Bacterial Fish Diseases Research Articles

Impact of climatic change on emergence of bacterial fish diseases

Impact of climatic change on emergence of bacterial fish diseases

Potential therapeutic use of dermaseptin S4 from the frog Phyllomedusa sauvagii and its derivatives against bacterial pathogens in fish.

Dermaseptins are one of the main families of antimicrobial peptides (AMPs) derived from the skin secretions of Hylidae frogs. Among them, dermaseptin S4 (DS4) is characterized by its broad-spectrum of activity against bacteria, protozoa, and fungi. In this study, the physicochemical properties of the native peptide DS4 (1-28) and two derivatives [DS4 (1-28)a and DS4 (1-26)a] isolated from the skin of the frog Phyllomedusa sauvagii were investigated and their antimicrobial properties against two marine pathogenic bacteria (Vibrio harveyi and Vibrio anguillarum) were examined. The results indicate that the peptide DS4 (1-26)a has high-antibacterial activity against the tested strains and low-hemolytic activity (<30% lysis at the highest tested concentration of 100 µg/mL) compared to the other two peptides tested. In addition, all three peptides affect the membrane and cell wall integrity of both pathogenic bacteria, causing leakage of cell contents, with DS4 (1-26)a having the most severe impact. These skills were corroborated by transmission electron microscopy and by the variation of cations in their binding sites due to the effects caused by the AMPs. These results suggest that DS4 and its derivatives, in particular the truncated and amidated peptide DS4 (1-26)a could be effective in the treatment of infections caused by these marine pathogenic bacteria. Future studies are required to validate the use of DS4 in vivo for the prevention of bacterial diseases in fish.

Multiplex PCR assay for the accurate and rapid detection and differentiation of Lactococcus garvieae and L. petauri.

Lactococcosis is a common bacterial fish disease caused by Lactococcus garvieae, L. petauri and L. formosensis. Although there are different PCR-based techniques to identify the etiological agent, none of these can differentiate these two bacteria without sequencing PCR-amplified fragments. In the present study, we developed a multiplex PCR assay for simultaneous detection and differentiation of L. garvieae and L. petauri. The specificity of the primers was validated against the bacterial DNA of the targeted and non-targeted bacteria. The sizes of the PCR amplicons were obtained as 204 bp for the DUF1430 domain-containing protein gene of L. garvieae, 465 bp for the Lichenan permease IIC component gene of L. petauri, and 302 bp for the teichoic acid biosynthesis protein F gene of both L. garvieae and L. petauri. The PCR amplicons were clearly separated by agarose gel electrophoresis. The multiplex PCR assay did not produce any amplification products with the DNA of the non-targeted bacteria. The multiplex PCR detection limits for L. garvieae and L. petauri were 5 and 4 CFU in pure culture and 50 and 40 CFU/g in spiked tissue samples, respectively. It takes less than 2 h from plate-cultured bacteria and 3 h from tissue samples to get results. In conclusion, the developed multiplex PCR assay is a rapid, specific, accurate, and cost-effective method for the detection and differentiation of L. garvieae and L. petauri and is suitable to be used for routine laboratory diagnosis of L. garvieae and L. petauri.

Prevalence of Bacterial Diseases in Ornamental Fish Rearing Units of Kolathur, Tamil Nadu, India

Background: Ornamental fishkeeping is a widely embraced hobby globally. In India, Kolathur, Chennai Tamil Nadu is an important ornamental fish hub involved in trading of ornamental fishes. As a lucrative industry, the ornamental fish trade faces significant challenges due to diseases caused by various pathogens, impacting market value and causing economic losses. Methods: A surveillance study was conducted in Kolathur, Chennai, from December 2022 to August 2023. Ornamental fish samples exhibiting clinical signs of bacterial diseases were collected from the farms and retail outlets. Bacterial isolation and identification techniques, including conventional and PCR detection, were employed to isolate and identify bacterial strains from infected fish samples. Result: Out of 196 fish samples, 51 (29.4%) were found infected with bacterial pathogens. The prevalent bacterial pathogens included Aeromonas veronii (47%), A.caviae (17%), Pseudomonas aeruginosa (15%), Streptococcus sp. (11.3%), Mycobacterium fortuitum (5.6%) and Shewanella sp. (3.7%). Different fish families exhibited varying susceptibility to bacterial diseases, with cyprinids being the most affected (56.6%). The findings stress the importance of adhering to health regulations to prevent transboundary spread and suggest the development of targeted management strategies to sustain the health of ornamental fish populations.

