The effect of Aeromonas hydrophila infection on the non-specific immunity of blunt snout bream (Megalobrama amblycephala)

Effects of berberine hydrochloride on antioxidant response and gut microflora in the Charybdis japonica infected with Aeromonas hydrophila

This study used berberine hydrochloride to treat the Asian paddle crab, Charybdis japonica infected with the Gram-negative bacterium Aeromonas hydrophila at concentrations of 0, 100, 200 and 300 mg/L. The effect of berberine hydrochloride on the survival rate and gut microbiota of C. japonica was investigated. Berberine hydrochloride improved the stability of the intestinal flora, with an increase in the abundance of probiotic species and a decrease in the abundance of both pathogenic bacteria after treatment with high concentrations of berberine hydrochloride. Berberine hydrochloride altered peroxidase activity (POD), malondialdehyde (MDA), and lipid peroxidation (LPO) in the intestinal tract compared to the control. Berberine hydrochloride could modulate the energy released from the enzyme activities of hexokinase (HK), phosphofructokinase (PFK), and pyruvate kinase (PK) in the intestinal tract of C. japonica infected with A. hydrophila. Zona occludens 1 (ZO-1), Zinc finger E-box binding homeobox 1 (ZEB1), occludin and signal transducer, and activator of transcription5b (STAT5b) expression were also increased, which improved intestinal barrier function. The results of this study provide new insights into the role of berberine hydrochloride in intestinal immune mechanisms and oxidative stress in crustaceans.

Coinfection of channel catfish (Ictalurus punctatus) with virulent Aeromonas hydrophila and Flavobacterium covae exacerbates mortality

Flavobacterium covae and virulent Aeromonas hydrophila are prevalent bacterial pathogens within the US catfish industry that can cause high mortality in production ponds. An assessment of in vivo bacterial coinfection with virulent A. hydrophila (ML09-119) and F. covae (ALG-00-530) was conducted in juvenile channel catfish (Ictalurus punctatus). Catfish were divided into seven treatments: (1) mock control; (2) and (3) high and low doses of virulent A. hydrophila; (4) and (5) high and low doses of F. covae; (6) and (7) simultaneous challenge with high and low doses of virulent A. hydrophila and F. covae. In addition to the mortality assessment, anterior kidney and spleen were collected to evaluate immune gene expression, as well as quantify bacterial load by qPCR. At 96 h post-challenge (hpc), the high dose of virulent A. hydrophila infection (immersed in 2.3 × 107  CFU mL-1 ) resulted in cumulative percent mortality (CPM) of 28.3 ± 9.5%, while the high dose of F. covae (immersed in 5.2 × 106  CFU mL-1 ) yielded CPM of 23.3 ± 12.9%. When these pathogens were delivered in combination, CPM significantly increased for both the high- (98.3 ± 1.36%) and low-dose combinations (76.7 ± 17.05%) (p < .001). Lysozyme activity was found to be different at 24 and 48 hpc, with the high-dose vAh group demonstrating greater levels than unexposed control fish at each time point. Three proinflammatory cytokines (tnfα, il8, il1b) demonstrated increased expression levels at 48 hpc. These results demonstrate the additive effects on mortality when these two pathogens are combined. The synthesis of these mortality and health metrics advances our understanding of coinfections of these two important catfish pathogens and will aid fish health diagnosticians and channel catfish producers in developing therapeutants and prevention methods to control bacterial coinfections.

Effects of Dietary Limonene Supplementation on Growth Performance and Immunological Parameters of Common Carp, Cyprinus carpio, Challenged by Aeromonas hydrophila

This study examined the impact of dietary limonene treatment on the growth performance, immune response, and disease resistance of common carp, Cyprinus carpio. The fish were fed with either a control diet (CTL; no limonene supplementation) or four experimental diets containing 50 (50 L), 100 (100 L), 200 (200 L), and 400 (400 L) mg/kg limonene over a 70-day period, followed by Aeromonas hydrophila challenge. The 200 L treatment resulted in a significant decrease in FCR compared to the CTL treatment. The highest post-challenge mortality was associated with the CTL treatment (62.7%), while the 200 L treatment had the lowest mortality (30.7%). Before the challenge, dietary limonene significantly increased humoral and skin mucosal immune parameters compared to the CTL treatment. The highest leukocyte, lymphocyte counts, skin mucosal protease activity, and intestinal lactic acid bacteria were observed in the 200 L treatment before the challenge. The highest plasma lysozyme activity was observed in the 400 L treatment, whereas the highest skin mucosal lysozyme and peroxidase activities were observed in the 100 L and 200 L treatments before the challenge. There were no significant differences in the blood neutrophil, monocyte, and eosinophil counts, humoral alternative complement activity, skin mucosal alkaline phosphatase activity, and the intestinal total viable bacteria among the treatments before the challenge. After the challenge, the 200 L treatment exhibited the highest leukocyte, neutrophil, and monocyte count, skin mucosal immune parameters, and intestinal lactic acid bacteria, whereas the highest blood eosinophil count was observed in the 100 L, 200 L, and 400 L treatments. At this time, the lowest blood lymphocyte counts were observed in the 100 L and 200 L, but the lowest intestinal total viable bacteria were observed in the 100 L, 200 L, and 400 L treatments. Based on these findings, dietary limonene at 200 mg/kg is ideal for common carp to promote feed efficiency, innate immunity boosting, and resistance against A. hydrophila.

