Traditional Chinese Medicine Enhances Growth, Immune Response, and Resistance to Streptococcus agalactiae in Nile Tilapia

Herbal supplements are suitable for improving fish health and combating diseases in fish culture. However, the mechanism of action of many herbal mixtures remains unclear. This study was conducted to evaluate the effects of traditional Chinese medicine (TCM; a mix of Astragalus membranaceus, Angelica sinensis, and Crataegus hupehensis at a ratio of 1:1:1 on a weight basis) on growth, immune response, and disease resistance in Nile tilapia Oreochromis niloticus. Experimental fish (mean ± SE weight = 57 ± 1 g) were divided into two groups: a control group and a TCM (10 g/kg) group. After 4 weeks of the experimental trial, a significant increase in weight gain and specific growth rate and a lower feed conversion ratio were observed in fish fed a TCM-supplemented diet compared with control fish. Similarly, the immune response of Nile Tilapia in the TCM group showed enhanced lysozyme, superoxide dismutase, catalase, and immunoglobulin levels compared with the control fish. In comparison with the control, fish fed TCM showed significant up-regulation of β-defensin, lysozyme, heat shock protein 70, superoxide dismutase, and catalase genes in the intestine and head-kidney tissues. After a Streptococcus agalactiae challenge, survival of Nile Tilapia in the TCM group was 70% compared with 35% in the control. These results indicate that the TCM mixture in this study can elevate the immune response and disease resistance of Nile Tilapia.

Characterization and expression of galectin-3 after Streptococcus agalactiae and Aeromonas hydrophila challenge in GIFT strain Nile tilapia (Oreochromis niloticus)

In mammals, Galectin-3 has been revealed to be widely expressed in immune cells and played important role in immune reactions. However, Galectin-3 is frequently less reported in teleost. In the present study, a molecular characterization and expression analysis of galectin-3 were conducted in GIFT strain Nile tilapia. The full-length cDNA is 1034 bp with 690 bp of protein coding sequences. The result of qRT-PCR showed that the mRNA of galectin-3 was widely expressed in various tissues (heart, liver, spleen, gill, kidney, brain, intestine, skin, muscle, and ovary), and the higher expression was observed in immune-related tissues (liver and spleen). The time-course expression analysis revealed that galectin-3 was significantly up-regulated in intestine (5 h, 50 h, and 7 d), liver (5 h, 50 h, and 7 d), spleen (5 and 50 h), head-kidney (5 and 50 h), gill (5 h and 7 d) after Streptococcus agalactiae challenge, and significantly up-regulated in intestine (18, 24, 36, 72, and 96 h), liver (6, 18, 24, 96 h, and 6 d), spleen (18, 24, 36, 72, and 96 h), head-kidney (6, 12, 18, 24, 36, 72, and 96 h), and gill (12, 18, 24, and 36 h) after Aeromonas hydrophila challenge. Taken together, these data suggest that galectin-3 plays a role in immune responses in Nile tilapia after bacterial challenge.

Dietary administration of Bacillus amyloliquefaciens R8 reduces hepatic oxidative stress and enhances nutrient metabolism and immunity against Aeromonas hydrophila and Streptococcus agalactiae in zebrafish (Danio rerio)

Zebrafish (Danio rerio) are an excellent model for assessing the beneficial effects of probiotics before applying them in aquaculture. This study evaluated the effects on zebrafish of dietary supplementation with the probiotic Bacillus amyloliquefaciens R8, which heterologously expresses xylanase from rumen fungi. Nutrient metabolism, hepatic oxidative stress, and innate immunity against pathogen infections were investigated. Treated zebrafish received feed supplemented with B. amyloliquefaciens R8 for 30 days and then were compared to zebrafish that were fed a control diet. The treated fish showed significant increases in xylanase activity in the intestines. The livers of the treated fish showed increased mRNA expressions of glycolysis-related genes of hexokinase, glucokinase, glucose-6-phosphatase, and pyruvate kinase; and higher enzyme activities of 3-hydroxyacyl-coenzyme A dehydrogenase and citrate synthase which are associated with fatty acid β-oxidation and mitochondrial integrity. The livers of treated fish also showed decreased mRNA expressions of oxidative stress-related genes (SOD, Gpx, NOS2, and Hsp70) and an apoptotic gene (tp53), as well as increased expression of an anti-apoptotic gene (bcl-2). The probiotics-treated fish had increased expression of innate immune-related genes (IL-1β, IL-6, IL-21, TNF-α, and TLR-1, -3, and -4). Following challenge with Aeromonas hydrophila and Streptococcus agalactiae, treated fish showed increased a higher survival rate than control fish. Overall, results showed that the administration of xylanase-expressing B. amyloliquefaciens R8 can potentially improve nutrient metabolism and hepatic stress tolerance, and enhance immunity and disease resistance against A. hydrophila and S. agalactiae in zebrafish.

