Toxic and enzymatic activities of Vibrio vulnificus biotype 2 with respect to host specificity

Vibrio vulnificus mutation rate: an in vitro approach

Vibrio vulnificus is a multi-host pathogenic species currently subdivided into five phylogenetic lineages (L) plus one pathovar with the ability to infect fish due to a transmissible virulence plasmid. This plasmid (or a fragment of it) has been transmitted between lineages within the species, contributing to the evolution of V. vulnificus. This study aimed to provide an experimental approximation to the V. vulnificus mutation rate by determining spontaneous mutation rates from bacterial cultures of representants of the different lineages by whole-genome sequencing. To this purpose, synonymous SNP differences, i.e., spontaneous mutation not subjected to the evolutive forces, between initial and final culture after serial growth were evaluated and used for mutation rate calculation.

Screening for Novel Beneficial Environmental Bacteria for an Antagonism-Based Erwinia amylovora Biological Control

Erwinia amylovora, the bacterial species responsible for fire blight, causes major economic losses in pome fruit crops worldwide. Chemical control is not always effective and poses a serious threat to the environment and human health. Social demands for eco-sustainable and safe control methods make it necessary to search for new biocontrol strategies such as those based on antagonists. A bacterial collection from different fire blight-free Mediterranean environments was tested for antagonistic activity against Spanish strains of E. amylovora. Antagonistic assays were carried out in vitro in culture medium and ex vivo in immature loquat and pear fruits. Results revealed that 12% of the 82 bacterial isolates tested were able to inhibit the growth of several strains of the pathogen. Some of the isolates also maintained their antagonistic activity even after chloroform inactivation. Selected isolates were further tested ex vivo, with several of them being able to delay and/or reduce fire blight symptom severity in both loquats and pears and having activity against some E. amylovora strains. The isolates showing the best antagonism also produced different hydrolases linked to biocontrol (protease, lipase, amylase, and/or DNAse) and were able to fix molecular nitrogen. Based on this additional characterization, four biocontrol strain candidates were further selected and identified using MALDI-TOF MS. Three of them were Gram-positive bacteria belonging to Bacillus and Paenarthrobacter genera, and the fourth was a Pseudomonas strain. Results provide promising prospects for an improvement in the biological control strategies against fire blight disease.

The Effect of the Environmental Temperature on the Adaptation to Host in the Zoonotic Pathogen Vibrio vulnificus

Vibrio vulnificus is a zoonotic pathogen that lives in temperate, tropical and subtropical aquatic ecosystems whose geographical distribution is expanding due to global warming. The species is genetically variable and only the strains that belong to the zoonotic clonal-complex can cause vibriosis in both humans and fish (being its main host the eel). Interestingly, the severity of the vibriosis in the eel and the human depends largely on the water temperature (highly virulent at 28°C, avirulent at 20°C or below) and on the iron content in the blood, respectively. The objective of this work was to unravel the role of temperature in the adaptation to the host through a transcriptomic and phenotypic approach. To this end, we obtained the transcriptome of a zoonotic strain grown in a minimum medium (CM9) at 20, 25, 28, and 37°C, and confirmed the transcriptomic results by RT-qPCR and phenotypic tests. In addition, we compared the temperature stimulon with those previously obtained for iron and serum (from eel and human, respectively). Our results suggest that warm temperatures activate adaptive traits that would prepare the bacteria for host colonization (metabolism, motility, chemotaxis, and the protease activity) and fish septicemia (iron-uptake from transferrin and production of O-antigen of high molecular weight) in a generalized manner, while environmental iron controls the expression of a host-adapted virulent phenotype (toxins and the production of a protective envelope). Finally, our results confirm that beyond the effect of temperature on the V. vulnificus distribution in the environment, it also has an effect on the infectious capability of this pathogen that must be taken into account to predict the real risk of V. vulnificus infection caused by global warming.

Outcomes of Third-Generation Cephalosporin Plus Ciprofloxacin or Doxycycline Therapy in Patients with Vibrio vulnificus Septicemia: A Propensity Score-Matched Analysis

Background

Combination therapy with a third-generation cephalosporin (TGC) and a tetracycline analogue is recommended for Vibrio vulnificus infection. The combination of a TGC and ciprofloxacin has synergistic in vitro bactericidal activity against V. vulnificus. No clinical study has compared the standard regimen with TGC plus ciprofloxacin therapy for V. vulnificus infection.

Methods

Patients with a confirmed V. vulnificus infection at two medical centers in Korea from 1991 to 2016 were enrolled in this study. The patients were grouped according to the type of antibiotic administered. A retrospective propensity-score-matched case-control study of patients treated with TGC plus doxycycline or TGC plus ciprofloxacin was performed. The clinical characteristics and outcomes of the patients were analyzed.