Immunoprotective role of aloin and disease resistance in Labeo rohita, infected with bacterial fish pathogen, Aeromonas hydrophila

The effect of aloin on mucosal immune response and disease resistance was elucidated in Labeo rohita infected with the bacterial fish pathogen, Aeromonas hydrophila. Fishes were divided into four groups: (i) control, (ii) vehicle control, (iii) bacteria infected and (iv) bacteria infected and aloin treated. Fish were intraperitoneally injected with A. hydrophila suspension at the dose of 2 × 10⁶ CFU/fish at 0 day (d). Following bacterial injection at 0 d, fish were treated with aloin at a dose of 1 mg/kg body weight intraperitoneally at an interval of 24 h for 4 consecutive days. Mucus collected from fish of each group was analyzed at 2 d, 4 d, 6 d, 8 d and 10 d. In bacteria-infected fish, a significant decrease (P < 0.05) in the activity of certain enzymatic and non-enzymatic immune parameters was observed. The activity of these immune parameters showed a gradual recovery on administration of aloin in bacteria-infected fish. Cumulative mortality was also found to be low in the aloin-treated group as compared to that in the infected group. Thus, aloin could act as an immunostimulant and play a protective role against disease caused by bacteria.

Protective effects of the fructooligosaccharide on the growth performance, biochemical indexes, and intestinal morphology of blunt snout bream (Megalobrama amblycephala) infected by Aeromonas hydrophila

The purpose of the study was to investigate the effects of dietary fructooligosaccharide (FOS) on growth performance, biochemical indexes, intestinal morphology, and growth-related gene expression of blunt snout bream (Megalobrama amblycephala) infected by Aeromonas hydrophila (AH). Two hundred twenty-five healthy blunt snout bream with an initial body weight of 38.41 ± 0.88 g were randomly divided into five groups with three replicates: control (basal diet), model (AH + basal diet), SFOS (AH + 2 g/kg FOS), MFOS (AH + 4 g/kg FOS), LFOS (AH + 6 g/kg FOS). After 9 weeks of feeding, the results showed that the FOS-added diet abrogated AH-induced retardation, hemorrhage, and inflammatory infiltration. FOS supplementation enhanced the growth performance degradation caused by AH, and the highest growth performance was observed at MFOS. Meanwhile, the addition of FOS to feed improved the blood immunity reduced by AH. In expansion, the mucosal epithelium of intestinal villi exfoliated, exposing the lamina propria, and a few villi were genuinely harmed in the model group. Fish fed with MFOS ameliorated the damaged intestine, evidenced by well-preserved intestine architecture. Furthermore, the model group downregulated the expression of growth-related genes (growth hormone receptor (GHR), insulin-like growth factor 1 (IGF-1)). Fish fed with 2 g/kg or 4 g/kg FOS upregulated the genes specified above expressions in the liver compared with the model group. In conclusion, the results mentioned above suggested that the dietary FOS could relieve the pressure to elevate the immune damage and intestine injury induced by AH and enhance the hepatic expression of IGF-1 and GHR.

Influence of biosynthesized nanoparticles exposure on mortality, residual deposition, and intestinal bacterial dysbiosis in Cyprinus carpio

Nanotechnology has revealed profound possibilities for the applications in applied sciences. The nanotechnology works based on nanoparticles. Among nanoparticles, silver nanoparticles largely introduced into aquatic environments during fabrication. Which cause severe contamination in the environment specially in freshwater fish. Therefore, the current study was a pioneer attempt to use the animal blood to fabricate AgNPs and investigate their toxicity in Cyprinus carpio (C. carpio) by recording mortality, tissue bioaccumulation, and influence on intestinal bacterial diversity. For this purpose, fish groups were exposed to different concentrations of B-AgNPs including 0.03, 0.06, and 0.09 mg/L beside the control group for 1, 10, and 20 days. Initially, the highest concentration caused mortality. The results revealed that B-AgNPs were significantly (p < 0.005) accumulated in the liver followed by intestines, gills, and muscles. In addition, the accumulation of B-AgNPs in the intestine led to bacterial dysbiosis in Cyprinus carpio. At the phylum level, Tenericutes, Bacteroidetes, and Planctomycetes were gradually decreased at the highest concentration of B-AgNPs (0.09 mg/L) on days 1, 10, and 20 days. The genera Cetobacterium and Luteolibactor were increased at the highest concentration on day 20. Moreover, the principal coordinate analysis (PCoA) based on Bray-Curtis showed that the B-AgNPs had led to a variation in the intestinal bacterial community. Based on findings, the B-AgNPs induced mortality, and residual deposition in different tissues, and had a stress influence on intestinal homeostasis by affecting the intestinal bacterial community in C. carpio which could have a significant effect on fish growth.

