The interactions of Vibrio vulnificus and the oyster Crassostrea virginica

Whole-genome DNA methylation profiling revealed epigenetic regulation of NF-κB signaling pathway involved in response to Vibrio alginolyticus infection in the Pacific oyster, Crassostrea gigas

An essential epigenetic alteration known as DNA methylation is tightly linked to a variety of biological processes, including immune response. To identify the epigenetic regulatory mechanism in Pacific oyster (Crassostrea gigas), whole-genome bisulfite sequencing (WGBS) was conducted on C. gigas at 0 h, 6 h, and 48 h after infection with Vibrio alginolyticus. At 6 h and 48 h, a total of 11,502 and 14,196 differentially methylated regions (DMRs) were identified (p < 0.05, FDR < 0.001) compared to 0 h, respectively. Gene ontology (GO) analysis showed that differentially methylated genes (DMGs) were significantly enriched in various biological pathways including immunity, cytoskeleton, epigenetic modification, and metabolic processes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that transcription machinery (ko03021) is one of the most important pathways. Integrated transcriptome and methylome analyses allowed identification of 167 and 379 DMG-related DEGs at 6 h and 48 h, respectively. These genes were significantly enriched in immune-related pathways, including nuclear factor kappa B (NF-κB) signaling pathway (ko04064) and tumor necrosis factor (TNF) signaling pathway (ko04668). Interestingly, it's observed that the NF-κB pathway could be activated jointly by TNF Receptor Associated Factor 2 (TRAF2) and Baculoviral IAP Repeat Containing 3 (BIRC3, the homolog of human BIRC2) which were regulated by DNA methylation in response to the challenge posed by V. alginolyticus infection. Through this study, we provided insightful information about the epigenetic regulation of immunity-related genes in the C. gigas upon V. alginolyticus infection, which will be valuable to understand how invertebrates modulate their innate immune system to defend against bacterial infection.

Interactive effects of elevated temperature and Photobacterium swingsii infection on the survival and immune response of marine mussels (Perna canaliculus): A summer mortality scenario

The New Zealand Greenshell™ mussel (Perna canaliculus) is an economically important aquaculture species. Prolonged increases in seawater temperature above mussel thermotolerance ranges pose a significant threat to mussel survival and health, potentially increasing susceptibility to bacterial infections. Using challenge experiments, this study examined the combined effects of increased seawater temperature and bacterial (Photobacterium swingsii) infection on animal survival, haemocyte and biochemical responses of adult mussels. Mussels maintained at three temperatures (16, 20 and 24 °C) for seven days were either not injected (control), injected with sterile marine broth (injection control) or P. swingsii (challenged with medium and high doses) and monitored daily for five days. Haemolymph and tissue samples were collected at 24, 48, 72, 96, 120 h post-challenge and analysed to quantify bacterial colonies, haemocyte responses and biochemical responses. Mussels infected with P. swingsii exhibited mortalities at 20 and 24 °C, likely due to a compromised immune system, but no mortalities were observed when temperature was the only stressor. Bacterial colony counts in haemolymph decreased over time, suggesting bacterial clearance followed by the activation of immune signalling pathways. Total haemocyte counts and viability data supports haemocyte defence functions being stimulated in the presence of high pathogen loads at 24 °C. In the gill tissue, oxidative stress responses, measured as total antioxidant capacity and malondialdehyde (MDA) levels, were higher in infected mussels (compared to the controls) after 24h and 120h post-challenge at the lowest (16 °C) and highest temperatures (24 °C), indicating the presence of oxidative stress due to temperature and pathogen stressors. Overall, this work confirms that Photobacterium swingsii is pathogenic to P. canaliculus and indicates that mussels may be more vulnerable to bacterial pathogens under conditions of elevated temperature, such as those predicted under future climate change scenarios.

Tools to Enumerate and Predict Distribution Patterns of Environmental Vibrio vulnificus and Vibrio parahaemolyticus

Vibrio vulnificus (Vv) and Vibrio parahaemolyticus (Vp) are water- and foodborne bacteria that can cause several distinct human diseases, collectively called vibriosis. The success of oyster aquaculture is negatively impacted by high Vibrio abundances. Myriad environmental factors affect the distribution of pathogenic Vibrio, including temperature, salinity, eutrophication, extreme weather events, and plankton loads, including harmful algal blooms. In this paper, we synthesize the current understanding of ecological drivers of Vv and Vp and provide a summary of various tools used to enumerate Vv and Vp in a variety of environments and environmental samples. We also highlight the limitations and benefits of each of the measurement tools and propose example alternative tools for more specific enumeration of pathogenic Vv and Vp. Improvement of molecular methods can tighten better predictive models that are potentially important for mitigation in more controlled environments such as aquaculture.

Fulminant Overwhelming Necrotizing Vibrio vulnificus Sepsis Secondary to Oyster Consumption

Vibrio vulnificus is an opportunistic gram-negative rod-shaped bacteria found in warm, low salinity waters. Transmission through open wounds or consumption of contaminated seafood can lead to wound infections, sepsis, and potentially death. A 44-year-old man with a history of poly-substance abuse, cirrhosis, and recent oyster consumption presented to the emergency department in June with acute onset bilateral leg pain associated with rash and fever. Within 6 hours of his arrival, the rash rapidly progressed to large bullae with extensive necrosis ascending to the level of the abdomen, and he developed septic shock. Despite prompt surgical intervention and appropriate antibiotic and resuscitative therapies, the patient had progressive multi-system organ failure and died 7 days after admission. Concurrent necrotizing fasciitis with sepsis secondary to V. vulnificus infection is rare and potentially fatal, as demonstrated in this case.