Results

A total of 218 patients were confirmed to have V. vulnificus septicemia during the study, and the 30-day survival rate was 39% (85/218). The patients were classified into the following six treatment groups: TGC monotherapy (n = 82), TGC plus doxycycline therapy (n = 42), TGC plus ciprofloxacin therapy (n = 39), ciprofloxacin monotherapy (n = 14), other β-lactam monotherapy (n = 10), and other (n = 31). The survival rates of these groups were as follows: TGC monotherapy (35%), TGC plus doxycycline (38%), TGC plus ciprofloxacin (54%), ciprofloxacin monotherapy (29%), other β-lactam (20%), and other (39%). The 30-day survival rate showed no significant difference between the TGC plus doxycycline and TGC plus ciprofloxacin groups (log-rank test, P = 0.18). Among the 81 patients treated with TGC plus doxycycline or TGC plus ciprofloxacin, 12 per treatment group were selected by propensity-score matching. There was no significant difference in the baseline characteristics or the frequency of fasciotomy between the two groups. The 30-day survival rate showed no significant difference between the TGC plus doxycycline (50%) and TGC plus ciprofloxacin (67%) groups (log-rank test, P = 0.46).

Conclusion

Our data suggest that the outcome of TGC plus ciprofloxacin therapy was comparable to that of TGC plus doxycycline therapy in patients with V. vulnificus septicemia.

The combination of a third-generation cephalosporin (TGC) and ciprofloxacin has synergy in vitro bactericidal activity against V. vulnificus. No clinical study has compared the standard regimen with TGC plus ciprofloxacin therapy for V. vulnificus infection. A total of 218 patients were enrolled who are confirmed to have V. vulnificus septicemia in two medical centers in Korea from 1991 to 2016. The 30-day survival rate was 39% (85/218) for all patients, 38% (16/42) for TGC plus doxycycline and 54% (21/39) for TGC plus ciprofloxacin (log rank test, P = 0.18). A propensity score-matched analysis was performed and 12 per treatment groups were selected. The 30-day survival rate showed no significant difference between the TGC plus doxycycline (50%, 6/12) and TGC plus ciprofloxacin (67%, 4/12) groups (log-rank test, P = 0.46). The outcome of TGC plus ciprofloxacin therapy was comparable to that of TGC plus doxycycline therapy in patients with V. vulnificus septicemia.

Bacteriophage Interactions with Marine Pathogenic Vibrios: Implications for Phage Therapy

A global distribution in marine, brackish, and freshwater ecosystems, in combination with high abundances and biomass, make vibrios key players in aquatic environments, as well as important pathogens for humans and marine animals. Incidents of Vibrio-associated diseases (vibriosis) in marine aquaculture are being increasingly reported on a global scale, due to the fast growth of the industry over the past few decades years. The administration of antibiotics has been the most commonly applied therapy used to control vibriosis outbreaks, giving rise to concerns about development and spreading of antibiotic-resistant bacteria in the environment. Hence, the idea of using lytic bacteriophages as therapeutic agents against bacterial diseases has been revived during the last years. Bacteriophage therapy constitutes a promising alternative not only for treatment, but also for prevention of vibriosis in aquaculture. However, several scientific and technological challenges still need further investigation before reliable, reproducible treatments with commercial potential are available for the aquaculture industry. The potential and the challenges of phage-based alternatives to antibiotic treatment of vibriosis are addressed in this review.

The involvement of cathepsin F gene (CTSF) in turbot (Scophthalmus maximus L.) mucosal immunity

Cathepsin F (CTSF) is a recently described papain-like cysteine protease and unique among cathepsins due to an elongated N-terminal pro-region, which contains a cystatin domain. CTSF likely plays a regulatory role in processing the invariant chain which is associated with the major histocompatibility complex (MHC) class II. In this regard, we identified the CTSF gene of turbot as well as its protein structure, phylogenetic relationships, and expression patterns in mucosal tissues following Vibrio anguillarum and Streptococcus iniae challenge. We also determined the expression patterns of CTSF in mucosal tissues after vaccinated with the formalin-inactivated V. vulnificus whole-cell vaccine. Briefly, turbot CTSF gene showed the closest relationship with that of Paralichthys olivaceus in phylogenetic analysis. And CTSF was ubiquitously expressed in all tested tissues with the highest expression level in gill. In addition, CTSF gene showed different expression patterns following different bacterial challenge. The significant quick regulation of CTSF in mucosal surfaces against infection indicated its roles in mucosal immunity. Functional studies should further characterize avail utilization of CTSF function to increase the disease resistance of turbot in maintaining the integrity of the mucosal barriers against infection and to facilitate selection of the disease resistant family/strain in turbot.

Clinical and environmental genotypes of Vibrio vulnificus display distinct, quorum-sensing-mediated, chitin detachment dynamics

The ability for bacteria to attach to and detach from various substrata is important for colonization, survival and transitioning to new environments. An opportunistic human pathogen, Vibrio vulnificus, can cause potentially fatal septicemia after ingestion of undercooked seafood. Based on genetic polymorphisms, strains of this species are subtyped into clinical (C) and environmental (E) genotypes. Vibrio vulnificus readily associates with chitin, thus we investigated chitin detachment dynamics in these disparate genotypes. We found that C-genotypes detach significantly more than E-genotypes after 24 hours in aerobic as well as anaerobic conditions. Furthermore, expression of genes involved in type IV pilin production was significantly downregulated in C-genotypes compared to E-genotypes, suggesting an importance in detachment. Interestingly, gbpA, a gene that has been shown to be important in host colonization in V. cholerae, was upregulated in the C-genotypes during detachment. Additionally, we found that C-genotypes detached to a greater extent, and produced more quorum-sensing (QS) autoinducer-2 molecules relative to E-genotypes, which suggests a role for QS in detachment. These findings suggest that for V. vulnificus, QS-mediated detachment may be a potential mechanism for transitioning into a human host for C-genotypes, while facilitating E-genotype maintenance in the estuarine environment.