ROS Induced by Streptococcus agalactiae Activate Inflammatory Responses via the TNF-α/NF-κB Signaling Pathway in Golden Pompano Trachinotus ovatus (Linnaeus, 1758)

Streptococcus agalactiae is common pathogenic bacteria in aquaculture and can cause mass mortality after fish infection. This study aimed to investigate the effects of S. agalactiae infection on the immune and antioxidant regulatory mechanisms of golden pompano (Trachinotus ovatus). Serum and liver samples were obtained at 0, 6, 12, 24, 48, 96, and 120 h after golden pompano infection with S. agalactiae for enzyme activity and gene expression analyses. After infection with S. agalactiae, the content of reactive oxygen species (ROS) in serum was significantly increased (p < 0.05). Serum levels of glucose (GLU), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and malondialdehyde (MDA) increased and then decreased (p < 0.05), reaching a maximum at 6 h. Serum antioxidant enzyme (LZM) activity increased significantly (p < 0.05) and reached a maximum at 120 h. In addition, the mRNA expression levels of antioxidant genes (SOD, CAT, and GPx) in the liver increased and then decreased, reaching the maximum at 24 h, 48 h, and 24 h, respectively. During the experimental period, the mRNA expression levels of NF-κB-related genes of the inflammatory signaling pathway inhibitory κB (IκB) showed an overall decreasing trend (p < 0.05) and the lowest expression at 120 h, whereas the mRNA expression levels of tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β), IκB kinase (IKK), and nuclear factor NF-κB increased significantly (p < 0.05) and the highest expression was at 120 h. In conclusion, these results showed that S. agalactiae could activate internal regulatory signaling in the liver of golden pompano to induce defense and immune responses. This study is expected to lay a foundation to develop the healthy aquaculture of golden pompano and promote a more comprehensive understanding of its disease resistance mechanisms.

From Farm to Fork: Streptococcus suis as a Model for the Development of Novel Phage-Based Biocontrol Agents

Bacterial infections of livestock threaten the sustainability of agriculture and public health through production losses and contamination of food products. While prophylactic and therapeutic application of antibiotics has been successful in managing such infections, the evolution and spread of antibiotic-resistant strains along the food chain and in the environment necessitates the development of alternative or adjunct preventive and/or therapeutic strategies. Additionally, the growing consumer preference for "greener" antibiotic-free food products has reinforced the need for novel and safer approaches to controlling bacterial infections. The use of bacteriophages (phages), which can target and kill bacteria, are increasingly considered as a suitable measure to reduce bacterial infections and contamination in the food industry. This review primarily elaborates on the recent veterinary applications of phages and discusses their merits and limitations. Furthermore, using Streptococcus suis as a model, we describe the prevalence of prophages and the anti-viral defence arsenal in the genome of the pathogen as a means to define the genetic building blocks that are available for the (synthetic) development of phage-based treatments. The data and approach described herein may provide a framework for the development of therapeutics against an array of bacterial pathogens.

A novel interleukin-1 receptor-associated kinase 4 from blunt snout bream (Megalobrama amblycephala) is involved in inflammatory response via MyD88-mediated NF-κB signal pathway

Interleukin-1 receptor-associated kinase 4 (IRAK4) plays a crucial role in the Toll-like receptor/IL-1R signal pathway, which mediates the downstream signal transduction involved in innate and adaptive immunity. In the present study, an IRAK4 homologue (named as MaIRAK4) from blunt snout bream (Megalobrama amblycephala) was cloned and characterized. The open reading frame (ORF) of MaIRAK4 contains 1422 nucleotides, encoding a putative protein of 473 amino acids. Protein structural analysis revealed that MaIRAK4 has an N-terminal death domain (DD) and a central kinase domain (S_TKc), similar to those of mammals and other fishes. Multiple sequence alignment demonstrated that MaIRAK4 is highly homologous with that of grass carp (97.67%). The qRT-PCR analysis showed that MaIRAK4 expressed widely in all examined tissues, including heart, liver, spleen, kidney, head-kidney, gill, intestine and muscle, with the highest expression in the liver and spleen. After stimulation with LPS, MaIRAK4 expression upregulated significantly and reached a peak at 6 h and 12 h post LPS stimulation in the spleen and head-kidney, respectively. After challenge with Aeromonas hydrophila, MaIRAK4 expression peaked at 48 h and 72 h in spleen/head-kidney and liver, respectively. These results implied that MaIRAK4 is involved in the host defense against bacterial infection. Subcellular localization analysis indicated that MaIRAK4 distributed in the cytoplasm. Co-immunoprecipitation and subcellular co-localization assay revealed that MaIRAK4 can combine with MaMyD88 through DD domain. MaIRAK4 overexpression can induce slightly the NF-κB promoter activity in HEK 293 cells. However, the activity of NF-κB promoter was dramatically enhanced after co-transfection with MaIRAK4 and MaMyD88 plasmids. The results showed that MaIRAK4 was involved in NF-κB signal pathway mediated by maMyD88. The expression level of pro-inflammatory cytokines (IL-1β, IL-6, IL-8 and TNF-α) decreased significantly after the siRNA-mediated knockdown of MaIRAK4. Together, these results suggest that MaIRAK4 plays an important function in the innate immunity of M. amblycephala by inducing cytokines expression.