Protein kinase D mediates inflammatory responses of human placental macrophages to Group B Streptococcus

PROBLEM

During pregnancy, Group B Streptococcus (GBS) can infect fetal membranes to cause chorioamnionitis, resulting in adverse pregnancy outcomes. Macrophages are the primary resident phagocyte in extraplacental membranes. Protein kinase D (PKD) was recently implicated in mediating pro-inflammatory macrophage responses to GBS outside of the reproductive system. This work aimed to characterize the human placental macrophage inflammatory response to GBS and address the extent to which PKD mediates such effects.

METHOD

Primary human placental macrophages were infected with GBS in the presence or absence of a specific, small molecule PKD inhibitor, CRT 0066101. Macrophage phenotypes were characterized by evaluating gene expression, cytokine release, assembly of the NLRP3 inflammasome, and NFκB activation.

RESULTS

GBS evoked a strong inflammatory phenotype characterized by the release of inflammatory cytokines (TNFα, IL-1β, IL-6 (P ≤ 0.05), NLRP3 inflammasome assembly (P ≤ 0.0005), and NFκB activation (P ≤ 0.05). Pharmacological inhibition of PKD suppressed these responses, newly implicating a role for PKD in mediating immune responses of primary human placental macrophages to GBS.

CONCLUSION

PKD plays a critical role in mediating placental macrophage inflammatory activation in response to GBS infection.

Effects of a commercial probiotic BS containing Bacillus subtilis and Bacillus licheniformis on growth, immune response and disease resistance in Nile tilapia, Oreochromis niloticus

The present study evaluated a commercial probiotic designated as BS (a mix of B. subtilis and B. licheniformis) to ascertain its efficacy and the dose necessary to improve growth, immune response, and disease resistance in tilapia, Oreochromis niloticus. Fish (53.01 ± 1.0 g) were fed with a basal diet supplemented with 0 g kg−1 (CT), 3 g kg−1(BS3), 5 g kg−1 (BS5), 7 g kg−1 (BS7), and 10 g kg−1 (BS10) [corrected] of the probiotic BS for 4 weeks. At the end of the feeding trial, the weight gain, specific growth rate, and feed conversion ration were enhanced in all probiotic BS enriched groups but with better (P < 0.05) improvement in the BS10 group. The lysozyme, protease, anti-protease, superoxide dismutase activities, and immunoglobulin M level were significantly (P < 0.05) highest in the BS10 group in both serum and skin mucus. Enhanced (P > 0.05) catalse activity in all treated groups in the serum and myeloperoxidase activity in the B10 group in both serum and skin mucus were observed. The expression of C-lysozyme, heat shock protein 70, β-defensin, transforming growth factor beta, and small body size decapentaplegic homolog 3, genes in the mid-intestines and the head-kidney were up-regulated in all treated groups with the BS10 group provoking the highest up-regulation (P < 0.05). After challenge with Streptococcus agalactiae, cumulative mortality was 80 %, 47.5 %, 42.8 %, 30 %, and 20 % [corrected] for fish fed with CT, BS3, BS5, BS7, BS10 groups respectively. In conclusion, probiotic BS application at 10 g kg−1(BS10) [corrected] can be considered to improve growth and immunological status in tilapia farming.

Spleen tyrosine kinase from Nile tilapia (Oreochromis niloticus): Molecular characterization, expression pattern upon bacterial infection and the potential role in BCR signaling and inflammatory response