MARTX of Vibrio vulnificus biotype 2 is a virulence and survival factor

Vibrio vulnificus biotype 2 is a polyphyletic group whose virulence for fish relies on a plasmid. This plasmid contains an rtxA gene duplicated in the small chromosome that encodes a MARTX (Multifunctional, Autoprocessing Repeats-in-Toxin) unique within the species in domain structure (MARTX type III). To discover the role of this toxin in the fitness of this biotype in the fish-farming environment, single- and double-knockout mutants were isolated from a zoonotic strain and analysed in a series of in vivo and in vitro experiments with eel, fish cell lines and amoebae isolated from gills. Mice, murine and human cell lines were also assayed for comparative purposes. The results suggest that MARTX type III is involved in the lysis of a wide range of eukaryotic cells, including the amoebae, erythrocytes, epithelial cells and phagocytes after bacterium-cell contact. In fish, MARTX type III may act as a toxin involved in the onset of septic shock, while in mice it may promote bacterial colonization by preventing phagocytosis of bacterial cells. Moreover, this toxin could protect bacteria from predation by amoebae, which would increase bacterial survival outside the host and would explain the fitness of this biotype in the fish-farming environment.

Induction of apoptosis in sea bream fibroblasts by Vibrio harveyi haemolysin and evidence for an anti-apoptotic role of heat shock protein 70

In this study, we exposed black sea bream, Mylio macrocephalus (Basilewsky), fibroblast (BSF) and silver sea bream, Sparus sarba Forsskål, fibroblast (SSF) cell lines to a recombinant Vibrio harveyi haemolysin (VHH) and investigated mechanisms involved in apoptosis. A decrease in mitochondrial membrane potential, followed by an increase in caspase 3 activity, occurred within 2-8 h of VHH exposure, in both cell lines; however, VHH did not alter cellular levels of reactive oxygen species. As heat shock protein 70 (HSP70) is known to prevent the onset of apoptosis in certain mammalian cells, we aimed to test whether such a protective effect is operative in VHH-exposed fibroblasts. The amounts of HSP70 were elevated in SSF and BSF via an acute heat shock or an acute heat shock followed by a 6 h recovery. It was found that the VHH-mediated reduction in mitochondrial membrane potential was suppressed in cells that had a 6 h post-heat shock recovery, and the protective effect of heat shock-induced HSP70 was attenuated following treatment of cells with the HSP70 inhibitor, quercetin. This study demonstrates how haemolysin causes cell death via induction of apoptosis and provides evidence as to the role of HSP70 as an anti-apoptotic factor.

Predictors of mortality in skin and soft-tissue infections caused by Vibrio vulnificus

BACKGROUND

Vibrio vulnificus infection can progress rapidly in skin or soft tissue, and it is potentially life-threatening. The purpose of the present study was to explore the predictors of mortality in patients with V. vulnificus infections of skin or soft tissue.

METHODS

The medical records of 119 consecutive patients aged > or =18 years, hospitalized for V. vulnificus infections of skin or soft tissue between January 2000 and December 2007 were reviewed. Co-morbidities, clinical manifestations, laboratory studies, treatments, and outcomes were analyzed. Multiple logistic regression with the exact method was performed.

RESULTS

The mean age of the patients was 63.7 +/- 12.0 years. Twenty-four patients died, yielding an overall case fatality rate of 20%. Of the 24 deaths, 20 (83%) occurred within 72 h after hospital admission. Of 119 patients, 45 patients had primary septicemia, and 74 patients had wound infection. Multivariate analysis revealed that the following factors were associated with mortality: hemorrhagic bullous skin lesions/necrotizing fasciitis (p = 0.003), primary septicemia (p = 0.042), a greater organ dysfunction and/or infection score (p = 0.005), absence of leukocytosis (p = 0.0001), and hypoalbuminemia (p = 0.003). Treatment with surgical intervention plus antibiotics (p = 0.038) and surgical intervention within 24 h after admission (p = 0.017) were protective factors.

CONCLUSIONS

This study demonstrates that the presence of hemorrhagic bullous skin lesions/necrotizing fasciitis, primary septicemia, a greater severity-of-illness, absence of leukocytosis, and hypoalbuminemia were the significant risk factors for mortality in these patients. Moreover, patients treated with surgery plus antibiotics, especially those receiving a prompt surgical evaluation within 24 h after hospital admission, may have a better prognosis.

Clinical outcomes and prognostic factors for patients with Vibrio vulnificus infections requiring intensive care: a 10-yr retrospective study

OBJECTIVE

Vibrio vulnificus infection is uncommon but potentially life-threatening. The aim of this study was to evaluate clinical outcomes and prognostic factors for patients with V. vulnificus infections admitted to an intensive care unit.

DESIGN

Retrospective study.

SETTING

Multidisciplinary intensive care unit in a 2300-bed teaching hospital.