Dose-dependent co-infection of Argulus sp. and Aeromonas hydrophila in goldfish (Carassius auratus) modulates innate immune response and antioxidative stress enzymes

Co-infection with parasites and bacteria is of frequent occurrence in aquaculture, leads to growth impedance otherwise mortality in fish depending on the varying degree of a load of primary pathogen either parasite or bacteria. The mechanistic regulation of immune response during co-infection in fish has merely documented. The aim of this study was to determine the impact of co-infection with Aeromonas hydrophila at three exposure doses of Argulus sp. on the innate immune responses and antioxidative stress enzymes of goldfish (Carassius auratus). The experimental fish were randomly distributed into eight treatment groups viz. T1 (control group without Argulus and A. hydrophila infection), T2 (fish exposed to a sub-lethal dose of A. hydrophila), T3 (low Argulus-infested fish), T4 (T3 + sub-lethal dose of A. hydrophila), T5 (moderate Argulus-infested fish), T6 (T5 + sub-lethal dose of A. hydrophila), T7 (high Argulus-infested fish) and T8 (T7+ sub-lethal dose of A. hydrophila) in duplicates. After distributing experimental fish into their respective treatment group, A. hydrophila was injected to T2, T4, T6 and T8. After the bacterial challenge, four fish from each experimental group were randomly sampled on 24, 72, and 168 h and subjected to the hematological, innate immune parameters and enzymatic analysis. In the co-infection group T8, a high degree of enhanced pathogenicity of A. hydrophila was noticed with increased mortalities (84.2%) in comparison to other groups. The current study shows a declining pattern in RBC, PCV and Hb values with the degree of parasite infestation without co-infection groups. Moreover, in the T8 group, exposure of a sub-lethal dose of bacteria resulted in a drastic reduction of the recorded parameters. Furthermore, a decreased value for WBC, monocyte and neutrophil was found in higher parasite group co-infected with a sub-lethal dose of bacteria relative to other co-infected groups during the experimental period. Also, a decrease in innate immune parameters and antioxidative stress enzymes were observed in the T8 group compared to T7 and T2 groups throughout the trial period. These findings indicate that a rise in the dose of Argulus infection improves A. hydrophila colonization in goldfish and contributes to suppression of the innate immune system and increased mortality.

Role of temperature and co-infection in mediating the immune response of goldfish

Aquatic Pathogens are expected to encounter tremendous levels of variation in their environment - both abiotic and biotic. Here we examined the change in innate immune parameters and mortality pattern of Carassius auratus during the interaction of co-infection due to an ectoparasite, Argulus and bacteria Aeromonas hydrophila, along with a temperature gradient. Experimental fish were assigned randomly to six treatment groups (T1-T6). Fish of groups T1, T3 and T5 are assigned for healthy fishes kept at 23, 28 and 33°c temperature and served as control. T2, T4 and T6 groups are the co-infected groups kept at temperature gradient. For the haematological and enzyme parameter analysis, sampling was done at 24 h, 72 h and 168 h post challenge from 4 fish in all experimental groups. A temperature dependent increase in intensity of Argulus was observed in the experimental group. Both in control group and co-infected group a temperature dependent mortality pattern was observed, showing an increased mortality of 60% in T6 and 20% in T5 group. A significant decrease of RBC, Hb, and PCV values was observed in co-infected group when compared with control fish in each of the experimental group. Also a temperature dependent increase in WBC, neutrophil and monocyte value was observed in control fish. Whereas, a significant reduction in WBC, neutrophil and monocyte was observed in co-infected fish exposed to 33 °C during the progression of infection. Furthermore, T4 group showed a significantly higher Nitroblue tetrazolium test, Myelo peroxidase and lyzozyme activity compared to other co-infection group. A significantly increased activity of Superoxide dismutase, Glutathione peroxidise and catalase activity was recorded in control fish exposed to 33 °C (T5) whereas, there was no significant difference observed in the activity of catalase and Glutathione peroxidise in the other control fish (T1 and T3 group). This result implies that increase in temperature not only accelerates the intensity of co-infection but also imbalance the health status of the fish by hampering the immunological and physiological parameters towards more detrimental side.

