Intraspecific characterization of Vibrio alginolyticus isolates recovered from cultured fish in Spain

Transcriptome analysis provides new insights into the immune response of Ruditapes philippinarum infected with Vibrio alginolyticus

Manila clam (Ruditapes philippinarum) is a bivalve species with commercial value, but it is easily infected by pathogenic microorganisms in aquaculture, which restricts the shellfish industry. Notably, the impact of Vibrio alginolyticus on clam culture is obvious. In this study, RNA-seq was performed to analyze clam hepatopancreas tissue in 48 h (challenge group, G48h) and 96 h (challenge group, G96h) after infection with V. alginolyticus and 0 h after injection of PBS (control group, C). The results showed that a total of 1670 differentially expressed genes were detected in the G48h vs C group, and 1427 differentially expressed genes were detected in the G96h vs C group. In addition, KEGG analysis showed that DEGs were significantly enriched in pathways such as Lysosome and Mitophagy. Moreover, 15 immune related DEGs were selected for qRT-PCR analysis to verify the accuracy of RNA-seq, and the results showed that the expression level of DEGs was consistent with that of RNA-seq. Therefore, the results obtained in this study provides a preliminary understanding of the immune defense of R. philippinarum and molecular insights for genetic breeding of V. alginolyticus resistance in Manila clam.

Smelly shark, smelly ray: what is infecting you?

AIMS

Although elasmobranchs are consumed worldwide, bacteriological assessments for this group are still sorely lacking. In this context, this study assessed bacteria of sharks and rays from one of the most important landing ports along the Rio de Janeiro coast.

METHODS AND RESULTS

Bacteria were isolated from the cloacal swabs of the sampled elasmobranchs. They were cultured, and Vibrio, Aeromonas, and Enterobacterales were isolated and identified. The isolated bacteria were then biochemically identified and antimicrobial susceptibility assays were performed. Antigenic characterizations were performed for Salmonella spp. and Polymerase Chain Reaction (PCR) assays were performed to identify Escherichia coli pathotypes. Several bacteria of interest in the One Health context were detected. The most prevalent Enterobacterales were Morganella morganii and Citrobacter freundii, while Vibrio harveyi and Vibrio fluvialis were the most prevalent among Vibrio spp. and Aeromonas allosacharophila and Aeromonas veronii bv. veronii were the most frequent among Aeromonas spp. Several bacteria also displayed antimicrobial resistance, indicative of Public Health concerns. A total of 10% of Vibrio strains were resistant to trimethoprim-sulfamethoxazole and 40% displayed intermediate resistance to cefoxitin. Salmonella enterica strains displayed intermediate resistance to ciprofloxacin, nalidixic acid and streptomycin. All V. cholerae strains were identified as non-O1/non-O139. The detected E. coli strains did not exhibit pathogenicity genes. This is the first study to perform serology assessments for S. enterica subsp. enterica isolated from elasmobranchs, identifying the zoonotic Typhimurium serovar. Salmonella serology evaluations are, therefore, paramount to identify the importance of elasmobranchs in the epidemiological salmonellosis chain.

CONCLUSIONS

The detection of several pathogenic and antibiotic-resistant bacteria may pose significant Public Health risks in Brazil, due to high elasmobranch consumption rates, indicating the urgent need for further bacteriological assessments in this group.

Vibrio alginolyticus growth kinetics and the metabolic effects of iron

IMPORTANCE

Transmission of V. alginolyticus occurs opportunistically through direct seawater exposure and is a function of its abundance in the environment. Like other Vibrio spp., V. alginolyticus are considered conditionally rare taxa in marine waters, with populations capable of forming large, short-lived blooms under specific environmental conditions, which remain poorly defined. Prior research has established the importance of temperature and salinity as the major determinants of Vibrio geographical and temporal range. However, bloom formation can be strongly influenced by other factors that may be more episodic and localized, such as changes in iron availability. Here we confirm the broad temperature and salinity tolerance of V. alginolyticus and demonstrate the importance of iron supplementation as a key factor for growth in the absence of thermal or osmotic stress. The results of this research highlight the importance of episodic iron input as a crucial metric to consider for the assessment of V. alginolyticus risk.

