Synergistic Effect of Dietary Supplementation with Sodium Butyrate, ß-Glucan and Vitamins on Growth Performance, Cortisol Level, Intestinal Microbiome and Expression of Immune-Related Genes in Juvenile African Catfish (Clarias gariepinus).

The effect of dietary supplementation with sodium butyrate, ß-glucan and vitamins (A, D3, E, K, C) on breeding indicators and immune parameters of juvenile African catfish was examined. The fish were fed with unenriched (group C) and enriched feed with a variable proportion of sodium butyrate/ß-glucan, and constant content of vitamins (W1-W3). After the experiment, blood and the middle gut were collected. The microbiome of the gut was determined using Next Generation Sequencing (NGS). Liver tissue was collected for determination of expression of immune-related genes (HSP70, IL-1ß, TNFα). W2 and W3 were characterized by the most favorable values of breeding indicators (p < 0.05). The highest blood cortisol concentration was in group C (71.25 ± 10.45 ng/mL), and significantly the lowest in W1 (46.03 ± 7.01 ng/ mL) (p < 0.05). The dominance of Cetobacterium was observed in all study groups, with the largest share in W3 (65.25%) and W1 (61.44%). Gene expression showed an increased number of HSP70 genes in W1. IL-1ß and TNFα genes peaked at W3. The W3 variant turns out to be the most beneficial supplementation, due to the improvement of breeding and immunological parameters. The data obtained can be used to create a preparation for commercial use in the breeding of this species.

Genomic characterization of Aeromonas spp. isolates from striped catfish with motile Aeromonas septicemia and human bloodstream infections in Vietnam.

Aeromonas spp. are commonly found in the aquatic environment and have been responsible for motile Aeromonas septicemia (MAS) in striped catfish, resulting in significant economic loss. These organisms also cause a range of opportunistic infections in humans with compromised immune systems. Here, we conducted a genomic investigation of 87 Aeromonas isolates derived from diseased catfish, healthy catfish and environmental water in catfish farms affected by MAS outbreaks in eight provinces in Mekong Delta (years: 2012-2022), together with 25 isolates from humans with bloodstream infections (years: 2010-2020). Genomics-based typing method precisely delineated Aeromonas species while traditional methods such as aerA PCR and MALDI-TOF were unable identify A. dhakensis. A. dhakensis was found to be more prevalent than A. hydrophila in both diseased catfish and human infections. A. dhakensis sequence type (ST) 656 followed by A. hydrophila ST251 were the predominant virulent species-lineages in diseased catfish (43.7 and 20.7 %, respectively), while diverse STs were found in humans with bloodstream infections. There was evidence of widespread transmission of ST656 and ST251 on striped catfish in the Mekong Delta region. ST656 and ST251 isolates carried a significantly higher number of acquired antimicrobial resistance (AMR) genes and virulence factors in comparison to other STs. They, however, exhibited several distinctions in key virulence factors (i.e. lack of type IV pili and enterotoxin ast in A. dhakensis), AMR genes (i.e. presence of imiH carbapenemase in A. dhakensis), and accessory gene content. To uncover potential conserved proteins of Aeromonas spp. for vaccine development, pangenome analysis has unveiled 2202 core genes between ST656 and ST251, of which 78 proteins were in either outer membrane or extracellular proteins. Our study represents one of the first genomic investigations of the species distribution, genetic landscape, and epidemiology of Aeromonas in diseased catfish and human infections in Vietnam. The emergence of antimicrobial resistant and virulent A. dhakensis strains underscores the needs of enhanced genomic surveillance and strengthening vaccine research and development in preventing Aeromonas diseases in catfish and humans, and the search for potential vaccine candidates could focus on Aeromonas core genes encoded for membrane and secreted proteins.

Development of a hyper-adhesive and attenuated Edwardsiella ictaluri strain as a novel immersion vaccine candidate in yellow catfish (Pelteobagrus fulvidraco).