Vibrio vulnificus, an Underestimated Zoonotic Pathogen

V. vulnificus, continues being an underestimated yet lethal zoonotic pathogen. In this chapter, we provide a comprehensive review of numerous aspects of the biology, epidemiology, and virulence mechanisms of this poorly understood pathogen. We will emphasize the widespread role of horizontal gene transfer in V. vulnificus specifically virulence plasmids and draw parallels from aquaculture farms to human health. By placing current findings in the context of climate change, we will also contend that fish farms act as evolutionary drivers that accelerate species evolution and the emergence of new virulent groups. Overall, we suggest that on-farm control measures should be adopted both to protect animals from Vibriosis, and also as a public health measure to prevent the emergence of new zoonotic groups.

Two novel genes identified by large-scale transcriptomic analysis are essential for biofilm and rugose colony development of Vibrio vulnificus

Many pathogenic bacteria form biofilms to survive under environmental stresses and host immune defenses. Differential expression (DE) analysis of the genes in biofilm and planktonic cells under a single condition, however, has limitations to identify the genes essential for biofilm formation. Independent component analysis (ICA), a machine learning algorithm, was adopted to comprehensively identify the biofilm genes of Vibrio vulnificus, a fulminating human pathogen, in this study. ICA analyzed the large-scale transcriptome data of V. vulnificus cells under various biofilm and planktonic conditions and then identified a total of 72 sets of independently co-regulated genes, iModulons. Among the three iModulons specifically activated in biofilm cells, BrpT-iModulon mainly consisted of known genes of the regulon of BrpT, a transcriptional regulator controlling biofilm formation of V. vulnificus. Interestingly, the BrpT-iModulon additionally contained two novel genes, VV1_3061 and VV2_1694, designated as cabH and brpN, respectively. cabH and brpN were shared in other Vibrio species and not yet identified by DE analyses. Genetic and biochemical analyses revealed that cabH and brpN are directly up-regulated by BrpT. The deletion of cabH and brpN impaired the robust biofilm and rugose colony formation. CabH, structurally similar to the previously known calcium-binding matrix protein CabA, was essential for attachment to the surface. BrpN, carrying an acyltransferase-3 domain as observed in BrpL, played an important role in exopolysaccharide production. Altogether, ICA identified two novel genes, cabH and brpN, which are regulated by BrpT and essential for the development of robust biofilms and rugose colonies of V. vulnificus.

Prevalence and Distribution of Potentially Human Pathogenic Vibrio spp. on German North and Baltic Sea Coasts

Global ocean warming results in an increase of infectious diseases including an elevated emergence of Vibrio spp. in Northern Europe. The European Centre for Disease Prevention and Control reported annual periods of high to very high risks of infection with Vibrio spp. during summer months along the North Sea and Baltic Sea coasts. Based on those facts, the risk of Vibrio infections associated with recreational bathing in European coastal waters increases. To obtain an overview of the seasonal and spatial distribution of potentially human pathogenic Vibrio spp. at German coasts, this study monitored V. cholerae, V. parahaemolyticus, and V. vulnificus at seven recreational bathing areas from 2017 to 2018, including the heat wave event in summer 2018. The study shows that all three Vibrio species occurred in water and sediment samples at all sampling sites. Temperature was shown to be the main driving factor of Vibrio abundance, whereas Vibrio community composition was mainly modulated by salinity. A species-specific rapid increase was observed at water temperatures above 10°C, reaching the highest detection numbers during the heat wave event with abundances of 4.5 log10 CFU+1/100 ml of seawater and 6.5 log10 CFU+1/100 g of sediment. Due to salinity, the dominant Vibrio species found in North Sea samples was V. parahaemolyticus, whereas V. vulnificus was predominantly detected in Baltic Sea samples. Most detections of V. cholerae were associated with estuarine samples from both seas. Vibrio spp. concentrations in sediments were up to three log higher compared to water samples, indicating that sediments are an important habitat for Vibrio spp. to persist in the environment. Antibiotic resistances were found against beta-lactam antibiotics (ampicillin 31%, cefazolin 36%, and oxacillin and penicillin 100%) and trimethoprim-sulfamethoxazole (45%). Moreover, isolates harboring pathogenicity-associated genes such as trh for V. parahaemolyticus as well as vcg, cap/wcv, and the 16S rRNA-type B variant for V. vulnificus were detected. All sampled V. cholerae isolates were identified as non-toxigenic non-O1/non-O139 serotypes. To sum up, increasing water temperatures at German North Sea and Baltic Sea coasts provoke elevated Vibrio numbers and encourage human recreational water activities, resulting in increased exposure rates. Owing to a moderate Baltic Sea salinity, the risk of V. vulnificus infections is of particular concern.

Invasive slipper limpets (Crepidula fornicata) act like a sink, rather than source, of Vibrio spp

A large knowledge gap exists regarding the disease profile and pathologic condition of the invasive, slipper limpet Crepidula fornicata. To help address this, we performed a year-long health survey at two sites in South Wales, UK – subtidal Swansea Bay and intertidal Milford Haven. In total, 1,800 limpets were screened systematically for haemolymph bacterial burdens using both general and vibrio-selective growth media (TSA + 2% NaCl and TCBS, respectively), haemolymph (blood) inspection using microscopy, a PCR-based assay targeting Vibrio spp., and multi-tissue histology. Over 99% of haemolymph samples contained cultivable bacterial colony-forming units, and 83% of limpets tested positive for the presence of vibrios via PCR (confirmed via Sanger sequencing). Vibrio presence did not vary greatly between sites, yet a strong seasonal effect was observed with significantly higher bacterial loads during the summer. Binomial logistic regression models revealed larger (older) limpets were more likely to harbour vibrios, and the growth of bacteria on TCBS was a key predictor for PCR-based vibrio detection. Histological assessment of > 340 animals revealed little evidence of inflammation, sepsis or immune reactivity despite the gross bacterial numbers. We contend that slipper limpets are not highly susceptible to bacteriosis at either site, and do not harbour vibrios known to be pathogenic to humans. The lack of susceptibility to local pathogenic bacteria may explain, in part, the invasion success of C. fornicata across this region.

