Human gut microbiome, diet, and mental disorders

Diet is one of the most important external factor shaping the composition and metabolic activities of the gut microbiome. The gut microbiome plays a crucial role in host health, including immune system development, nutrients metabolism, and the synthesis of bioactive molecules. In addition, the gut microbiome has been described as critical for the development of several mental disorders. Nutritional psychiatry is an emerging field of research that may provide a link between diet, microbial function, and brain health. In this study, we have reviewed the influence of different diet types, such as Western, Mediterranean, vegetarian, and ketogenic, on the gut microbiota composition and function, and their implication in various neuropsychiatric and psychological disorders.

An updated overview on the relationship between human gut microbiome dysbiosis and psychiatric and psychological disorders

There is a lot of evidence establishing that nervous system development is related to the composition and functions of the gut microbiome. In addition, the central nervous system (CNS) controls the imbalance of the intestinal microbiota, constituting a bidirectional communication system. At present, various gut-brain crosstalk routes have been described, including immune, endocrine and neural circuits via the vagal pathway. Several empirical data have associated gut microbiota alterations (dysbiosis) with neuropsychiatric diseases, such as Alzheimer's disease, autism and Parkinson's disease, and with other psychological disorders, like anxiety and depression. Fecal microbiota transplantation (FMT) therapy has shown that the gut microbiota can transfer behavioral features to recipient animals, which provides strong evidence to establish a causal-effect relationship. Interventions, based on prebiotics, probiotics or synbiotics, have demonstrated an important influence of microbiota on neurological disorders by the synthesis of neuroactive compounds that interact with the nervous system and by the regulation of inflammatory and endocrine processes. Further research is needed to demonstrate the influence of gut microbiota dysbiosis on psychiatric and psychological disorders, and how microbiota-based interventions may be used as potential therapeutic tools.

Immune response of DNA vaccinated-gilthead seabream (Sparus aurata) against LCDV-Sa infection: relevance of the inflammatory process

Lymphocystis disease is one of the main viral pathologies affecting cultured gilthead seabream (Sparus aurata) in the Mediterranean region. Recently, we have developed a DNA vaccine based on the major capsid protein (MCP) of the Lymphocystis disease virus 3 (LCDV-Sa). The immune response triggered by either LCDV-Sa infection or vaccination have been previously studied and seem to be highly related to the modulation of the inflammatory and the IFN response. However, a comprehensive evaluation of immune-related gene expression in vaccinated fish after viral infection to identify immunogenes involved in vaccine-induced protection have not been carried out to date. The present study aimed to fulfill this objective by analyzing samples of head-kidney, spleen, intestine, and caudal fin from fish using an OpenArray® platform containing targets related to the immune response of gilthead seabream. The results obtained showed an increase of deregulated genes in the hematopoietic organs between vaccinated and non-vaccinated fish. However, in the intestine and fin, the results showed the opposite trend. The global effect of fish vaccination was a significant decrease (p<0.05) of viral replication in groups of fish previously vaccinated, and the expression of the following immune genes related to viral recognition (tlr9), humoral and cellular response (rag1 and cd48), inflammation (csf1r, elam, il1β, and il6), antiviral response (isg15, mx1, mx2, mx3), cell-mediated cytotoxicity (nccrp1), and apoptosis (prf1). The exclusive modulation of the immune response provoked by the vaccination seems to control the progression of the infection in the experimentally challenged gilthead seabream.

Evaluation of Gilthead Seabream (Sparus aurata) Immune Response after LCDV-Sa DNA Vaccination

Simple Summary

Lymphocystis disease is the main viral pathology in gilthead seabream aquaculture. Currently, there are no treatments or vaccines to control this disease, thus our main goal was to construct a DNA vaccine that can be used in the future to stop the spread of this pathology in sea farms. The vaccine consisted of a plasmid DNA that contains a known viral gene. Once it was established that the vaccine drives the expression of the antigenic viral protein in fish, vaccination experiments were conducted to determine if the vaccinated fish become protected against the viral infection. In addition, the immune response triggered by the vaccine was also evaluated in order to understand the mechanisms underlying such protection. The obtained results showed that in vaccinated fish an activation of several genes relating to both the inflammatory process and the mucosal immunity were produced, as well as specific anti-viral antibodies. Although limited, our results deserve further investigation to assess the efficacy of the vaccine in bigger fish populations and to confirm the mode of action of the vaccine.

Abstract

Lymphocystis disease is the main viral pathology reported in gilthead seabream. Its etiological agent is Lymphocystis disease virus 3 (LCDV-Sa), genus Lymphocystivirus, family Iridoviridae. There are no effective treatments or vaccines for LCDV control, thus the main aim of this study was to develop a DNA vaccine, and to evaluate both the protection conferred against LCDV-Sa infection and the immune response in vaccinated fish. The vaccine was constructed by cloning the mcp gene (ORF LCDVSa062R) into pcDNA3.1/NT-GFP-TOPO. Two independent vaccination trials were conducted. In the first one, 5–7 g fish were intramuscularly injected with the vaccine (pcDNA-MCP) or the empty-plasmid, and the distribution and expression of the vaccine was investigated. Furthermore, vaccinated fish were challenged with LCDV-Sa in order to access the protective capacity of the vaccine. In the second trial, 70–100 g fish were vaccinated as specified, and the immune response was evaluated analyzing the expression of 23 immune-related genes and the production of specific antibodies. The results showed that the vaccine triggers an immune response characterized by the overexpression of genes relating to the inflammatory process, but not the innate antiviral immunity relating to type I IFN (interferon), and also induces the production of specific neutralizing antibodies, which could explain the protection against LCDV-Sa in vaccinated fish.

Persistence of Lymphocystis Disease Virus (LCDV) in Seawater

Lymphocystis disease virus (LCDV), the causative agent of lymphocystis disease (LCD), is a waterborne pathogen that uses the external surfaces, including the gills, as portals to gain access to fish host. However, there are no data on LCDV persistence in the aquatic environment. In this study, the persistence of LCDV in natural (raw), treated (autoclaved and filtered) and synthetic seawater held at 22 and 18 °C has been evaluated. The estimated T₉₉ values for LCDV in seawater ranged from 2.7 to 242 days depending on seawater type and temperature, with the highest value recorded at 22 °C in autoclaved seawater. Microbiota and temperature seem to be the main factors affecting the persistence of LCDV in seawater. The results indicated that LCDV is more stable in treated seawater than most of the fish pathogenic viruses studied so far, supporting the relevance of this medium for the prevalence of LCD in fish farms.

Virulence properties of three new Photobacterium species affecting cultured fish

AIMS

Several virulence factors of three new Photobacterium species: Photobacterium toruni, Photobacterium malacitanum and Photobacterium andalusiense associated with diseases of cultured redbanded seabream (Pagrus auriga) were studied. The exoenzymatic activities, adherence and cytotoxic capabilities, and iron-uptake mechanisms were determined both in bacterial extracellular products (ECP) and whole bacterial cells. The histopathology damages provoked on redbanded seabream by the ECP was also studied.