Edwardsiella ictaluri, a Gram-negative intracellular pathogen, is the causative agent of enteric septicemia in channel catfish, and catfish aquaculture in China suffers heavy economic losses due to E. ictaluri infection. Vaccination is an effective control measure for this disease. In this study, an attenuated E. ictaluri strain was acquired through deletion mutation of the T3SS protein eseJei, and the ΔeseJei strain fails to replicate in the epithelioma papillosum of carp cells. The type 1 fimbria plays a pivotal role in the adhesion of E. ictaluri, and it was found in this study that deletion of -245 to -50 nt upstream of fimA increases its adhesion to around five times that of the WT strain. A hyper-adhesive and highly attenuated double mutant (ΔeseJeiΔfimA-245--50 strain) was constructed, and it was used as a vaccine candidate in yellow catfish via bath immersion at a dosage of 1 × 105 CFU/mL. It was found that this vaccine candidate can stimulate protection when challenged with E. ictaluri HSN-1 at 5 × 107 CFU/mL (∼20 × LD50). The survival rate was 83.61% for the vaccinated group and 33.33% for the sham-vaccinated group. The RPS (relative percent of survival) of the vaccination trial reached 75.41%. In conclusion, the ΔeseJeiΔfimA-245--50 strain developed in this study can be used as a vaccine candidate. It excels in terms of ease of delivery (via bath immersion) and is highly efficient in stimulating protection against E. ictaluri infection.

Pathological and Ultrastructural Characterization of an Edwardsiella ictaluri Triple hemR Mutant.

Enteric septicemia of catfish, which is caused by Edwardsiella ictaluri, is detrimental to farmed Channel Catfish Ictalurus punctatus. The hemin receptor HemR is involved in binding and uptake of heme into bacteria. Here, we explored pathological and ultrastructural changes in catfish fry that were immunized with a triple hemR mutant of E. ictaluri and challenged with wild-type E. ictaluri (EiWT) 28 d after immunization. Following immunization, pathological changes in the triple hemR-immunized fry were less severe compared to the EiWT-exposed control fry. Widely disseminated bacteria and severe necrosis in most organs, especially the kidney and spleen, were detected in both groups at days 4, 5, and 6. Multifocal granulomatous encephalitis with bacteria was seen in hemR-immunized fry at days 21 and 28 and in EiWT-exposed control fry at day 14. Phagocytic cells in the kidney and spleen of EiWT-exposed control fry contained more replicating bacteria compared to hemR-immunized fry. During the EiWT challenge of immunized fry, a robust immune response was observed in the triple hemR-immunized fry compared to the sham-vaccinated group. Many activated phagocytic cells were detected in the kidney and spleen with fragmented or no bacteria in the triple hemR-immunized fry. Our data suggested that virulence of triple hemR was lower and the onset of the lesions was delayed compared to EiWT. Additionally, triple hemR-immunized fry could mount an immune response and had milder lesions compared to the sham control after EiWT exposure.

Cupriavidus in the intestinal microbiota of Tibet endemic fish Glyptosternum maculatum can help it adapt to habitat of the Qinghai Tibet Plateau.

BACKGROUND: Gut microbes play an important role in the growth and development of fish. The Tibetan Plateau fish Glyptosternum maculatum is a unique species of sisorid catfish living in the river up to 4200 m altitude. RESULTS: To understand the mechanisms underlying the ability of G. maculatum to adapt to the high-altitude habitat, the intestinal microbiota of G. maculatum was studied. We used high-throughput sequencing of the 16S ribosomal RNA gene of intestinal microorganisms of wild and cultured G. maculatum to explore the characteristics of intestinal microorganisms and compared the gut microbial community of wild and cultured G. maculatum. The results showed that the α-diversity and richness of the intestinal microbiome were higher in wild G. maculatum than in cultured fish. The most abundant phylum in both G. maculatum were Fusobacteria, Proteobacteria, Firmicutes, and Bacteroidetes; Cetobacterium and Cupriavidus are the most dominant genus. The membership and structure of intestinal bacterial communities in wild G. maculatum are similar to the cultured fish, suggesting that a core microbiota is present in both G. maculatum intestinal bacterial communities. Metastats analysis showed that six genera were differentially represented between the wild and cultured G. maculatum. CONCLUSIONS: The most interesting characteristic of the intestinal microbial communities of G. maculatum is that there were large numbers of Cupriavidus, which may play an important role in the adaptation of G. maculatum to the water of the Yarlung Zangbo River with a high Cu content. This result, in turn, can guide us on breeding G. maculatum.

The impact of Achyranthes aspera seeds and leaves supplemented feeds on the survival, growth, immune system and specific genes involved in immunostimulation in Clarias batrachus fry challenged with Aeromonas hydrophila in pond conditions.