Impact of plastic bags on the benthic system of a tropical estuary: An experimental study

Plastic bags are among the most discarded waste items as they are generally only used once and are often improperly eliminated and transported by rivers and estuaries to the ocean. We developed an experimental design to mimic the effect of plastic bag deposition in a tropical estuary and investigated its short-term impact on benthic community structure. We observed a significant influence of the presence of plastic bags on the abundance, richness and diversity of benthic fauna after an eight-week exposure period. Plastic bags acted as a barrier and interfered in processes that occur at the water-sediment interface, such as organic matter and silt-clay deposition. Our results indicate that plastic bags, in addition to directly affecting benthic fauna, may alter processes such as carbon burying, known as "blue carbon", thus making its storage in the sediment more difficult.

Impact of parasitism on levels of human-pathogenic Vibrio species in eastern oysters

AIMS

To investigate the relationships between individual health status of oysters, particularly with regard to parasitic infection, and variability in abundance of human-pathogenic Vibrio species.

METHODS AND RESULTS

Aquacultured eastern oysters, Crassostrea virginica, were analysed individually for infection by the protozoan parasite Perkinsus marinus through quantitative PCR, and total Vibrio vulnificus and total and pathogenic Vibrio parahaemolyticus abundance was assessed using a most probable number (MPN)-qPCR approach. Additionally, perspective on general oyster health and other parasitic infections was obtained through histopathology. Perkinsus marinus infection and human-pathogenic Vibrio species levels were not correlated, but through histology, analyses revealed that oysters infected by Haplosporidium nelsoni harboured more V. vulnificus.

CONCLUSIONS

The highly prevalent parasite P. marinus had little influence on human-pathogenic Vibrio species levels in eastern oysters, but the less prevalent parasite, H. nelsoni, may influence V. vulnificus levels, highlighting the potential nuances of within-oyster dynamics of Vibrio species.

SIGNIFICANCE AND IMPACT OF THE STUDY

Human-pathogenic bacteria continue to be a concern to the oyster industry and causes for individual oyster variation in bacterial levels remain unknown. The major oyster pathogen P. marinus does not appear to affect levels of these bacteria within oysters, suggesting that other factors may influence Vibrio spp. levels in oysters.

Physiological Variation in Response to Vibrio and Hypoxia by Aquacultured Eastern Oysters in the Southeastern United States

Eastern oysters (Crassostrea virginica) have long been recognized as model organisms of extreme environmental tolerance, showing resilience to variation in temperature, salinity, hypoxia and microbial pathogens. These phenotypic responses, however, show variability between geographic locations or habitats (e.g., tidal). Physiological, morphological and genetic differences occur in populations throughout a species' geographical range, which may have been shaped by regional abiotic and biotic variations. Few studies of C. virginica have explored the combined factors of physiological mechanisms of divergent phenotypes between locations and the genetic relationships of individuals between these locations. To characterize genetic relationships of four locations with aquacultured oysters along the North Carolina and Virginia coast, we sequenced a portion of cytochrome oxidase subunit I (COI) that revealed significant variation in haplotype distribution between locations. We then measured mitochondrial physiology and expression of the innate immunity response of hemocytes to lab acclimation and combined stress conditions to compare basal expression and stress response in oysters between these locations. For stress sensing genes, toll-like receptors had the strongest location-specific response to hypoxia and Vibrio, whereas mannose receptor and a stress-receptor were specific to hypoxia and bacteria, respectively. The expression of stress response genes also showed location-specific and stressor-specific changes in expression, particularly for big defensin and the complement gene Cq3. Our results further suggested that genetic similarity of oysters from different locations was not clearly related to physiological and molecular responses. These results are informative for understanding the range of physiological plasticity for stress responses in this commercially important oyster species. They also have implications in the oyster farming industry as well as conservation efforts to restore endangered native oyster beds.

A Master Regulator BrpR Coordinates the Expression of Multiple Loci for Robust Biofilm and Rugose Colony Development in Vibrio vulnificus

Vibrio vulnificus, a fulminating human pathogen, forms biofilms to enhance its survival in nature and pathogenicity during host infection. BrpR is the transcriptional regulator governing robust biofilm and rugose colony formation in V. vulnificus, but little is known about both the direct regulon of BrpR and the role of BrpR in regulation of downstream genes. In this study, transcript analyses revealed that BrpR is highly expressed and thus strongly regulates the downstream gene in the stationary and elevated cyclic di-GMP conditions. Transcriptome analyses discovered the genes, whose expression is affected by BrpR but not by the downstream regulator BrpT. Two unnamed adjacent genes (VV2_1626-1627) were newly identified among the BrpR regulon and designated as brpL and brpG in this study. Genetic analyses showed that the deletion of brpL and brpG impairs the biofilm and rugose colony formation, indicating that brpLG plays a crucial role in the development of BrpR-regulated biofilm phenotypes. Comparison of the colony morphology and exopolysaccharide (EPS) production suggested that although the genetic location and regulation of brpLG are distinct from the brp locus, brpABCDFHIJK (VV2_1574-1582), brpLG is also responsible for the robust EPS production together with the brp locus genes. Electrophoretic mobility shift assays and DNase I protection assays demonstrated that BrpR regulates the expression of downstream genes in distinct loci by directly binding to their upstream regions, revealing a palindromic binding sequence. Altogether, this study suggests that BrpR is a master regulator coordinating the expression of multiple loci responsible for EPS production and thus, contributing to the robust biofilm and rugose colony formation of V. vulnificus.