Overview on the role of dietary Spirulina platensis on immune responses against Edwardsiellosis among Oreochromis niloticus fish farms

Edwardsiellosis is a bacterial fish disease that mostly occurs in freshwater farms and is characterized by a high mortality rate. Edwardsiella tarda strain was recovered from 17 fish out of 50 Nile tilapia, which were harboring clinical signs of systemic septicemia. The level of un-ionized ammonia (NH3) in the fish farm’s water was 0.11–0.15 mg/L, which was stressful for the Nile tilapia.Sequencing of the gyrB1 gene confirmed that the isolate was E. tarda JALO4, and it was submitted to NCBI under the accession number PP449014. The isolated E. tarda harbored the virulence gene edw1 AHL-synthase (quorum sensing). In addition, the isolate was sensitive to trimethoprim and sulfamethoxazole mean while it was intermediate to florfenicol. The median lethal dose (LD50) of E. tarda JALO4 was determined to be 1.7 × 105 CFU/mL in Nile tilapia.In the indoor experiment, Nile tilapia (45.05 ± 0.4 g), which received dietary Spirulina platensis (5 and 10 g/kg fish feed), showed optimum growth and feed utilization. Meanwhile, after receiving dietary S. platensis, the fish’s feed conversion ratio (FCR) was significantly enhanced compared to the control, which was 1.94, 1.99, and 2.88, respectively. The expression of immune-related genes interleukin (IL)-1β and tumor necrosis factor (TNF)-α were upsurged in E. tarda-challenged fish with higher intensity in S. platensis groups. Dietary S. platensis at a dose of 10 g/kg fish feed could provide a relative protection level (RPL) of 22.2% Nile tilapia challenged against E. tarda. Nile tilapia experimentally infected E. tarda, drastically altering their behavior: higher operculum movement, low food apprehension, and abnormal swimming dietary S. platensis (10 g/kg fish feed) could rapidly restore normal status.It was concluded that Edwardsiellosis could alter Nile tilapia behavior with a high loss in fish population. Fish received dietary-S. platensis could rapidly restore normal behavior after E. tarda infection. It is recommended the incorporation of S. platensis at doses of 10 g/kg into the Nile tilapia diet to boost their immunity and counteract E. tarda infection.

Streptomyces enissocaesilis L-82 has broad-spectrum antibacterial activity and promotes growth for Carassius auratus.

Aeromonas is the main pathogen causing bacterial diseases in fish. The disadvantages of chemical drugs to control fish diseases have been highlighted, and it is urgent to find an eco-friendly control method. In this study, an actinomycete strain with antibacterial activity against fish pathogenic bacteria was screened from soil samples. Combined with morphological characteristics, physiological and biochemical characteristics, and gyrB gene and whole genome comparison analysis, it was identified as a new strain of Streptomyces enissocaesilis, named Streptomyces enissocaesilis L-82. The strain has broad-spectrum antibacterial activity against fish pathogens. A substance with a mass-to-charge ratio of 227.20 [M + H] + was isolated and purified by high-performance liquid chromatography and mass spectrometry. It was presumed to be a derivative of 5-dimethylallylindole-3-acetonitrile. The strain is safe and non-toxic to crucian carp, and can stably colonize crucian carp and inhibit the proliferation of A. hydrophila. After feeding the feed containing 1 × 108CFU/mL strain concentration, the weight growth rate and specific growth rate of crucian carp increased, the activity of ACP and SOD in serum increased, and the survival rate of crucian carp increased after challenge. Genome-wide analysis showed that the strain had strong ability to metabolize and tolerate extreme environments. And has a strong potential for disease resistance. Therefore, the strain is expected to be developed as a feed additive for fish farming. KEY POINTS: • The new Streptomyces enissocaesilis L-82 has a broad spectrum and stable antibacterial activity and meets the safety standards of feed additives. • Strain L-82 can colonize crucian carp, improve the growth, antioxidant, and immune performance of the host, and improve the survival rate after being infected with A. hydrophila. • Genome-wide analysis suggests that the strain has great disease resistance potential and is expected to be developed as a feed additive for fish culture.

