Identification of antigenic Edwardsiella tarda surface proteins and their role in pathogenesis

Edwardsiella tarda in Tambaqui (Colossoma macropomum): A Pathogenicity, Antimicrobial Susceptibility, and Genetic Analysis of Brazilian Isolates

Edwardsiella tarda is a crucial pathogenic bacterium in tropical aquaculture. This bacterium was recently isolated from tambaqui (Colossoma macropomum), a commercially important fish species in Brazil. This study assessed the antimicrobial susceptibility, pathogenicity, and genetic diversity of the tambaqui-derived E. tarda isolates. Fourteen bacterial isolates isolated from tambaqui were identified as E. tarda by using matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry and dnaJ gene sequencing. Antimicrobial susceptibility tests were conducted against seven drugs using the disc diffusion assay. The pathogenicity test conducted by intraperitoneal injection of 2.4 × 107 colony-forming units (CFU) fish-1 of E. tarda (ED38-17) into tambaqui juveniles eventually revealed that neither clinical signs nor death were present. However, splenomegaly and whitish areas in the spleen and kidneys were observed. The histological investigation also revealed granulomatous splenitis, nephritis, and hepatitis occurring internally. Repetitive extragenic palindromic-PCR fingerprinting separated the 14 isolates into three genetic groups. The antibiogram revealed that all E. tarda isolates were wild-type (WT) to florfenicol (FLO), norfloxacin (NOR), neomycin (NEO), erythromycin (ERY), and oxytetracycline (OXY); however, some were non-wild-type to sulfamethoxazole/trimethoprim (7.1%) and amoxicillin (21.4%). Therefore, through experimental infection, E. tarda ED38-17 could induce pathogenic effects in C. macropomum. Additionally, three distinct genetic types were found, and the E. tarda isolates were WT to FLO, NOR, NEO, ERY, and OXY. These findings raise awareness of a bacteria causing unseen lesions, a pathogen that will potentially impact tambaqui aquaculture in the future.

Splenic protection network revealed by transcriptome analysis in inactivated vaccine-immunized flounder (Paralichthys olivaceus) against Edwardsiella tarda infection

The protective immune response produced by fish after vaccination is crucial for vaccine effectiveness. Our previous studies have shown inactivated vaccine against Edwardsiella tarda can induce immune response in flounder (Paralichthys olivaceus). To elucidate the protective immune response at the genetic level, in this study, flounder was immunized with inactivated E. tarda for 5 weeks, and then they were challenged with E. tarda. The spleen was dissected at 7th day post immunization, 1st and 7th day post challenge, respectively. Transcriptome analysis showed that average of 46 million clean reads were obtained per library, while percentage of clean reads being mapped to reference genome was more than 89% in all cases, which suggested good quality of samples. As for differentially expressed genes (DEGs) identification in inactivated E. tarda groups, at 7th day post immunization, 1422 DEGs were identified and significantly enriched in innate immune-related pathways, such as Phagosome, Cell adhesion molecules and NF-kappa B signaling pathway; At 1st post challenge day, 1210 DEGs were identified and enriched to Antigen processing and presentation and Cell adhesion molecules, indicating that the pathogen was rapidly recognized and delivered; At 7th post challenge day, 1929 DEGs were identified, belonged to Toll-like receptor signaling pathway, Antigen processing and presentation, Th1 and Th2 cell differentiation and Th17 cell differentiation. Compared to 7th post immunization day, 73 immune-associated DEGs were identified at 1st post challenge day. Protein-protein interaction networks analysis revealed 11 hub genes (TLR7, TLR3, CXCR4, IFIH1, TLR8 etc), associated with recognition of pathogens and activation of innate immunity; while for 7th post challenge day, 141 immune-associated DEGs were identified. 30 hub genes (IL6, STAT1, HSP90A.1, TLR7, IL12β etc) were associated with stimulation of lymphocyte differentiation and activation of cellular immunity. Ten immune-related genes were randomly selected for RT-qPCR validation at each time point. In conclusion, data revealed protection of flounder against E. tarda infection by inactivated vaccine is mediated via immediate recognition of pathogen and subsequently activation of cellular immunity. Results give new aspect for vaccine protection cascades, is good references for vaccine evaluation.

Evaluation of bivalent vaccines candidates among VAA, OmpK and OmpR from Vibrio anguillarum in flounder (Paralichthys olivaceus)

Outer membrane protein (Omp) K, OmpR and VAA have been identified with good immunogenicity from Vibrio anguillarum, and their recombinant proteins showed variable relative percent survival (RPS) in previous study. In order to develop effective bivalent vaccine candidates, recombinant (r) VAA + rOmpK (AK), rVAA + rOmpR (AR), rOmpK + rOmpR (KR) among VAA, OmpK and OmpR, or formalin-killed cells (FKC) of V. anguillarum were immunized in flounder, respectively. Results revealed that AK, AR, KR and FKC could induce the proliferation of surface membrane immunoglobulin-positive B lymphocytes or CD3⁺ T lymphocytes in peripheral blood lymphocytes, and significantly enhance the total antibodies, specific antibodies and immune-related gene than those of control group. AK, AR, KR or FKC showed RPS of 74.92%, 78.49%, 82.09% and 56.99%, respectively. These results indicated that three bivalent vaccines AK, AR and KR could induce strong cellular and humoral immunity, and had high protection against V. anguillarum infection in flounders.