Transcription activation of two clusters for exopolysaccharide biosynthesis by phosphorylated DctD in Vibrio vulnificus

NtrC-mediated production of exopolysaccharides (EPS), essential components for Vibrio vulnificus biofilms, is highly increased in the presence of dicarboxylic or tricarboxylic acids. Gel-shift assays showed that regulation of the EPS-gene cluster I (EPS-I cluster) by NtrC was direct via binding of phosphorylated NtrC (p-NtrC) to the regulatory region of the EPS-I cluster. In contrast, p-NtrC did not bind to the EPS-II and EPS-III clusters, suggesting that NtrC regulation was not direct and another transcription factor belonging to an NtrC-regulon might play a role in activating their transcription. A candidate transcription factor, DctD, of which expression was induced by NtrC, activated the expression of the EPS-II and EPS-III clusters via direct binding to their upstream regions. Under growth conditions with either dicarboxylic or tricarboxylic acids, the expression of NtrC was induced and the transcription of dctD was activated. Furthermore, DctD exhibited higher transcriptional activity under the conditions with dicarboxylic acids than with tricarboxylic acids. Therefore, this study demonstrates that under dicarboxylate-rich conditions, both the abundance and activity of DctD were markedly induced, which activates the expression of two EPS clusters to maximize biosynthesis of EPS facilitating biofilm maturation in V. vulnificus.

Vibrio-bivalve interactions in health and disease

In the marine environment, bivalve mollusks constitute habitats for bacteria of the Vibrionaceae family. Vibrios belong to the microbiota of healthy oysters and mussels, which have the ability to concentrate bacteria in their tissues and body fluids, including the hemolymph. Remarkably, these important aquaculture species respond differently to infectious diseases. While oysters are the subject of recurrent mass mortalities at different life stages, mussels appear rather resistant to infections. Thus, Vibrio species are associated with the main diseases affecting the worldwide oyster production. Here, we review the current knowledge on Vibrio-bivalve interaction in oysters (Crassostrea sp.) and mussels (Mytilus sp.). We discuss the transient versus stable associations of vibrios with their bivalve hosts as well as technical issues limiting the monitoring of these bacteria in bivalve health and disease. Based on the current knowledge of oyster/mussel immunity and their interactions with Vibrio species pathogenic for oyster, we discuss how differences in immune effectors could contribute to the higher resistance of mussels to infections. Finally, we review the multiple strategies evolved by pathogenic vibrios to circumvent the potent immune defences of bivalves and how key virulence mechanisms could have been positively or negatively selected in the marine environment through interactions with predators.

A Regulatory Network Controls cabABC Expression Leading to Biofilm and Rugose Colony Development in Vibrio vulnificus

Biofilms provide bacteria with protection from environmental stresses and host immune defenses. The pathogenic marine bacterium Vibrio vulnificus forms biofilms and colonizes environmental niches such as oysters. The cabABC operon encodes an extracellular matrix protein CabA and the corresponding type I secretion system, which are essential for biofilm and rugose colony development of V. vulnificus. In this study, molecular biological analyses revealed the roles of three transcriptional regulators BrpR, BrpT, and BrpS in the regulatory pathway for the cabABC operon. BrpR induces brpT and BrpT in turn activates the cabABC operon in a sequential cascade, contributing to development of robust biofilm structures. BrpT also activates brpS, but BrpS represses brpT, constituting a negative feedback loop that stabilizes brpT expression. BrpT and BrpS directly bind to specific sequences upstream of cabA, and they constitute a feedforward loop in which BrpT induces brpS and together with BrpS activates cabABC, leading to precise regulation of cabABC expression. Accordingly, BrpS as well as BrpT plays a crucial role in complete development of rugose colonies. This elaborate network of three transcriptional regulators BrpR, BrpT, and BrpS thus tightly controls cabABC regulation, and contributes to successful development of robust biofilms and rugose colonies in V. vulnificus.

Toxigenic V. cholerae, V. parahaemolyticus, and V. vulnificus in oysters from the Gulf of Mexico and sold in Mexico City

Oysters can accumulate potentially pathogenic bacteria, such as Vibrio cholerae, V. parahaemolyticus, and V. vulnificus. The aim of this study was to detect the presence of these Vibrio species and their toxigenic variants in oysters from the Gulf of Mexico sold in Mexico City. Oyster samples were studied using traditional culture and molecular polymerase chain reaction analysis. V. cholerae was present in 30.4% of the samples and its toxigenic variant chxA+ in 26.1%. It was isolated only in deshelled oysters, mainly in the dry season. V. parahaemolyticus was present in 95.7% of the samples and the toxigenic variant was found in 17.4%. V. vulnificus was identified in 60.9% of the samples, 38% of which corresponded to the environmental genotype and 21.7% to the clinical genotype, mainly in the cold season. Consumption of the oysters analyzed poses health risks due to the presence of Vibrio species, especially in deshelled oysters.

Responses of marine mussel Mytilus galloprovincialis (Bivalvia: Mytilidae) after infection with the pathogen Vibrio splendidus

Bivalve molluscs possess effective cellular and humoral defence mechanisms against bacterial infection. Although the immune responses of mussels to challenge with pathogenic vibrios have been largely investigated, the effects at the site of injection at the tissue level have not been so far evaluated. To this aim, mussels Mytilus galloprovincialis were herein in vivo challenged with Vibrio splendidus to assess the responses induced in hemolymph and posterior adductor muscle (PAM), being the site of bacterial infection. The number of living intra-hemocyte bacteria increased after the first hour post-injection (p.i.), suggesting the occurrence of an intense phagocytosis, while clearance was observed within 24 h p.i. A recruitment of hemocytes at the injection site was found in mussel PAM, together with marked morphological changes in the volume of muscular fibers, with a recovery of muscle tissue organization after 48 h p.i. A concomitant impairment in the osmoregulatory processes were observed in PAM by an initial inhibition of aquaporins and increased immunopositivity of Na⁺/K⁺ ATPase ionic pump, strictly related to the histological alterations and hemocyte infiltration detected in PAM. Accordingly, an intense cell turnover activity was also recorded following the infection event. Overall, results indicated the hemolymph as the system responsible for the physiological adaptations in mussels to stressful factors, such as pathogenicity, for the maintenance of homeostasis and immune defence. Also, the osmotic balance and cell turnover can be used as objective diagnostic criteria to evaluate the physiological state of mussels following bacterial infection, which may be relevant in aquaculture and biomonitoring studies.