The present study was conducted to evaluate the effect of dietary inclusion of Achyranthes aspera seeds and leaves on the immune system of magur Clarias batrachus challenged with Aeromonas hydrophila in pond conditions. Magur fry (0.51 ± 0.032 g) were cultured in hapas set inside a pond and were fed with three feeds. Two experimental feeds FS1 and FS2 were supplemented with 0.5% seeds and leaves of A. aspera, respectively and FC3 was the control one. After 90 days of feeding, fish were challenged with A. hydrophila. In FC3, 70% fish died within 48 h of challenge, while 25 and 30% mortality were recorded in FS1 and FL2, respectively. The cumulative mortality rates were 70, 45 and 35% in FC3, FL2 and FS1, respectively. The average weight and specific growth rate of magur were significantly higher in FS1 compared to others. Serum lysozyme, myeloperoxidase, nitric oxide synthase and superoxide dismutase levels were significantly higher in FS1 compared to others. Thiobarbituric acid reactive substances and carbonyl protein levels were significantly lower in FS1 compared to others. In liver and head kidney of FS1 and FS2 fed magur, the iNOS, SOD-C, TNF-α, Cytochrome c, Caspase 9 were up-regulated. Caspase 3 was also significantly up-regulated in FS1 and it was followed by FL2 treatment. A. aspera incorporated feeds improved the immune system of fish and gave protection against bacteria even in the pond conditions.

TLR22-mediated activation of TNF-α-caspase-1/IL-1ß inflammatory axis leads to apoptosis of Aeromonas hydrophila-infected macrophages.

Toll-like receptors (TLRs) represent first line of host defence against microbes. Amongst different TLRs, TLR22 is exclusively expressed in non-mammalian vertebrates, including fish. The precise role of TLR22 in fish-immunity remains abstruse. Herein, we used headkidney macrophages (HKM) from Clarias gariepinus and deciphered its role in fish-immunity. Highest tlr22 expression was observed in the immunocompetent organ - headkidney; nonetheless expression in other tissues suggests its possible involvement in non-immune sites also. Aeromonas hydrophila infection up-regulates tlr22 expression in HKM. Our RNAi based study suggested TLR22 restricts intracellular survival of A. hydrophila. Inhibitor and RNAi studies further implicated TLR22 induces pro-inflammatory cytokines TNF-α and IL-1ß. We observed heightened caspase-1 activity and our results suggest the role of TLR22 in activating TNF-α/caspase-1/IL-1ß cascade leading to caspase-3 mediated apoptosis of A. hydrophila-infected HKM. We conclude, TLR22 plays critical role in immune-surveillance and triggers pro-inflammatory cytokines leading to caspase mediated HKM apoptosis and pathogen clearance.

Genetic variability of Edwardsiella piscicida isolates from Mississippi catfish aquaculture with an assessment of virulence in channel and channel × blue hybrid catfish.

The bacterium Edwardsiella piscicida causes significant losses in global aquaculture, particularly channel (Ictalurus punctatus) × blue (I. furcatus) hybrid catfish cultured in the south-eastern United States. Emergence of E. piscicida in hybrid catfish is worrisome given current industry trends towards increased hybrid production. The project objectives were to assess intraspecific genetic variability of E. piscicida isolates recovered from diseased channel and hybrid catfish in Mississippi; and determine virulence associations among genetic variants. Repetitive extragenic palindromic sequence-based PCR (rep-PCR) using ERIC I and II primers was used to screen 158 E. piscicida diagnostic case isolates. A subsample of 39 E. piscicida isolates, representing predominant rep-PCR profiles, was further characterized using BOX and (GTG)5 rep-PCR primers, virulence gene assessment and multilocus sequence analysis (MLSA) targeting housekeeping genes gyrb, pgi and phoU. The MLSA provided greater resolution than rep-PCR, revealing 5 discrete phylogroups that correlated similarly with virulence gene profiles. Virulence assessments using E. piscicida representatives from each MLSA group resulted in 14-day cumulative mortality ranging from 22% to 54% and 63 to 72% in channel and hybrid fingerlings, respectively. Across all phylogroups, mortality was higher in hybrid catfish (p < .05), supporting previous work indicating E. piscicida is an emerging threat to hybrid catfish aquaculture in the south-eastern United States.