METHODS AND RESULTS

The highest exoenzymatic activities of the ECP were alkaline- and acid-phosphatase, phosphohydrolase and lipase. The ECP were strongly lethal for fish at 4-96 h post-inoculation (p.i). Histological changes were evident at 96 hpi of ECP, affecting head kidney, splenic parenchyma and heart. Cytotoxicity assays, on three fish lines and one human cell line, were conducted using whole bacterial cells and their ECP. The new species tested were cytotoxic only for fish cell lines using whole bacterial cells. Bacterial adherence showed an adherence index moderate on CHSE-214 cell line. All strains showed variable haemolytic activity, and were able to grow under iron-limiting conditions, although the CAS reactivitiy was very low. However, all strains produced high amounts of extracelullar citrate that could be used as iron carrier, and use haem as iron source, except the P. toruni strains because a deletion in the genomic region encoding this ability in all Vibrionaceae members.

CONCLUSIONS

The toxic activity of the bacterial ECPs was thermolabile, and not associated with their thermoresistant lipopolysaccharide content. The virulence of the strains tested could not be related to the haemolytic activity. Iron uptake could be based on the use of endogenous citrate as iron carrier and P. toruni lacks the ability to use haem as iron source.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study analyses for the first time the virulence properties of three new species of Photobacterium pathogenic for fish.

Immune gene expression in gilthead seabream (Sparus aurata) after Lymphocystis disease virus (LCDV-Sa) challenge resulting in asymptomatic infection

AIMS

To determine the immune gene expression response of gilthead seabream (Sparus aurata) that is experimentally infected with the lymphocystivirus LCDV-Sa.

METHODS AND RESULTS

Viral DNA and transcripts were detected by qPCR in all samples from fish injected with LCDV-Sa, demonstrating that the virus establish a systemic and asymptomatic infection. The expression of 23 immune-related genes was also analysed by RT-qPCR in the head kidney (HK) and intestine at several times post-infection (dpi). In HK, the expression of five type I interferon (IFN)-related genes (ifn, irf3, mx2, mx3 and isg15), il10 and ck10 was upregulated at 1-3 dpi, while genes related to the inflammation process (tnfα, il1ß, il6, casp1) were not differentially expressed or even downregulated. The expression profile in the intestine was different regarding type I INF-related genes. An upregulated c3 and ighm expression was observed in both HK and intestine at 3-8 dpi. Finally, the transcription of nccrp1 and mhcIIα was induced in HK, whereas tcrβ expression was downregulated in both organs.

CONCLUSIONS

LCDV-Sa seems to trigger an immune response in gilthead seabream characterized by a partial activation of type I IFN system and a lack of systemic inflammatory response which may be related to viral persistence.

SIGNIFICANCE AND IMPACT OF THE STUDY

The immune response observed in gilthead seabream infected by LCDV-Sa could be implicated in the establishment of an asymptomatic persistent infection.

Feed and immersion challenges with lymphocystis disease virus (LCDV) reveals specific mechanisms for horizontal transmission and immune response in senegalese sole post-larvae

The horizontal transmission of lymphocystis disease virus (LCDV) through contaminated water and feed (using artemia as vehicle) and the associated immune gene expression profiles in Senegalese sole post-larvae were investigated. All specimens analyzed were positive for LCDV DNA detection at 1-day post-challenge (1 dpc) with the highest viral levels in specimens infected through the immersion route. However, the percentage of LCDV-positive animals and number of viral DNA copies dropped progressively at 2 and 7 dpc. The histological analysis identified structural changes in the skin, muscle and gills of sole post-larvae LCDV-challenged by immersion. In situ hybridization confirmed a wide distribution of LCDV in the skin, gut, surrounding vessels in trunk muscle and head kidney in the immersion route, while the signals were restricted to the liver and lamina propria in the feeding treatment. Expression analysis using a set of 22 genes related to innate immune defense system demonstrated clear differences in the time-course response to LCDV as function of the infection route. Most antiviral defense genes, the proinflammatory cytokines, the complement c3, g-type lysozyme and T-cell markers cd4 and cd8a were rapidly induced in the feeding-infected post-larvae, and they were remained activated at 2 dpc. In contrast, in the immersion-infected post-larvae the induction of most defensive genes was delayed, with a low intensity at 2 dpc. All these data demonstrate that LCDV can horizontally infect Senegalese sole post-larvae through the water or feed although with different patterns of histopathological disorders, virus distribution and route-specific expression profiles.

Revisiting the genus Photobacterium: taxonomy, ecology and pathogenesis

The genus Photobacterium, one of the eight genera included in the family Vibrionaceae, contains 27 species with valid names and it has received attention because of the bioluminescence and pathogenesis mechanisms that some of its species exhibit. However, the taxonomy and phylogeny of this genus are not completely elucidated; for example, P. logei and P. fischeri are now considered members of the genus Aliivibrio, and previously were included in the genus Vibrio. In addition, P. damselae subsp. piscicida was formed as a new combination for former Vibrio damsela and Pasteurella piscicida. Moreover, P. damselae subsp. damselae is an earlier heterotypic synonym of P. histaminum. To avoid these incovenences draft and complete genomic sequences of members of Photobacterium are increasingly becoming available and their use is now routine for many research laboratories to address diverse goals: species delineation with overall genomic indexes, phylogenetic analyses, comparative genomics, and phenotypic inference. The habitats and isolation source of the Photobacterium species include seawater, sea sediments, saline lake waters, and a variety of marine organisms with which the photobacteria establish different relationships, from symbiosis to pathogenic interactions. Several species of this genus contain bioluminescent strains in symbiosis with marine fish and cephalopods; in addition, other species enhance its growth at pressures above 1 atmosphere, by means of several high-pressure adaptation mechanisms and for this, they may be considered as piezophilic (former barophilic) bacteria. Until now, only P. jeanii, P. rosenbergii, P. sanctipauli, and the two subspecies of P. damselae have been reported as responsible agents of several pathologies on animal hosts, such as corals, sponges, fish and homeothermic animals. In this review we have revised and updated the taxonomy, ecology and pathogenicity of several members of this genus. [Int Microbiol 20(1): 1-10 (2017)].

Lymphocystis disease virus (LCDV-Sa), polyomavirus 1 (SaPyV1) and papillomavirus 1 (SaPV1) in samples of Mediterranean gilthead seabream

Lymphocystis disease, caused by the iridovirus lymphocystis disease virus (LCDV), is characterized by the appearance of tumour-like lesions on the skin of affected animals associated with several environmental factors and/or with stress due to the intensive culture conditions of fish farms. In a previous study, the genomes of a new LCDV species, LCDV-Sa, were detected, together with 2 previously unknown viruses, Sparus aurata papillomavirus 1 (SaPV1) and Sparus aurata polyomavirus 1 (SaPyV1). Gilthead seabream from 17 fish farms in Spain, Italy and Turkey were sampled between 2009 and 2015 to investigate the role of the newly described SaPV1 and SaPyV1 viruses in lymphocystis disease development. Our results show that in diseased fish, either or both of the new viruses are almost invariably detected together with LCDV (98%). In asymptomatic fish, these viruses were detected in a much lower percentage (28%) and mostly in concurrence with LCDV (24%). These data confirm the suspected association among the 3 different viruses during lymphocystis disease development in gilthead seabream and warrant future studies to establish their respective contributions.