Dispersal of potentially pathogenic bacteria by plastic debris in Guanabara Bay, RJ, Brazil

Analyses of thermotolerant coliform and heterotrophic bacteria as well as Escherichia coli and Vibrio species were carried out on plastic samples and in the surrounding waters of Guanabara Bay to evaluate plastic debris as vehicles of bacterial dispersal. Chemical characterizations of plastics were performed using Fourier transform infrared spectroscopy (FTIR). Plastic debris with high coliform contents were found, while their respective water samples had only low titers. No correlations were observed, however, between the amounts of bacteria and the chemical compositions of the plastic debris. Forty-four bacterial strains were PCR-confirmed as E. coli pathotypes, and 59 strains of Vibrio spp. (with 12 being identified as Vibrio cholerae [6], Vibrio vulnificus [5], and Vibrio mimicus [1]). These findings suggest these plastics can function as a substrate for bacterial biofilms (including pathogens). These debris, in turn, can be dispersed in aquatic environments not otherwise showing recent fecal bacterial contamination.

Stimulation of Vibrio vulnificus Pyruvate Kinase in the Presence of Glucose to Cope With H2O2 Stress Generated by Its Competitors

The bacterial phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS) regulates a variety of cellular processes in addition to catalyzing the coupled transport and phosphorylation of carbohydrates. We recently reported that, in the presence of glucose, HPr of the PTS is dephosphorylated and interacts with pyruvate kinase A (PykA) catalyzing the conversion of PEP to pyruvate in Vibrio vulnificus. Here, we show that this interaction enables V. vulnificus to survive H₂O₂ stress by increasing pyruvate production. A pykA deletion mutant was more susceptible to H₂O₂ stress than wild-type V. vulnificus without any decrease in the expression level of catalase, and this sensitivity was rescued by the addition of pyruvate. The H₂O₂ sensitivity difference between wild-type and pykA mutant strains becomes more apparent in the presence of glucose. Fungi isolated from the natural habitat of V. vulnificus retarded the growth of the pykA mutant more severely than the wild-type strain in the presence of glucose by glucose oxidase-dependent generation of H₂O₂. These data suggest that V. vulnificus has evolved to resist the killing action of its fungal competitors by increasing pyruvate production in the presence of glucose.

Different abundance and correlational patterns exist between total and presumed pathogenic Vibrio vulnificus and V. parahaemolyticus in shellfish and waters along the North Carolina coast

Monitoring of Vibrio vulnificus and V. parahaemolyticus abundance is pertinent due to the ability of these species to cause disease in humans through aquatic vectors. Previously, we performed a multiyear investigation tracking Vibrio spp. levels in five sites along the southeastern North Carolina coast. From February 2013 to October 2015, total V. vulnificus and V. parahaemolyticus abundance was measured in water, oysters and clams. In the current study, pathogenic subpopulations were identified in these isolates using molecular markers, revealing that 5.3% of V. vulnificus isolates possessed the virulence-correlated gene (vcgC), and 1.9% of V. parahaemolyticus isolates harbored one or both of the virulence-associated hemolysin genes (tdh and trh). Total V. parahaemolyticus abundance was not sufficient to predict the abundance of pathogenic subpopulations. Specifically, pathogenic V. parahaemolyticus isolates were more often isolated in cooler waters and were sometimes isolated when no other V. parahaemolyticus strains were detectable. Vibrio vulnificus clinical (C-) genotypes correlated with total V. vulnificus; however, salinity, water depth and total suspended solids influenced C- and E-genotypes differently. Lastly, we documented individual oysters harboring significantly higher V. vulnificus levels for which there was no ecological explanation, a phenomenon that deserves closer attention due to the potentially elevated health hazard associated with these 'hot' shellfish.

Differences in Abundances of Total Vibrio spp., V. vulnificus, and V. parahaemolyticus in Clams and Oysters in North Carolina

Filter feeding shellfish can concentrate pathogenic bacteria, including Vibrio vulnificus and Vibrio parahaemolyticus, as much as 100-fold from the overlying water. These shellfish, especially clams and oysters, are often consumed raw, providing a route of entry for concentrated doses of pathogenic bacteria into the human body. The numbers of foodborne infections with these microbes are increasing, and a better understanding of the conditions that might trigger elevated concentrations of these bacteria in seafood is needed. In addition, if bacterial concentrations in water are correlated with those in shellfish, then sampling regimens could be simplified, as water samples can be more rapidly and easily obtained. After sampling of oysters and clams, either simultaneously or separately, for over 2 years, it was concluded that while Vibrio concentrations in oysters and water were related, this was not the case for levels in clams and water. When clams and oysters were collected simultaneously from the same site, the clams were found to have lower Vibrio levels than the oysters. Furthermore, the environmental parameters that were correlated with levels of Vibrio spp. in oysters and water were found to be quite different from those that were correlated with levels of Vibrio spp. in clams.

IMPORTANCE

This study shows that clams are a potential source of infection in North Carolina, especially for V. parahaemolyticus These findings also highlight the need for clam-specific environmental research to develop accurate Vibrio abundance models and to broaden the ecological understanding of clam-Vibrio interactions. This is especially relevant as foodborne Vibrio infections from clams are being reported.

Killing of Vibrio cholerae and Escherichia coli Strains Carrying D-mannose-sensitive Ligands by Mytilus Hemocytes is Promoted by a Multifunctional Hemolymph Serum Protein

In aquatic environments, bivalve mollusks represent an important ecological niche for microorganisms. Persistence of bacteria in bivalve tissues partly depends on their capacity to survive the bactericidal activity of the hemolymph due to both cellular (hemocyes) and soluble serum factors (e.g., enzymes, lectins, opsonins). The extrapallial protein (EP) present in serum of Mytilus galloprovincialis (MgEP) has been recently shown to work as an opsonin promoting D-mannose sensitive (MS) interactions of the bivalve pathogen Vibrio aestuarianus 01/032 strain with the hemocytes. In this study, the role of MgEP in adhesion and killing of other bacteria carrying MS sensitive ligands was investigated. MgEP enhanced adhesion to and killing by hemocytes of Vibrio cholerae ElTor N16961, expressing the MS hemagglutin (MSHA), as well as of Escherichia coli MG1655, carrying type 1 fimbriae. These results further support the recent finding that the multifunctional MgEP also acts as an opsonin involved in mussel defense towards bacteria carrying MS ligands. In addition, these results contribute to elucidate the ecology of bacterial pathogens that can be transmitted to humans via shellfish consumption.