Spleen tyrosine kinase (SYK), a member of non-receptor tyrosine kinase family, plays an important role in immune responses against pathogen infection, which is capable of activating B cells signaling pathway and regulating inflammatory response. In this study, Nile tilapia (Oreochromis niloticus) ortholog (OnSYK) was identified and characterized at expression pattern against bacterial infection, function in B cells activation pathway and inflammatory response. The cDNA of OnSYK ORF contained 1851 bp of nucleotide sequence encoding polypeptides of 616 amino acids. The deduced OnSYK protein was highly homologous to other species SYK, containing two SH2 domains and a TyrKc domain. Spatial mRNA expression analysis revealed that OnSYK had wide tissue distribution and was highly expressed in the liver. After challenge of Streptococcus agalactiae (S. agalactiae) in vivo, mRNA expression of OnSYK was significantly up-regulated in the head kidney, spleen and liver. The up-regulation of OnSYK transcript was also displayed in the head kidney and spleen leukocytes stimulation with S. agalactiae and LPS in vitro, which was confirmed at protein level in the head kidney leukocytes by FACS analysis. In addition, after induction with mouse anti-OnIgM monoclonal antibody in vitro, the expressions of OnSYK and its downstream molecules (OnLYN, OnBLNK and OnAP-1) were significantly up-regulated in the head kidney leukocytes, and pharmacological inhibition of SYK activity with inhibitor (P505-15) significantly attenuated the expressions of OnLYN, OnBLNK and OnAP-1. Moreover, upon LPS challenge, the expressions of OnSYK, OnTNF-α, OnIL-6 and OnAP-1 were also up-regulated in the head kidney monocytes/macrophages. After treatment with SYK inhibitor (BAY 61-3606), the expressions of OnTNF-α, OnIL-6 and OnAP-1 were inhibited in the LPS-challenged head kidney monocytes/macrophages. Taken together, the results of this study indicated that OnSYK, playing potential roles in BCR signaling and inflammatory response, was likely to get involved in host defense against bacterial infection in Nile tilapia.

Sylimarin as hepatic protector and immunomodulator in Nile tilapia during Streptococcus agalactiae infection

This study investigated the use of silymarin, an extract obtained from the milk thistle (Silybum marianum) and its effects as a possible hepatoprotector in Nile tilapia (Oreochromis niloticus). Silymarin was used as feed additive to the diet at a concentration of 0.1% (1 kg per ton of dry ration) with the commercial product named Di-Heptarine S^® (16% silymarin phosphatide). A total of 90 juvenile tilapia with approximately 45 days old and mean weight of 0.72 ± 0.04 g were distributed in two groups, one fed with a diet with the hepatoprotector and the other without the additive. At the end of the assay (55 days after feeding), samples of blood were collected for hematological, immunological, histological (liver, spleen and intestine) and enzymatic analysis such as superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST). After 55 days all fish were challenged with Streptococcus agalactiae serotype Ib to verify the sylimarin effects on the immunological parameters and its protection effect while challenged. During the challenge period another biological material sample was collected for hematological, immunological and histopathological analysis (liver, spleen and intestine). Before the challenge, an increase on the count of thrombocyte was found in the supplemented fish. In the liver, dilation of the sinusoids was observed in unsupplemented fish while supplemented fish the alteration was less severe. No significant alteration was found in SOD, CAT and GST between the groups. Histological changes after the challenge were provoked by bacterial toxins as a result of inflammatory processes. Periacinar degeneration was less intense in unsupplemented fish when compared to supplemented fish. On the other hand, eosinophilic and lymphocytic infiltrate did occur in unsupplemented fish differently from supplemented fish which did not show the alteration. The survival was 28% higher in silymarin supplemented fish when compared to unsupplemented fish that presented no survival. Silymarin supplementation in the diet provided a hepatoprotective and immunomodulatory effect on Nile tilapia.

The complement component 1 q (C1q) in Nile tilapia (Oreochromis niloticus): Functional characterization in host defense against bacterial infection and effect on cytokine response in macrophages

Complement component 1q (C1q) is the initial protein of the classical complement pathway and plays an important role in immune response against bacterial infection. In this study, the full-length of C1q subcomponent A, B and C chain genes (C1qA, C1qB and C1qC) were identified and characterized from Nile tilapia (Oreochromis niloticus). Molecular characterization of these three C1q subcomponents (OnC1qs) harbored conserved amino acids through analyses of multiple sequence alignment and phylogenetic tree, which were homologous to other teleost species. Expression analysis revealed that the OnC1qs were highly expressed in liver. After the in vivo challenges of Streptococcus agalactiae and LPS, the mRNA expressions of OnC1qs were significantly up-regulated in liver. Meanwhile, the concentration variation of OnC1qs at the protein level from tilapia serum after challenge with S. agalactiae were measured by a competitive-inhibition ELISA. In addition, the up-regulation expressions of OnC1qs were also demonstrated in head kidney adherent leukocytes and the cell culture medium in vitro stimulation with S. agalactiae, Aeromonas hydrophila and LPS, respectively. Moreover, the recombinant OnC1qs enhanced expression of cytokines IL-6, IL-8 and IL-10 in head kidney adherent leukocytes, and were able to bind both heat-aggregated mouse IgG and IgM. Taken together, the results of this study indicated that OnC1qs might be involved in host defense against bacterial infection in Nile tilapia.

Clinical characteristics and etiology of bacterial meningitis in Chinese children >28 days of age, January 2014-December 2016: A multicenter retrospective study

OBJECTIVE

To explore the clinical characteristics and etiology of bacterial meningitis (BM) in Chinese children.