Differential antiviral activity of European sea bass interferon-stimulated 15 protein (ISG15) against RGNNV and SJNNV betanodaviruses

ISG15 is an antiviral protein acting intracellularly, by conjugation to viral or cellular proteins, or extracellularly, as cytokine. In this work, an in vitro system, consisting of E-11 cells over-expressing European sea bass ISG15 (Dl_ISG15_E11 cells), has been developed to evaluate the European sea bass ISG15 protein activity against RGNNV and SJNNV isolates. Regarding RGNNV, RNA2 copy number and viral titres were similar in E-11 and Dl_ISG15_E11 cells, and the cellular survival analyses demonstrated that Dl_ISG15_E11 cells were not protected from this virus. In contrast, ISG15 compromises SJNNV replication, since a reduction of the SJNNV genome synthesis has been recorded. The ISG15 anti-SJNNV activity was confirmed by viral titration and survival assays. In addition, a role of the intracellular ISG15 in modulating the transcription of endogenous genes has being recorded, with tlr3 gene being knocked out and e3 gene being up-regulated in RGNNV-inoculated Dl_ISG15_E11 cells. Sea bass ISG15 has also been detected extracellularly, and its activity has been evaluated by co-culture. The survival rate of RGNNV-inoculated E-11 cells increased from 25% to 46% when they were co-cultured with ISG15-producing cells. Similarly, the survival rate of SJNNV-inoculated E-11 cells increased from 27% to 51% in co-culture with ISG15-producing cells. To our knowledge, this is the first description of a differential antiviral activity of an ISG15 protein against two betanodavirus species, and the first evaluation of the cytokine-like activity of a fish ISG15 protein on non-immune cells.

Modification of betanodavirus virulence by substitutions in the 3' terminal region of RNA2

Betanodaviruses have bi-segmented positive-sense RNA genomes, consisting of RNAs 1 and 2. For some members of the related genus alphanodavirus, the 3' terminal 50 nucleotides (nt) of RNA2, including a predicted stem-loop structure (3'SL), are essential for replication. We investigate the possible existence and role of a similar structure in a reassortant betanodavirus strain (RGNNV/SJNNV). In this study, we developed three recombinant strains containing nucleotide changes at positions 1408 and 1412. Predictive models showed stem-loop structures involving nt 1398-1421 of the natural reassortant whereas this structure is modified in the recombinant viruses harbouring point mutations r1408 and r1408-1412, but not in r1412. Results obtained from infectivity assays showed differences between the reference strains and the mutants in both RNA1 and RNA2 synthesis. Moreover, an imbalance between the synthesis of both segments was demonstrated, mainly with the double mutant. All these results suggest an interaction between RNA1 and the 3' non-coding regions (3'NCR) of RNA2. In addition, the significant attenuation of the virulence for Senegalese sole and the delayed replication of r1408-1412 in brain tissues may point to an interaction of RNA2 with host cellular proteins.

Transcriptomic Profiles of Senegalese Sole Infected With Nervous Necrosis Virus Reassortants Presenting Different Degree of Virulence

Betanodaviruses [nervous necrosis virus (NNV)] are the causative agent of the viral encephalopathy and retinopathy, a disease that affects cultured Senegalese sole (Solea senegalensis). NNV reassortants, combining genomic segments from redspotted grouper nervous necrosis virus (RGNNV) and striped jack nervous necrosis virus (SJNNV) genotypes, have been previously isolated from several fish species. The wild-type reassortant wSs160.03, isolated from Senegalese sole, has been proven to be more virulent to sole than the parental genotypes (RGNNV and SJNNV), causing 100% mortality. Mutations at amino acids 247 (serine to alanine) and 270 (serine to asparagine) in the wSs160.03 capsid protein have allowed us to obtain a mutant reassortant (rSs160.03_247+270), which provokes a 40% mortality decrease. In this study, the RNA-Seq technology has been used to comparatively analyze Senegalese sole transcriptomes in two organs (head kidney and eye/brain) after infection with wild-type and mutant strains. A total of 633 genes were differentially expressed (DEGs) in animals infected with the wild-type isolate (with higher virulence), whereas 393 genes were differentially expressed in animals infected with the mutant strain (37.9% decrease in the number of DEGs). To study the biological functions of detected DEGs involved in NNV infection, a gene ontology (GO) enrichment analysis was performed. Different GO profiles were obtained in the following subclasses: (i) biological process; (ii) cellular component; and (iii) molecular function, for each viral strain tested. Immune response and proteolysis have been the predominant biological process after the infection with the wild-type isolate, whereas the infection with the mutant strain induces proteolysis in head kidney and inhibition of vasculogenesis in nervous tissue. Regarding the immune response, genes coding for proteins acting as mediators of type I IFN expression (DHX58, IRF3, IRF7) and IFN-stimulated genes (ISG15, Mx, PKR, Gig1, ISG12, IFI44, IFIT-1, to name a few) were upregulated in animals infected with the wild-type isolate, whereas no-differential expression of these genes was observed in samples inoculated with the mutant strain. The different transcriptomic profiles obtained could help to better understand the NNV pathogenesis in Senegalese sole, setting up the importance as virulence determinants of amino acids at positions 247 and 270 within the RNA2 segment.

Immuno-related gene transcription and antibody response in nodavirus (RGNNV and SJNNV)-infected European sea bass (Dicentrarchus labrax L.)

The immune response of European sea bass to RGNNV and SJNNV infections has been evaluated by quantifying the transcription of some genes involved in the IFN I system, as well as in the inflammatory and adaptive immune mechanisms. The transcription of IFN-I, ISG-12, ISG-15 and MxA genes has been analyzed in brain and head kidney, showing that RGNNV genotype induces a more intense response of the IFN I system than SJNNV in both organs. In addition, the results obtained indicate the importance of the inflammatory response in nodavirus pathogenesis, with the transcription of IL-8 and TNF-α significantly higher in brain than in head kidney, being RGNNV the strongest inductor. An important difference between the immune response induced by both genotypes refers to the IgM titre in sera, which was higher in SJNNV-inoculated fish. The acquired response is also important locally, since TR-γ transcription is higher in brain than in head kidney (especially in the RGNNV-inoculated group). To our knowledge, this is the first study addressing the sea bass anti-SJNNV immune response.