Isolation of potential zoonotic Mycobacterium spp. from diseased freshwater angelfish (Pterophyllum scalare) from an aquarium.

Nontuberculous mycobacteria infection is one of the most common chronic bacterial diseases in ornamental aquarium fish and appears to be directly related to stressful husbandry practices. Furthermore, it also represents zoonotic potential. Here we present the isolation and characterization of non-tuberculous mycobacteria from diseased freshwater angelfish (Pterophyllum scalare) in São Paulo, Brazil. Nine discarded breeding females with signs of disease were evaluated. The fish exhibited lethargy, loss of appetite, cachexia, skin ulcers, and exophthalmia. At necropsy, four fishes presented macroscopic granulomas in the spleen. Mycobacterium chelonae, M. fortuitum, M. gordonae, M. intracellulare and M. peregrinum were isolated and identified by hsp65 PCR restriction analysis. Histopathological analysis revealed microscopic lesions compatible with mycobacteriosis, and Mycobacterium bacillus were observed by Ziehl-Neelsen stain. Notably, all Mycobacterium species identified in this study have already been reported in human patients; therefore, diseased animals may be a source of infection for people who handle fish and aquariums.

Biofloc technology: A sustainable approach towards wastewater utilization and fish production

AbstractBiofloc technology (BFT) has gained popularity recently as the aquaculture industry faces significant economic losses due to water pollution creating various pathogens. Many bacterial, viral and fungal diseases in fish cause a decrease in annual world fish production. Therefore, owing to a growing demand for healthy fish, zero‐water exchange is widely practiced in fish and shellfish production. It minimizes the release of aquaculture wastewater into the aquatic ecosystem, which contains nutrients, organic matter and pathogens. It uses a minimal amount of land, which provides an impartial cost–benefit ratio to maintain socio‐economic sustainability. Besides sustainability, fish cultured in the BFT have also expressed better health status after being challenged by different pathogens. However, this review explores the use of BFT as a sustainable approach to wastewater utilization and fish and shellfish production. Apart from this, the review highlights the potential of BFT to enhance fish production in aquaculture systems and discusses various factors that affect the performance of systems, such as carbon‐to‐nitrogen ratios, aeration and the use of probiotics. It also investigates the role of biofloc in improving water quality, fish and shellfish health prophylactic properties, and its effect on gut microflora. The review further examines the economic feasibility of BFT and discusses about the cost‐effectiveness of implementing systems and the potential for generating additional revenue through the sale of bioflocs as a value‐added product. Overall, this review highlights the potential of BFT as a sustainable solution for wastewater utilization and increasing fish production. It provides valuable insights into the factors affecting the performance of BFT systems and suggests areas for further research and development in this field.

A nanocarrier immersion vaccine encoding surface immunogenic protein confers cross-immunoprotection against Streptococcus agalactiae and Streptococcus iniae infection in tilapia