Mass kills in hatchery-reared European seabass (Dicentrarchus labrax) triggered by concomitant infections of Amyloodinium ocellatum and Vibrio alginolyticus

Amyloodiniosis and vibriosis are serious diseases in European seabass (Dicentrarchus labrax) hatcheries with noticeable high mortality. This study was conducted on tank-cultured D. labrax frys at a private marine hatchery near Mariout Lake (Alexandria, Egypt). Frys showed a high mortality rate (70%), lethargy, darkening, asphyxia, ascites, and velvety skin appearance. Both infectious agents were presumptively identified in all investigated frys. The identities of the two recovered agents were confirmed by molecular assay and phylogenetic analysis. On the tissue level, histopathological examination of skin, splenic, and renal tissue indicated severe alterations due to the direct impacts of both infections. On the cellular level, scanning electron micrographs showed both protozoal and bacterial pathogens on/in gill epithelial cells in solitary and colonial forms. Vibrio alginolyticus showed variable results for tested antibiotics, with a higher sensitivity to florfenicol. A successful control strategy was strictly adopted to overcome infections and stop mortalities. Copper sulphate and hydrogen peroxide were efficiently applied to tank water to overcome A. ocellatum infections. Further, florfenicol was effectively used to overcome systemic V. alginolyticus infections. The efficacy of treatments was confirmed by the absence of infectious agents in randomly collected fish samples. To the best of the authors’ knowledge, this study is one of the earliest Egyptian studies that dealt with the dilemma of mass kills associated with external parasitic/systemic bacterial infections among hatchery-reared European seabass.

Description of the microbiota in epidermal mucus and skin of sharks (Ginglymostoma cirratum and Negaprion brevirostris) and one stingray (Hypanus americanus)

Skin mucus in fish is the first barrier between the organism and the environment but the role of skin mucus in protecting fish against pathogens is not well understood. During copulation in sharks, the male bites the female generating wounds, which are then highly likely to become infected by opportunistic bacteria from the water or from the male shark's mouth. Describing the microbial component of epithelial mucus may allow future understanding of this first line of defense in sharks. In this study, we analyzed mucus and skin samples obtained from 19 individuals of two shark species and a stingray: the nurse shark (Ginglymostoma cirratum), the lemon shark (Negaprion brevirostris) and the southern stingray (Hypanus americanus). Total DNA was extracted from all samples, and the bacterial 16S rRNA gene (region V3-V4) was amplified and sequenced on the Ion Torrent Platform. Bacterial diversity (order) was higher in skin and mucus than in water. Order composition was more similar between the two shark species. Alpha-diversities (Shannon and Simpson) for OTUs (clusters of sequences defined by a 97% identity threshold for the16S rRNA gene) were high and there were non-significant differences between elasmobranch species or types of samples. We found orders of potentially pathogenic bacteria in water samples collected from the area where the animals were found, such as Pasteurellales (i.e., genus Pasteurella spp. and Haemophilus spp.) and Oceanospirillales (i.e., genus Halomonas spp.) but these were not found in the skin or mucus samples from any species. Some bacterial orders, such as Flavobacteriales, Vibrionales (i.e., genus Pseudoalteromonas), Lactobacillales and Bacillales were found only in mucus and skin samples. However, in a co-occurrence analyses, no significant relationship was found among these orders (strength less than 0.6, p-value > 0.01) but significant relationships were found among the order Trembayales, Fusobacteriales, and some previously described marine environmental Bacteria and Archaea, including Elusimicrobiales, Thermoproteales, Deinococcales and Desulfarculales. This is the first study focusing on elasmobranch microbial communities. The functional role and the benefits of these bacteria still needs understanding as well as the potential changes to microbial communities as a result of changing environmental conditions.

Identification of Vibrio alginolyticus virulent strain-specific DNA regions by suppression subtractive hybridization and PCR

AIMS

Vibrio alginolyticus was frequently isolated from diseased farmed fish in the coaster waters of Hainan Island over the past two decades. In this study, we attempted to identify candidates of virulent strain-specific DNA regions for this pathogen.

METHODS AND RESULTS

Suppression subtractive hybridization (SSH) and PCR were successively performed between the typical virulent strain and avirulent strain of V. alginolyticus, in which they shared 99·54% homology of 16S rDNAs. Out of 2873 subtracted clones, nine clones were finally indicated to harbour virulent strain-specific DNA fragments. The receivable functions of the major fragments in the nine clones were believed to encode methyl-accepting chemotaxis protein (n = 1), type VI secretion system-associated FHA domain protein TagH (n = 1), diguanylate cyclase (n = 1), AraC family transcriptional regulator (n = 1), ABC-type uncharacterized transport system permease component (n = 1) and hypothetical proteins (n = 4). Two hypothetical proteins contain several disordered regions.

