Aeromonas Hydrophila Research Articles

Summer mortality syndrome bacterial pathogens in farmed Nile tilapia (Oreochromis niloticus).

The high summer mortality in many fish farms, which had detrimental economic and social implications, was a serious challenge that the fish industry had to deal with. With an examination of the most effective antibiotic, the ongoing research was intended to shed light on the identification of the main bacterial pathogens associated with the summer mortality syndrome in the diseased farmed Nile tilapia. Six hundred dead Nile tilapia samples that had suffered from summer mortality were collected from several fish farms between May and October of 2022. The gathered fish displayed hemorrhagic areas on the skin, scale detachment, fin degeneration, erosions, skin ulcers, and corneal opacity with unilateral and/or bilateral exophthalmia. The most prominent internal appearance was swelling of the internal organs with sanguineous ascetic fluid. There were 225 bacterial isolates found. Six species were identified through phenotypic and biochemical analysis; they were Aeromonas, Vibrio, Streptococcus, Pseudomonas, Enterococcus, and Edwardsiella spp., in descending percentage, respectively. Aeromonas spp., Vibrio spp., and Streptococcus spp. were the three most frequent isolated bacterial pathogens. The identification of Aeromonas hydrophila, Vibrio spp., and Streptococcus iniae, the three most common bacterial isolates, was confirmed by molecular analysis by polymerase chain reaction. Most of the tested strains were found to be responsive to Ciprofloxacin (CIP), Gentamicin (CN), and Chloramphenicol (C) but resistant to Amoxicillin (AMX), according to an antibiotic sensitivity test. The three most dangerous common bacterial infections discovered during mass-farmed tilapia summer mortality are A. hydrophil a, Vibrio sp., and S. iniae. This makes it clear that high water temperatures may raise the possibility of bacterial infections, which could cause widespread tilapia mortality and substantial financial losses. Therefore, it is crucial to maintain a beneficial fish culture, environment, and husbandry practices to enhance the tilapia-rearing environment and lessen the virulence of the disease. Isolated bacterial strains showed low levels of resistance to AMX but were vulnerable to CIP, CN, and C.

Dietary β‐Mannanase Affects the Growth, Antioxidant, and Immunes Responses of African Catfish, Clarias gariepinus, and Its Challenge Against Aeromonas hydrophila Infection

One of the most farmed fishes is the African catfish, Clarias gariepinus. Its production has increased by 20% annually on average during the last 20 years, but the occurrence of fish diseases, especially bacterial such as Aeromonas hydrophila infections, is hindering its activities. Also, the incorporation of plant‐derived substances in aquafeeds is limited since they frequently contain different antinutritional factors, like nonstarch polysaccharides (NSPs). However, supplementing fish diets with β‐mannanase could increase growth, antioxidants, and immunity. Despite the advantage of β‐mannanase, its effects on growth, digestive enzymes, antioxidants, and immunity in African catfish need to be elucidated. This study examined the effects of dietary β‐mannanase on the growth performance, liver enzymes, antioxidant profiles, immunity, and protection of African catfish, C. gariepinus, against A. hydrophila infection. Five isonitrogenous diets were prepared to have 400 g/kg crude protein and supplemented with β‐mannanase at 0, 1500, 3000, 4500, or 6000 thermostable endo, 1,4‐β‐mannanase units (TMUs)/kg diet and fed to 300 juveniles of the African catfish, C. gariepinus (mean weight 12.1 ± 0.1 g) for 12 weeks. Then, 10 fish from each tank received an intraperitoneal injection of 0.1 mL of A. hydrophila (5.0 × 105 CFU/mL) and observed for 14 days. Results showed dietary β‐mannanase levels considerably improved growth performance but did not affect fish survival. Also, amylase, protease, and lipase levels were significantly promoted in the fish fed with β‐mannanase‐fortified diets than the control group (p < 0.05). Enhanced gut villi and intestinal absorption areas, haematlogical profiles, and liver enzymes but reduced gut viscosity were observed in fish‐fed β‐mannanase‐fortified diets (p < 0.05). In a dose‐dependent order, including β‐mannanase in the meals of African catfish raised the levels of glutathione (GSH), glutathione peroxidase (GPx), superoxide dismutase (SOD), glutathione‐S‐transferase (GST), and glutamate cysteine ligase (GCL) activities and decreased the malondialdehyde (MDA) values in African catfish (p < 0.05). Also, fish immunity was greatly (p < 0.05) enhanced due to supplementation of the diet with β‐mannanase. In addition, fish‐fed diets comprising 6000 TMU β‐mannanase/kg diet showed the lowest rates of fish mortality (7.5%) (p < 0.05). Therefore, feeding African catfish, Clarias gariepinus, β‐mannanase enhanced growth performance, increased activity of digestive enzymes, gut morphology, enhanced generation of short‐chain fatty acids, digesta potential of hydrogen (pH), and improved antioxidant profiles and immunity at the optimum dose of 5800 TMU/kg diet. Additionally, β‐mannanase protected African catfish against A. hydrophila infection.