Role of extracellular matrix protein CabA in resistance of Vibrio vulnificus biofilms to decontamination strategies

Biofilms are recalcitrant and raise safety problems in the food industry. In this study, the role of CabA, an extracellular matrix protein, in the resistance of the biofilms of Vibrio vulnificus, a foodborne pathogen, to decontamination strategies was investigated. Biofilms of the cabA mutant revealed reduced resistance to detachment by vibration and disinfection by sodium hypochlorite compared to the biofilms of the parental wild type in vitro. The reduced resistance of the cabA mutant biofilms was complemented by introducing a recombinant cabA, indicating that the reduced resistance of the cabA mutant biofilms is caused by the inactivation of cabA. The expression of cabA was induced in cells bound to oyster, the primary vehicle of the pathogen. The cabA mutant biofilms on oyster are defective in biomass and resistance to detachment and disinfection. The bacterial cells in the wild-type biofilms are clustered by filaments which are not apparent in the cabA mutant biofilms. The combined results indicated that CabA contributes to the structural integrity of V. vulnificus biofilms possibly by forming filaments in the matrix and thus rendering the biofilms robust, suggesting that CabA could be a target to control V. vulnificus biofilms on oyster.

The Biology of Vibrio vulnificus

Vibrio vulnificus, carrying a 50% fatality rate, is the most deadly of the foodborne pathogens. It occurs in estuarine and coastal waters and it is found in especially high numbers in oysters and other molluscan shellfish. The biology of V. vulnificus, including its ecology, pathogenesis, and molecular genetics, has been described in numerous reviews. This article provides a brief summary of some of the key aspects of this important human pathogen, including information on biotypes and genotypes, virulence factors, risk factor requirements and the role of iron in disease, association with oysters, geographic distribution, importance of salinity and water temperature, increasing incidence associated with global warming. This article includes some of our findings as presented at the "Vibrios in the Environment 2010" conference held in Biloxi, MS.

The trans-kingdom identification of negative regulators of pathogen hypervirulence

Modern society and global ecosystems are increasingly under threat from pathogens, which cause a plethora of human, animal, invertebrate and plant diseases. Of increasing concern is the trans-kingdom tendency for increased pathogen virulence that is beginning to emerge in natural, clinical and agricultural settings. The study of pathogenicity has revealed multiple examples of convergently evolved virulence mechanisms. Originally described as rare, but increasingly common, are interactions where a single gene deletion in a pathogenic species causes hypervirulence. This review utilised the pathogen-host interaction database (www.PHI-base.org) to identify 112 hypervirulent mutations from 37 pathogen species, and subsequently interrogates the trans-kingdom, conserved, molecular, biochemical and cellular themes that cause hypervirulence. This study investigates 22 animal and 15 plant pathogens including 17 bacterial and 17 fungal species. Finally, the evolutionary significance and trans-kingdom requirement for negative regulators of hypervirulence and the implication of pathogen hypervirulence and emerging infectious diseases on society are discussed.

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.

Skin, soft tissue and systemic bacterial infections following aquatic injuries and exposures

: Bacterial infections following aquatic injuries occur commonly in fishermen and vacationers after freshwater and saltwater exposures. Internet search engines were queried with the key words to describe the epidemiology, clinical manifestations, diagnostic and treatment strategies and outcomes of both the superficial and the deeper invasive infections caused by more common, newly emerging and unusual aquatic bacterial pathogens. Main findings included the following: (1) aquatic injuries often result in gram-negative polymicrobial infections with marine bacteria; (2) most marine bacteria are resistant to 1st- and 2nd-generation penicillins and cephalosporins; (3) nontuberculous, mycobacterial infections should be considered in late-onset, culture-negative and antibiotic-resistant marine infections; (4) superficial marine infections and pre-existing wounds exposed to seawater may result in deeply invasive infections and sepsis in immunocompromised patients. With the exception of minor marine wounds demonstrating localized cellulitis, most other marine infections and all gram-negative and mycobacterial marine infections will require therapy with antibiotic combinations.

Draft Genome Sequences of Four Closely Linked Vibrio vulnificus Isolates from the Biotype 1 Environmental Genotype

Biotype 1 of Vibrio vulnificus, which causes severe invasive intestinal and wound infections, is split into two genotypes with all previously sequenced clinical isolates from the C genotypes. We report here the whole-genome sequencing of two clinical isolates and two closely linked oyster isolates from the E genotype for comparative studies.

Development of a matrix tool for the prediction of Vibrio species in oysters harvested from North Carolina

The United States has federal regulations in place to reduce the risk of seafood-related infection caused by the estuarine bacteria Vibrio vulnificus and Vibrio parahaemolyticus. However, data to support the development of regulations have been generated in a very few specific regions of the nation. More regionally specific data are needed to further understand the dynamics of human infection relating to shellfish-harvesting conditions in other areas. In this study, oysters and water were collected from four oyster harvest sites in North Carolina over an 11-month period. Samples were analyzed for the abundances of total Vibrio spp., V. vulnificus, and V. parahaemolyticus; environmental parameters, including salinity, water temperature, wind velocity, and precipitation, were also measured simultaneously. By utilizing these data, preliminary predictive management tools for estimating the abundance of V. vulnificus bacteria in shellfish were developed. This work highlights the need for further research to elucidate the full suite of factors that drive V. parahaemolyticus abundance.

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.