Streptococcosis is a highly contagious aquatic bacterial disease that poses a significant threat to tilapia. Vaccination is a well-known effective measure to prevent and control fish bacterial diseases. Among the various immunization methods, immersion vaccination is simple and can be widely used in aquaculture. Besides, nanocarrier delivery technology has been reported as an effective solution to improve the immune effect of immersion vaccine. In this study, the surface immunogenic protein (Sip) was proved to be conserved and potential to provide cross-immunoprotection for both Streptococcus agalactiae (S. agalactiae) and Streptococcus iniae (S. iniae) by multiple sequences alignment and Western blotting analysis. On this basis, we expressed and obtained the recombinant protein rSip and connected it with functionalized carbon nanotubes (CNT) to construct the nanocarrier vaccine system CNT-rSip. After immersion immunization, the immune effect of CNT-rSip against above two streptococcus infections was evaluated in tilapia based on some aspects including the serum specific antibody level, non-specific enzyme activities, immune-related genes expression and relative percent survival (RPS) after bacteria challenge. The results showed that compared with control group, CNT-rSip significantly (P < 0.05) increased the serum antibody levels, related enzyme activities including acid phosphatase, alkaline phosphatase, lysozyme and total antioxidant capacity activities, as well as the expression levels of immune-related genes from 2 to 4 weeks post immunization (wpi), and all these indexes peaked at 3 wpi. Besides, the above indexes of CNT-rSip were higher than those of rSip group with different extend during the experiment. Furthermore, the challenge test indicated that CNT-rSip provided cross-immunoprotection against S. agalactiae and S. iniae infection with RPS of 75 % and 72.41 %, respectively, which were much higher than those of other groups. Our study indicated that the nanocarrier immersion vaccine CNT-rSip could significantly improve the antibody titer and confer cross-immuneprotection against S. agalactiae and S. iniae infection in tilapia.

Lactococcus garvieae ile Enfekte Archocentrus centrarchus’ta Bağışıklıkla İlişkili Enzim Gen Etkileşimleri

Unsuitable environmental conditions and low host resistance in the aquatic environment are the most important factors in fish diseases. Bacterial diseases in fish can be treated with different preparations. The aim of this study is to determine the disease symptoms, expression levels of TNF and IL genes and some biochemical parameter changes in Archocentrus centrarchus by using herbal extract for the treatment of the disease caused by Lactococcus garvieae bacteria. Gene expression was performed by Real-Time PCR and enzyme activities were determined by spectrophotometric analysis method. It was observed that the expression level of TNF gene was 2.5 times more effective in the antibiotic (oxytetracycline) group and 14 times more effectively in the extract application. It was found that the antibiotic group had a close expression level compared to the control at the IL gene expression level, while the extract group expressed 5.5 times more. Glutathione s-transferase activity in the extract group increased significantly compared to the control and antibiotic groups. Superoxide dismutase activity was significantly higher in the extract group compared to the antibiotic and bacterial groups. It can be said that oxidative stress caused by bacterial infection is tried to be eliminated more in the extract group. It was determined that the andiz root extract which at the patent stage, which was used for the first time in the treatment of A. centrarchus fish infected with L. garvieae, one of the most important bacterial agents in the field of aquaculture, is applicable.

Transcriptional regulation of the Japanese flounder Cu,Zn-SOD (Jfsod1) gene in RAW264.7 cells during oxidative stress caused by causative bacteria of edwardsiellosis

Edwardsiellosis is one of the most important bacterial diseases in fish, sometimes causing extensive economic losses in the aquaculture industry. Our previous studies demonstrated that the Cu,Zn-SOD (sod1) activity has significantly increased in Japanese flounder, Paralichthys olivaceus, hepatopancreas infected by causative bacteria of edwardsiellosis Edwardsiella tarda NUF251. In this study, NUF251 stimulated intracellular superoxide radical production in mouse macrophage RAW264.7 cells, which was reduced by N-acetylcysteine. This result suggests that NUF251 infection causes oxidative stress. To evaluate the regulatory mechanism of Jfsod1 at transcriptional levels under oxidative stress induced by NUF251 infection, we cloned and determined the nucleotide sequence (1124 bp) of the 5′-flanking region of the Jfsod1 gene. The sequence analysis demonstrated that the binding sites for the transcription factors C/EBPα and NF-IL6 involved in the transcriptional regulation of the mammalian sod1 gene existed. We constructed a luciferase reporter system with the 5′-flanking region (−1124/−1) of the Jfsod1 gene, and a highly increased transcriptional activity of the region was observed in NUF251-infected RAW264.7 cells. Further studies using several mutants indicated that deletion of the recognition region of NF-IL6 (−272/−132) resulted in a significant decrease in the transcriptional activity of the Jfsod1 gene in NUF251-infected RAW264.7 cells. In particular, the binding site (−202/−194) for NF-IL6 might play a major role in upregulating the transcriptional activity of the 5′-flanking region of the Jfsod1 gene in response to oxidative stress induced by NUF251 infection. These results could be provided a new insight to understand the pathogenic mechanism of causative bacteria of edwardsiellosis.