Diversity of Antibiotic-resistant of Tentative Motile Aeromonas Species Isolated From Clarias gariepinus (Burchell 1822) Cultured in Earthen Ponds

Background: Aeromonas species is one of the most important causes of diseases in Clarias gariepinus, a public health threat with significant economic losses. Objectives: In this research, the prevalence and variety of Aeromonas species isolated from C. gariepinus cultured in an earthen pond were investigated, as well as the antibiogram and multiple antibiotic resistance index Methods: Aeromonas species were isolated by culture and biochemical test and confirmed using a Microbact 24E kit. The antibiotic susceptibility to 10 antibiotics was determined using the Kirby-Bauer disk diffusion method. Results: Aeromonas species were isolated with a prevalence of 43.1% with 4 different phenospecies with the highest prevalence of 46(24 %) for Aeromonas hydrophila followed by 15(7.8%) for Aeromonas caviae, then 10(5.2%) for Aeromonas veronii sobria, and the least was observed for Aeromonas veronii veronii 6(3.1%). The Aeromonas species showed high resistance to amoxicillin, ampicillin, colistin sulfate, oxytetracycline, trimethoprim/sulfamethoxazole, and penicillin, with varying resistant patterns, and the multiple antibiotic resistance index values ranged between 0.20 and 0.80. Conclusion: There was a diversity of Aeromonas species associated with multiple antibiotic-resistant leading to the wide spread of antimicrobial resistance. Therefore, there is a need to control the use of antibiotics and ensure the effective use of biosecurity and preventive management measures in fish farms.

Antibacterial Activity of Extract Green Seaweed Ulva intestinalis in North Waters of Aceh

The appearance of bacterial resistance and pathogenic infections makes efforts to find new drugs as natural bacterial agents continue. One of them is through the utilization of marine organisms such as seaweed. Some studies show the content of seaweed bioactive compounds has potential in the pharmacological field. This study aims to determine the type of secondary metabolite compounds and antibacterial activity of ethanol extract of Ulva intestinalis. Seaweed extraction using the maceration method for 3 x 24 hours and antibacterial activities were tested by disc diffusion method. The results showed that there were 5 types of secondary metabolite compounds in the extract, namely alkaloids, flavonoids, glycosides, saponins, and steroids. The antibacterial activity test of seaweed extract against Propionibacterium acnes and Aeromonas hydrophila bacteria in the concentration range of 50% to 100% showed a moderate inhibition zone diameter

The Immune Response and Passive Protective Abilities of the Outer Membrane Lipoprotein Slp of Aeromonas hydrophila against the Major Pathogenic Bacteria of Freshwater Aquaculture in Fish

The Immune Response and Passive Protective Abilities of the Outer Membrane Lipoprotein Slp of Aeromonas hydrophila against the Major Pathogenic Bacteria of Freshwater Aquaculture in Fish

Curcuma longa and Allium sativum as health promoters in genetically improved farmed Tilapia (GIFT) - A green drug approach in hi-tech aquaculture using biofloc