Impact of Hurricane Irene on Vibrio vulnificus and Vibrio parahaemolyticus concentrations in surface water, sediment, and cultured oysters in the Chesapeake Bay, MD, USA

To determine if a storm event (i.e., high winds, large volumes of precipitation) could alter concentrations of Vibrio vulnificus and V. parahaemolyticus in aquacultured oysters (Crassostrea virginica) and associated surface water and sediment, this study followed a sampling timeline before and after Hurricane Irene impacted the Chesapeake Bay estuary in late August 2011. Aquacultured oysters were sampled from two levels in the water column: surface (0.3 m) and near-bottom (just above the sediment). Concentrations of each Vibrio spp. and associated virulence genes were measured in oysters with a combination of real-time PCR and most probable number (MPN) enrichment methods, and in sediment and surface water with real-time PCR. While concentration shifts of each Vibrio species were apparent post-storm, statistical tests indicated no significant change in concentration for either Vibrio species by location (surface or near bottom oysters) or date sampled (oyster tissue, surface water, and sediment concentrations). V. vulnificus in oyster tissue was correlated with total suspended solids (r = 0.41, P = 0.04), and V. vulnificus in sediment was correlated with secchi depth (r = -0.93, P <0.01), salinity (r = -0.46, P = 0.02), tidal height (r = -0.45, P = 0.03), and surface water V. vulnificus (r = 0.98, P <0.01). V. parahaemolyticus in oyster tissue did not correlate with environmental measurements, but V. parahaemolyticus in sediment and surface water correlated with several measurements including secchi depth [r = -0.48, P = 0.02 (sediment); r = -0.97, P <0.01 (surface water)] and tidal height [r = -0.96, P <0.01 (sediment), r = -0.59, P <0.01 (surface water)]. The concentrations of Vibrio spp. were higher in oysters relative to other studies (average V. vulnificus 4 × 10(5) MPN g(-1), V. parahaemolyticus 1 × 10(5) MPN g(-1)), and virulence-associated genes were detected in most oyster samples. This study provides a first estimate of storm-related Vibrio density changes in oyster tissues, sediment, and surface water at an aquaculture facility in the Chesapeake Bay.

Skin and soft tissue infections following marine injuries and exposures in travelers

BACKGROUND

Bacterial skin and soft tissue infections (SSTIs) in travelers often follow insect bites and can present a broad spectrum of clinical manifestations ranging from impetigo to necrotizing cellulitis. Significant SSTIs can also follow marine injuries and exposures in travelers, and the etiologies are often marine bacteria.

METHODS

To meet the objectives of describing the pathogen-specific presenting clinical manifestations, diagnostic and treatment strategies, and outcomes of superficial and deep invasive infections in travelers caused by commonly encountered and newly emerging marine bacterial pathogens, Internet search engines were queried with the key words as MESH terms.

RESULTS

Travel medicine practitioners should maintain a high index of suspicion regarding potentially catastrophic, invasive bacterial infections, especially Aeromonas hydrophila, Vibrio vulnificus, Chromobacterium violaceum, and Shewanella infections, following marine injuries and exposures.

CONCLUSIONS

Travelers with well-known risk factors for the increasing severity of marine infections, including those with open wounds, suppressed immune systems, liver disease, alcoholism, hemochromatosis, hematological disease, diabetes, chronic renal disease, acquired immunodeficiency syndrome, and cancer, should be cautioned about the risks of marine infections through exposures to marine animals, seawater, the preparation of live or freshly killed seafood, and the accidental ingestion of seawater or consumption of raw or undercooked seafood, especially shellfish. With the exception of minor marine wounds demonstrating localized cellulitis or spreading erysipeloid-type reactions, most other marine infections and all Gram-negative and mycobacterial marine infections will require therapy with antibiotic combinations.

Draft Genome Sequence of Israeli Outbreak-Associated Vibrio vulnificus Biotype 3 Clinical Isolate BAA87

Vibrio vulnificus is a seafood-associated pathogen that causes severe wound and intestinal infections. Biotype 3 of V. vulnificus emerged in 1996 as the cause of an Israeli outbreak associated with the handling of infected tilapia. Here, we describe the whole-genome sequence of the ATCC biotype 3 clinical isolate BAA87 (CDC9530-96).

Associations and dynamics of Vibrionaceae in the environment, from the genus to the population level

The Vibrionaceae, which encompasses several potential pathogens, including V. cholerae, the causative agent of cholera, and V. vulnificus, the deadliest seafood-borne pathogen, are a well-studied family of marine bacteria that thrive in diverse habitats. To elucidate the environmental conditions under which vibrios proliferate, numerous studies have examined correlations with bulk environmental variables—e.g., temperature, salinity, nitrogen, and phosphate—and association with potential host organisms. However, how meaningful these environmental associations are remains unclear because data are fragmented across studies with variable sampling and analysis methods. Here, we synthesize findings about Vibrio correlations and physical associations using a framework of increasingly fine environmental and taxonomic scales, to better understand their dynamics in the wild. We first conduct a meta-analysis to determine trends with respect to bulk water environmental variables, and find that while temperature and salinity are generally strongly predictive correlates, other parameters are inconsistent and overall patterns depend on taxonomic resolution. Based on the hypothesis that dynamics may better correlate with more narrowly defined niches, we review evidence for specific association with plants, algae, zooplankton, and animals. We find that Vibrio are attached to many organisms, though evidence for enrichment compared to the water column is often lacking. Additionally, contrary to the notion that they flourish predominantly while attached, Vibrio can have, at least temporarily, a free-living lifestyle and even engage in massive blooms. Fine-scale sampling from the water column has enabled identification of such lifestyle preferences for ecologically cohesive populations, and future efforts will benefit from similar analysis at fine genetic and environmental sampling scales to describe the conditions, habitats, and resources shaping Vibrio dynamics.

