vulnificus is of high priority. We performed a transcriptome analysis on V. vulnificus after infection of human intestinal HT29-methotrexate cells and found induction of plpA, encoding a putative phospholipase, VvPlpA. Bioinformatics, biochemical, and genetic analyses demonstrated that VvPlpA is a phospholipase A₂ secreted in a type II secretion system-dependent manner. Compared with the wild type, the plpA mutant exhibited reduced mortality, systemic infection, and inflammation in mice as well as low cytotoxicity toward the human epithelial INT-407 cells. Moreover, plpA mutation attenuated the release of actin and cytosolic cyclophilin A from INT-407 cells, indicating that VvPlpA is a virulence factor essential for causing lysis and necrotic death of the epithelial cells. plpA transcription was growth phase-dependent, reaching maximum levels during the early stationary phase. Also, transcription factor HlyU and cAMP receptor protein (CRP) mediate additive activation and host-dependent induction of plpA Molecular biological analyses revealed that plpA expression is controlled via the promoter, P _plpA , and that HlyU and CRP directly bind to P _plpA upstream sequences. Taken together, this study demonstrated that VvPlpA is a type II secretion system-dependent secretory phospholipase A₂ regulated by HlyU and CRP and is essential for the pathogenicity of V. vulnificus.