Your browser does not support JavaScript!

Home    Collections    Type of Work    Doctoral theses  

Doctoral theses

Current Record: 18 of 2177

Back to Results Previous page
Next page
Add to Basket
[Add to Basket]
Identifier 000441534
Title Συγκριτική μελέτη στελεχών Aeromonas veronii ως νοσογόνου παράγοντα σε εκτρεφόμενα λαβράκια. Ανάπτυξη αυτεμβολίων για την πρόληψη της ασθένειας
Alternative Title Comparative study on Aeromonas veronii isolates as disease agent in farmed European seabass. Development of autogenus vaccines for the prevention of the disease
Author Σμυρλή, Μαρία Ν
Thesis advisor Παυλίδης, Μιχαήλ
Reviewer Καθάριος, Παντελής
Αθανασάκη, Ειρήνη
Καλαντίδης, Κρίτων
Μπακόπουλος, Βασίλειος
Ντότσικα, Ελένη
Χαμηλός, Γεώργιος
Abstract The object of the study was a bacterial disease affecting farmed European seabass caused by Aeromonas veronii bv. sobria. The disease affects farmed sea bass weighing> 50 g on fish farms in the Aegean Sea, mainly in the west. It occurs in temperature > 21- 22oC, while the outbreaks occur mainly in the summer months. The cumulative mortality can reach up to 80% of the farmed population. The current study concerns an emerging pathology for seabass fish farming and was initially considered a local, individual case. The pathology and epidemiological features of the disease were studied. Pathogen diversity was studied with molecular (16S rRNA and gyrB) and biochemical (Biolog and API20E) tools. As part of the work, a genus-based detection protocol was developed. The infectivity of the pathogen was tested in vivo, with experimental infections in healthy seabass and zebrafish and in vitro, on a blood agar medium. The genomes of representative strains were sequenced, and the phylogenetic relationships and the antigenic nature and diversity of the pathogen were studied. Τhe principles of reverse vaccinology were applied to detect conserved membrane proteins–antigens for the development of the widely used Aeromonas veronii vaccine. Finally, a bacterial vaccine (water and oil-based) was developed. The efficacy of the vaccine was tested by challenge tests on the vaccinated fish, by measuring the titer of antibodies (ELISA) in the blood serum and by the expression of selected genes related to the immune system via qPCR. Three phenotypes of the pathogen were identified which are distinguished in terms of motility and pigment production and correspond to different regions of the Aegean Sea. Strains from different regions were almost (ppsA) indistinguishable with the studied housekeeping genes used as genetic markers. The symptoms of the disease were reproduced in artificial infections in seabass, confirming the pathogenicity of A. veronii. The use of zebrafish for the study of bacterial infectivity in Greek fish farming species is encouraged by the results since infections induced mortality in zebrafish too. Genomic analyses showed high similarity between A. veronii strains of seabass in different regions of the Aegean Sea. However, their differentiation was possible by single nucleotide polymorphisms corresponding to the phenotypic groups mentioned above and the different geographical origins of the strains (East /West Aegean). The outer membrane antigenic proteins also showed a high degree of similarity at the amino acid sequence, but differences were found in the S-layer protein, maltoporin LamB, and O-antigen, suggesting the use of a multivalent vaccine for Aegean seabass culture. The injectable bivalent adjuvanted (NS+PDB+Montanide) vaccine offered protection to adult seabass against bath challenge with strain PDB (RPS = 62.5%). The aqueous bivalent (NS + PDB) vaccine administered by immersion in seabass fry also provided protection against strain PDB (RPS = 89.4%). The antibody titer for NS and PDB antigens was stable for at least 60 days after injection vaccination with bivalent adjuvanted (NS+PDB+Montanide) vaccine. Gene expression of MHCII-β, IgM and especially TCR-β genes in the head kidney tissue increased up to day 15 after vaccination by injection with aqueous and adjuvanted injectable vaccine with strain NS, while cellular immunity (CD4) appears to be activated on day 30 only in the group vaccinated with the adjuvanted preparation. The results produced here encourage the use of autogenous vaccines for the control of A. veronii disease in farmed European seabass. Boost vaccinations and/or increased antigen doses are proposed in the future to increase the vaccine efficacy.
Language Greek
Subject Aegean sea
Αιγαίο πέλαγος
Issue date 2021-07-29
Collection   School/Department--School of Sciences and Engineering--Department of Biology--Doctoral theses
  Type of Work--Doctoral theses
Permanent Link Bookmark and Share
Views 60

Digital Documents
No preview available

No permission to view document.
It won't be available until: 2023-07-30