Interspecific quorum sensing mediates the resuscitation of viable but nonculturable vibrios

Entry and exit from dormancy are essential survival mechanisms utilized by microorganisms to cope with harsh environments. Many bacteria, including the opportunistic human pathogen Vibrio vulnificus, enter a form of dormancy known as the viable but nonculturable (VBNC) state. VBNC cells can resuscitate when suitable conditions arise, yet the molecular mechanisms facilitating resuscitation in most bacteria are not well understood. We discovered that bacterial cell-free supernatants (CFS) can awaken preexisting dormant vibrio populations within oysters and seawater, while CFS from a quorum sensing mutant was unable to produce the same resuscitative effect. Furthermore, the quorum sensing autoinducer AI-2 could induce resuscitation of VBNC V. vulnificus in vitro, and VBNC cells of a mutant unable to produce AI-2 were unable to resuscitate unless the cultures were supplemented with exogenous AI-2. The quorum sensing inhibitor cinnamaldehyde delayed the resuscitation of wild-type VBNC cells, confirming the importance of quorum sensing in resuscitation. By monitoring AI-2 production by VBNC cultures over time, we found quorum sensing signaling to be critical for the natural resuscitation process. This study provides new insights into the molecular mechanisms stimulating VBNC cell exit from dormancy, which has significant implications for microbial ecology and public health.

Implications of chitin attachment for the environmental persistence and clinical nature of the human pathogen Vibrio vulnificus

Vibrio vulnificus naturally inhabits a variety of aquatic organisms, including oysters, and is the leading cause of seafood-related death in the United States. Strains of this bacterium are genetically classified into environmental (E) and clinical (C) genotypes, which correlate with source of isolation. E-genotype strains integrate into marine aggregates more efficiently than do C-genotype strains, leading to a greater uptake of strains of this genotype by oysters feeding on these aggregates. The causes of this increased integration of E-type strains into marine "snow" have not been demonstrated. Here, we further investigate the physiological and genetic causalities for this genotypic heterogeneity by examining the ability of strains of each genotype to attach to chitin, a major constituent of marine snow. We found that E-genotype strains attach to chitin with significantly greater efficiency than do C-genotype strains when incubated at 20°C. Type IV pili were implicated in chitin adherence, and even in the absence of chitin, the expression level of type IV pilin genes (pilA, pilD, and mshA) was found to be inherently higher by E genotypes than by C genotypes. In contrast, the level of expression of N-acetylglucosamine binding protein A (gbpA) was significantly higher in C-genotype strains. Interestingly, incubation at a clinically relevant temperature (37°C) resulted in a significant increase in C-genotype attachment to chitin, which subsequently provided a protective effect against exposure to acid or bile, thus offering a clue into their increased incidence in human infections. This study suggests that C- and E-genotype strains have intrinsically divergent physiological programs, which may help explain the observed differences in the ecology and pathogenic potential between these two genotypes.

Mechanistic and statistical models of total Vibrio abundance in the Neuse River Estuary

Bacteria in the genus Vibrio are ubiquitous to estuarine waters worldwide and are often the dominant genus recovered from these environments. This genus contains several potentially pathogenic species, including Vibrio vulnificus, Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio alginolyticus. These bacteria have short generation times, as low as 20-30 min, and can thus respond rapidly to changing environmental conditions. A five-parameter mechanistic model was generated based on environmental processes including hydrodynamics, growth, and death rates of Vibrio bacteria to predict total Vibrio abundance in the Neuse River Estuary of eastern North Carolina. Additionally an improved statistical model was developed using the easily monitored parameters of temperature and salinity. This updated model includes data that covers more than eight years of constant bacterial monitoring, and incorporates extreme weather events such as droughts, storms, and floods. These models can be used to identify days in which bacterial abundance might coincide with increased health risks.

LuxR homologue SmcR is essential for Vibrio vulnificus pathogenesis and biofilm detachment, and its expression is induced by host cells

Quorum sensing is a cell-to-cell communication system known to control many bacterial processes. In the present study, the functions of quorum sensing in the pathogenesis of Vibrio vulnificus, a food-borne pathogen, were assessed by evaluating the virulence of a mutant deficient in SmcR, a quorum-sensing regulator and homologue of LuxR. When biofilms were used as an inoculum, the smcR mutant was impaired in virulence and colonization capacity in the infection of mice. The lack of SmcR also resulted in decreased histopathological damage in mouse jejunum tissue. These results indicated that SmcR is essential for V. vulnificus pathogenesis. Moreover, the smcR mutant exhibited significantly reduced biofilm detachment. Upon exposure to INT-407 host cells, the wild type, but not the smcR mutant, revealed accelerated biofilm detachment. The INT-407 cells increased smcR expression by activating the expression of LuxS, an autoinducer-2 synthase, indicating that host cells manipulate the cellular level of SmcR through the quorum-sensing signaling of V. vulnificus. A whole-genome microarray analysis revealed that the genes primarily involved in biofilm detachment and formation are up- and downregulated by SmcR, respectively. Among the SmcR-regulated genes, vvpE encoding an elastolytic protease was the most upregulated, and the purified VvpE appeared to dissolve established biofilms directly in a concentration-dependent manner in vitro. These results suggest that the host cell-induced SmcR enhances the detachment of V. vulnificus biofilms entering the host intestine and thereby may promote the dispersal of the pathogen to new colonization loci, which is crucial for pathogenesis.

Integration of Vibrio vulnificus into marine aggregates and its subsequent uptake by Crassostrea virginica oysters

Marine aggregates are naturally forming conglomerations of larvacean houses, phytoplankton, microbes, and inorganics adhered together by exocellular polymers. In this study, we show in vitro that the bacterial pathogen Vibrio vulnificus can be concentrated into laboratory-generated aggregates from surrounding water. We further show that environmental (E-genotype) strains exhibit significantly more integration into these aggregates than clinical (C-genotype) strains. Experiments where marine aggregates with attached V. vulnificus cells were fed to oysters (Crassostrea virginica) resulted in greater uptake of both C and E types than nonaggregated controls. When C- and E-genotype strains were cocultured in competitive experiments, the aggregated E-genotype strains exhibited significantly greater uptake by oyster than the C-genotype strains.