Description of New and Amended Clades of the Genus Photobacterium

Phylogenetic relationships between species in the genus Photobacterium have been poorly studied despite pathogenic and ecological relevance of some of its members. This is the first phylogenetic study that includes new species of Photobacterium (validated or not) that have not been included in any of the previously described clades, using 16S rRNA sequences and multilocus sequence analysis (MLSA) in concatenated sequences of gyrB, gapA, topA, ftsZ and mreB housekeeping genes. Sequence analysis has been implemented using Maximum-parsimony (MP), Neighbour-joining (NJ) and Maximum likelihood (ML) treeing methods and the predicted evolutionary relationship between the Photobacterium clades was established on the basis of bootstrap values of >75% for 16S rRNA sequences and MLSA. We have grouped 22 species of the genus Photobacterium into the following 5 clades: Phosphoreum (comprises P. aquimaris, “P. carnosum,” P. iliopiscarium, P. kishitanii, P. phosphoreum, “P. piscicola” and “P. toruni”); clade Profundum (composed of P. aestuarii, P. alginatilyticum, P. frigidiphilum, P. indicum, P. jeanii, P. lipolyticum, “P. marinum,” and P. profundum); clade Damselae (two subspecies of P. damselae, damselae and piscicida); and two new clades: clade Ganghwense (includes P. aphoticum, P. aquae, P. galatheae, P. ganghwense, P. halotolerans, P. panuliri and P. proteolyticum); and clade Leiognathi (composed by P. angustum, P. leiognathi subsp. leiognathi and “P. leiognathi subsp. mandapamensis”). Two additional clades, Rosenbergii and Swingsii, were formed using a phylogenetic method based on 16S rRNA gene, although they are not confirmed by any MLSA methods. Only P. aplysiae could not be included in none of the established clade, constituting an orphan clade.

The theoretical reliability of PCR-based fish viral diagnostic methods is critically affected when they are applied to fish populations with low prevalence and virus loads

AIMS

The reliability of polymerase chain reaction (PCR) techniques is an important issue in viral diagnosis, and it is even crucial when they must be applied for detection of viruses in asymptomatic carriers. The problems will arise when the aim is to study wild fish populations, where the viral loads and prevalence values are extremely low. We have evaluated several PCR procedures employed by two laboratories for monitoring fish captured in several oceanographic campaigns performed in the Gulf of Cádiz.

METHODS AND RESULTS

To evaluate the reliability of different diagnostics test used, we have re-analysed fish samples that had been previously subjected to diagnosis for a surveillance of viruses performed in 2010-2011 in wild fish populations. The following parameters were employed: the clinical sensitivity (Ss), the clinical specificity (Sp), the predictive positive value, the predictive negative value, and the positive and negative likelihood ratio (LR⁺ and LR^- ). For viral nervous necrosis virus, a RT-PCR procedure supplemented by nested PCR showed the highest values (100%) for all the parameters. For viral haemorrhagic septicaemia virus, the highest values were provided by RT-PCR supplemented by dot-blot hybridization. In the case of infectious pancreatic necrosis virus, none of the procedures yielded 100% for any parameter.

CONCLUSIONS

The results obtained for viral prevalence indicate: (i) that the conservation of the samples at -80°C did not affect to the capacity of detection of the virus in the tissues, and (ii) that the reproducibility of the diagnosis can be affected by factors including the staff experience and/or the materials employed. Finally, the use of a combination of procedures in advised to ensure the maximum reliability of the diagnosis when it is applied to asymptomatic fish populations.

SIGNIFICANCE AND IMPACT OF THE STUDY

This paper describes a strategy of combining diagnostic tests for the surveillance and monitoring of wild fish populations to reduce underestimation of the prevalence of viruses this type of populations.

Genomic analysis of the marine fish pathogen Photobacterium damselae subsp. piscicida: Insertion sequences proliferation is associated with chromosomal reorganisations and rampant gene decay

Photobacterium damselae subsp. piscicida (Pdp) is an intracellular fish pathogen that causes photobacteriosis, a disease proven deadly in farmed fish worldwide. This work focuses on the analysis of genome sequences, chromosomes structure and gene contents of two strains from Sparus aurata (DI21) and Solea senegalensis (L091106-03H), isolated on the Spanish Atlantic coast. The comparative genomic analysis revealed that DI21 and L091106-03H share 98% of their genomes, including two virulence plasmids: pPHDP70 encoding siderophore piscibactin synthesis and pPHDP10 encoding the apoptotic toxin AIP56. Both genomes harbour a surprisingly large number of IS elements accounting for 12-17% of the total genome, representing an IS density of 0.15 elements per kb, one of the highest IS density values in a bacterial pathogen. This massive proliferation of ISs is responsible for the generation of a high number of pseudogenes that caused extensive loss of biological functions. Pseudogene formation is one of the main features of Pdp genome that explains most of the ecological and phenotypic differences with respect to its sibling subspecies P. damselae subsp. damselae and to other Vibrionaceae. Evidence was also found proving the existence of two chromosomal configurations depending on the origin of the strains: an European and an Asian/American types of genome organisation, reinforcing the idea of the existence of two geographically-linked clonal lineages in Pdp. In short, our study suggests that the host-dependent lifestyle of Pdp allowed massive IS proliferation and gene decay processes, which are major evolutionary forces in the shaping of the Pdp genome.

Gene expression profiles associated with lymphocystis disease virus (LCDV) in experimentally infected Senegalese sole (Solea senegalensis)

In the present study, the pathogenesis of lymphocystis disease virus (LCDV) and the immune gene expression patterns associated with this viral infection were determined in the flatfish Senegalese sole. The results indicate that LCDV spreads rapidly from the peritoneal cavity through the bloodstream to reach target organs such as kidney, gut, liver, and skin/fin. The viral load was highest in kidney and reduced progressively thorough the experiment in spite of the viral major capsid protein gene was transcribed. The LCDV injection activated a similar set of differentially expressed transcripts in kidney and intestine although with some differences in the intensity and time-course response. This set included antiviral-related transcripts (including the mx and interferon-related factors irf1, irf2, irf3, irf7, irf8, irf9, irf10), cytokines (il1b, il6, il8, il12 and tnfa) and their receptors (il1r, il8r, il10r, il15ra, il17r), chemokines (CXC-type, CC-type and IL-8), prostaglandins (cox-2), g-type lysozymes, hepcidin, complement fractions (c2, c4-1 and c4-2) and the antigen differentiation factors cd4, cd8a, and cd8b. The expression profile observed indicated that the host triggered a systemic defensive response including inflammation able to cope with the viral challenge.

Target organs for lymphocystis disease virus replication in gilthead seabream (Sparus aurata)

The lymphocystis disease (LCD), the main viral pathology described in cultured gilthead seabream (Sparus aurata), is a self-limiting condition characterized by the appearance of hypertrophied fibroblasts (named lymphocysts) in the connective tissue of fish, primarily in the skin and fins. The causative agent of the disease is the Lymphocystis disease virus (LCDV), a member of the Iridoviridae family. In the present study, LCDV genome and transcripts were detected by real-time PCR in caudal fin, as well as in several internal organs, such as intestine, liver, spleen, kidney and brain, from asymptomatic, diseased and recovered gilthead seabream juveniles. These results indicate that the LCDV has a broad range tissue tropism, and can establish a systemic infection, even in subclinically infected fish. As showed by in situ hybridization, the permissive cells for LCDV infection seem to be fibroblasts, hepatocytes and cells of the mononuclear phagocyte system. Histopathological alterations associated with LCD were observed in all the organs analysed, including necrotic changes in liver and kidney, inflammatory response in the intestine submucosa or brain haemorrhage, although lymphocysts were only detected in the dermis of the caudal fin. Nevertheless, these histological changes were reverted in recovered animals.

