Bacterial Pathogen Aeromonas Salmonicida Research Articles

Cell atlas of the Atlantic salmon spleen reveals immune cell heterogeneity and cell-specific responses to bacterial infection

The spleen is a conserved secondary lymphoid organ that emerged in parallel to adaptive immunity in early jawed vertebrates. Recent studies have applied single cell transcriptomics to reveal the cellular composition of spleen in several species, cataloguing diverse immune cell types and subpopulations. In this study, 51,119 spleen nuclei transcriptomes were comprehensively investigated in the commercially important teleost Atlantic salmon (Salmo salar L.), contrasting control animals with those challenged with the bacterial pathogen Aeromonas salmonicida. We identified clusters of nuclei representing the expected major cell types, namely T cells, B cells, natural killer-like cells, granulocytes, mononuclear phagocytes, endothelial cells, mesenchymal cells, erythrocytes and thrombocytes. We discovered heterogeneity within several immune lineages, providing evidence for resident macrophages and melanomacrophages, infiltrating monocytes, several candidate dendritic cell subpopulations, and B cells at distinct stages of differentiation, including plasma cells and an igt + subset. We provide evidence for twelve candidate T cell subsets, including cd4+ T helper and regulatory T cells, one cd8+ subset, three γδT subsets, and populations double negative for cd4 and cd8. The number of genes showing differential expression during the early stages of Aeromonas infection was highly variable across immune cell types, with the largest changes observed in macrophages and infiltrating monocytes, followed by resting mature B cells. Our analysis provides evidence for a local inflammatory response to infection alongside B cell maturation in the spleen, and upregulation of ccr9 genes in igt + B cells, T helper and cd8+ cells, and monocytes, consistent with the recruitment of immune cell populations to the gut to deal with Aeromonas infection. Overall, this study provides a new cell-resolved perspective of the immune actions of Atlantic salmon spleen, highlighting extensive heterogeneity hidden to bulk transcriptomics. We further provide a large catalogue of cell-specific marker genes that can be leveraged to further explore the function and structural organization of the salmonid immune system.

The immune response of a warm water fish orange-spotted grouper (Epinephelus coioides) infected with a typical cold water bacterial pathogen Aeromonas salmonicida is AhR dependent

The present study reported the first pathogenic Aeromonas salmonicida (SRW-OG1) isolated from the warm water fish orange-spotted grouper (Epinephelus coioides), and investigated the function of Aryl hydrocarbon receptor (AhR), a ligand-dependent transcriptional factor which has been recently found to be closely associated with immune response in mammals and E. coioides. Our results showed that AhR was activated by an unknown ligand in the spleen, intestine and macrophages. Meanwhile, ahr1a and ahr1b were significantly increased in the spleen, intestine and macrophages, whereas ahr2 was only increased in the intestine, which indicated that the contribution of AhR2 to the immune response may be less than that of AhR1a and AhR1b. Some key genes involved in the macrophage inflammatory response, bacterial recognition, and intestinal immunity were significantly up-regulated in the SRW-OG1 infected E. coioides. Nevertheless, declining macrophage ROS production and down-regulation of related genes were also observed, suggesting that SRW-OG1 utilized its virulence mechanisms to prevent macrophage ROS production. Furthermore, AhR inhibitor 3′, 4′-DMF and the silence of ahr1a or ahr1b significantly rescued the increased IL-1β and IL-8 induced by SRW-OG1 infection, which proved that the induction of IL-1β and IL-8 in E. coioides macrophages was mediated by AhR. However, BPI/LBP, ROS production and related genes were not affected by AhR. The survival rate and immune escape rate of SRW-OG1 in the ahr1a/ahr1b knocked-down and 3′, 4′-DMF treated macrophages were significantly increased compared with those in wild type macrophages. Taken together, it was preliminarily confirmed that ahr1a and ahr1b played an important role in the immune response against A. salmonicida SRW-OG1.

Potensi Antagonistik Bakteri Lactobacillus plantarum terhadap Bakteri Patogen Aeromonas salmonicida Secara In Vitro <br><i>[The Potential Antagonistic Bacterium Lactobacillus plantarum Against Bacterial Pathogens Aeromonas salmonicida By In Vitro]<I>

Abstract Problems were often experienced by fish farmers is bacterial pathogen Aeromonas salmonicida which causes furunculosis disease in fish. The way to control the growth of this pathogenic bacteria was using antagonist bacteria of Lactobacillus plantarum. Growth of L. plantarum may inhibit contamination of pathogenic bacterial because of its ability to produce bacteriocins, produce lactic, moreover that these bacteria can produce hydrogen peroxide which can function as an antibacterial. This research aimed to provide information on the use of bacterial antagonists L. plantarum in inhibiting the growth of pathogenic bacteria A. salmonicida on In Vitro. This research was conducted on October 2012 until January 2013 at dry laboratory in Fisheries and Marine Faculty of Airlangga University Surabaya. This research used Completely Randomized Design (CRD) with five treatments and four replications. Bacteria L. plantarum with 0 concentration for control (A), 106 (B), 107 (C), 108 (D), 109 (E) tested challenge by paper disc method with 106 concentrate of pathogenic bacteria A. salmonicida in vitro. The results showed that L. plantarum with a concentration of 109 CFU/ml (E) was a treatment that produced average of obstacle on the distribution of A. salmonicida amounted to 12,375 mm. Then the treatment with a concentration of 108 CFU/ml (D) with the average of obstacle 8,95 mm. While treatment with a concentration of 107 CFU/ml (C) and 106 CFU/ml (B) was having average of obstacle 6.8 mm and 6 mm was not significantly different from the control (A) which had an average 6 mm obstacle. So it could be concluded that bacteria L. plantarum had antagonistic potential against bacterial pathogens A.salmonicida which indicated by the obstacle produced by L. plantarum on growth of pathogenic bacteria A.salmonicida.