METHOD

BM cases in children 28days to 18 years old were collected from January 2014-December 2016 and screened according to World Health Organization standards. Clinical features, pathogens, and resistance patterns were analyzed.

RESULTS

Overall, 837 cases were classified into five age groups: 28 days-2 months (17.0%), 3-11 months (27.8%), 12-35 months (24.0%), 3-6 years (13.9%), and >6years (17.3%). Major pathogens were Streptococcus pneumoniae (S. pneumoniae, n=136, 46.9%), group B Streptococcus (GBS, n=29, 10.0%), and Escherichia coli (E. coli, n=23, 7.9%). In infants <3 months old, GBS (46.5%) and E. coli (23.3%) were most common; in children >3 months old, S. pneumoniae (54.7%), which had a penicillin non-susceptibility rate of 55.4% (36/65), was most frequent. The resistance rates of S. pneumoniae and E. coli to cefotaxime and ceftriaxone were 14.0%/40.0% and 11.3%/68.4%, respectively. All GBS isolates were sensitive to penicillin.

CONCLUSIONS

The occurrence of BM peaked in the first year of life, while S. pneumoniae was the predominant pathogen in children >3months of old. The antibiotic resistance of S. pneumoniae was a concern.

Cloning, characterization and functional analysis of dctn5 in immune response of Chinese tongue sole (Cynoglossus semilaevis)

In mammals, microtubule-dependent trafficking could participate the immune response, where the motor proteins are suggested to play an important role in this process, while the related study in fish was rare. In this study, dctn5, a subunit of dyactin complex for docking motor protein, was obtained by previous immune QTL screening. The full-length cDNAs of two dctn5 transcript variants were cloned and identified (named dctn5_tv1 and dctn5_tv2, respectively). Tissue distribution showed that dctn5_tv1 was widely distributed and high transcription was observed in immune tissue (skin), while dctn5_tv2 was predominantly detected in gonad and very low in other tissues. Time-course expression analysis revealed that dctn5_tv1 could be up-regulated in gill, intestine, skin, spleen, and kidney after Vibrio harveyi challenge. Moreover, recombinant Dctn5_tv1 exhibited high antimicrobial activity against Escherichia coli and Streptococcus agalactiae due to binding to bacteria cells. Taken together, these data suggest Dctn5_tv1 is involved in immune response of bacterial invasion in Chinese tongue sole.

Validation of IgY for the diagnosis of Streptococcus agalactiae-caused endocarditis and bacterial meningitis in Nile tilapia (Oreochromis niloticus)

Streptococcus agalactiae (Sta), which belongs to Lancefield group B, causes sepsis, endocarditis and bacterial meningitis in human neonates and Nile tilapia. Because the pathophysiology of Sta infection is partially similar in both species, the identification of biomarkers for the diagnosis and study of this disease is of importance for human and animal health. Therefore, in the present study, we produced an immunoglobulin Y (IgY) by immunizing laying hens with Sta proteins and evaluated its ability to detect Sta in paraffinized tilapia brain and cardiac tissue by direct immunofluorescence (IMF) and indirect immunohistochemistry (IHC). The IgY produced was effective in the diagnosis of Sta infection in Nile tilapia, justifying the use of this species as a biomodel for the study of this disease.

TLR3 gene in Japanese sea perch (Lateolabrax japonicus): Molecular cloning, characterization and expression analysis after bacterial infection

Toll-like receptors (TLRs) play important roles in fish innate immune and are involved in the defense process of bacteria invasion. In the present study, the full-length cDNA of TLR3 from the sea perch, Lateolabrax japonicus, was cloned and characterized. The full length of LjTLR3 cDNA was 3265 bp including an open reading frame of 2679 bp encoding a peptide of 922 amino acids. Tissues distribution analysis indicated that LjTLR3 showed a tissue-specific variation with high expression in spleen, head-kidney and liver. In order to investigate LjTLR3 functions against bacteria infection, the expression patterns of LjTLR3 after Vibrio harveyi and Streptococcus agalactiae challenge were detected by qRT-PCR, and the results showed that LjTLR3 was significant up-regulated after both bacteria stimulation in head-kidney, spleen and liver in a time-depended manner. Furthermore, the results by in situ hybridization experiments showed that positive signals of LjTLR3 mRNA in infected spleen and head-kidney were more numerous than that in the control group. In addition, intracellular localization revealed that LjTLR3 is distributed in the cytoplasm. In summary, these findings suggest that LjTLR3 was involved in the immune process under bacteria infection. This study would benefit to further clarify the roles of fish TLRs in the immune process and contribute to further study on enhancing disease resistance of L. japonicus.