PATIENTS

Eighty-five adult patients (≥ 18 yrs) with V. vulnificus infections who required intensive care were enrolled and reviewed during a 10-yr period.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Thirty-four of the 85 patients died, giving an intensive care unit mortality rate of 40%. The mean Acute Physiology and Chronic Health Evaluation II score on intensive care unit admission was 18.4 (95% confidence interval, 17.1-19.8). The most common underlying disease was hepatic disease (48%) followed by diabetes mellitus (22%). Multivariate analysis showed that risk factors for intensive care unit mortality were the presence of hemorrhagic bullous skin lesions/necrotizing fasciitis (relative risk, 2.4; 95% confidence interval, 1.3-4.5; p = .006), skin/soft tissue infections involving two or more limbs (relative risk, 2.5; 95% confidence interval, 1.1-5.7; p = .025), and higher Acute Physiology and Chronic Health Evaluation II scores on intensive care unit admission (relative risk, 1.2; 95% confidence interval, 1.1-1.3; p = .0001). In contrast, surgical treatment < 24 hrs after arrival was inversely associated with intensive care unit mortality (relative risk, 0.35; 95% confidence interval, 0.15-0.79; p = .012). In addition, the area under the receiver operating characteristic curve for Acute Physiology and Chronic Health Evaluation II for predicting intensive care unit mortality was 0.945 (95% confidence interval, 0.873-0.983; p = .0001). An optimal cutoff Acute Physiology and Chronic Health Evaluation II score of ≥ 20 had a sensitivity of 97% and a specificity of 86% with a 41.4-fold increased risk of fatality (p = .0003).

CONCLUSIONS

This study found that V. vulnificus-infected patients with hemorrhagic bullous skin lesions/necrotizing fasciitis, skin/soft tissue infections involving two or more limbs, or higher Acute Physiology and Chronic Health Evaluation II scores have high risks of intensive care unit mortality. However, patients receiving prompt surgical treatments within 24 hrs after admission have better prognoses.

Characterization and identification of virulent Klebsiella oxytoca isolated from abalone (Haliotis diversicolor supertexta) postlarvae with mass mortality in Fujian, China

An epidemic of mass mortality of abalone (Haliotis diversicolor supertexta) postlarvae aged 40 days or less has existed across south coast of China since the second half of 2002. Among 20 bacterial strains isolated from diseased abalone postlarvae on 2216E marine agar plates during an outbreak of postlarval disease in August 2005, a predominant strain (designated strain 20) was demonstrated to be virulent to postlarvae with an LD(50) value of 1.0x10(5) colony forming units (CFUml(-1)) on day 4, while the other 19 strains were either avirulent (16 strains) or weakly virulent (3 strains). The same bacterium could be re-isolated from postlarvae after bacterial challenge using 2216E marine agar plates. Preliminary toxicity tests of ECPs of strain 20 revealed that at 2.77mgproteinml(-1), crude ECPs completely liquefied postlarvae within 24h, leaving only shells. API 20E analysis identified strain 20 as Klebsiella oxytoca. 16S and ITS rDNA sequencing and phylogenetic analyses further confirmed this identification. Antibiotic susceptibility tests showed that strain 20 exhibited 94% of susceptibility to 16 various antibiotics tested and only showed resistance to streptomycin. Results of this work demonstrated that K. oxytoca is also linked to this epidemic in Fujian, China. This is considered to be the first report regarding K. oxytoca involved in the mass mortality of postlarval abalone in south China and the world.

A common virulence plasmid in biotype 2 Vibrio vulnificus and its dissemination aided by a conjugal plasmid

Strains of Vibrio vulnificus, a marine bacterial species pathogenic for humans and eels, are divided into three biotypes, and those virulent for eels are classified as biotype 2. All biotype 2 strains possess one or more plasmids, which have been shown to harbor the biotype 2-specific DNA sequences. In this study we determined the DNA sequences of three biotype 2 plasmids: pR99 (68.4 kbp) in strain CECT4999 and pC4602-1 (56.6 kb) and pC4602-2 (66.9 kb) in strain CECT4602. Plasmid pC4602-2 showed 92% sequence identity with pR99. Curing of pR99 from strain CECT4999 resulted in loss of resistance to eel serum and virulence for eels but had no effect on the virulence for mice, an animal model, and resistance to human serum. Plasmids pC4602-2 and pR99 could be transferred to the plasmid-cured strain by conjugation in the presence of pC4602-1, which was self-transmissible, and acquisition of pC4602-2 restored the virulence of the cured strain for eels. Therefore, both pR99 and pC4602-2 were virulence plasmids for eels but not mice. A gene in pR99, which encoded a novel protein and had an equivalent in pC4602-2, was further shown to be essential, but not sufficient, for the resistance to eel serum and virulence for eels. There was evidence showing that pC4602-2 may form a cointegrate with pC4602-1. An investigation of six other biotype 2 strains for the presence of various plasmid markers revealed that they all harbored the virulence plasmid and four of them possessed the conjugal plasmid in addition.