Rapid and Sensitive Detection of Lymphocystis Disease Virus Genotype VII by Loop-Mediated Isothermal Amplification

Lymphocystis disease virus (LCDV) infections have been described in gilthead seabream (Sparus aurata L.) and Senegalese sole (Solea senegalensis, Kaup), two of the most important marine fish species in the Mediterranean aquaculture. In this study, a rapid, specific, and sensitive detection method for LCDV genotype VII based on loop-mediated isothermal amplification (LAMP) was developed. The LAMP assay, performed using an apparatus with real-time amplification monitoring, was able to specifically detect LCDV genotype VII from clinically positive samples in less than 12 min. In addition, the assay allowed the detection of LCDV in all asymptomatic carrier fish analysed, identified by qPCR, showing an analytical sensitivity of ten copies of viral DNA per reaction. The LCDV LAMP assay has proven to be a promising diagnostic method that can be used easily in fish farms to detect the presence and spread of this iridovirus.

Evaluation of an integrated cell culture RT-PCR assay to detect and quantify infectious lymphocystis disease virus

The lymphocystis disease virus (LCDV), a member of the Iridoviridae family, infects a wide range of fish species including gilthead seabream (Sparus aurata L.), the most important species cultured in the Mediterranean. LCDV is difficult to propagate in cell culture and does not produce clear and consistent cytopathic effects (CPE), especially in samples collected from subclinically infected fish. An integrated cell culture reverse transcription-polymerase chain reaction (ICC-RT-PCR) assay, followed by dot-blot hybridization of the RT-PCR products, was developed to improve the detection of infectious LCDV. The sensitivity of the ICC-RT-PCR assay, which can be performed in 7 d, was at least 100-fold higher than viral diagnosis obtained by CPE development. The developed assay thus allows the determination of infectious titres in samples with low viral loads, including those from asymptomatic carrier fish, in which no CPE was recorded after a 14-d incubation period. The ICC-RT-PCR assay enables rapid, specific and sensitive detection and quantification of infectious LCDV, and may be a valuable tool in the study of aspects of LCDV infection including transmission or epizootiology.

Genetic characterization and transcription analyses of the European sea bass (Dicentrarchus labrax) isg15 gene

Fish interferons are cytokines involved in its resistance to viral infections by inducing the transcription of several interferon-induced genes, such as isg15. The aim of the present study was the genetic characterization of the European sea bass isg15 gene, describing the regulatory motifs found in its sequence. In addition, an in vivo analysis of transcription in response to betanodavirus (RGNNV genotype) and poly I:C has been performed. The analysis of the resulting sequences showed that sea bass isg15 gene is composed of two exons and a single 276-bp intron located at the 5'-UTR region. The full length cDNA is 1143-bp, including a 102-bp 5'-UTR region, a 474-bp ORF, and a 291-bp 3'-UTR region. Several mRNA-regulatory elements, including three unusual ATTTA instability motifs in the intron, and four ATTTA motifs along with a cytoplasmic polyadenylation element in the 3'-UTR region, have been found in this sequence. The in vivo analyses revealed a similar kinetics and level of transcription in fish brain and head kidney after poly I:C inoculation; however, the induction caused by RGNNV started earlier in brain, where the upregulation of isg15 gene transcription was high. The present study contributes to further characterize the European sea bass IFN I response against RGNNV infections.

Application of a new real-time polymerase chain reaction assay for surveillance studies of lymphocystis disease virus in farmed gilthead seabream

Background

Lymphocystis disease (LCD) is the main viral infection reported to affect cultured gilthead seabream (Sparus aurata) in Europe. The existence of subclinical Lymphocystis disease virus (LCDV) infection in this fish species has been recognised by using polymerase chain reaction (PCR)-based methods. Nevertheless, these methods do not provide quantitative results that can be useful in epidemiological and pathological studies. Moreover, carrier fish have been involved in viral transmission, therefore the use of specific and sensitive diagnostic methods to detect LCDV will be relevant for LCD prevention.

Results

We have developed a real-time PCR (qPCR) assay to detect and quantify LCDV. The assay was evaluated for viral diagnosis in surveillance studies in gilthead seabream farms, and also to identify viral reservoirs in a hatchery. The prevalence of LCDV infection in the asymptomatic gilthead seabream populations tested varied from 30 to 100 %, including data from one farm without previous records of LCD. Estimated viral load in caudal fin of subclinically infected fish was two to five orders of magnitude lower than in diseased fish. The qPCR assay allowed the detection of carrier fish in broodstock from a farm with a history of clinical LCD in juvenile fish. In addition, the quantitative detection of LCDV was achieved in all samples collected in the hatchery, including fertilized eggs, larvae and fingerlings, and also rotifer cultures and artemia metanauplii and cysts used for larval rearing.

Conclusions

The qPCR assay developed in this study has proved to be a rapid, sensitive, and reliable method for LCDV diagnosis, which could be valuable to identify LCDV reservoirs or to study viral replication in gilthead seabream.

SJNNV down-regulates RGNNV replication in European sea bass by the induction of the type I interferon system

European sea bass is highly susceptible to the betanodavirus RGNNV genotype, although the SJNNV genotype has also been detected in this fish species. The coexistence of both genotypes may affect the replication of both viruses by viral interaction or by stimulation of the host antiviral defense system in which the IFN I system plays a key role. IFN I triggers the transcription of interferon-stimulated genes, including Mx genes, whose expression has been used as a reporter of IFN I activity. The present study evaluated the effect of a primary exposure to an SJNNV isolate on a subsequent RGNNV infection and analyzed the role of the IFN I system in controlling VNNV infections in sea bass using different in vivo approaches. VNNV infection and Mx transcription were comparatively evaluated after single infections, superinfection (SJ+RG) and co-infection (poly I:C+RG). The single RGNNV infection resulted in a 24% survival rate, whereas the previous SJNNV or poly I:C inoculation increased the survival rate up to 96 and 100%, respectively. RGNNV replication in superinfection was reduced compared with RGNNV replication after a single inoculation. Mx transcription analysis shows differential induction of the IFN I system by both isolates. SJNNV was a potent Mx inducer, whereas RGNNV induced lower Mx transcription and did not interfere with the IFN I system triggered by SJNNV or poly I:C. This study demonstrates that an antiviral state exists after SJNNV and poly I:C injection, suggesting that the IFN I system plays an important role against VNNV infections in sea bass.

Evidence for horizontal gene transfer, gene duplication and genetic variation as driving forces of the diversity of haemolytic phenotypes in Photobacterium damselae subsp. damselae

Photobacterium damselae subsp. damselae, a marine bacterium that causes infections in marine animals and in humans, produces up to three different haemolysins involved in virulence, which include the pPHDD1 plasmid-encoded damselysin (Dly) and HlyApl , and the chromosome-encoded HlyAch . We screened 45 isolates from different origins, and found a correlation between their haemolytic phenotypes and the differential haemolysin gene content. All highly and medium haemolytic strains harboured pPHDD1, with amino acid substitutions in HlyApl and HlyAch being the cause of the medium haemolytic phenotypes in some pPHDD1-harbouring strains. Weakly haemolytic strains contained only hlyAch , whereas nonhaemolytic isolates, in addition to lacking pPHDD1, either lacked hlyAch or contained a hlyAch pseudogene. Sequence analysis of the genomic context of hlyAch uncovered an unexpected genetic diversity, suggesting that hlyAch is located in an unstable chromosomal region. Phylogenetic analysis suggested that hlyApl and hlyAch originated by gene duplication within P. damselae subsp. damselae following acquisition by horizontal transfer. These observations together with the differential distribution of pPHDD1 plasmid among strains suggest that horizontal gene transfer has played a main role in shaping the haemolysin gene baggage in this pathogen.