In biofloc-based fish farming, the pathogen Aeromonas hydrophila poses substantial financial risks, while chemotherapeutics in such a system can disrupt delicate microbial balance and promote antimicrobial resistance. Hence, our study aims to evaluate the impact of dietary supplementation of Curcuma longa (turmeric) and Allium sativum (garlic) extracts on the health of Genetically Improved Farmed Tilapia (GIFT) in the biofloc system. Initially, in a 45-day feeding trial followed by 15-day challenge study, four experimental diets with varying turmeric (TE) and garlic extract (GE) doses (T1: 0.05% TE, T2: 0.1% TE, T3: 0.05% GE, T4: 0.1% GE) were tested against a control group as a prophylactic measure. The basal diet for the control group was devoid of herbal extract. The health of botanicals-fed groups in terms of growth performance (percentage weight gain, protein efficiency ratio, feed conversion ratio, and specific growth rate) and immune response (haematological parameters, total serum protein, albumin, globulin, oxidative burst activity, myeloperoxidase activity, and total Immunoglobulin) was significantly (p < 0.05) improved compared to control. The T2 and T4 groups, which received a higher dose of herbal extract (0.1%), demonstrated better relative percent survival (RPS) at 40% and 35%, respectively, after the challenge. In a subsequent 30-day challenge study, to evaluate the therapeutic efficacy of turmeric and garlic extracts, three diets were prepared with different ratios of turmeric and garlic extract (T1: 75:25, T2: 50:50, T3: 25:75) at a maximum dosage of 0.1% herbal inclusion based on the finding of the first experiment. The T1 group showed the highest RPS at 54%, followed by T2 (42%) and T3 (35%). Overall, the present study suggests that dietary supplementation of 0.1% turmeric and garlic extracts separately as a prophylactic measure and a 0.1% mixed herbal supplementation at a 75:25 ratio (turmeric to garlic) as a therapeutic measure may effectively control A. hydrophila infection in GIFT farming using biofloc.

Fountain Water as a Source of Opportunistic Escherichia coli and Aeromonas hydrophila Strains in Atmospheric Air

Fountain Water as a Source of Opportunistic Escherichia coli and Aeromonas hydrophila Strains in Atmospheric Air

Prevalence of Pangasius Fish Disease in Nepal

Objectives: This study was conducted to identify bacterial pathogens in both symptomatic and asymptomatic enteric septicemic infection of Pangasiaus hypophthalmus and evaluate their susceptibility to antibiotics. Methods: The totals of 120 kidney and liver swab samples of fish were collected from different places of Nepal. The samples were processed to identify the causative agent using pure culture of bacteria through streak plate techniques and different biochemical tests. To assess the susceptibility of the isolated bacteria to antibiotics Ciprofloxacin, Tetracycline, Doxycycline, Gentamycin, Ampicillin/ sulbactam, and Tobramycin were used. Results: The estimated prevalence of pathogenic bacteria is 27 per 10000 populations. Three pathogenic bacteria i.e. Edwardsiella ictaluri 57.7% (56/97), Aeromonas hydrophila 24.7% (24/97), and Pseudomonas fluorescence 17.5% (17/97) were identified in the studied asymptomatic and symptomatic Pangas fish disease. E. ictaluri was major isolates which was causative agent for the disease, enteric septicemia of catfish. Among the total bacterial isolates 100% bacterial isolates were sensitive to Ciprofloxacin and 84% to Gentamycin. Whereas 100% were resistance to Ampicillin and 84% to Tetracycline. And Tobramycin (60.8%) and Doxycycline (64.9%) showed intermediate result. Conclusion: Ciprofloxacin and Gentamycin could be administered to control enteric septicemia of catfish in Pangas. This study provides information to strategies to reduce economic losses to farmer and reduce possible health hazards.

Activity of Natural Compound Pothos tener Wall on Aeromonas hydrophila Infection to Prevent of Antibiotics