Role of the metalloprotease Vvp and the virulence plasmid pR99 of Vibrio vulnificus serovar E in surface colonization and fish virulence

The virulence for eels of Vibrio vulnificus biotype 2 serovar E (VSE) is conferred by a plasmid that codifies ability to survive in eel serum and cause septicaemia. To find out whether the plasmid and the selected chromosomal gene vvp plays a role in the initial steps of infection, the VSE strain CECT4999, the cured strain CT218 and the Vvp-deficient mutant CT201 (obtained in this work by allelic exchange) were used in colonization and virulence experiments. The eel avirulent biotype 1 (BT1) strain YJ016, whose genome has been sequenced, was used for comparative purposes. The global results demonstrate that the plasmid does not play a significant role in surface colonization because (i) CECT4999 and CT218 were equally chemoattracted towards and adherent to eel mucus and gills, and (ii) CT218 persisted in gills from bath-infected eels 2 weeks post infection. In contrast, mutation in vvp gene reduced significantly chemoattraction and attachment to eel mucus and gills, as well as virulence degree by immersion challenge. Co-infection experiments by bath with CECT4999 and CT201 confirmed that Vvp was involved in eel colonization and persistence in gills, because CECT4999 was recovered at higher numbers compared with CT201 from both internal organs of moribund fish (ratio 4:1) and gills from survivors (ratio 50:1). Interestingly, YJ016 also showed chemoattraction and attachment to mucus, and complementation of CT201 with BT1-vvp gene restored both activities together with virulence degree by immersion challenge. Additional experiments with algae mucus and purified mucin gave similar results. In conclusion, the protease Vvp of V. vulnificus seems to play an essential role in colonization of mucosal surfaces present in aquatic environments. Among the V. vulnificus strains colonizing fish mucus, only those harbouring the plasmid could survive in blood and cause septicaemia.

The eel immune system: present knowledge and the need for research

The European eel, Anguilla anguilla, is one of the most important warm water fish species cultured in southern Europe and the Mediterranean as well as in northern countries including Germany, the Netherlands and Denmark. The Japanese eel, A. japonica, is an important cultured fish in several Asiatic countries including Japan, China and Taiwan. During recent decades, research has been performed to elucidate the immune response of these species against different pathogens (viruses, bacteria or parasites). Nevertheless, there is very limited information in terms of both cellular and humoral immune responses. This review summarizes the present knowledge relating to the eel immune system and includes new data.

Modulation of beta-actin, insulin-like growth factor 1 and glucose-6-phosphate dehydrogenase gene expression during vibriosis of sea bream, Sparus (=Rhabdosargus) sarba Forsskål

Gene expression changes, related to growth regulation, were investigated in silver sea bream, Sparus (=Rhabdosargus) sarba, subjected to vibriosis. Using reverse transcriptase polymerase chain reaction assays, transcript levels of beta-actin, insulin-like growth factor 1 (IGF-1) and glucose-6-phosphate dehydrogenase (G6PDH) were analysed. A tissue-specific response for beta-actin was found, as transcript levels in the kidney increased during early- and mid-stage vibriosis, but remained unchanged in liver tissue. The gene transcript levels of IGF-1 were found to decrease in both liver and kidney from an early stage of vibriosis. The gene transcript levels of G6PDH increased at early and mid stages of vibriosis in liver and kidney before decreasing during the late stage of vibriosis. Further studies on G6PDH demonstrated that chemical inhibition of G6PDH in silver sea bream fibroblasts resulted in increased cell death upon exposure to hydrogen peroxide. The results from the present study demonstrate the complexity of growth-related gene expression events that occur in fish tissues during disease.

Evidence for disruption of Na(+)-K(+)-ATPase and hsp70 during vibriosis of sea bream, Sparus (=Rhabdosargus) sarba Forsskål

Osmoregulation via the sodium pump (Na(+)-K(+)-ATPase) and cytoprotection via expression of different families of heat shock protein (hsp) were studied at transcriptional/translational levels during progressive vibriosis in silver sea bream, Sparus (=Rhabdosargus) sarba Measurements of Na(+)-K(+)-ATPase activity showed that an early and drastic decline occurred in the kidney of infected fish. This reduction in Na(+)-K(+)-ATPase activity was not caused by transcriptional downregulation of genes coding for either the Na(+)-K(+)-ATPase alpha or beta subunits. Using specific antibodies, data from immunoassays showed that the decreased sodium pump activity was caused by the specific loss of the translated glycosylated Na(+)-K(+)-ATPase beta subunit. Data from immunoassays of different hsp families demonstrated that the expression of hsp90 and hsp60 remained unchanged throughout vibriosis whereas expression of the hsp70 family decreased in kidney and liver tissues. As hsp70 is a multigene family, the expression of the constitutive (hsc70) and inducible (hsp70) members of the hsp70 family were studied and it was found that hsp70 and hsc70 expression decreased from an early stage of infection in the kidney and the liver respectively. Reverse transcriptase-polymerase chain reaction analysis of the hsp70 transcription-inducing factor, hsf1, demonstrated that loss of cytoprotective function during vibriosis was mediated by a downregulation of hsf1 transcription.