Antioxidant defence system based oxidative stress mitigation through dietary jamun tree leaf in experimentally infected snubnose pompano, Trachinotus blochii

A 45-day feeding trial was conducted to evaluate the effect of dietary jamun tree leaf (JL) on the antioxidant defence system-based disease resistance in juveniles of Trachinotus blochii. The juveniles of snubnose pompano were distributed into four treatment groups in triplicates. Each treatment was fed with a diet containing either 0 (0JL), 0.5 (0.5JL), 1 (1JL) and 1.5% JL (1.5JL) in the feed. After feeding trial, the fishes were experimentally infected with Vibrio parahaemolyticus. The activities of oxidative stress enzymes such as superoxide dismutase and catalase were found to be increasing with increasing level of dietary JL incorporation, and the lower value was witnessed in control group in pre- and post-challenge. After challenge, the alanine and aspartate aminotransferase activities in all the treatments were significantly increased (P < 0.05) than the pre-challenge condition and exhibited reverse trend with the antioxidant enzymes. The alkaline and acid phosphatase activities were found higher in 1.5JL group and showed significant difference (P < 0.05) among the treatments. The respiratory burst activity and liver glycogen content showed an increasing trend as the level of inclusion of JL increased in the diet. The acetylcholinesterase activity was significantly plunged (P < 0.05) after experimental infection, and JL diet fed groups showed better activity. After experimental infection with V. parahaemolyticus, the highest relative percentage of survival was observed in 1JL and 1.5JL groups. Hence, dietary supplementation of jamun tree leaf at the level of 1% is adequate to reduce the oxidative stress and improved the innate immune status through antioxidant defence system.

Isolation, characterization and genomic analysis of vB-AhyM-AP1, a lytic bacteriophage infecting Aeromonas hydrophila

AIMS

Aeromonas hydrophila is a zoonotic pathogen displaying resistance to multiple antibiotics. Here, we aim to develop a candidate biocontrol agent against A. hydrophila.

METHODS AND RESULTS

In this study, we isolated and characterized the phage vB-AhyM-AP1 from sewage. It showed lytic activity against A. hydrophila strains. One-step growth curve revealed that the latent period lasted for 40 min. The burst size of one lytic cycle was 1413 PFU per infected cell. Temperature stability studies showed that the phage vB-AhyM-AP1 was active over temperatures ranging from 4 to 45°C for 1 h. pH stability studies indicated that the phage remained active within a pH range of 5-10 after 24 h of incubation. Stability tests in salt solutions showed that the phage was stable at salinities ranging from 0·1 to 2%. The phage also showed stabilities in organic solvents when incubated for 10 min. The Illumina Hiseq sequencing of its genome indicated that the phage vB-AhyM-AP1was a jumbo phage with a genome size of 2, 54 490 bp and GC content of 40·3%. The phylogenetic analysis of the terminase large subunit and major capsid protein indicated that the phage closely clustered with other Tevenvirinae phages. The genome encoded 455 ORFs and 22 tRNAs. The phage resulted in a reduction of 0·8 log units of viable A. hydrophila cells in biofilms grown on PVC coupons maintained in a low nutrient medium for 10 days.

CONCLUSIONS

The phage showed lytic activity against planktonic and biofilm cells of A. hydrophila. Genome-based prediction showed it to be a strictly lytic phage without any virulence or antibiotic resistance genes indicating safety for environmental and clinical applications.

SIGNIFICANCE AND IMPACT OF THE STUDY

The multidrug-resistant strains of A. hydrophila pose a significant health risk to both cultured fishes and consumers leaving few options for treatment. Phage vB-AhyM-AP1 may be used as a candidate biocontrol agent against A. hydrophila strains.

Fish infections associated with the genus Aeromonas: a review of the effects on oxidative status

The aim of this review was to summarize the current knowledge regarding the effects of aeromonosis on fish oxidative status. The bibliographic survey was carried out on the research platforms: Scopus and Science Direct. The keywords 'Aeromonas', 'fish' and 'oxidative status' (or 'oxidative stress', 'oxidative damage' and similar terms) were used. Scientific papers and short communications were considered. Studies involving fish aeromonosis and enzymatic or non-enzymatic markers of oxidative status were selected. The results of antioxidant enzymes activities/expressions after infection lack consistency, suggesting that these findings should be interpreted with caution. Most of the analysed studies pointed to an increase in reactive oxygen species, malondialdehyde and protein carbonylation levels, indicating possible oxidative damage caused by the infection. Thus, these three biomarkers are excellent indicators of oxidative stress during infection. Regarding respiratory burst activity, several studies have indicated increased activity, but other studies have indicated unchanged activity after infection. Nitric oxide levels also increased after infection in most studies. Therefore, it is suggested that the fish's immune system tries to fight a bacterial infection by releasing reactive oxygen and nitrogen species.