Transmission of lymphocystis disease virus to cultured gilthead seabream, Sparus aurata L., larvae

The transmission of lymphocystis disease virus (LCDV) to gilthead seabream, Sparus aurata L., larvae was investigated using fertilized eggs from a farm with previous reports of lymphocystis disease. LCDV genome was detected by PCR-hybridization in blood samples from 17.5% of the asymptomatic gilthead seabream broodstock analysed. Using the same methodology, eggs spawned from these animals were LCDV positive, as well as larvae hatched from them. The presence of infective viral particles was confirmed by cytopathic effects development on SAF-1 cells. Whole-mount in situ hybridization (ISH) and immunohistochemistry (IHC) showed the presence of LCDV in the epidermis of larvae hatched from LCDV-positive eggs. When fertilized eggs were disinfected with iodine, no viral DNA was detected either in eggs (analysed by PCR-hybridization) or in larvae (PCR-hybridization and ISH). These results suggest the vertical transmission of LCDV, the virus being transmitted on the egg surface. Larvae hatched from disinfected eggs remain LCDV negative during the endotrophic phase, as showed by PCR-hybridization, ISH and IHC. After feeding on LCDV-positive rotifers, viral antigens were observed in the digestive tract, which suggests that viral entry could be achieved via the alimentary canal, and that rotifers can act as a vector in LCDV transmission to gilthead seabream larvae.

High incidence of antibiotic multi-resistant bacteria in coastal areas dedicated to fish farming

Marine bacteria exposed to antibiotics in fish farms can acquire antimicrobial resistance by mobile genetic elements and horizontal gene transfer. A total of 872 autochthonous marine bacterial strains was isolated from samples collected from four different fish farms located at northern and southern Italian Adriatic Sea. Resistance to only tetracycline (17%) and to trimethoprim-sulfadiazine (7%) were the most frequent patterns obtained, while flumequine resistance has recorded in only 0.3% of the strains. Comparing strains isolated from coastal areas and fish farms, a significant higher incidence (4% versus 10%) of multi-resistant strains in aquaculture centers was found. Significant differences in antibiotic resistance incidence were also detected among the four fish farms due probably to different approaches in farm management and the more or less frequent use of antibiotics. Antibiotic-resistant and multi-resistant strains isolated constitute an environmental reservoir directly involved in the seafood chain and might represent a public health concern.

Antiviral specificity of the Solea senegalensis Mx protein constitutively expressed in CHSE-214 cells

Interferons play a key role in fish resistance to viral infections by inducing the expression of antiviral proteins, such as Mx. The aim of the present study was to test the antiviral activity of the Senegalese sole Mx protein (SsMx) against RNA and DNA viruses pathogenic to fish, i.e. the infectious pancreatic necrosis virus (IPNV, dsRNA), the viral haemorrhagic septicaemia virus (VHSV, ssRNA), and the European sheatfish virus (ESV, dsDNA), using a CHSE-214 cell clone expressing this antiviral protein. A strong inhibition of IPNV and VHSV replication was recorded in SsMx-expressing cells, as has been shown by the virus yield reduction and the decrease in the synthesis of the viral RNA encoding the polyprotein (for IPNV) and the nucleoprotein (for VHSV). The titres of these viruses replicating on SsMx-expressing cells were 100 times lower than those recorded on non-transfected cells. In contrast, SsMx did not inhibit ESV replication since no significant differences were observed regarding the virus yield or the major capsid protein gene transcription in transfected and non-transfected cells.

Toxicity of Photobacterium damselae subsp. damselae strains isolated from new cultured marine fish

The in vivo and in vitro toxicity of bacterial cells and their extracellular products (ECPs) from 16 strains of Photobacterium damselae subsp. damselae isolated from 7 epizootic outbreaks were evaluated. On the basis of their 50% lethal dose (LD50) values (about 1 x 10(50 CFU), these strains may be considered as moderately virulent. However, their ECPs were strongly lethal for redbanded seabream Pagrus auriga causing fish death within 2 h post-inoculation (protein concentration ranged between 2.1 and 6.41 microg g(-1) fish). The bacterial ECPs tested exhibited several enzymatic activities, such as amylase, lipase, phospholipase, alkaline phosphatase, esterase-lipase, acid phosphatase, and beta-glucosaminidase. These ECPs displayed a strong cytotoxic effect on 4 fish and 2 mammalian cell lines, although this activity disappeared when ECPs were heated at 100 degrees C. The virulence of the strains tested could not be related to the hemolytic activity or to the production of the toxin damselysin. Therefore, another unknown type of toxin could play an important role in the virulence mechanisms of this bacterial pathogen.

A combined RT-PCR and dot-blot hybridization method reveals the coexistence of SJNNV and RGNNV betanodavirus genotypes in wild meagre (Argyrosomus regius)

AIMS

To detect the possible coexistence of striped jack nervous necrosis virus (SJNNV) and red-spotted grouper nervous necrosis virus (RGNNV) genotypes in a single fish, a methodology based on the combination of PCR amplification and blot hybridization has been developed and applied in this study.

METHODS AND RESULTS

The degenerate primers designed for the PCR procedure target the T4 region within the capsid gene, resulting in the amplification of both genotypes. The subsequent hybridization of these amplification products with two different specific digoxigenin-labelled probes resulted in the identification of both genotypes separately. The application of the RT-PCR protocol to analyse blood samples from asymptomatic wild meagre (Argyrosomus regius) specimens has shown a 46.87% of viral nervous necrosis virus carriers. The combination of RT-PCR and blot hybridization increases the detection rate up to 90.62%, and, in addition, it has shown the coexistence of both genotypes in 18 out of the 32 specimens analysed (56.25%).

CONCLUSIONS

This study reports the coexistence of betanodaviruses belonging to two different genotypes (SJNNV and RGNNV) in wild fish specimens.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report demonstrating the presence of SJNNV and RGNNV genotypes in the same specimen. This study also demonstrates a carrier state in this fish species for the first time.

Detection of infectious pancreatic necrosis virus (IPNV) from asymptomatic redbanded seabream, Pagrus auriga Valenciennes, and common seabream, Pagrus pagrus (L.), using a non-destructive procedure

A non-destructive procedure based on nested RT-PCR and dot-blot hybridization has been developed for the detection of asymptomatic IPNV-carrier fish. The pair of primers designed for RT-PCR amplified a 599-bp fragment of the pVP2 region within the polyprotein gene, resulting in the detection of IPNV genotype III.1. The use of a nested RT-PCR allowed the amplification of IPNV genotypes III.1 and I.2. In addition, a 191-bp probe was designed for hybridization studies used in combination with the nested RT-PCR. The application of the nested RT-PCR to analyse blood samples from asymptomatic redbanded seabream, Pagrus auriga, and common seabream, P. pagrus, specimens showed a 53.1% and 77.8% prevalence of IPNV-carriers, respectively. The combination of nested RT-PCR and dot-blot hybridization increased the detection rates up to 100% for redbanded seabream and 94.4% for common seabream. Therefore, the protocol described in this study is highly sensitive and specific for the detection of IPNV in asymptomatic carrier fish, and, in addition, the results demonstrate the carrier state in two newly cultured sparid species in southern Spain.