Immunogenic antigens of the eel pathogen Vibrio vulnificus serovar E

The immunogenic antigens of Vibrio vulnificus serovar E were investigated in the eel. Fish were vaccinated by immersion with Vulnivaccine (V), revaccinated 2 years later by intraperitoneal injection (RV) and bath infected 15 days post-revaccination (RVI). The specific immune response in serum was followed in all groups, and selected sera were used for immunostaining of surface (SA) and extracellular antigens (ECA). Bacteria were grown in iron-rich (TSB and MSWYE) and iron-poor media (TSB and MSWYE plus human transferrin (TSB-T and MSWYE-T)) as well as eel serum (ES), and their SA and ECA were extracted and electrophoretically analysed. Cells grown in MSWYE-T and ES presented the same antigenic profiles, which suggests that iron-restriction is the main growth-limiting factor in vivo. The electrophoretic pattern of SA, but not that of ECA, varied with iron-availability in the growth medium. Further, SA extracted from bacteria grown in iron restriction were strongly immunogenic for eels, especially after vaccination and infection. Among the immunogenic antigens over expressed in iron-restriction, three outer membrane proteins of around 70-80 kDa, including the putative receptor for vulnibactin, together with the rapid and slow migrating forms of the lipopolysaccharide (LPS), were identified. The response was not so evident in the case of capsule, which was not clearly stained with any of the eel sera. With respect to ECA, two proteins, identified as the V. vulnificus protease (Vvp) and the major outer membrane protein (OMP), probably liberated to the medium after cell death, were recognised by RV and, more strongly, by RVI sera. The specific antibodies against the mentioned OMPs, LPS bands and the Vvp may contribute to the protection of vaccinated eels against infection, giving a reasonable explanation for the high effectiveness of Vulnivaccine.

Influence of aquatic microbiota on the survival in water of the human and eel pathogen Vibrio vulnificus serovar E

The eel and human pathogen Vibrio vulnificus serovar E (biotype 2) is seldom isolated from natural waters, although it can survive in sterilized artificial seawater microcosms for years. The main objective of the present study was to investigate whether aquatic microbiota can limit its survival and recovery from water samples. A set of preliminary experiments of survival in microcosms containing natural seawater and water from eel farms showed that the persistence of this pathogen was mainly controlled by grazing, and secondarily by bacterial competition. The bacterial competition was further analysed in artificial seawater microcosms co-inoculated with selected virulent serovar E (VSE) strains and potential competitors. Competitors included V. vulnificus biotype 1 isolates and strains of selected species that can grow on the selective media designed for V. vulnificus isolation from water samples. Evidences of bacterial competition that was detrimental for VSE recovery were recorded. Thus, some species produced a deleterious effect on VSE strains under starvation, and others were able to use the resources more efficiently under nutrient input. These results suggest that an overgrowth of more efficient competitor bacteria in conventional media used for isolation of V. vulnificus could mask the recovery of VSE strains and explain the scarcity of reports on the isolation of this human and eel pathogen from natural waters.

A fatal case of Vibrio vulnificus meningoencephalitis

The objective of this paper is to report a rare case of Vibrio vulnificus presenting as meningoencephalitis without a wound infection. Vibrio vulnificus is capable of causing severe and often fatal infections in susceptible individuals. It commonly causes necrotizing wound infections, primary septicemia, and gastroenteritis. A 69-year-old man had meningoencephalitis with lesion on the red nucleus, substantia nigra, basal ganglia, and dentate nucleus as the initial clinical manifestation of a V. vulnificus infection. This is the first case of V. vulnificus infection in which MRI demonstrated the involvement of deep nuclei of the brain.

Vibrio species isolated from diseased farmed sole, Solea senegalensis (Kaup), and evaluation of the potential virulence role of their extracellular products

Bacteria isolated from an outbreak with moderate mortalities in farmed sole, Solea senegalensis (Kaup), in the south of Spain were identified as Vibrio harveyi and V. parahaemolyticus. Only bacterial strains showing swarming were virulent in sole and caused mortalities in experimentally inoculated fish. However, the signs of the disease were only reproduced with V. harveyi. The intramuscular inoculation of the extracellular products (ECPs) of both species produced mortalities in inoculated fish and the appearance of surface ulcers in the case of V. harveyi. However, the inoculation of sublethal doses of ECPs to fish showed a protective effect against V. harveyi.

Adaptation of an [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay to evaluate the cytotoxicity of the extracellular products of micro-organisms pathogenic to fish

AIMS

Adaptation of a colorimetric assay using [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] (MTT) to evaluate the cytotoxicity of the extracellular products of micro-organisms pathogenic to fish.

METHODS AND RESULTS

The optimal conditions for the colorimetric assay were determined and this method was compared with the trypan blue exclusion assay. The protein concentration of extracellular products causing the death of 50% of the cell population (CI50) was determined.

CONCLUSIONS

This assay enables quantitative and objective comparison of the cytotoxicity of the extracellular products of micro-organisms pathogenic to fish. It was shown to be more accurate than conventional counting with the trypan blue exclusion assay.

SIGNIFICANCE AND IMPACT OF THE STUDY

This method may also be useful for characterizing the cytotoxicity of specific components of extracellular products.