Disease resistance and health parameters of growth-hormone transgenic and wild-type coho salmon, Oncorhynchus kisutch

To extend previous findings regarding fish health and disease susceptibility of growth-enhanced fish, hematological and immunological parameters have been compared between growth hormone (GH) transgenic and wild-type non-transgenic coho salmon (Oncorhynchus kisutch). Compared to non-transgenic coho salmon, transgenic fish had significantly higher hematocrit (Hct), hemoglobin (Hb), mean cellular hemoglobin (MCH), mean cellular volume (MCV), and erythrocyte numbers, and lower white cell numbers. In addition, resistance to the bacterial pathogen Aeromonas salmonicida (causal agent of furunculosis) has been assessed between the strains. Higher susceptibility of transgenic fish to this disease challenge was observed in two separate year classes of fish. The present findings provide fundamental knowledge of the disease resistance on GH enhanced transgenic coho salmon, which is of importance for assessing the fitness of transgenic strains for environmental risk assessments, and for improving our understanding effects of growth modification on basic immune functions.

Non-ribosomal peptide synthetase AsbD is expressed in iron-limited conditions in the bacterial pathogen Aeromonas salmonicida

Iron is an essential nutrient for most living bacteria. One of the main mechanisms which allow bacterial pathogens to obtain iron is siderophore-mediated iron acquisition. Aeromonas salmonicida subsp. salmonicida, the aetiological agent of furunculosis in fish produces a catecholate siderophore under iron-limiting conditions. A. salmonicida siderophore biosynthesis genes include genes that encode non-ribosomal peptide synthetases. In this study using a siderophore biosynthesis gene cluster previously described, the asbD gene which encodes a non-ribosomal peptide synthetase was studied. Total protein of null mutant and wild-type strains, in iron-repleted and iron-depleted conditions, was extracted and loaded onto polyacrylamide gel. Only the wild-type strain in iron-depleted conditions expressed a 160-KDa protein. These results confirmed that asbD is an iron-regulated gene, and AsbD protein is expressed only in iron-limited conditions.

Nano- and microparticles as adjuvants in vaccine design: Success and failure is related to host natural antibodies

Bovine serum albumin (BSA) and the surface A-layer protein (AP) of an atypical strain of fish bacterial pathogen Aeromonas salmonicida were covalently linked with polymeric nano- and microparticles, and antigenicity of the resulted conjugates was compared in mice and goldfish. Distinct albeit different levels of natural BSA and AP antibodies were present in both animal species. Significant stimulation of the anti-AP antibody response in mice strikingly contrasted to unresponsiveness or even suppression in fish. The results negatively correlate with the levels of respective natural antibodies in the host and are discussed in context of problems related to fish vaccination. The work reinforces the instructive role of natural antibodies in adaptive immune response.

Identification of genes differentially expressed in Atlantic salmon ( Salmo salar) in response to infection by Aeromonas salmonicida using cDNA microarray technology

The response of Atlantic salmon, Salmo salar, to infection by the bacterial pathogen Aeromonas salmonicida (the causative agent of furunculosis), was investigated using a cohabitation model and a custom Atlantic salmon cDNA microarray consisting of over 4000 different amplicons. Pooled samples of each of three immune-relevant tissues (spleen, head kidney and liver) were obtained from fish exposed to infected salmon for 13 days. Reverse transcription-PCR assays were used to verify the differential expression of 12 candidate genes uncovered by microarray analysis. Among the differentially expressed genes were several previously revealed by suppression subtractive hybridization and EST surveys and that are recognized to encode humoral components of the innate immune system. Other genes identified in this study were not previously associated with infection. In addition, a number of genes with no known homologs were uncovered. Determination of their specific roles during infection may lead to a better understanding of innate immunity.

The role of reactive oxygen species in the killing of the bacterial fish pathogen Aeromonas salmonicida by rainbow trout macrophages

The role of reactive oxygen species (ROS) in the killing of the bacterial pathogen Aeromonas salmonicida by in vitro cultured rainbow trout (Oncorhynchus mykiss) head kidney macrophages has been investigated. Using a microtitre plate bactericidal assay the respiratory burst pathway responsible for ROS generation was inhibited completely using the NADPH oxidase inhibitor trifluoperazine and partially by the use of ROS scavengers (formate and/or mannitol) and the antioxidative enzymes SOD and/or catalase. Increased bacterial survival of an avirulent strain (MT004) in the presence of trifluoperazine, catalase and formate confirmed that ROS such as hydrogen peroxide and hydroxyl radicals were indeed an important killing agent. This was further confirmed using sodium nitroprusside and aminotriazole, inhibitors of SOD and catalase respectively. The presence of aminotriazole caused a significantly increased bactericidal activity against a virulent strain (MT423) normally resistant to killing by cultured resident rainbow trout head kidney macrophages.