Basal polarization of the immune responses to Streptococcus agalactiae susceptible and resistant tilapia (Oreochromis niloticus)

One of the highest priority areas for improvement is the development of effective strategies for decreasing disease mortality levels in aquaculture production, a better understanding of the components of the fish immune system and their functions in the context of pathogen invasion is needed. Tilapia is the most common fish in South China, and Streptococcus agalactiae has become the most serious disease problem for tilapia industry in China. Here, we profiled gene expression differences between tilapia differing in their susceptibility to S. agalactiae both basally (before infection) and at three early timepoints post-infection (5 h, 50 h, and 7 d). Between group comparisons revealed 5756 unique genes differentially expressed greater than 2-fold at one or more timepoints. And the resistant fish showed much more strong ability in pathogen recognition, antigen presentation, immune activation, while the susceptible fish showed fast activation of apoptosis. Taken together, the immune profiles expand our knowledge for molecular mechanisms for disease resistance, as well as provide solid molecular resources for further identification of the candidate markers for disease-resistant selection and evaluation of disease prevention and treatment options for tilapia industry.

Expression and functional characterization of transferrin in Nile tilapia (Oreochromis niloticus) in response to bacterial infection

Transferrin (TF), an iron-binding glycoprotein, plays an important role in host defense against pathogenic infection, which inhibits the growth and proliferation of pathogens, deprives iron from invading pathogens, and activates anti-microbial responses in macrophages. In this study, a TF homologue (OnTF) was identified from Nile tilapia (Oreochromis niloticus) and characterized at expression pattern against bacterial infection and capability binding bacterial pathogens. The open reading frame of OnTF is 2118 bp of nucleotide sequence encoding polypeptides of 705 amino acids. The deduced protein is highly homology to the other species, containing two conserved iron binding lobes: N-lobe and C-lobe. Expression analysis revealed that the OnTF was extremely highly expressed in liver tissue; however, much weakly exhibited in other examined tissues including spleen and head kidney. The OnTF expression was significantly up-regulated in the liver, spleen and head kidney following infection of a Gram-positive bacterial pathogen (Streptococcus agalactiae) and a Gram-negative bacterial pathogen (Aeromonas hydrophila). The up-regulation of OnTF expression was also demonstrated in hepatocytes and macrophages in vitro stimulated with S. agalactiae and A. hydrophila. In addition, recombinant OnTF ((r)OnTF) protein possessed capability to bind both S. agalactiae and A. hydrophila in vitro. Taken together, the present study indicated that OnTF might be involved in host defense against bacterial infection in Nile tilapia.

Transgenic expression of tilapia piscidin 3 (TP3) in zebrafish confers resistance to Streptococcus agalactiae

To study the biological role of tilapia piscidin 3 (TP3) in Streptococcus agalactiae infection in vivo, TP3/DsRed overexpressing transgenic zebrafish were generated. Under normal growth conditions, TP3/DsRed transgenic zebrafish exhibited an orange-red body color, without any other obvious abnormalities. However, when compared to wild type fish, TP3/DsRed transgenic zebrafish were resistant to S. agalactiae infection. After infection, the TP3 overexpressing fish exhibited higher expression of Toll-like receptor 4a (TLR4a), interleukin (IL)-10, IL-22, and C3b. Furthermore, TP3/DsRed transgenic zebrafish exhibited reduced induction of proinflammatory cytokines, including TNFα, IL-1β, IL-21, MyD88, and nuclear factor (NF)-κB. Taken together, our data show that TP3 overexpression in zebrafish can effectively suppress proinflammatory responses and enhance production of C3b. Together, these actions are conducive to the resolution of inflammation and bacterial clearance. We further postulate that TP3 may exert its anti-inflammatory effects by enhancing TLR4a-mediated negative regulation of NF-κB.

Epizootics of Streptococcus agalactiae infection in captive rays from Queensland, Australia

The aim of this study was to describe two epizootics of high mortalities from infection with Streptococcus agalactiae, occurring in captive rays held in a marine display aquarium in south-east Queensland, Australia, in 2009 and 2010. Five different species of rays were affected, including mangrove whiprays (Himantura granulata), estuary rays (Dasyatis fluviorum), eastern shovelnose rays (Aptychotrema rostrata), white-spotted eagle rays (Aetobatus narinari) and blue-spotted mask rays (Neotrygon kuhlii). This report describes the history of both epizootics including collection, quarantine and husbandry of rays, the disease epizootics, clinico-pathological features of the disease, antimicrobial therapy, autogenous vaccine production, and laboratory studies including clinical and histopathology, bacteriology, PCR, molecular serotyping and sequencing of the bacterium S. agalactiae.