Comparison of two commercial recirculated aquacultural systems and their microbial potential in plant disease suppression.

BACKGROUND: Aquaponics are food production systems advocated for food security and health. Their sustainability from a nutritional and plant health perspective is, however, a significant challenge. Recirculated aquaculture systems (RAS) form a major part of aquaponic systems, but knowledge about their microbial potential to benefit plant growth and plant health is limited. The current study tested if the diversity and function of microbial communities in two commercial RAS were specific to the fish species used (Tilapia or Clarias) and sampling site (fish tanks and wastewaters), and whether they confer benefits to plants and have in vitro antagonistic potential towards plant pathogens. RESULTS: Microbial diversity and composition was found to be dependent on fish species and sample site. The Tilapia RAS hosted higher bacterial diversity than the Clarias RAS; but the later hosted higher fungal diversity. Both Tilapia and Clarias RAS hosted bacterial and fungal communities that promoted plant growth, inhibited plant pathogens and encouraged biodegradation. The production of extracellular enzymes, related to nutrient availability and pathogen control, by bacterial strains isolated from the Tilapia and Clarias systems, makes them a promising tool in aquaponics and in their system design. CONCLUSIONS: This study explored the microbial diversity and potential of the commercial RAS with either Tilapia or Clarias as a tool to benefit the aquaponic system with respect to plant growth promotion and control of plant diseases.

Effect of dietary histamine on intestinal morphology, inflammatory status, and gut microbiota in yellow catfish (Pelteobagrus fulvidraco).

The toxic effect of dietary histamine on the intestine of aquatic animals has been demonstrated, but reports on the morphological observation of the intestine are limited. Thus, a feeding trial was conducted to determine the effect of dietary histamine on intestinal histology, inflammatory status and gut microbiota of yellow catfish (Pelteobagrus fulvidraco). Here, we showed that histamine-rich diets caused severe abnormality and damage to the intestine, including a decreased villi length and reduced villi number. In addition, the quantitative real-time PCR (qRT-PCR) demonstrates that histamine-rich diets increased the expression of pro-inflammatory genes (Tnfα, Il1ß, and Il8) and decreased the expression of an anti-inflammatory gene (Il10). Furthermore, the alpha-diversity (observed OTUs, Chao1, Shannon and Simpson) and beta-diversity (non-metric multidimensional scaling, with the stress value of 0.17) demonstrated that histamine-rich diets caused alterations in gut microbiota composition and diversity. Co-occurrence networks analysis of the gut microbiota community showed that the histamine influenced the number and the relationship between bacteria species in the phyla of Acidobacteria, Proteobacteria, and Bacteroidetes, which caused the instability of the intestinal microbiota community. Additionally, random forest selected six bacterial species as the biomarkers to separate the three groups, which are Lachnospiraceae Blautia (V520), Bacteroidales S24.7 (V235), Chloroplast Streptophyta (V368), Actinomycetales Streptomycetaceae (V152), Clostridia Clostridiales (V491) and Paraprevotellaceae Prevotella (V245). Finally, Pearson correlation analysis demonstrated that V520, V235, and V491 were negatively correlated with pro-inflammatory factors (Tnfα, Il1ß, and Il8) and positively correlated with an anti-inflammatory factor (Il10), which indicated that V520, V235, and V491 might be anti-inflammatory. These findings improved our understanding of the toxic effect of dietary histamine to intestinal histological damage, the induction of mucosa inflammatory status, and the alteration of gut microbiota.

The Dynamic Immune Response of Yellow Catfish (Pelteobagrus fulvidraco) Infected With Edwardsiella ictaluri Presenting the Inflammation Process.

Edwardsiella ictaluri is a highly destructive pathogen in cultured yellow catfish, thus it was very necessary to study the immune response of yellow catfish against bacterial infection. In this study, RNA-Seq technology was used to study the immune response in two distinct tissues of yellow catfish at eight different time points (h) after E. ictaluri infection. The number of differentially expressed genes (DEGs) in the spleen and liver was low at 3 h and 6 h post-infection, respectively. Afterwards, the most number of DEGs in the spleen was detected at 72 h, while the number of DEGs in the liver maintained a high level from 24 h to 120 h. The GO and KEGG enrichment analyses of DEGs at different time points uncovered that cytokines were continuously transcribed at 6 h to 120 h; whereas the liver is the main organ that secretes the components of the complement system, and metabolic regulation was activated from 12 h to 120 h. Moreover, an overview of the inflammation response of yellow catfish was exhibited including pattern-recognition receptors, inflammatory cytokines, chemokines, complements, and inflammation-related signal pathways. The similar expression tendency of nine genes by qRT-PCR validated the accuracy of transcriptome analyses. The different transcriptomic profiles obtained from the spleen and liver will help to better understand the dynamic immune response of fish against bacterial infection, and will provide basic information for establishing effective measures to prevent and control diseases in fish.