This study aims to discover how influential Photos tener Wall is as an anti-bacterial treatment for Aeromonas hydrophila. Methods: Cyprinus Carpio were reared for 28 days, and on the 29th and 30th days before Aeromonas hydrophila infection, the fish were adequately fasted. On the 31st day, they were intramuscularly challenged with A. hydrophila (105 CFU/mL) (the first day in A. hydrophila infection). The treatments given were (I) immersed trial with fresh (live) P tener Wall: (H1) Immersed with 15 g of P. tener Wall plant, (H2) Immersed with 30 g of P. tener Wall plant, and (H3) Immersed with 60 g of P. tener; (II) feeding trials in which the treatments given were (P1) 2% of P. tener Wall powder mixed with 1 kg commercial diet and (P2) 4% of P. tener Wall powder mixed with 1 kg commercial diet; Experiment III combined the best results from experiment I (H2) and experiment II (P2) and Oxytetracycline 5 g/kg feed as a control antibiotic. The result obtained was that the treatment of 30 g of fresh P. tener Wall or adding 4% simplicial P. tener Wall in the diet could increase koi fish's immune response and resistance to A. Hydrophila has a survival rate that reaches 100%. This treatment has the same effect as using antibiotic Oxytetracycline 5 g/kg of feed. An important aspect for further research is that P. tener wall can be tested on other fish diseases caused by bacteria or fungi.

Activity of Natural Compound Pothos tener Wall on Aeromonas hydrophila Infection to Prevent of Antibiotics

This study aims to discover how influential Photos tener Wall is as an anti-bacterial treatment for Aeromonas hydrophila. Methods: Cyprinus Carpio were reared for 28 days, and on the 29th and 30th days before Aeromonas hydrophila infection, the fish were adequately fasted. On the 31st day, they were intramuscularly challenged with A. hydrophila (105 CFU/mL) (the first day in A. hydrophila infection). The treatments given were (I) immersed trial with fresh (live) P tener Wall: (H1) Immersed with 15 g of P. tener Wall plant, (H2) Immersed with 30 g of P. tener Wall plant, and (H3) Immersed with 60 g of P. tener; (II) feeding trials in which the treatments given were (P1) 2% of P. tener Wall powder mixed with 1 kg commercial diet and (P2) 4% of P. tener Wall powder mixed with 1 kg commercial diet; Experiment III combined the best results from experiment I (H2) and experiment II (P2) and Oxytetracycline 5 g/kg feed as a control antibiotic. The result obtained was that the treatment of 30 g of fresh P. tener Wall or adding 4% simplicial P. tener Wall in the diet could increase koi fish's immune response and resistance to A. Hydrophila has a survival rate that reaches 100%. This treatment has the same effect as using antibiotic Oxytetracycline 5 g/kg of feed. An important aspect for further research is that P. tener wall can be tested on other fish diseases caused by bacteria or fungi.

Bacterias resistente a los antibióticos en aguas mineromedicinales “Santagua Chachimbiro”, Ecuador

Bacterial biodiversity in mineral medicinal waters and the antibiotic resistance profiles, is a developing topic in Ecuador. The objective of the work was to know the bacterial microbiota and its resistance profiles to antibiotics of the mineral medicinal waters of the Santagua Chachimbiro spa, located in the Province of Imbabura-Ecuador. 16 water samples were collected. The isolation of the bacterial species was carried out by the membrane filtration technique, using different types of culture media. The identification was carried out according to the schemes proposed by MacFaddin (2003), complemented with the tests of the Microgen galleries. The antibiotic resistance profile was determined by the Kirby and Bauer (1966) plate diffusion method. 85 strains were isolate of which 61% were Gram negative and 39% Gram positive. The main species identified were Aeromonas caviae, Aeromonas eucrenophila, Aeromonas hydrophila, Aeromonas media, Aeromonas salmonicida, Aeromonas schubertii, Bacillus subtilis, Bacillus mycoides, Bacillus spp, Burkholderia cepacia, Citrobacter freundii, Comamonas spp, Pseudomonas aeruginosa, Pseudomonas fluorescenscens, Pseudomonas putida, Pseudomonas stutzeri, Ralstonia pickettii, Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus lugdenensis, Staphylococcus saprophyticus, Staphylococcus spp, Staphylococcus warneri and Staphylococcus xylosus. Regarding antimicrobial resistance, most of the Gram negative strains were resistant to penicillin and cephalosporins. Gram positive to oxacillin and penicillin 66,67% were multiresistant to more than three antibiotics. The “Termas de Santagua de Chachimbiro” spa presents a diversity of bacterial species and the presence of environmental resistomes. Keywords: mineral medicinal waters; bacterial biodiversity; resistance to antibiotics; Santagua Chachimbiro Spa

Study of Antimicrobial Quality of Tobacco Leaves Extract (Nicotiana tabacum) on Aeromonas hydrophila and Escherichia coli.