Enolase-based nanovaccine immersion immunization induces robust immunity and protection against Streptococcus infection in tilapia

Streptococcal disease is one of the most serious diseases in tilapia, causing huge economic losses to the tilapia farming industry. Streptococcus agalactiae (S. agalactiae) and Streptococcus iniae (S. iniae) are the two main pathogens of tilapia streptococcosis. Vaccination has been proved to be an effective measure to control fish bacterial diseases. In this study, we selected the Enolase (Eno) as the candidate vaccine antigen, which is the common antigen of S. agalactiae and S. iniae with high similarity (97.2%), the rEno was obtained and the CNT-rEno nanocarrier vaccine system was constructed by connecting the rEno protein with functionalized carbon nanotubes (CNTs), the immersion immune effect against S. agalactiae and S. iniae infection was evaluated. The results showed that, compared with the control group, CNT-rEno significantly enhanced the serum antibody production, related enzyme activities and immune-related genes expression. It was worth noting that CNT-rEno demonstrated better immunoprotection against S. agalactiae and S. iniae infection, with relative percent survivals of 73.68% (S. agalactiae) and 68.96% (S. iniae), respectively, which were both much higher than those of rEno groups (36.84% and 31.03%, respectively). Our study indicated that the CNT-rEno nanovaccine had the ability to elicit robust immune responses in tilapia by immersion immunization, and had the potential to offer cross-protection against S. agalactiae and S. iniae infection.

Study on Diagnosis Precaution and Control of Bacterial Diseases in Fish

Study on Diagnosis Precaution and Control of Bacterial Diseases in Fish

Interplay between a bacterial pathogen and its host in rainbow trout isogenic lines with contrasted susceptibility to cold water disease

Infectious diseases are a major constraint on aquaculture. Genetic lines with different susceptibilities to diseases are useful models to identify resistance mechanisms to pathogens and to improve prophylaxis. Bacterial cold-water disease (BCWD) caused by Flavobacterium psychrophilum represents a major threat for freshwater salmonid farming worldwide. A collection of rainbow trout (Oncorhynchus mykiss) isogenic lines was previously produced from a French domestic population. Here, we compared BCWD resistance phenotypes using a subset of isogenic lines chosen for their contrasted susceptibilities to F. psychrophilum. We applied individual monitoring to document the infection process, including time-course quantification of bacteremia and innate immune response. Strikingly, BCWD resistance was correlated with a lower bacterial growth rate in blood. Several immune genes were expressed at higher levels in resistant fish regardless of infection: the Type II arginase (arg2), a marker for M2 macrophages involved in anti-inflammatory responses and tissue repair, and two Toll-like receptors (tlr2/tlr7), responsible for pathogen detection and inflammatory responses. This study highlights the importance of innate and intrinsic defense mechanisms in determining the outcome of F. psychrophilum infections, and illustrates that non-lethal time-course blood sampling for individual monitoring of bacteremia is a powerful tool to resolve within-host pathogen behavior in bacterial fish diseases.

Exopolysaccharides-Mediated ZnO Nanoparticles for the Treatment of Aquatic Diseases in Freshwater Fish Oreochromis mossambicus.

Bacterial fish disease outbreaks are a key concern for aquaculture. Complementary feed additives such as immunostimulants can serve as an ideal solution for disease prevention. Herein, we scrutinized the efficacy of exopolysaccharides (EPSs) from probiotic Bacillus licheniformis and EPS-mediated zinc oxide nanoparticles (EPS-ZnO NPs) for a diet to evaluate growth parameters, antioxidant enzyme activities, and immune stimulation together with disease resistance against Aeromonas hydrophila and Vibrio parahaemolyticus in Mozambique tilapia Oreochromis mossambicus. Fish were separated into seven groups, with six experimental groups fed with EPS and EPS-ZnO NPs at 2, 5, and 10 mg/g and a control fed a basal diet. The fish ingesting feed supplemented with EPS and EPS-ZnO NPs at 10 mg/g showed improved growth performance. Cellular and humoral-immunological parameters were tested in serum and mucus after 15 and 30 days of feeding. These parameters were substantially enriched with a 10 mg/g diet (p < 0.05) of EPS and EPS-ZnO NPs in comparison with the control. Furthermore, the EPS and EPS-ZnO NP supplemental diet actively enhanced the antioxidant response (glutathione peroxidase, superoxide dismutase, and catalase). In addition, the supplemental diet of EPS and EPS-ZnO NPs lowered the death rate and improved the disease resistance of O. mossambicus following assessment with A. hydrophila and V. parahaemolyticus at 50 µL. Hence, the overall results suggest that the supplemental diet of EPS and EPS-ZnO NPs might be used to ensure aquaculture feed additives.