Are the defined substrate-based methods adequate to determine the microbiological quality of natural recreational waters?

Monitoring the microbiological quality of water used for recreational activities is very important to human public health. Although the sanitary quality of recreational marine waters could be evaluated by standard methods, they are time-consuming and need confirmation. For these reasons, faster and more sensitive methods, such as the defined substrate-based technology, have been developed. In the present work, we have compared the standard method of membrane filtration using Tergitol-TTC agar for total coliforms and Escherichia coli, and Slanetz and Bartley agar for enterococci, and the IDEXX defined substrate technology for these faecal pollution indicators to determine the microbiological quality of natural recreational waters. ISO 17994:2004 standard was used to compare these methods. The IDEXX for total coliforms and E. coli, Colilert, showed higher values than those obtained by the standard method. Enterolert test, for the enumeration of enterococci, showed lower values when compared with the standard method. It may be concluded that more studies to evaluate the precision and accuracy of the rapid tests are required in order to apply them for routine monitoring of marine and freshwater recreational bathing areas. The main advantages of these methods are that they are more specific, feasible and simpler than the standard methodology.

Cellular and molecular immune responses of the sea bass (Dicentrarchus labrax) experimentally infected with betanodavirus

Naïve sea bass juveniles (38.4 + or - 4.5 g) were intramuscularly infected with a sublethal dose of betanodavirus isolate 378/I03, followed after 43 days by a similar boosting. This infection resulted in an overall mortality of 7.6%. At various intervals, sampling of fish tissues was performed to investigate: i) B and T lymphocyte content in organs and tissues; ii), proliferation of leucocytes re-stimulated in vitro with inactivated virus; iii) presence of serum antibody specific for betanodavirus; iv) expression of genes coding for the following immunoregulatory molecules involved in innate and acquired responses: type I IFN, Mx, IL-1, Cox-2; IL-10, TGF-beta, TCRbeta, CD4, CD8alpha, IgM, by using a quantitative PCR array system developed for sea bass. The obtained results showed a detectable increase of T cells and B cells in PBL during betanodavirus infection. Furthermore, leucocytes obtained from blood, head kidney, and gills showed a detectable "in vitro" increase in viability upon addition of inactivated viral particles, as determined by measuring intracellular ATP concentration. ELISA analysis of sera showed that exposure to nodavirus induced a low, but specific antibody titer measured 43 days after infection, despite the presence of measurable levels of natural antibody. Finally, a strong upregulation of genes coding for type I IFN, Mx, and IgM was identified after both infection and boosting. Interestingly, an upregulation of Cox-2 until boosting, and of TGF-beta and IL-10 after boosting was also observed, while the other tested genes did not show any significant variations with respect to mock-treated fish. Overall, our work represents a first comprehensive analysis of cellular and molecular immune parameters in a fish species exposed to a pathogenic virus.

Application of in situ detection techniques to determine the systemic condition of lymphocystis disease virus infection in cultured gilt-head seabream, Sparus aurata L

Immunohistochemistry (IHC) and in situ hybridization (ISH) techniques have been used for the detection of lymphocystis disease virus (LCDV) in formalin-fixed, paraffin-embedded tissues from gilt-head seabream, Sparus aurata L. Diseased and recovered fish from the same population were analysed. IHC was performed with a polyclonal antibody against a 60-kDa viral protein. A specific digoxigenin-labelled probe, obtained by PCR amplification of a 270-bp fragment of the gene coding the LCDV major capsid protein, was used for ISH. LCDV was detected in skin dermis and gill lamellae, as well as in several internal organs such as the intestine, liver, spleen and kidney using both techniques. Fibroblasts, hepatocytes and macrophages seem to be target cells for virus replication. The presence of lymphocystis cells in the dermis of the skin and caudal fin, and necrotic changes in the epithelium of proximal renal tubules were the only histological alterations observed in fish showing signs of the disease.

c-Lysozyme from Senegalese sole (Solea senegalensis): cDNA cloning and expression pattern

Lysozymes are key molecules of innate immunity and proved high bactericidal activity in fish, thus becoming attractive as tools for enhancing fish defences. In this study, a full-length c-type lysozyme cDNA from Senegalese sole (Solea senegalensis) has been cloned and characterized. The cDNA sequence was inferred from two overlapping fragments obtained by RACE-PCR and consisting on 631bp coding for 143 aminoacids. Catalytic and other conserved residues required for lysozyme activity were identified. Pair wise alignments showed the higher identities with c-type lysozyme from other flatfish. Expression patterns under various conditions showed a basal level and a clear upregulation mostly in hematopoietic organs after stimulation with LPS or infection with Photobacterium damselae. This study represents a first step on the genetics and function of the c-lysozyme of Senegalese sole, though disclosing g-DNA structure, allelic variability and antibacterial activity must be requirements prior its immunological properties might have biotechnological applications.

Poly I:C induces Mx transcription and promotes an antiviral state against sole aquabirnavirus in the flatfish Senegalese sole (Solea senegalensis Kaup)

Mx is an interferon-induced protein that protects against viral infections. In this study the absolute number of Mx transcripts after poly I:C injection (a synthetic dsRNA) or sole aquabirnavirus (solevirus) inoculation in Senegalese sole (Solea senegalensis Kaup) has been quantified. Mx expression profiles differed clearly in both experimental conditions; the induction response was faster and more intense after poly I:C injection than after solevirus inoculation. Moreover, pre-injection of soles with poly I:C prior to solevirus infection eliminated the induction of Mx expression associated with this virus. To evaluate the possible interference of poly I:C treatments on solevirus replication, the mRNA levels of the virus capsid protein (VP2) were determined by RT-PCR. VP2 transcripts were hardly detected in poly I:C pre-injected animals from 12 to 72 h after solevirus inoculation. All these data suggest that poly I:C is able to induce an antiviral state that interferes with solevirus replication, and support the suitability of Mx expression analysis as a marker to study the defensive response against solevirus.

In vitro inhibition of sole aquabirnavirus by Senegalese sole Mx

Senegalese sole, Solea senegalensis, is a flat fish of growing interest in European aquaculture. In its culture viral infections are constant threats, thus understanding antiviral defences is a key factor for a successful industry. Mx proteins are IFN-induced proteins widespread in eukaryotes; however, their antiviral activity is unclear and the results variable among species. Therefore assessment of the putative Mx antiviral activity in each species is of interest. Our group has recently cloned the Senegalese sole Mx (SsMx) cDNA and in this study its antiviral activity was assessed by infecting CHSE-214 cells expressing recombinant SsMx, with sole aquabirnavirus. The antiviral activity against this pathogen was demonstrated by reduction in induced cytopathic effects, reduction in virus yield and decrease in viral transcripts. These findings contribute to our understanding of fish antiviral mechanisms and open the possibility of using this protein as a tool for fighting viral infections in aquaculture.