ABSTRACT: Tobacco is a perennial herb and its belong to family Solanaceae. Tobacco leaves have some antimicrobial substance such as alkaloids, phenol and some essential oils. The leaves extract of this plant show some microbial Quality and influence on both gram positive and gram negative bacteria. The aim of this work to determine the effectiveness of tobacco (Nicotiana tabacum) leaves extract in inhibiting on Aeromonas hydrophila and Escherichia coli. The antibacterial test performed on Mueller Hinton Agar (MHA) media. Test result indicate the leaves extract of tobacco showed positive result in Aeromonas hyrdophilla. Tobacco extract can inhibit Aeromonas hyrdophilla growth and a clear zone are found, in case of E. coli it showed negative result in both the cases. Tobacco extract cannot inhibit E. coli growth and the diameter of the inhibitory zone is not clear. The result shown that tobacco leaf extract can be source of an active antimicrobial substance.

Isolation and characterisation of potential bacterialpathogens from Oreochromis niloticus (Linnaeus, 1758) of Lake Hawassa, Ethiopia

The aim of the current study was to isolate and identify potential bacterial pathogens from Nile tilapia, Oreochromis niloticus (Linnaeus, 1758) in Lake Hawassa, Ethiopia. The study was conducted during January to December 2021. A total of 360 Nile tilapia were sampledfrom Lake Hawassa and subjected to bacteriological investigations. The results showed 64.2% prevalence of bacterial infection in Nile tilapia from the lake. Potential bacterial pathogens such as Aeromonas hydrophila, Escherichia coli, Edwardsiella tarda, Vibrio sp,,Bacillus sp., Staphylococcus sp., Salmonella sp., Flavobacterum sp., Pseudomonas sp. and Shigella sp. were isolated. The prevalence of infection in female fish (52.4%) was higher compared to male fish (47.6%). Comparatively higher prevalence was recorded in thesmaller fish group than in the larger ones. The average bacterial loads recorded in various organs such as intestine, skin, gill, liver and kidney were, 4.86±0.56 x 105, 4.72±0.48 x 105, 4.14±0.53 x 105, 3.45±0.23 x 105 and 2.63±0.324 x 105 CFU ml-1 respectively. Significantly high bacterial loads were recorded from the intestine (5.81±0.01 x 105 CFU ml-1) of fishduring the summer season (p&lt;0.05). The results of the study indicated that there is a risk of occurrence of disease outbreak under stressful situations. Moreover, the recovery of these bacteria in the fish which are potentially pathogenic to humans, suggests that if the fish are improperly handled, undercooked or consumed raw, may cause diseases to susceptible individuals. Keywords:Bacterial pathogens, Lake Hawassa, Oriochromis niloticus, Prevalence

Photodynamic Antimicrobial Chemotherapy Reduces Bacterial Load in Live Feeds in Aquaculture

Live feeds are one of the route of entry of pathogenic bacteria in larval rearing systems in aquaculture. Current study discusses the disinfection of bacteria associated with live feed (Artemia nauplii) using photodynamic antimicrobial chemotherapy (PACT). More than 90 % of Aeromonas hydrophila in solution and total bacteria associated with live feed were killed on exposure to 5 μM of curcumin under photoexcitation for 30 minutes. The cell wall of A. hydrophila was disrupted by the reactive oxygen species generated by photoexcited curcumin. Up to 50 μM curcumin and their photoexcitation products were not toxic to Artemia nauplii. The findings of the current study propose photodynamic antimicrobial chemotherapy as a propitious tool for One Health approach and restricting the use of antibiotics in aquaculture settings. SAARC J. Agric., 21(2): 239-250 (2023)

A DM9-containing protein from crab Eriocheir sinensis functions as a novel multipotent pattern recognition receptor