Vibrio vulnificus infection complicated by acute respiratory distress syndrome in a child with nephrotic syndrome

A 9-year-old girl with nephrotic syndrome visited a local hospital after developing fever, chills, and edematous changes and multiple hemorrhagic bullae on both legs over 2 days. Cultures of blood and an aspirate from the bullae yielded Vibrio vulnificus. The patient was transferred to our hospital because of persistent fever, generalized edema, acute renal failure, and disseminated intravascular coagulopathy. We treated this patient as a V. vulnificus infection complicated with necrotizing fasciitis. With minocycline and ceftazidime combination therapy was instituted. Emergency fasciotomy and continuous peritoneal dialysis were performed. The patient developed acute respiratory distress syndrome (ARDS) during the hospitalization, requiring intubation and mechanical ventilation. She eventually died. The histopathological findings showed diffuse alveolar damage with lobular pneumonitis. Hyaline membranes, composed of proteinaceous exudate and cellular debris, covered the alveolar surfaces. Microscopic examinations of lung could not distinguish the effects of cytolysin from other insults to lungs that occur in ARDS. This report highlights the postmortem pathological findings in V. vulnificus infection in a child with nephrotic syndrome complicated by ARDS.

Isolation of Vibrio vulnificus serovar E from aquatic habitats in Taiwan

The existence of strains of Vibrio vulnificus serovar E that are avirulent for eels is reported in this work. These isolates were recovered from water and oysters and differed from eel virulent strains in (i) fermentation and utilization of mannitol, (ii) ribotyping after HindIII digestion, and (iii) susceptibility to eel serum. Lipopolysaccharide of these strains lacked the highest molecular weight immunoreactive bands, which are probably involved in serum resistance.

Comparative study of biological properties and electrophoretic characteristics of lipopolysaccharide from eel-virulent and eel-A virulent Vibrio vulnificus strains

In Vibrio vulnificus, virulence for eels is associated with serovar E strains. In this study, we investigated some biological properties of purified lipopolysaccharides (LPSs) from serovar E and non-serovar E strains. Purified LPSs retained their O-polysaccharidic side chains and did not show any differences that could be related to host specificity, except for serological differences.

Heterogeneity among isolates of Vibrio vulnificus recovered from eels (Anguilla anguilla) in Denmark

The findings of this study demonstrate that Vibrio vulnificus isolates recovered from diseased eels in Denmark are heterogeneous as shown by O serovars, capsule types, ribotyping, phage typing, and plasmid profiling. The study includes 85 V. vulnificus isolates isolated from the gills, intestinal contents, mucus, spleen, and kidneys of eels during five disease outbreaks on two Danish eel farms from 1995 to 1997, along with a collection of 12 V. vulnificus reference strains. The results showed that more than one serovar may be capable of causing disease in eels and that these isolates are genetically heterogenous as shown by ribotyping. Ribotyping also showed that the same isolates may persist in an eel farm and cause recurrent outbreaks. Phage typing did not correlate with ribotyping or serotyping. However, we observed that 26 of 28 isolates, which were not susceptible to any of the phages, showed the same ribotype, O serovar, and capsule type. This suggests that these isolates may possess features that make them resistant to lysis by the phages used in this study. Ninety-three of 97 isolates harbored between one and three high-molecular-weight plasmids which previously had been suggested to be associated with eel virulence. The subdivision of V. vulnificus into two biotypes based on the indole reaction can no longer be supported, since 82 of 97 isolates in this study were indole positive, and a subdivision into serovars appears to be more correct.

Pathogenicity of Vibrio alginolyticus for cultured gilt-head sea bream (Sparus aurata L.)

The in vivo and in vitro pathogenic activities of whole cells and extracellular products of Vibrio alginolyticus for cultured gilt-head sea bream were evaluated. The 50% lethal doses ranged from 5.4 x 10(4) to 1.0 x 10(6) CFU/g of body weight. The strains examined had the ability to adhere to skin, gill, and intestinal mucus of sea bream and to cultured cells of a chinook salmon embryo cell line. In addition, the in vitro ability of V. alginolyticus to adhere to mucus and skin cells of sea bream was demonstrated by scanning electron microscopy. The biological activities of extracellular products of V. alginolyticus were hydrolytic activities; the products were able to degrade sea bream mucus. V. alginolyticus was cytotoxic for fish cell lines and lethal for sea bream. Moreover, the extracellular products could degrade sea bream tissues. However, experiments performed with the bath immersion inoculation technique demonstrated that V. alginolyticus should be considered a pathogen for sea bream only when the mucus layer is removed and the skin is damaged.

Neurotoxic effect on two fish species and a PC12 cell line of the supernate of Vibrio alginolyticus and Vibrio anguillarum

The biological effects of supernates obtained from different strains of Vibrio alginolyticus and Vibrio anguillarum isolated from diseased fish have been studied by inoculation on two fish species, eel and rainbow trout, and two fish cell lines. These supernates possess neuroexcitatory properties, and so, when they are injected into both fish species, they trigger convulsions, wriggling, contortive swimming and respiratory arrest coupled with increased respiratory reflex. Furthermore, after the application of the supernates on cultures of noradrenergic pheochromocytoma PC12 cells, an increase of acetylcholine, released from the cells was obtained. The amount of released acetylcholine depends on the source of assayed supernates and on the dose applied to the cells. On the basis of the results obtained with PC12 cells, we suggest that the supernates from pathogenic Vibrio strains injected into fish may elicit an increased release of acetylcholine in the motor endplate of some muscles related to locomotion and ventilation of the inoculated fish.