Molecular characterization, expression and functional analysis of NOD1, NOD2 and NLRC3 in Nile tilapia (Oreochromis niloticus)

The nucleotide-binding oligomerization domain proteins NOD1, NOD2 and NLRC3 are cytoplasmic pattern recognition receptors (PRRs) of the Nod-like receptor (NLR) family. In the present study, the Nile tilapia (Oreochromis niloticus) NOD1 (ntNOD1), NOD2 (ntNOD2) and NLRC3 (ntNLRC3) genes were cloned and characterized. The full-length ntNOD1, ntNOD2 and ntNLRC3 genes were 3924, 3886 and 4574 bp, encoding 941, 986 and 1130 amino acids, respectively. The three Nod-like receptors have a NACHT domain and a C-terminal leucine-rich repeat (LRR) domain. In addition, ntNOD1 and ntNOD2 have a N-terminal CARD domain (ntNOD2 has two). Phylogenetic analysis showed that the three NLRs are highly conserved. Tissue expression analysis of the three receptors revealed that the highest mRNA and protein levels of ntNOD1, ntNOD2 and ntNLRC3 were in the spleen. The expression patterns of NLRs during embryonic development showed that the expression levels of ntNOD2 and ntNLRC3 significantly increased from 2 to 8 days post-fertilization (dpf). The expression levels of ntNOD1 significantly increased from 2 to 6 dpf, decreased at 7 dpf and then increased at 8 dpf. Upon stimulation with an intraperitoneal injection of Streptococcus agalactiae, expression levels of the ntNOD1, ntNOD2 and ntNLRC3 mRNA and protein were clearly altered in the blood, spleen, kidney, intestine and gill. Furthermore, after cotransfection with an NF-κB reporter plasmid, NF-κB activation in ntNOD1-overexpressing 293T cells significantly increased compared with that in control cells, before or after i-EDPA-stimulation. By contrast, compared with control, ntNOD2 and ntNLRC3 had no effect on NF-κB activation in 293T cells, when their potential ligands were not stimulated. However, after MDP-stimulation, ntNOD2 and ntNLRC3 overexpression increased NF-κB activation in 293T cells. NOD1 and NLRC3 were uniformly distributed throughout the cytoplasm in 293T cells, whereas NOD2 was distributed throughout the cytoplasm and nucleus. Our results indicate that the three Nod-like receptors are functionally conserved and may play pivotal roles in defense against pathogens such as Streptococcus agalactiae.

NK-lysin from Oreochromis niloticus improves antimicrobial defence against bacterial pathogens

NK-lysin, an effector of cytotoxic T cells and natural killer cells, is a potent antimicrobial peptide widely distributed in mammals. Homologues of NK-lysin have been discovered in several teleost species, but only several of their natural functions was recorded so far. Here we identified an NK-lysin from Nile tilapia (Oreochromis niloticus), On-NKL, and analysed its expression model and biological effects on pathogen infection. The open reading frame of On-NKL sequence spans 432 bp, codes for 143 amino acids and shares 27%-62% overall sequence identities with NK-lysin of other species. The deduced mature peptide of On-NKL possesses a saposin B domain and six well-conserved cysteine residues that essential for antimicrobial activity by forming three intrachain disulphide bonds. The results of qRT-PCR showed that On-NKL expression was observed in multiple tissues and head kidney leucocytes and nonspecific cytotoxic cells (NCCs) and is most abundant in gills. After bacterial challenge, On-NKL expression significantly varied in different tissues and NCCs. Following bacterial infection, On-NKL-overexpressing fish featured significantly lower pathogen loads in tissues than control fish. On-NKL-overexpressing fish also exhibited 33.3% relative percent survival compare with control groups. Findings suggested that On-NKL could be the potential effector of NCCs and act as immune-related gene that enhances antimicrobial defence.

Characterization and expression analysis of a chitinase gene (PmChi-5) from black tiger shrimp (Penaeus monodon) under pathogens infection and ambient ammonia-N stress

Chitinases are crucial enzymes for crustaceans. Previous researches had already revealed that chitinases play important roles in digestion, molting and defense against viruses. In the present study, a chitinase cDNA was identified from black tiger shrimp (Penaeus monodon) and designated as PmChi-5. The full-length PmChi-5 cDNA was 2860 bp in size, containing an open reading frame (ORF) of 1731 bp that encoded a protein of 576 amino acids with a deduced molecular weight of 64.8 kDa. Expression of the PmChi-5 mRNA was ubiquitously detected in all selected tissues, with the highest level in the gill and hepatopancreas. PmChi-5 was expressed throughout the whole larvae stages, and the highest level at Mysis3 stage, which indicated that PmChi-5 may be involved in larval metamorphosis. After challenged with Streptococcus agalactiae and Vibrio harveyi, the transcripts of PmChi-5 were found to be up-regulated significantly both in hepatopancreas and gill. Besides, the ammonia nitrogen stress treatment was also carried out, PmChi-5 transcripts were significantly changed in hepatopancreas and gill. The results showed that PmChi-5 may be involved in molting, larval metamorphosis, the immune defenses to pathogens infection and ammonia-N stress.