Development of molecular techniques for detection of lymphocystis disease virus in different marine fish species

AIMS

The development and evaluation of a protocol based on polymerase chain reaction (PCR) and nucleic acid hybridization techniques for the specific detection of lymphocystis disease virus (LCDV) in several marine fish species.

METHODS AND RESULTS

The pair of primers for PCR, OBL3 and OBL4, was designed based on published nucleotide sequence (LCDV-1) and amplifies a fragment within the major capsid protein. The sensitivity was evaluated using DNA from purified viral particles, as well as from cells inoculated with several viral concentrations. The PCR combined with slot blot was the most sensitive methodology, detecting 2.5 ng of viral DNA. Using this methodology LCDV was detected at 5 days postinoculation from SAF-1 cells initially inoculated with 10(-5) TCID(50) ml(-1). The combination of PCR with membrane hybridization has also been proved to be adequate to detect LCDV from apparently healthy carriers by means of caudal fin sample analysis. This asymptomatic infection was also demonstrated by classical virological methods (cell culture and immunoblot).

CONCLUSIONS

The protocol described in this study allows the specific detection of LCDV, both in cell cultures and in fin homogenates from asymptomatic fish.

SIGNIFICANCE AND IMPACT OF THE STUDY

The detection of asymptomatic carriers by a rapid molecular method using caudal fin sampling, which does not imply animal killing, could be an important tool to control epizootics caused by LCDV, as fish could be analysed before their introduction and/or mobilization in farm facilities.

Co-occurrence of viral and bacterial pathogens in disease outbreaks affecting newly cultured sparid fish

Several microbial disease outbreaks in farm stocks of newly cultured sparid fish species, such as common seabream, redbanded seabream, and white seabream, were recorded from 2004 to 2006. This study describes the isolation and characterization of the potential causative agents, either bacteria or viruses, of these outbreaks. The isolated bacterial strains were characterized according to traditional taxonomical analyses and sequencing of a 16S rDNA fragment. Most bacteria were identified as Vibrio spp. and Photobacterium damselae subsp. damselae. The development of cytopathic effects (CPE) on different fish cell lines, the application of specific nested-PCR tests for infectious pancreatic necrosis virus (IPNV), viral nervous necrosis virus (VNNV) and viral hemorrhagic septicemia virus (VHSV), and subsequent sequence analyses were used for virus detection and identification. VNNV, related to the striped jack neural necrosis virus (SJNNV) genotype, and VHSV, related to the genotype Ia, were the only viruses detected. VNNV was isolated from the three fish species under study in five different outbreaks, whereas VHSV was isolated from common seabream and white seabream during two of these outbreaks. IPNV was not detected in any case.

Cloning and expression analysis of Mx cDNA from Senegalese sole (Solea senegalensis)

Senegalese sole (Solea senegalensis) is a promising fish species of growing interest in European aquaculture. In fish farming, viral infections are a constant threat therefore, understanding fish defence mechanisms is a main priority to avoid economic losses. Mx proteins are involved in the innate antiviral response of fish. They are induced by type I interferons (alpha and beta) and are essential to investigate viral defence mechanisms in fish, due to the difficulty in tracking interferon activity in these species. In this study a full-length Senegalese sole Mx cDNA has been RT-PCR cloned, resulting in 2322bp coding for 623 amino acids. The sequence accounts for the main characteristics of Mx proteins but lacking nuclear localisation signal (NLS), which suggests cytoplasmic localisation. The alignments of Senegalese sole Mx sequence showed the highest identity with the flatfish species, 80.1% identity with flounder and 78.9% with halibut. The spatial and temporal expression pattern has been analysed in control and challenged fish by RT-PCR. In control fish a constitutive level of sole Mx expression has been obtained and a clear induction was observed after treatment with Poly[I:C], which supports a putative role for the Mx in Senegalese sole viral defence. These findings contribute to increasing the knowledge of the role of interferon pathway in fish innate immunity and to develop new tools to fight virus infections in the culture of this species.

Microbiological quality of reclaimed water used for golf courses' irrigation

Microbial quality of reclaimed water used for irrigation in two golf courses located in the southern Iberian Peninsula (Spain and Portugal) was evaluated. Bacterial indicators for faecal pollution (total and faecal coliforms, Escherichia coli and enterococci) were tested by membrane filtration using appropriate selective media. In addition, somatic E. coli bacteriophages, enteric viruses (entero-, hepatitis A and rota-) and Legionella pneumophila were also analysed. The results obtained showed that all wastewater treatment processes reduced adequately the number of indicator microorganisms although a significant correlation between pathogenic and indicator microorganisms tested was not found. L. pneumophila was detected by PCR but not confirmed by culture. Survival experiments of pathogenic microorganisms in aerosols and irrigated turf are conducted to determine the health hazards for the golf practice and to propose a microbial standard for wastewater used for irrigation of golf courses.

Detection of lymphocystis disease virus (LCDV) in asymptomatic cultured gilt-head seabream (Sparus aurata, L.) using an immunoblot technique

An immunoblot technique for the detection of lymphocystis disease virus (LCDV) in naturally infected gilt-head seabream (Sparus aurata, L.) has been developed. A specific antiserum against a 60 kDa viral protein has been proven to be an appropriate tool for LCDV diagnosis either from inoculated cell cultures or from fish tissues using the immunoblot assay. The sensitivity of this technique varied between 10(-1) and 10(2) TCID50. LCDV has also been detected in fish tissues from both, diseased and asymptomatic gilt-head seabream. For the asymptomatic fish detection, a viral amplification step in cell culture and a subsequent viral concentration using polyethylene glycol (PEG) (600 wt) are required. On the contrary, immunoblot allowed the detection of LCDV antigens directly from tissue homogenates of diseased fish. The method described in this study shows higher sensitivity than classical detection techniques based on cell culture inoculation.

Isolation of lymphocystis disease virus from sole, Solea senegalensis Kaup, and blackspot sea bream, Pagellus bogaraveo (Brunnich)

Two viruses were isolated from cultured sole, Solea senegalensis, and wild blackspot sea bream, Pagellus bogaraveo, and preliminarily characterized as lymphocystis disease viruses (LCDVs). Viral isolates were characterized by morphological, biochemical and biophysical properties. In addition, the susceptibility of four fish cell lines was also tested. LCDV isolates developed cytopathic effects on the SAF-1 cell line at 5 and 6 days post-infection and reached titres of 10(6) TCID50 mL(-1). The antigenic and structural protein analysis of the two new LCDV isolates showed identical profiles to that obtained for LCDV strain Leetown NFH (ATCC VR-342), used as a reference viral strain, and for an LCDV isolate collected from gilt-head sea bream, Sparus aurata, cultured in southern Spain. Molecular confirmation was performed by polymerase chain reaction. Specific primers for LCDV produced a 270-bp DNA fragment, the expected size for LCDV.