CONCLUSIONS

Some specific DNA regions existed in the virulent strain of V. alginolyticus, and the SSH assay could be a highly sensitive method for identifying virulent regions in pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

This report is the first to describe the identification of virulent strain-specific DNA regions in the V. alginolyticus genome, which is helpful in developing virulent strain-specific rapid detection methods and is a pivotal precondition for clarifying the molecular virulence mechanism of V. alginolyticus.

Occurrence of Vibrio spp. along the Algerian Mediterranean coast in wild and farmed Sparus aurata and Dicentrarchus labrax

Background and Aim:

Vibrio bacteria are autochthonous inhabitants of aquatic and marine environments. Certain strains are responsible for important seafood-borne outbreaks in developed nations. The aim of this study was to investigate the occurrence of Vibrio spp. along the Algerian Mediterranean coast in several samples of two prominent wild and farmed marine fishes, Sparus aurata and Dicentrarchus labrax.

Materials and Methods:

A total of 350 S. aurata (n=280 farmed and n=70 wild) and 340 D. labrax (n=250 farmed and n=90 wild) were sampled among three different locations along the Algerian Mediterranean coastal area. The samples were processed for Vibrio research according to the ISO methods. Isolated colonies were identified utilizing biochemical tests and consecutively confirmed with matrix-assisted laser desorption ionization-time-of-flight mass spectrometry, combined with polymerase chain reaction (PCR) analysis when appropriate, or confirmed with PCR analysis alone.

Results:

A total of 42 Vibrio spp. were detected only among the farmed fishes. Taking into account, all 690 fishes sampled, the incidence of Vibrio spp. was 6.08% (with peaks up to 7.92%) among the total number of farmed fishes. Overall, 25 strains were isolated from S. aurata and 17 strains were isolated from D. labrax. The isolated strains belonged to four different species and were represented as follows: Vibrio alginolyticus (n=20), Vibrio cholerae (n=15), Vibrio fluvialis (n=5), and Vibrio hollisae (n=2). The incidence of Vibrio was higher in places characterized by greater levels of anthropogenic contamination of seawater.

Conclusion:

Considering the growing production and consequent rising consumption of farmed fish in Algeria, the reported incidence of Vibrio and the presence of potentially pathogenic strains of Vibrio such as V. cholerae cause particular concern for food safety matters. Even if innovative and natural techniques are desired in aquaculture, proper hygiene and manufacturing practices are essential for the correct management of Vibrio infection risk in farmed fishes at both industrial and domestic levels.

Industrial enzymes-producing marine bacteria from marine resources

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Lipase is the most dominant industrial enzyme produced by cultivated marine bacteria.

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Genetic variation determines the yield of enzyme production.

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Proteobacteria (Vibrio spp.) is the main producer of industrial enzymes.

Industrial enzymes are important for various biotechnological applications. Currently, the diversity of industrial enzymes-producing marine bacteria from Malaysia remains mostly unknown. This study investigated the diversity of industrial enzyme-producing marine bacteria from culture collections at the Institute of Marine Biotechnology, Universiti Malaysia Terengganu. Out of 200 bacterial isolates revived, 163 bacteria isolate were successfully growth. Marine bacteria produced enzymes with total scoring higher than four were selected for molecular identification using 16S rDNA. About 161 bacteria isolate secreted amylase (68.7 %), lipase (88.3 %) and protease (68.7 %). The phylogenetic analysis led to the identification of three major phyla, namely Proteobacteria, Firmicutes and Bacteroidetes. These phyla were differentiated into nine genera consisted of Bacillus, Chryseomicrobium, Photobacterium, Pseudoalteromonas, Ruegeria, Shewanella, Solibacillus, Tenacibaculum and Vibrio. Genetic variation was more likely to occur within similar marine bacteria species. The microbial community was found to affect the production of industrial enzymes and the diversity of marine bacteria.