Intracellular Bacterial Infections: A Challenge for Developing Cellular Mediated Immunity Vaccines for Farmed Fish

Aquaculture is one of the most rapidly expanding farming systems in the world. Its rapid expansion has brought with it several pathogens infecting different fish species. As a result, there has been a corresponding expansion in vaccine development to cope with the increasing number of infectious diseases in aquaculture. The success of vaccine development for bacterial diseases in aquaculture is largely attributed to empirical vaccine designs based on inactivation of whole cell (WCI) bacteria vaccines. However, an upcoming challenge in vaccine design is the increase of intracellular bacterial pathogens that are not responsive to WCI vaccines. Intracellular bacterial vaccines evoke cellular mediated immune (CMI) responses that “kill” and eliminate infected cells, unlike WCI vaccines that induce humoral immune responses whose protective mechanism is neutralization of extracellular replicating pathogens by antibodies. In this synopsis, I provide an overview of the intracellular bacterial pathogens infecting different fish species in aquaculture, outlining their mechanisms of invasion, replication, and survival intracellularly based on existing data. I also bring into perspective the current state of CMI understanding in fish together with its potential application in vaccine development. Further, I highlight the immunological pitfalls that have derailed our ability to produce protective vaccines against intracellular pathogens for finfish. Overall, the synopsis put forth herein advocates for a shift in vaccine design to include CMI-based vaccines against intracellular pathogens currently adversely affecting the aquaculture industry.

Edwardsiella piscicida lacking the cyclic AMP receptor protein (Crp) is avirulent and immunogenic in fish

Edwardsiella piscicida is a Gram-negative pathogen that generally causes lethal septicemia in marine and freshwater fish. We generated a E. piscicida CK216 Δcrp mutant to investigate various biological roles related to this organism, including pathogenesis. Lack of Crp in CK216 was demonstrated by immunoblotting using a Crp-specific antibody. Compared to the parental strain, the mutant exhibited changes in three biochemical phenotypes, including ornithine decarboxylation, citrate utilization, and H₂S production. Complementation of crp deletion in trans rescued the phenotype of the parental strain. This study proved that hemolytic activity in E. piscicida is controlled by Crp. In addition, significantly reduced motility of E. piscicida CK216 was observed, which resulted from a lack of flagella synthesis. To examine the virulence in fish, E. piscicida cells were injected into the goldfish (Carassius auratus) via intraperitoneal route. The LD₅₀ of CK216 was 9.25 × 10⁸ CFU, while that of the CK108 parental strain was 9.24 × 10⁵ CFU, attenuated 1000 fold in goldfish. Fish immunized with CK216 elicited IgM responses. Moreover, 80% of goldfish immunized with 1 × 10⁶ CFU survived after administration of a lethal dose (1 × 10⁷ CFU) of virulent E. piscicida CK41, suggesting the potential for E. piscicida CK216 to serve as a live attenuated vaccine in aquaculture.

Analysis of zebrafish (Danio rerio) behavior in response to bacterial infection using a self-organizing map

BACKGROUND

Animal behavioral responses have been recently established as a suitable tool for detecting contaminants in the environment for risk assessment in situ. In this study, we observed movement behavior of zebrafish (Danio rerio) before and after infection with Edwardsiella tarda CK41 for 3 days until death.

METHODS

Infection status of zebrafish was confirmed through PCR and colonization assay as time progressed and lesion development in the tails of zebrafish was also examined. Movement behaviors in response to bacterial infection were patterned by self-organizing map (SOM) based on movement parameters, including speed (mm/s), acceleration (mm/s (2) ), stop duration (t), stop number (n), locomotory rate (mm/s), turning rate (rad/s), and meander (rad/mm).

RESULTS

According to SOM result, clusters were identified firstly according to time and secondly according to infection. Two movement patterns were observed in the early period of infection: one group with minimum turning rate and meander (i.e., stiff movement) and the other group with maximum strop number. Late infection was characterized by long stop duration.

CONCLUSION

SOM was suitable for extracting complex behavioral data and thus can serve as a referencing system for diagnosing disease development in order to reveal the mechanism of the infection process.

Comparative proteomic study of Edwardsiella tarda strains with different degrees of virulence

Edwardsiella tarda is an enteric opportunistic pathogen that causes a great loss in aquaculture. This species has been described as a phenotypical homogeneous group; in contrast, serological studies and molecular typing revealed a wide heterogeneity. In this work, a proteomic study of differential expression of a virulent isolate from turbot cultured in the Norwest of Spain in comparison with an avirulent collection strain was performed in order to recognize proteins involved in virulence. One hundred and three proteins that presented different abundance were successfully identified and classified into 11 functional categories according to their biological processes: amino acid, carbohydrate and lipid metabolism, tricarboxylic cycle, stress response and protein fate, protein synthesis, biogenesis of cellular components, cell rescue defence and virulence, cell membrane and transport, signal transduction and purine and pyrimidine metabolism. Twenty three protein spots detected only in turbot isolate were identified. It was shown that the same proteins appeared in different spots in the two isolates. Mass spectra obtained by MALDITOF/TOF of some of these proteins and DNA sequencing explained the changes as a result of different amino acid sequences. Several proteins related with the virulence of E. tarda (FliC, ArnA or FeSODI) were only detected in the turbot European isolate. This article is part of a Special Issue entitled: HUPO 2014.