Antibacterial activity in secondary metabolite extracts of heterotrophic bacteria against Vibrio alginolyticus, Aeromonas hydrophila, and Pseudomonas aeruginosa

Background: Disease causing bacteria such as Vibrio alginolyticus, Aeromonas hydrophila, and Pseudomonas aeruginosa present a problem for fish farming. Treatment to remove them are generally carried out using antibiotics which have side effects on fish, the environment and humans. However, the use of antibacterial compounds derived from heterotrophic bacteria serve as a good alternative for antibiotics. Therefore, this study aimed to explore antibacterial activity in the secondary metabolite extracts of heterotrophic bacteria against Vibrio alginolyticus, Aeromonas hydrophila, and Pseudomonas aeruginosa. Methods: Heterotrophic bacteria namely Bacillus sp. JS04 MT102913.1, Bacillus toyonensis JS08 MT102920.1, Bacillus cereus JS10 MT102922.1, Bacillus sp. JS11 MT102923.1, Pseudoalteromonas sp. JS19 MT102924.1, Bacillus cereus JS22 MT102926.1, and Bacillus sp. strain JS25 MT102927.1 were used in this study. The sequences of these bacteria have been deposited and are available from NCBI GenBank. Each heterotrophic bacterium was cultured on 6L nutrient broth for 8 days, and extracts produced using ethyl acetate to obtain their secondary metabolites. These extracts were tested for their phytochemical contents using FT-IR and also tested for their inhibitory property in pathogenic bacteria by agar diffusion method. Results: Phytochemical test results showed that the seven heterotrophic bacterial isolates produced terpenoid compounds. Based on the inhibitory test, the secondary metabolite extracts from Bacillus sp strain JS04 had the highest inhibitory effect on the growth of pathogenic bacteria namely, V. alginolyticus (17.5 mm), A. hydrophila (16.8 mm), and P. aeruginosa (17.3 mm). Conclusion: It was concluded that the secondary metabolite extracts of heterotrophic bacteria inhibit the growth of V. alginolyticus, A. hydrophila, and P. aeruginosa.

VLRs expression were significantly affected by complement C3 knockdown morphants in Lampetra morii

The complement component 3 of the lamprey, a jawless vertebrate, functions as an opsonin during the phagocytosis of rabbit red cells. Furthermore, lamprey C3 may be activated and cleaved into C3b, which is attached to the surface of target cells in the cytolytic process. However, the mechanism mediating the biological function of C3 in the lamprey is unknown. To our knowledge, this study is the first to show that variable lymphocyte receptors (VLRs) expression were significantly affected by complement C3 knockdown morphants in Lampetra morii. We identified the C3 gene in the lamprey genome based on its orthologs, conserved synteny, functional domains, phylogenetic tree, and conserved motifs. Additionally, we determined the optimal infection concentration of Aeromonas hydrophila to perform immune stimulation experiments in the lamprey larvae. The quantitative real-time polymerase chain reaction and immunofluorescence analyses revealed that the expression of Lampetra morii C3 (lmC3) was significantly upregulated in the larvae infected with 10⁷ CFU/mL of A. hydrophila. The lmC3 morphants (lmC3 MO) of lamprey larvae were generated by morpholino-mediated knockdown. The lmC3 MO larvae were highly susceptible to A. hydrophila infection, which indicated that lmC3 is critical in lamprey immune response. The expression of a selected panel of orthologous genes was comparatively analyzed in the infected wild type, infected lmC3 MO, infected control MO, uninfected wild type and uninfected lmC3 MO one-month-old ammocoete larvae. The knockdown of lmC3 strongly affected the expression of VLRA⁺/VLRB⁺/VLRC⁺-associated genes, which was also confirmed by immunohistochemical analysis. Thus, VLR expression were significantly affected by complement C3 knockdown morphants in Lampetra morii.

Effects of chlorantraniliprole insecticide on innate immune response of silver catfish (Rhamdia quelen) naturally infected with Aeromonas hydrophila

It is well documented today that pesticides, used in crop production, may modulate the immune system of healthy fish. However, there is still only limited information regarding the effects of these anthropogenic stressors in conjunction with natural stressors (pathogens), on the innate immune responses of freshwater fish. Thus, the aim of this investigation was to compare the innate immune response of two groups of fish (Rhamdia quelen), naturally infected with Aeromonas hydrophila, exposed and unexposed to a non-lethal concentration of chlorantraniliprole (CAP) insecticide (0.0 and 1.3 μg/L/24 h). Unhealthy fish exposed to CAP showed significant higher total leukocyte counts and neutrophils percentage compared to non-exposed infected fish). However, the monocytes and eosinophils percentage significantly decreased in fish exposed to CAP. Furthermore, lysozyme activity values measured in plasma, skin mucus, gill and intestine significantly reduced in fish exposed to CAP. The CAP-induced immunomodulation may interfere on the ability of the animal to heal or fight the infection, and possible contribute to the spread of bacterial infection in fish production or environment.