Probiotic supplementation influences the diversity of the intestinal microbiota during early stages of farmed senegalese sole (Solea Senegalensis, Kaup 1858)

Ingestion of bacteria at early stages results in establishment of a primary intestinal microbiota which likely undergoes several stages along fish life. The role of this intestinal microbiota regulating body functions is crucial for larval development. Probiotics have been proved to modulate this microbiota and exert antagonistic effects against fish pathogens. In the present study, we aimed to determine bacterial diversity along different developmental stages of farmed Senegalese sole (Solea senegalensis) after feeding probiotic (Shewanella putrefaciens Pdp11) supplemented diet for a short period (10-30 days after hatching, DAH). Intestinal lumen contents of sole larvae fed control and probiotic diets were collected at 23, 56, 87, and 119 DAH and DNA was amplified using 16S rDNA bacterial domain-specific primers. Amplicons obtained were separated by denaturing gradient gel electrophoresis (DGGE), cloned, and resulting sequences compared to sequences in GenBank. Results suggest that Shewanella putrefaciens Pdp11 induces a modulation of the dominant bacterial taxa of the intestinal microbiota from 23 DAH. DGGE patterns of larvae fed the probiotic diet showed a core of bands related to Lactobacillus helveticus, Pseudomonas acephalitica, Vibrio parahaemolyticus, and Shewanella genus, together with increased Vibrio genus presence. In addition, decreased number of clones related to Photobacterium damselae subsp piscicida at 23 and 56 DAH was observed in probiotic-fed larvae. A band corresponding to Shewanella putrefaciens Pdp11 was sequenced as predominant from 23 to 119 DAH samples, confirming the colonization by the probiotics. Microbiota modulation obtained via probiotics addition emerges as an effective tool to improve Solea senegalensis larviculture.

First characterization of bacterial pathogen, Vibrio alginolyticus, for Porites andrewsi White syndrome in the South China Sea

Background

White syndrome, a term for scleractinian coral disease with progressive tissue loss, is known to cause depressed growth and increased morality of coral reefs in the major oceans around the world, and the occurrence of this disease has been frequently reported in the past few decades. Investigations during April to September in both 2010 and 2011 identified widespread Poritesandrewsi White syndrome (PAWS) in Xisha Archipelago, South China Sea. However, the causes and etiology of PAWS have been unknown.

Methodology/Principal Findings

A transmission experiment was performed on P. andrewsi in the Qilianyu Subgroup (QLY). The results showed that there was a significant (P ≤ 0.05) difference between test and control groups after 28 days if the invalid replicates were excluded. Rates of tissue loss ranged from 0.90-10.76 cm² d^-1 with a mean of 5.40 ± 3.34 cm² d^-1 (mean ± SD). Bacterial strains were isolated from the PAWS corals at the disease outbreak sites in QLY of the Xisha Archipelago, South China Sea, and included in laboratory-based infection trials to satisfy Koch’s postulates for establishing causality. Following exposure to bacterial concentrations of 10⁵ cells mL^-1, the infected colonies exhibited similar signs to those observed in the field. Using phylogenetic 16S rRNA gene analysis, classical phenotypic trait comparison, Biolog automatic identification system, MALDI-TOF mass spectrometry and MALDI Biotyper method, two pathogenic strains were identified as Vibrioalginolyticus.

Conclusion/Significance

This is the first report of V. alginolyticus as a pathogenic agent of PAWS in the South China Sea. Our results point out an urgent need to develop sensitive detection methods for V. alginolyticus virulence strains and robust diagnostics for coral disease caused by this and Vibrio pathogenic bacterium in the South China Sea.

An Overview of the Immunological Defenses in Fish Skin

The vertebrate immune system is comprised of numerous distinct and interdependent components. Every component has its own inherent protective value, and the final combination of them is likely to be related to an animal’s immunological history and evolutionary development. Vertebrate immune system consists of both systemic and mucosal immune compartments, but it is the mucosal immune system which protects the body from the first encounter of pathogens. According to anatomical location, the mucosa-associated lymphoid tissue, in teleost fish is subdivided into gut-, skin-, and gill-associated lymphoid tissue and most available studies focus on gut. The purpose of this paper is to summarise the current knowledge of the immunological defences present in skin mucosa as a very important part of the fish immune system, serving as an anatomical and physiological barrier against external hazards. Interest in defence mechanism of fish arises from a need to develop health management tools to support a growing finfish aquaculture industry, while at the same time addressing questions concerning origins and evolution of immunity in vertebrates. Increased knowledge of fish mucosal immune system will facilitate the development of novel vaccination strategies in fish.