Occurrence of Vibrio vulnificus biotypes in Danish marine environments

During the unusually warm summer in Denmark in 1994, 11 clinical cases of Vibrio vulnificus infection were reported. These reports initiated an investigation of the occurrence of V. vulnificus biotypes in Danish marine environments. Samples of coastal water, sediment, shellfish, and wild fish were analyzed by preenrichment in alkaline peptone water amended with polymyxin B (2.0 x 10(4) U/liter) followed by streaking onto modified cellobiose-polymyxin B-colistin agar. V. vulnificus-like colonies were tested with a V. vulnificus-specific DNA probe. Low densities of V. vulnificus were detected in water (0.8 to 19 CFU/liter) from June until mid-September and in sediment (0.04 to > 11 CFU/g) from July until mid-November. The presence of V. vulnificus was strongly correlated with water temperature. However, we isolated V. vulnificus from water from a mussel farm at a lower temperature than previously reported (7 degrees C). In 1 of the 13 locations studied, V. vulnificus was found in mussels in 7 of 17 samples analyzed; this is the first report of V. vulnificus in European shellfish. V. vulnificus was also isolated from gills, intestinal contents, and mucus from wild fish. Although biotyping of 706 V. vulnificus strains isolated during our investigations revealed that the majority of the strains (99.6%) belonged to biotype 1, biotype 2 was detected in seawater at a low frequency (0.4%). Our findings provide further evidence that seawater can serve as a reservoir and might facilitate spread of V. vulnificus biotype 2 to eels, with subsequent spread to persons handling eels. In conclusion, our data demonstrate that V. vulnificus is ubiquitous in a temperature marine environment and that V. vulnificus biotype 2 is not strictly confined to eels.

The lipopolysaccharide O side chain of Vibrio vulnificus serogroup E is a virulence determinant for eels

Vibrio vulnificus is a gram-negative bacterium capable of producing septicemic infections in eels and immunocompromised humans. Two biotypes are classically recognized, with the virulence for eels being specific to strains belonging to biotype 2, which constitutes a homogeneous lipopolysaccharide (LPS)-based O serogroup (which we have designated serogroup E). In the present study we demonstrated that the O side chain of this LPS determines the selective virulence of biotype 2 for eels: (i) biotype 1 strains (which do not belong to serogroup E) are destroyed by the bactericidal action of nonimmune eel serum (NIS) through activation of the alternative pathway of complement, (ii) biotype 2 strains (of serogroup E) are resistant to NIS, and (iii) rough mutants of biotype 2 lacking the O polysaccharide side chain are sensitive to NIS and avirulent for eels.

Phenotypic and genotypic characterization of Vibrio vulnificus: proposal for the substitution of the subspecific taxon biotype for serovar

The classification of Vibrio vulnificus strains into two biotypes has been maintained on the basis of phenotypic properties and eel virulence. Biotype 2 is virulent for eels, negative for the indole reaction, and serologically homogeneous (serogroup E), whereas strains of biotype 1 are avirulent, indole positive, and serologically heterogeneous. In the present study, we phenotypically and genotypically characterized 21 V. vulnificus isolates, recovered mainly from northern Europe, by comparing them with reference strains of both biotypes to look for new isolates of biotype 2. The results of this work revealed that the majority of isolates virulent for eels presented phenotypic traits previously considered characteristics of biotype 2 and specific ribotypes with HindIII. However, among the new isolates we found (i) a serogroup E strain virulent for eels but indole positive and (ii) one isolate not belonging to serogroup E but pathogenic for eels. Since no biochemical test for specific serogroup can with certainty be associated with eel virulence, we propose to classify V. vulnificus strains into serovars instead of biotypes. Thus, we suggest serovar E as the denomination of those strains previously classified as biotype 2. Finally, the occurrence of serogroup E in eels cultured in Norway and Sweden, as well as from human infections and shrimp, has been demonstrated.

An enzyme-linked immunosorbent assay for detection of Vibrio vulnificus biotype 2: development and field studies

Vibrio vulnificus biotype 2 is a primary eel pathogen which constitutes a lipopolysaccharide (LPS)-based homogeneous O serogroup within the species. In the present work, we have developed an enzyme-linked immunosorbent assay (ELISA) based on the specificity of LPS for the detection of this pathogen. The ELISA specificity was confirmed after testing 36 biotype 2 strains from laboratory cultures and environmental samples, 31 clinical and environmental biotype 1 isolates, and several strains of Vibrio, Aeromonas, and Yersinia species, including the fish pathogens V. anguillarum, V. furnissii, A. hydrophila, and Y. ruckerii. The detection limits for biotype 2 cells were around 10(4) to 10(5) cells/well, and the immunoassay was also able to detect cells in the nonculturable state. Artificially infected eels and environmental samples were analyzed, and the immunodetection was confirmed by cultural methods (isolation on selective and nonselective media before and after broth enrichment). With this methodology, V. vulnificus biotype 2 was successfully detected in infected eels and asymptomatic carriers, which suggests that eels can act as a reservoir for this pathogen.