DM9-containing protein in invertebrates functions as pattern recognition receptor (PRR) to play significant roles in innate immunity. In the present study, a novel DM9-containg protein (defined as EsDM9CP-1) was identified from the Chinese mitten crab Eriocheir sinensis. EsDM9CP-1 is composed of 330 amino acids containing a Methyltransf_FA domain and two tandem DM9 repeats. The deduced amino acid sequence of EsDM9CP-1 shared low similarity with the previously identified DM9CPs from other species, and it was closely clustered with Platyhelminthes DM9CPs and then assigned into the branch of invertebrate DM9CPs in the unrooted phylogenetic tree. The mRNA transcripts of EsDM9CP-1 were highly expressed in haemocytes, gill, and heart. After Aeromonas hydrophila stimulation, the expression levels of EsDM9CP-1 mRNA in haemocytes increased significantly at 3 h (3.88-fold, p < 0.05) and 6 h (2.71-fold, p < 0.05), compared with that of PBS group, respectively. EsDM9CP-1 protein was mainly distributed in the cytoplasm and membrane of haemocytes. The recombinant EsDM9CP-1 protein (rEsDM9CP-1) exhibited binding affinity to MAN, PGN, LPS and Poly (I:C), and also to Gram-positive bacteria (Staphylococcus aureus, Micrococcus luteus and Bacillus subtilis), Gram-negative bacteria (Escherichia coli, A. hydrophila and Vibrio splendidus) and fungi (Pichia pastoris and Metschnikowia bicuspidata) in a Ca2+-dependent manner. It was able to agglutinate A. hydrophila, S. aureus, M. luteus, M. bicuspidata and P. pastoris, and inhibit the growth of A. hydrophila and M. bicuspidate. These results suggested that EsDM9CP-1 in crab not only functioned as a PRR, but also agglutinated and inhibited the growth of microbes.

Probiotic Supplement Enhances the Hematological Parameters and Immune Response of Common Carp against Fish Pathogen Aeromonas hydrophila

Probiotic bacteria play an important role in the growth and health of aquatic animals by improving their immune system. A 60-day experiment study was carried out to evaluate the effect of probiotic bacteria Bacillus subtilis dietary supplement enhances the hematological parameters and Immune response of fish Common carp against the pathogenic Aeromonas hydrophila. The experimental fish with an average mean weight of 15.15 ± 1.05 g were distributed randomly into 3 groups (Control (CTRL (Basal feed and without A. hydrophila), Exp1 (Basal feed and with A. hydrophila, and Exp2 (108 CFU/ml with probiotic supplement with A. hydrophila). On the 56th day, experimental groups were then challenged with A. hydrophila (1.0 × 107 CFU/mL), after 72 hrs of infection, blood samples were collected randomly from five fish from each group. Results showed that probiotic supplementation improved Hematological parameters such as RBCs, WBCs, Hb, PCV, and Immune response parameters (Nitroblue Tetrazolium Activity, aminotransferase, Serum lysozyme activity, total protein, and immunoglobulin). This present study suggests that the probiotic diet enhances the disease resistance against Aeromonas hydrophila in the culture of Common carp.

The role and molecular mechanism of flgK gene in biological properties, pathogenicity and virulence genes expression of Aeromonas hydrophila

Aeromonas hydrophila is a highly pathogenic aquatic resident bacterium that can cause co-morbidity in aquatic animals, waterfowl, poultry, and humans. Flagellum is the motility organ of bacteria important for bacterium tissue colonization and invasion. The flgK gene encodes a flagellar hook protein essential for normal flagellar formation. In order to explore the role of flgK in A. hydrophila, a flgK gene mutant strain of A. hydrophila (∆flgK-AH) was constructed using an efficient suicide plasmid-mediated homologous recombination method, and gene sequencing confirmed successful mutation of the flgK gene. The biological properties, pathogenicity and virulence genes expression were compared. The results showed that there was no significant difference in the growth, hemolytic, and swarming abilities, but the swimming and biofilm formation abilities of ∆flgK-AH were significantly reduced and the transmission electron microscope (TEM) results showed that the ∆flgK-AH strain did not have a flagellar structure. The median lethal dose (LD50) value of the ∆flgK-AH in Carassius auratus was 1.47-fold higher than that of the wild-type strain (WT-AH). The quantitative real-time PCR results showed that only the expression level of the lapA gene was up-regulated by 1.47 times compared with the WT-AH, while the expression levels of other genes were significantly down-regulated. In conclusion, flgK gene mutant led to a decline in the pathogenicity possibly by reducing swimming and biofilm formation abilities, these biological properties might result from the down-regulated expression of flagellate and pilus-related genes.