Enhancement of seaweed polysaccharides (fucoidan and laminarin) on the phagocytosis of macrophages via activation of intelectin in blunt snout bream (Megalobrama amblycephala)

Fucoidan and laminarin are polymolecular compounds that extracted from seaweed. As functional polysaccharides, they possess various biological functions such as immunomodulatory, anti-inflammatory, antiviral and antioxidant bioactivities. Fucoidan and laminarin modulate host immune responses by activating immune cells (macrophages, neutrophils, T lymphocytes) and inducing the expression of cytokines (TNFα, IL-1β, IL-6, IL-8, NF-κB). Intelectin is a novel lectin that plays important roles in bacterial agglutination and bactericidal effects by recognizing the polysaccharide components on the cell surface of pathogens, which can also enhance the phagocytosis of macrophages. The present study intends to explore the immunomodulatory effects of fucoidan, laminarin and intelectin on the macrophages of Megalobrama amblycephala. The results showed that the incubation of both fucoidan and laminarin at the concentration of 100 μg/mL for 4 h could enhance the phagocytic capacity of M. amblycephala macrophages, which also showed remodeled cytoskeleton with extended pseudopodia. In addition, fucoidan and laminarin could induce the expression of M. amblycephala intelectin (MaINTL) in the primary hepatocytes and macrophages, and the recombinant MaINTL (rMaINTL) could bind with fucoidan and laminarin. Furthermore, fucoidan and laminarin induced the expression of cytoskeletal remodeling related genes in the primary M. amblycephala macrophages, such as Rac1 and WASP, which should contribute to the enhancement of seaweed polysaccharides (fucoidan and laminarin) and MaINTL on the phagocytosis of M. amblycephala macrophages. However, even though fucoidan and laminarin could induced the expression of CXCL8, while the chemotaxis of M. amblycephala macrophages on neutrophils was not affected by them. These findings suggested that fucoidan and laminarin enhanced the phagocytic capacity of M. amblycephala macrophages via activation of MaINTL and up-regulation of the expression of downstream cytoskeletal remodeling related genes Rac1 and WASP. Therefore, fucoidan and laminarin could be used as immune enhancers to improve host immunity and disease resistance in M. amblycephala, which provided novel insights into the prevention and protection of fish bacterial diseases.

Discovery of Novel Bactericides from Aspergillus alabamensis and Their Antibacterial Activity against Fish Pathogens.

The emerging outbreak of bacterial diseases is a major challenge for the aquaculture industry. The development of new antibacterial agents from natural resources to curb fish bacterial diseases in aquaculture is becoming increasingly popular. In this study, eight new benzoic acid-containing alkaloids, asperalin A-F (1-6), asperalumazine A (7), and N-(3-acetamidopropyl)-3,4-dihydroxybenzamide (8), along with four known compounds (9-12) were isolated and identified from a seagrass-derived Aspergillus alabamensis. Their chemical structures were established on the basis of extensive spectroscopic analyses (including HRESIMS, 1D and 2D NMR spectroscopy), NMR computational methods, and electronic circular dichroism (ECD) calculations. Compounds 1-6 exhibited moderate or potent inhibitory activities against at least one fish pathogenic bacterium, among Edwardsiella ictalurid, Streptococcus iniae, and Streptococcus parauberis, and these compounds represent the first report of the coupling of dihydroquinolone alkaloids with benzoic acid derivatives. Compounds 3 and 4 showed strong activities against Staphylococcus aureus, S. iniae, and S. parauberis, with an MIC value of 10.1, 5.0, and 10.1 μM, respectively. Compound 5, an N-alkylated product of 4, exhibited the strongest inhibitory effects against S. iniae, with an MIC value of 2.2 μM. Notably, compound 6, as a new natural bactericide, showed moderate to potent inhibitory activity toward all strains tested, including one Gram-negative bacterium E. ictalurid (10.9 μM, MIC) and four Gram-positive bacteria S. iniae (43.6 μM, MIC), S. aureus (21.8 μM, MIC), S. parauberis (87.3 μM, MIC), and Bacillus subtilis (21.8 μM, MIC). Compound 7 represents the first example of a lumazine derivative directly coupled to a benzoic acid moiety by a hydroxymethyl group.