Protective Effect of Leek Extract (Allium ampeloprasum L.) on Catfish (Clarias gariepinus) Experimentally Challenged with Aeromonas hydrophila.

BACKGROUND AND OBJECTIVE: Leek (Allium ampeloprasum) is one of the most commonly used herbal foods all over the world. This study was conducted to evaluate the protective effect of leek extract on catfish experimentally challenged with Aeromonas hydrophila, a problematic bacterial pathogen that affects various freshwater fish species. MATERIALS AND METHODS: Aeromonas hydrophila was isolated and identified from catfish showing clinical signs of septicemia. The in vitro activity of leek extract to control the growth of Aeromonas hydrophila was investigated. In the in vivo experiment, about 240 adult catfish (Clarias gariepinus) were fed three different leek extract concentrations (10, 25 and 50 mg kg-1 body weight) for 1 month. Later on, a challenge study was conducted using an identified A. hydrophila strain. Morbidity and mortality were recorded throughout one week post-challenge. Furthermore, the effect of leek extract on some immune-related genes was investigated. RESULTS: Under the in vitro testing, a significant increase (10 and 13 mm) in the inhibition zone was recorded in wells treated with 25 and 50 mg L-1 leak extract, respectively. A significant reduction in fish mortalities was reported in all leek extract treated groups compared to the control group which was given water. TLR1 gene expression was upregulated in fish treated with leek extract while TNFα gene expression was down-regulated. CONCLUSION: Overall, results suggested that the leek extract has immunostimulating effects that can help control bacterial infections in catfish and probably other fish species.

Adhesion and colonization of potential probiont Pseudomonas aeruginosa FARP72 in the intestine of yellowtail catfish, Pangasius pangasius.

Adhesion is recognized as the first important step of a probiont for intestinal colonization. This study assessed the ability of an antagonistic Pseudomonas aeruginosa FARP72 to adhere and colonize the intestine of yellowtail catfish, Pangasius pangasius both in vitro and in vivo. For the in vitro assay, the whole intestines of each of two starved P. pangasius were introduced separately into tubes containing bluish-green pigment-producing P. aeruginosa FARP72 at 8.00 log10 CFU/mL and physiological saline (0.85% sodium chloride) and incubated for 1 h at 30 ± 1 °C. The homogenate mucus solutions from the intestine samples were serially diluted and plated onto Pseudomonas isolation agar to determine the counts of bluish-green pigment-producing P. aeruginosa (BPPAC). The difference between the numbers of BPPAC and presumptive Pseudomonas counts (PPC) in the treated and control intestines was attributed to the adherence of P. aeruginosa FARP72. The levels of BPPAC and PPC in the treated intestines were 6.09 ± 0.59 log10 CFU/g. Similarly, following 30 days of feeding P. pangasius with P. aeruginosa FARP72 supplemented diet, the intestine of catfish recorded the BPPAC of 5.83 ± 0.64 log CFU/g. In control samples, the BPPACs were recorded as < 3.00 log10 CFU/g. The scanning electron micrograph of the intestines of P. pangasius following the in vitro and in vivo adhesion assays confirmed the ability of this bacterium to strongly adhere to the intestine, thus making it most suitable candidate probiont for use in freshwater catfish aquaculture.

Effects of high-molecular-weight chitosan coating prepared in different solvents on quality of catfish fillets during 6-month frozen storage.