Comparative study on the antibiotic susceptibility and plasmid profiles of Vibrio alginolyticus strains isolated from four Tunisian marine biotopes

The antibiotic resistance patterns and the plasmids profiles of the predominant etiological agent responsible for vibriosis in Tunisia, V. alginolyticus were studied to contribute to control their spread in some Mediterranean aquaculture farms and seawater. The sixty-nine V. alginolyticus strains isolated from different marine Tunisian biotopes (bathing waters, aquaculture and conchylicole farms and a river connected to the seawater during the cold seasons) were multi-drug resistant with high resistance rate to ampicillin, kanamycin, doxycyclin, erythromycin, imipinem, and nalidixic acid. The multiple resistance index ranged from 0.3 to 0.7 for the isolates of Khenis, from 0.5 to 0.8 for those of Menzel Jmil, from 0.5 to 0.75 (Hergla) and from 0.3 to 0.7 for the isolates of Oued Soltane. The high value of antibiotic resistance index was recorded for the V. alginolyticus population isolated from the fish farm in Hergla (ARI = 0.672) followed by the population isolated from the conchylicole station of Menzel Jmil (ARI = 0.645). The results obtained by the MIC tests confirmed the resistance of the V. alginolyticus to ampicillin, erythromycin, kanamycin, cefotaxime, streptomycin and trimethoprim. Plasmids were found in 79.48 % of the strains analyzed and 30 different plasmid profiles were observed. The strains had a high difference in the size of plasmids varying between 0.5 and 45 kb. Our study reveals that the antibiotic-resistant bacteria are widespread in the aquaculture and conchylicole farm relatively to others strains isolated from seawater.

Establishment of a Caenorhabditis elegans infection model for Vibrio alginolyticus

Vibrio alginolyticus, a common bacterium in the marine environment, is a threat to marine animals and humans by causing serious infections. The present study reveals the establishment of a Caenorhabditis elegans infection model for Vibrio alginolyticus. The infection and colonization was localized in the animal by tagging V. alginolyticus with GFP and using Confocal Laser Scanning Microscopy. Chemotactic response of C. elegans to V. alginolyticus, pharyngeal distention and blockage of vulval region leading to internal hatching were analyzed. The time required for causing infection, and the bacterial loads in the intestine of C. elegans were determined. Regulation of innate immune related genes, lys-7, clec-60 and clec-87, were also analyzed using real time PCR. The pathogen infected animals appeared to ward-off infection by up-regulating the candidate antimicrobial gene(s) for few hours, before succumbing to the pathogen. For the first time, the pathogenicity of V. alginolyticus at both physiological and molecular level has been studied in detail using the model organism C. elegans.

Genotyping of Vibrio alginolyticus isolates from Daya Bay by infrequent-restriction-site PCR and pulsed-field gel electrophoresis

Vibrio alginolyticus is a serious bacterial pathogen that hampered the whole industry of fish farming in Guangdong, China. In order to facilitate epidemiologic studies and improve the control of disease, we developed a highly efficient method of genotyping for V. alginolyticus using infrequent-restriction-site PCR (IRS-PCR) technology. With the enzyme combination of NotI-HhaI, optimized, unique, and easy-to-interpret patterns were generated. Forty-five V. alginolyticus isolates from aquatic animals and the marine environment in Daya Bay in Guangdong were fingerprinted by IRS-PCR and pulsed-field gel electrophoresis (PFGE). The reproducibility of the IRS-PCR method was high (100%) in conformity with PFGE. When primer PN-T or PN-G was used, IRS-PCR obtained the identical clustering as PFGE, producing 24 different patterns, respectively. Moreover, IRS-PCR presented a high discriminatory power (D=0.953) identical to that of PFGE. In conclusion, the IRS-PCR fingerprinting method using NotI-HhaI can provide a potentially useful tool for epidemiologic investigations of V. alginolyticus isolates.

Virulence and enterobacterial repetitive intergenic consensus PCR of Vibrio alginolyticus strains isolated from Tunisian cultured gilthead sea bream and sea bass outbreaks

Vibrio alginolyticus was isolated from the internal organs of diseased gilthead sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax) cultured in two fish farms located on the Tunisian Mediterranean coast, from 2003 to 2005. After phenotypic characterisation, a selection of 34 isolates from gilthead sea bream and sea bass were molecularly typed by repetitive intergenic consensus PCR (ERIC-PCR) showing a high polymorphism among the isolated strains (19 genotypes). Most of the isolates were resistant to atleast two antimicrobial agents. All the tested strains were resistant to ampicillin. However, 91.17% were resistant to nitrofurantoin and 35.29% to tetracycline. Several strains isolated from diseased gilthead sea bream and sea bass were tested for virulence in both fish species by intraperitoneal injection. The selected isolates (n=7) were pathogenic for gilthead sea bream and sea bass. LD(50) values ranged from 5.01 x 10(4) to 6.20 x 10(7)CFU/fish. This is the first report on characterisation and virulence of V. alginolyticus for sea bass and sea bream in Tunisia.