JunD functions as a transcription factor of IL-10 to regulate bacterial infectious inflammation in grass carp (Ctenopharyngodon idella)

IL-10 is a key anti-inflammatory mediator ensuring the protection of a host from excessive inflammation in response to pathogen infections, whose transcription or expression levels are tightly linked to the onset and progression of infectious diseases. An AP-1 family member called CiJunD was shown to be a transcription factor of IL-10 in grass carp (Ctenopharyngodon idella) in the current study. CiJunD protein harbored the conserved Jun and bZIP domains. Mutant experiments demonstrated that CiJunD bound to three specific sites on IL-10 promoter, i.e., 5′-ATTATTCATA-3′, 5′-AGATGAGACATCT-3′, and 5′-ATTATTCATC-3′, mainly relying on the bZIP domain, and initiated IL-10 transcription. Expression data from the grass carp spleen infected by Aeromonas hydrophila and lipopolysaccharide (LPS) challenged spleen leukocytes indicated that the expressions of CiJunD and IL-10 were positively correlated, while the expression of pro-inflammatory cytokines, such as IL-1β, IL-6, IL-8, IFN-γ, and TNF-α, showed an overall downward trend when CiJunD and IL-10 peaked. The ability of CiJunD to down-regulate the production of pro-inflammatory cytokines and up-regulate the expression of IL-10, both with and without LPS stimulation, was confirmed by overexpression experiments. Meanwhile, the subcellular fractionation assay revealed that the nuclear translocation of CiJunD was significantly enhanced after the LPS challenge. Moreover, in vivo administration of grass carp with Oxamflatin, a potent agonist of JunD activity, could promote IL-10 but suppress the expression of pro-inflammatory cytokines. Intriguingly, tissue inflammation lesions and the survival rates of grass carp infected with A. hydrophila were also significantly improved by Oxamflatin administration. This work sheds light on the regulation mechanism by JunD of IL-10 expression and bacterial infectious inflammation for the first time, and it may present a viable method for preventing infectious diseases in fish by regulating IL-10 expression and inflammatory response.

Identification and characterisation of emerging fish pathogens Aeromonas veronii and Aeromonas hydrophila isolated from naturally infected Channa punctata.

Naturally infected Channa punctata exhibiting bacterial septicemic syndrome including ulcerations along with mortality records were collected from a fish farm in Assam during winter season (early November 2020 to early January 2021). The moribund fishes were subjected for bacterial isolation followed by identification of the bacteria. Two dominant emerging bacterial pathogens were identified as Aeromonas veronii (isolate ZooGURD-01) and Aeromonas hydrophila (isolate ZooGURD-05) by standard biochemical characterization and 16S rRNA and rpo B gene amplification. Re-infection experiments of both the bacterial isolates in healthy disease-free C. punctata showed similar symptoms to that of natural infection thus confirming their virulence. The LD50 calculated during challenge test for both the isolates ZooGURD-01 and ZooGURD-05 found to be pathogenic at 2.6 × 104 and 1.6 × 104CFU/fish respectively. Further PCR amplification of specific virulent genes (aerolysin, hemolysin and enterotoxin) confirmed pathogenicity for both isolates. Histopathological examinations of liver and kidney in re-infection experiments showed prominent changes supporting bacterial septicaemia. Antibiotic sensitivity pattern showed that the isolates ZooGURD-01 and ZooGURD-05 were sensitive to 22 and 19 out of 25 antimicrobials respectively. The present study was the first report on the mortality of farmed C. punctata associated with natural infection caused by A. veronii and A. hydrophila with no record of pathogenicity of A. veronii in C. punctata.

Paraprobiotic supplementation to fish feed: effects on the immune support system and control of Aeromonas hydrophila infection in Labeo rohita

Paraprobiotic supplementation to fish feed: effects on the immune support system and control of Aeromonas hydrophila infection in Labeo rohita