Effects of high-molecular-weight (800 kDa) chitosan coating on quality of catfish fillets were examined during 6-month frozen (-20 °C) storage. Coating solutions, included distilled water (Control), 800AC1% (1% w/v chitosan in 1% v/v acetic acid), AS3% (3% w/v aspartic acid), and 800AS3% (3% w/v chitosan in 3% w/v aspartic acid). Changes in physicochemical, microbial, and consumer perception of chitosan-coated catfish fillets during frozen storage were examined. The 800AS3% coating was found to be effective in inhibiting microbial growth, controlling lipid oxidation, reducing drip loss and cooking loss, and retaining color and texture of catfish fillet during frozen storage. After 6-month frozen storage, the aroma of thawed fillets coated with 800AS3% was accepted by 77.92% of consumers with 66% positive purchase intent. This study demonstrated that a nonpungent aspartic acid, instead of commonly used pungent acetic acid, can be used in preparation of preservative high-molecular-weight chitosan coating. PRACTICAL APPLICATION: The findings of this study indicated that high-molecular-weight chitosan coating showed preservative effects on quality of frozen raw catfish fillets. In our previous study, chitosan (800 kDa) at 1% and 3% concentrations showed antibacterial activity in vitro. The nonpungent aspartic acid can be used as a solvent to dissolve high-molecular-weight chitosan instead of the commonly used pungent acetic acid. The most effective coating treatment was 3% w/v chitosan in 3% w/v aspartic acid. This finding would be applicable to other seafood and fish products.

The early response expression profiles of miRNA-mRNA in farmed yellow catfish (Pelteobagrus fulvidraco) challenged with Edwardsiella tarda infection.

Edwardsiella tarda, the bacterial pathogen that causes ascites disease and red-head disease, poses a serious threat to yellow catfish (Pelteobagrus fulvidraco) aquaculture. In this study, the spleens of E. tarda-infected and non-infected yellow catfish were sequenced to obtain the microRNA (miRNA) and mRNA expression profiles. We obtained 657 differentially expressed (DE) miRNAs and 6867 DE mRNAs between two groups and annotated them using the KEGG database. In addition, the 43 negatively correlated miRNA-mRNA pairs were identified using integrated miRNA-mRNA analysis, which including immune-related miRNAs and target genes such as miR-144, miR-1260, miR-1388, miR-33, miR-338, miR-181b, miR-34c, miR-135 and CLEC4E, LITR, PIKfyve, NCF4, IL-12ß, IP6K2, TNFRSF9, IL-4Rα, IRF2, Mx2. We verified 8 DE miRNAs pairs and 10 DE mRNAs by quantitative real-time PCR. Finally, the CLEC4E and Mx2 mRNAs were selected for further verification using in situ hybridization. Together, our results provide valuable information for further analyses of the mechanisms of yellow catfish defense against E. tarda infection.

Physiological parameters and gut microbiome associated with different dietary lipid levels in hybrid yellow catfish (Tachysurus fulvidracoâ™€× Pseudobagrus vachellii♂).

Yellow catfish are intensively farmed in China and are often fed a high-fat diet (HFD) with the aim of using less protein. However, an excess of dietary lipids is likely to affect the gut microflora, which strongly affects immunity and nutrient digestion. To determine the effects of different lipid levels on the growth, physiological parameters and gut microbiome of hybrid yellow catfish, we conducted an 8-week feeding experiment with a low-fat diet (2% lipids, LFD), a normal-fat diet (9% lipids, NFD), and a HFD (15% lipids) (120 fish per group). The HFD group showed higher serum alanine aminotransferase and aspartate transaminase activities, which suggests that excess dietary lipids cause liver damage. A total of 1138 operational taxonomic units, 11 phyla, and 117 genera were identified from fish gut samples. Neither the HFD nor the LFD strongly affected the microbial composition in gut samples. Compared with fish in the NFD, those in the HFD and LFD showed significantly decreased intestinal microbial diversity. The composition of macronutrients in the different diets affected the composition of intestinal microflora, mainly the phyla Fusobacteria, Proteobacteria, and Firmicutes. The HFD and the LFD favored the growth of Fusobacteria, while the HFD and LFD resulted in decreased abundance of Firmicutes and Proteobacteria, respectively. These findings shed light on the complex relationships among diet, intestinal microorganisms, and host metabolism. When using an HFD for farmed fish, its effects on the gut microbiome should be considered to avoid illness and poor growth.

Molecular characterization and expression analysis of Tf_TLR4 and Tf_TRIL in yellow catfish Tachysurus fulvidraco responding to Edwardsiella ictaluri challenge.