Conservation of structural and interactional features of CD28 and CD80/86 molecules from Nile tilapia (Oreochromis niloticus)

Interaction of CD28 with CD80 or CD86 molecules provides a costimulatory signals required in T cell activation. In this study, we cloned and analyzed a CD28 gene (On-CD28) and a CD80/86 gene (On-CD80/86) from Nile tilapia (Oreochromis niloticus). Sequence analysis revealed the typical characteristics of On-CD28 protein; for instance, the proline-based motif (¹¹⁷TYPPPL¹²²) is essential in binding of CD28 to CD80/86 ligands. Moreover, an extracellular Ig domain was found in On-CD80/86; this domain is responsible in binding of CD28 to CD80/86 receptors. Subcellular localization analysis showed that both On-CD28 and On-CD80/86 were distributed predominantly in the cytomembrane. Yeast two-hybrid assay showed that On-CD28 directly interacted with On-CD80/86. On-CD28 and On-CD80/86 transcripts were detected in all the examined tissues of healthy Nile tilapia, and the highest expression levels of On-CD28 and On-CD80/86 were detected in the brain and heart, respectively. Following a bacterial challenge using Streptococcus agalactiae in vivo, On-CD28 and On-CD80/86 were upregulated in head kidney, spleen, intestines, and brain. However, they showed different expression profiles in response to stimulation with inactivated S. agalactiae in vitro. These findings indicated that the interaction of On-CD28 with On-CD80/86 provides a costimulatory signals that possibly play an important role in T cell activation during S. agalactiae infection.

Different β-glucans improve the growth performance and bacterial resistance in Nile tilapia

The role of glucan as a biologically active immunomodulator has been well documented for more than 40 years. However, the wide diversity of β-glucan forms and the extraction process has implications for the benefits of these compounds. Biorigin developed two samples of β-glucans using different biotechnological processes. Thus, in the present study, we fed Nile tilapia (Oreochromis niloticus) diets containing these two β-glucan molecules (BG01 and BG02) for 30 days prior to bacterial infection with Streptococcus agalactiae. The results showed that the different β-glucan samples exhibited biologically differently behaviors, but both increased the resistance against bacterial infection. Specifically, BG01 increased immunostimulation, while BG02 improved growth performance. In summary, these findings confirm the benefits of β-glucans in aquaculture and also provide further evidence of the growth promotion of these compounds.

Transcriptome analysis of hybrid tilapia (Oreochromis spp.) with Streptococcus agalactiae infection identifies Toll-like receptor pathway-mediated induction of NADPH oxidase complex and piscidins as primary immune-related responses

Streptococcus agalactiae infection is one of the most significant bacterial diseases in tilapia aquaculture. Identification of immune-related genes associated with Streptococcus agalactiae infection may provide a basis for breeding selection or therapeutics to augment disease resistance. Therefore, we utilized transcriptome profiling to study the host response in tilapia following Streptococcus agalactiae infection. Based on GO and KEGG enrichment analyses, we found that differentially expressed genes are widely involved in immune-related pathways, including the induction of antimicrobial peptides. Moreover, the main components of two immune-related pathways (Toll-like receptor signaling and leukocyte transendothelial migration) and four environmental information processing pathways (TNF, PI3K-Akt, Jak-STAT and MAPK) were identified. Finally, a time-course expression profile for several of the identified transcripts including tilapia piscidin 3 (TP3), tilapia piscidin 4 (TP4), TLR2, TLR5, MyD88, TRAF6, p38, and interleukin components was performed by qRT-PCR. Collectively, these results provide a starting point to study molecular mechanisms of tilapia immune response to Streptococcus agalactiae infection and may be applied as a basis for developing disease resistant strains by breeding selection.