Molecular characterization and expression patterns of CXCL8 gene from blunt snout bream (Megalobrama amblycephala) and its chemotactic effects on macrophages and neutrophils

CXCL8 is a typical CXC-type chemokine, which mediates the migration of immune cells from blood vessels to the site of inflammation or injury to clear pathogenic microorganisms and repair damaged tissues. In this study, Megalobrama amblycephala CXCL8 (MaCXCL8) gene was identified and characterized. Sequence analysis showed that the deduced MaCXCL8 protein possessed the typical structure of CXCL8 from other species, with the characteristic CXC cysteine residues in the N-terminal and accompanied by a DLR motif (Asp-Leu-Arg motif). Phylogenetic analysis revealed that MaCXCL8 was homologous to that of Ctenopharyngodon idella and other cyprinid fishes. MaCXCL8 gene was expressed in all detected healthy tissues, with the highest expression levels in the spleen, and its expression was significantly up-regulated upon the challenge of Aeromonas hydrophila and Lipopolysaccharide (LPS) both in juvenile M. amblycephala tissues and primary macrophages. The immunohistochemical assay showed that MaCXCL8 was mainly distributed in the nucleus and cytoplasm, and its expression levels increased observably with the prolongation of bacterial infection. In addition, recombinant MaCXCL8 protein exhibited significant chemotactic effects on neutrophils and macrophages. In conclusion, MaCXCL8 is involved in the immune response of M. amblycephala, and these findings will be helpful to understand the biological roles of MaCXCL8 and provide a theoretical basis for the prevention and control of fish bacterial diseases.

Comparative Expression Profiling Reveals the Regulatory Effects of Dietary Mannan Oligosaccharides on the Intestinal Immune Response of Juvenile Megalobrama amblycephala against Aeromonas hydrophila Infection.

Mannan oligosaccharides (MOS) are functional oligosaccharides with beneficial effects on the non-specific immunity of Megalobrama amblycephala, but systematic studies on the immunomodulatory mechanisms of MOS are still lacking. To investigate the protective mechanisms of three different levels of dietary MOS supplementation on the intestinal immunity of juvenile M. amblycephala, comparative digital gene expression (DGE) profiling was performed. In this study, 622 differentially expressed genes (DEGs) were identified, while the similar expression tendency of 34 genes by qRT-PCR validated the accuracy of the DGE analyses. Gene Ontology (GO) enrichment revealed that the DEGs were mainly enriched in two functional categories of biological process and molecular function. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that the DEGs were mainly related to complement and coagulation cascades, coagulation cascades, platelet activation, natural killer cell mediated cytotoxicity, Fc gamma R-mediated phagocytosis and antigen processing and presentation. In addition, the pro-inflammatory, apoptosis and tight junction-related genes were more significantly up-regulated upon infection in the dietary MOS groups to enhance host immune functions and maintain the stability of the intestinal barrier. These results will be helpful to clarify the regulatory mechanism of MOS on the intestinal immunity of M. amblycephala and lay the theoretical foundation for the prevention and protection of fish bacterial diseases.

Incidence, Transmission Mechanisms and Pathologic Implications of Bacterial Zoonotic Diseases of Fish

Incidence, Transmission Mechanisms and Pathologic Implications of Bacterial Zoonotic Diseases of Fish