Toll-like receptors play significant roles in defensing against pathogen invasion. In this study, TLR4 and TRIL from Yellow catfish Tachysurus fulvidraco (Tf), were identified and characterized. The open reading frames of the Tf_TLR4 and Tf_TRIL genes were 2466 bp and 1827 bp in length, encoding 821 and 608 amino acids, respectively. The Tf_TLR4 consists of LRRs, a transmembrane domain and a TIR domain, and Tf_TRIL only contains LRRs and TIR domain. Homologous identity revealed that both Tf_TLR4 and Tf_TRIL have high protein sequence similarity with that of channel catfish Ictalurus punctatus. Both the Tf_TLR4 and Tf_TRIL genes were highly expressed in head kidney and brain, respectively. The mRNA expression levels of Tf_TLR4 and Tf_TRIL genes were up-regulated in intestine and immune-related tissues after challenge of Edwardsiella ictaluri. The microscopic observation of the gut showed that the pathological changes in midgut and hindgut are more obvious than that in foregut after challenged with E. ictaluri. These results indicate that these two genes play potential roles in the host defense against E. ictaluri invasion. This study will provide valuable information to better understand the synergistic roles of TLR4 and TRIL in the innate immune system of yellow catfish and other fish.

Virulence, Resistance, and Genomic Fingerprint Traits of Vibrio cholerae Isolated from 12 Species of Aquatic Products in Shanghai, China.

Vibrio cholerae is a waterborne bacterium and can cause epidemic cholera disease worldwide. Continuous monitoring of V. cholerae contamination in aquatic products is imperative for assuring food safety. In this study, we determined virulence, antimicrobial susceptibility, heavy metal tolerance, and genomic fingerprints of 370 V. cholerae isolates recovered from 12 species of commonly consumed aquatic products collected from July to September of 2018 in Shanghai, China. Among the species, Leiocassis longirostris, Ictalurus punetaus, Ophiocephalus argus Cantor, and Pelteobagrus fulvidraco were for the first time detected for V. cholerae. Toxin genes ctxAB, tcpA, ace, and zot were absent from all the V. cholerae isolates. However, high occurrence of virulence-associated genes was detected, such as hapA (82.7%), hlyA (81.4%), rtxCABD (81.4%, 24.3%, 80.3%, and 80.8%, respectively), and tlh (80.5%). Approximately 62.2% of the 370 V. cholerae isolates exhibited resistance to streptomycin, followed by ampicillin (60.3%), rifampicin (53.8%), trimethoprim (38.4%), and sulfamethoxazole-trimethoprim (37.0%). Moreover, ∼57.6% of the isolates showed multidrug resistant phenotypes with 57 resistance profiles, which was significantly different among the 12 species (multiple antimicrobial resistance index, p < 0.001). Meanwhile, high incidence of tolerance to heavy metals Hg2+ (69.5%), Ni2+ (32.4%), and Cd2+ (30.8%) was observed among the isolates. The enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR)-based fingerprinting profiles classified the 370 V. cholerae isolates into 239 different ERIC-genotypes, which demonstrated diverse genomic variation among the isolates. Overall, the results in this study meet the increasing need of food safety risk assessment of aquatic products.

Complete genome sequence of a novel lytic phage infecting Aeromonas hydrophila, an infectious agent in striped catfish (Pangasianodon hypophthalmus).

The bacteriophage vB_AhM_PVN02 (PVN02), infecting Aeromonas hydrophila, was isolated from a striped catfish pond water sample in Can Tho City, Vietnam. The phage had high lytic activity with a latent period and burst size of approximately 20 min and 105 plaque-forming units per cell, respectively. Observation of the phage by transmission electron microscopy indicated that PVN02 belongs to the family Myoviridae. The genome of PVN02 is a double-stranded linear DNA with a length in 51,668 bp and a content of 52% GC. Among the 64 genes, 16 were predicted to encode proteins with predicted functions. No virulence or antibiotic resistance genes were found in the genome, suggesting it would be a useful biocontrol agent. Classification of the phage based on sequence comparisons, phylogenetic analysis, and gene-sharing networks was carried out, and it was found to be the first representative of a new species within a previously undefined genus in the family Myoviridae. This study confirmed that PVN02 is a novel lytic phage that could potentially be used as an agent to control Aeromonas hydrophila in striped catfish in the Mekong Delta, Vietnam.