C1r and C1s from Nile tilapia (Oreochromis niloticus): Molecular characterization, transcriptional profiling upon bacterial and IFN-γ inductions and potential role in response to bacterial infection

The complement components C1r and C1s play a vital role in immunity with the activation of C1 complex in the classical complement pathway against pathogen infection. In this study, Nile tilapia (Oreochromis niloticus) C1r and C1s orthologs (OnC1r and OnC1s) were identified and characterized. The cDNA of OnC1r and OnC1s ORFs consisted of 1902 bp and 2100 bp of nucleotide sequence encoding polypeptides of 633 and 699 amino acids, respectively. The deduced OnC1r and OnC1s proteins both possessed CUB, EGF, CCP and SP domains, which were significantly homology to teleost. Spatial mRNA expression analysis revealed that the OnC1r and OnC1s were highly expressed in liver. After the in vivo challenges of Streptococcus agalactiae (S. agalactiae) and lipopolysaccharide (LPS), the mRNA expressions of OnC1r and OnC1s were significantly up-regulated in liver and spleen, which were consistent with immunohistochemical detection at the protein level. The up-regulation of OnC1r and OnC1s expressions were also demonstrated in head kidney monocytes/macrophages in vitro stimulated with LPS, S. agalactiae, and recombinant OnIFN-γ. Taken together, the results of this study indicated that OnC1r and OnC1s were likely to get involved in the immune response of Nile tilapia against bacterial infection.

Thymosin β4 is involved in the antimicrobial immune response of Golden pompano, Trachinotus ovatus

Thymosin beta belongs to the thymosin family, which consists of a series of highly conserved peptides involved in various biological processes. In teleosts, understanding of the immunological functions of thymosin beta is limited, particularly in vivo, which is essentially unknown. In the current study, we cloned and identified thymosin beta 4 from the teleost fish Golden pompano (Trachinotus ovatus), which we have named TroTβ4. We investigated the expression patterns and functions of TroTβ4 in both in vivo and in vitro assays. TroTβ4 is composed of 44 amino acids and shares high sequence identities with known thymosin β4 species in other teleosts, which contains a highly conserved actin-binding motif (LKKTET). The expression of TroTβ4 was most abundant in immune organs, and was significantly up-regulated in response to infection bacterial with one of a number of bacteria (including Edwardsiella tarda, Vibrio harveyi, and Streptococcus agalactiae). Purified recombinant TroTβ4 (rTroTβ4) inhibited the growth of bacteria, as measured using an automatic growth curve analyzer, indicating that TroTβ4 has antimicrobial functions. When administered in vivo, overexpression of TroTβ4 in T. ovatus, bacterial colonization of tissues was significantly reduced. In contrast, when a DNA vector-based siRNA technology was used to knock down TroTβ4 expression, bacterial dissemination and colonization of tissues increased significantly. Taken together, these results provide the first in vivo evidence to indicate that teleost thymosin beta 4 plays a significant role in innate antibacterial immune responses in addition to in vitro bacteriostatic activity. This provides valuable information regarding the biological functions of teleost thymosin beta.

Efficacy of viable Bacillus pumilus isolated from farmed fish on immune responses and increased disease resistance in Nile tilapia (Oreochromis niloticus): Laboratory and on-farm trials

Applications of viable Bacillus pumilus AQAHBS01 isolated from Nile tilapia farms as probiotics were studied in both laboratory and farm conditions. In the laboratory, feeding fish (approximately 50 g) with feed containing viable B. pumilus at concentrations of 1 × 10⁷-10⁹ colony forming units (CFU)/kg elevated fish immune responses, as indicated by their phagocytic activity and superoxide anion levels, and led to more effective disease resistance against Streptococcus agalactiae. However, when these concentrations were applied to Nile tilapia cultures growing in cage culture systems, only B. pumilus AQAHBS01 at concentrations of 1 × 10⁸ and 10⁹ CFU/kg diet could effectively enhance disease resistance against S. agalactiae during the critical period of early to middle April when the temperature reached 33 °C, whereas control fish and fish that consumed B. pumilus AQAHBS01 at concentrations of 1 × 10⁷ CFU/kg showed very rapid streptococcosis-induced mortality. However, in late April, massive levels of organic matter-containing water flowed into the culture areas, causing all fish groups to become infected with Flavobacterium columnare. Moreover, the dissolved oxygen levels in the river declined to critical levels of approximately 1.0-1.5 mg/L, causing anorectic effects in fish for long periods of time. This effect may have also gradually killed the cultured fish until the end of the experiment. This information strongly demonstrates the effective application of B. pumilus as a probiotic for streptococcosis resistance in both laboratory and field culture conditions. For on-farm cage culture practices, however, fluctuations in water quality remain a significant constraint for probiotic application, as they usually induce negative effects on fish health. This decline in health makes fish more fragile and more susceptible to problems from both infectious and non-infectious diseases, which farmers must consider carefully.