Complement component C1q plays a critical role in VLRA/VLRC-mediated immune response

In jawless vertebrates, the lamprey complement component C1q (LC1q) acts as a lectin and activates lamprey complement component C3 (LC3) in association with mannose-binding lectin (MBL)-associated serine protease (MASP) via the lectin pathway. Furthermore, LC1q may interact with variable lymphocyte receptor B (VLRB) in a complex with antigens and mediate the activation of LC3, leading to cytolysis. In the present study, we found, for the first time, that LC1q plays a critical role in VLRA/VLRC-mediated immune response. Escherichia coli, Shigella flexneri, Aeromonas hydrophila, Pseudomonas plecoglossicida, Aeromonas allosaccharophila, P. luteola, Brevundimonas diminuta, and Bacillus cereus were isolated from infected Lampetra morii in our laboratory and identified using the 16s rRNA method. A. hydrophila was confirmed as a rapidly spreading lethal pathogen in the larvae of L. morii and was used in subsequent immune stimulation experiments. The results of real-time quantitative polymerase chain reaction (Q-PCR) and immunofluorescence analyses indicated that the RNA and protein expression levels of LC1q were upregulated following exposure to 10⁷ cfu/mL of A. hydrophila, compared to the levels of the naïve group. We obtained LC1q morphants (LC1q MO) of lamprey larvae by morpholino-mediated knockdowns. We found that LC1q played key roles in the embryonic development of lamprey. The median lethal time (LT50) of LC1q MO larvae was 2 d after being exposed to the pathogens, whereas the LT50 of control MO was 5 d. The drastic decrease in LT50 values after LC1q knockdown implies that LC1q plays a critical role in lamprey immune response. Gene expression profiles of LC1q-deficient A. hydrophila, control MO A. hydrophila, wild type A. hydrophila, and naive 1-month-old ammocoetes larvae were compared by examining the expression levels of a selected panel of orthologous genes. It is worth mentioning that LC1q MO affected the VLRA+/VLRC + population genes but did not affect the VLRB + populations. Immunohistochemical data indicated that LC1q deficiency also affected VLRA and VLRC but not VLRB. Thus, LC1q plays a critical role in VLRA/VLRC-mediated immune response in lamprey.

Lamprey VLRB participates in pathogen detection, VLRB/L-BLNK/L-NF-κB (B-like cells) signal transduction, and development

In jawed vertebrates, B cell receptors (BCR) are primary pathogen detectors that activate downstream signaling pathways to express adaptive immune effectors. In jawless vertebrates, the variable lymphocyte receptors (VLR) B positive lymphocytes can express and secrete specific VLRB molecules in an analogous manner to that of immunoglobulins by B cells in jawed vertebrates. Our study is the first to demonstrate the possibility of incubation of fertilized eggs and artificial breeding of Lampetra morii larvae throughout their life cycle under laboratory condition. We also found that VLRB, lamprey B-cell linker (L-BLNK), and lamprey nuclear factor-kappa B (L-NF-κB) play key roles in early larval development. Aeromonas hydrophila was found to be a lethal pathogen of L. morii larvae causing rapid infection at a concentration of 10⁷ cfu/mL qRT-PCR results revealed that gene expression levels of VLRB, L-BLNK, and L-NF-κB were up-regulated significantly. Ten-day infection trials showed that VLRB, L-BLNK, and L-NF-κB are crucial for lamprey immune response. Furthermore, the expression levels of L-BLNK and L-NF-κB were down-regulated drastically both at mRNA and protein levels after bacterial infection than in the naive group of VLRB morphants. A similar expression pattern of VLRB and L-BLNK was found in L-NF-κB morphants post bacterial infection. The results were strikingly different in the other two morphants. The VLRB and L-NF-κB expression levels were found to be down-regulated at mRNA and protein levels by less than 30% and 45%, respectively, in L-BLNK morphants compared to those in the naive group. These results indicate that L-BLNK and L-NF-κB might participate in VLRB-mediated immune response. Additionally, in VLRB morphants, the mRNA expression levels of some genes, especially the ones expressed in VLRB⁺ lymphocytes but not in VLRA⁺ lymphocytes, were found to be affected. Therefore, these findings of B-like lymphocytes in lamprey offer key evidence with regard to the evolution of adaptive immunity.

Novel pectin isolated from Spirulina maxima enhances the disease resistance and immune responses in zebrafish against Edwardsiella piscicida and Aeromonas hydrophila

In this study, we demonstrate the enhanced disease resistance and positive immunomodulation of novel pectin isolated from Spirulina maxima (SmP) in zebrafish model. Zebrafish larvae exposed to SmP had significantly (p < 0.05) higher cumulative percent survival (CPS) at 25 (44.0%) and 50 μg/mL (67.0%) against Edwardsiella piscicida compared to the control. However, upon Aeromonas hydrophila challenge, SmP exposed larvae at 50 μg/mL had slightly higher CPS (33.3%) compared to control group (26.7%). SmP supplemented zebrafish exhibited the higher CPS against E. piscicida (93.3%) and A. hydrophila (60.0%) during the early stage of post-infection (<18 hpi). qRT-PCR results demonstrated that exposing (larvae) and feeding (adults) of SmP, drive the modulation of a wide array of immune response genes. In SmP exposed larvae, up-regulation of the antimicrobial enzyme (lyz: 3.5-fold), mucin (muc5.1: 2.84, muc5.2: 2.11 and muc5.3: 2.40-fold), pro-inflammatory cytokines (il1β: 1.79-fold) and anti-oxidants (cat: 2.87 and sod1: 1.82-fold) were identified. In SmP fed adult zebrafish (gut) showed >2-fold induced pro-inflammatory cytokine (il1β) and chemokines (cxcl18b, ccl34a.4 and ccl34b.4). Overall results confirmed the positive modulation of innate immune responses in larval stage and it could be the main reason for developing disease resistance against E. piscicida and A. hydrophila. Thus, non-toxic, natural and biodegradable SmP could be considered as the potential immunomodulatory agent for sustainable aquaculture.

Effects of dietary Gelsemium elegans alkaloids on growth performance, immune responses and disease resistance of Megalobrama amblycephala

The present study aim to investigate the effects of dietary Gelsemium elegans alkaloids supplementation in Megalobrama amblycephala. A basal diet supplemented with 0, 5, 10, 20 and 40 mg/kg G. elegans alkaloids were fed to M. amblycephala for 12 weeks. The study indicated that dietary 20 mg/kg and 40 mg/kg G. elegans alkaloids supplementation could significantly improve final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR), feed conversion ratio (FCR) and protein efficiency ratio (PER) (P < 0.05). The 20 mg/kg and 40 mg/kg G. elegans alkaloids groups showed significantly higher whole body and muscle crude protein and crude lipid contents compared to the control group (P < 0.05). The amino acid contents in muscle were also significantly increased in 20 mg/kg and 40 mg/kg groups (P < 0.05). Dietary 40 mg/kg G. elegans alkaloids had a significant effect on the contents of LDH, AST, ALT, ALP, TG, TC, LDL-C, HDL-C, ALB and TP in M. amblycephala (P < 0.05). Fish fed 20 mg/kg and 40 mg/kg dietary G. elegans alkaloids showed significant increase in complement 3, complement 4 and immunoglobulin M contents. The liver antioxidant enzymes (SOD, CAT and T-AOC) and MDA content significantly increased at 20 mg/kg and 40 mg/kg G. elegans alkaloids supplement (P < 0.05). The mRNA levels of immune-related genes IL-1β, IL8, TNF-α and IFN-α were significantly up-regulated, whereas TGF-β and IL10 genes were significantly down-regulated in the liver, spleen and head kidney of fish fed dietary supplementation with 20 mg/kg and 40 mg/kg G. elegans alkaloids. After challenge with Aeromonas hydrophila, significant higher survival rate was observed at 20 mg/kg and 40 mg/kg G. elegans alkaloids supplement (P < 0.05). Therefore, these results indicated that M. amblycephala fed a diet supplemented with 20 mg/kg and 40 mg/kg G. elegans alkaloids could significantly promote its growth performance, lipids and amino acids deposition, immune ability and resistance to Aeromonas hydrophila.

Phagolysosomal activity of macrophages in Nile tilapia (Oreochromis niloticus) infected in vitro by Aeromonas hydrophila: Infection and immunotherapy

The biochemical mechanisms involved in phagocytosis and the intracellular survival of Aeromonas hydrophila (Ah) in host macrophages (MΦs) are complex processes that affect infection success or failure. Thus, in the present study, we described the in vitro infection of Nile tilapia MΦs by a homologous bacterium and tested the effects of anti-A. hydrophila immunoglobulin Y (IgY) on the phagolysosomal activity and intracellular survival of the pathogen. The anti-Ah IgY modulated lysosomal acid phosphatase (LAP) activity as well as the production of reactive oxygen intermediates (ROIs) and nitric oxide (NO), thereby potentiating phagocytosis and the elimination of Ah. Thus, we assume that the specific IgY had a beneficial effect on infection control and postulated the use of the Nile tilapia MΦs as an important in vitro experimental model for the functional and therapeutic study of Ah infection.

Histopathological analysis and the immune related gene expression profiles of mandarin fish (Siniperca chuatsi) infected with Aeromonas hydrophila

Hemorrhagic septicemia of mandarin fish (Siniperca chuatsi) was mainly caused by Aeromonas hydrophila which was an opportunistic pathogen. In recent years, the disease has caused tremendous economic loss with high morbidity and mass mortality in the mandarin fish breeding industry. Histopathological analysis and the immune related gene expression profiles of mandarin fish (S. chuatsi) infected with A. hydrophila were investigated in this study. Transmission electron microscopy (TEM) images showed that the cells of A. hydrophila densely covered with a mass of fimbriae. Histopathological analysis revealed that inflammation, vacuolization and extensive necrosis existed in the gill, liver, spleen and head kidney of the diseased fish. Quantitative real-time PCR was performed to measure mRNA expression levels for six immune related genes in mandarin fish after A. hydrophila infection. The transcriptional analysis of these immune related genes demonstrated that the expression levels of major histocompatibility complex class II (MHC II), T cell receptor α (TCRα), tumor necrosis factor α (TNFα), CC chemokine 3, interleukin 8 (IL-8) and Hepcidin were strongly up-regulated in spleen and head kidney of mandarin fish post-infection. These results will contribute to further study on the pathogenesis and host defensive system in A. hydrophila infection.