Title of thesis:
Comparative analysis of pathogenicity among Streptococcus agalactiae serotypes in Nile tilapia: Exploring strain’s diversity, immune response, and epigenetic regulation during infection.
Title of trial lecture:
Pathogenic mechanisms of blood-brain-barrier infections.
Evaluation Committee:
Professor Henrique César Pereira Figueiredo, Veterinary School, Federal University of Minas Gerais (UFMG), Brazil
Professor Erling Olaf Koppang, Anatomy Unit, Norwegian University of Life Science (NMBU), Norway
Professor Hetroney Mweemba Munang’Andu, Faculty of biosciences and aquaculture (FBA), Nord University, Norway
Supervisory Committee:
Senior Researcher Jorge Manuel de Oliveira Fernandes, Department of renewable marine resources, Institute of Marin Sciences (ICM-CSIC), Spain
Professor Laurival Antônio Vilas-Boas, Department of general biology, State University of Londrina, Brazil
Professor Lucienne Garcia Pretto-Giordano, Department of preventive veterinary medicine, State University of Londrina, Brazil
Senior Researcher Rajesh Joshi, GenoMar Genetics AS, Norway
Postdoctoral fellow Ioannis Kostantinidis, Faculty of biosciences and aquaculture (FBA), Nord University, Norway
Thesis summary:
Nile tilapia is one of the most important farmed fish species worldwide, but its production is threatened by Streptococcus agalactiae, a pathogenic bacterium that causes a severe disease, resulting in massive economic losses. This thesis investigates how genetic differences between two S. agalactiae serotypes (Ib and III) influence disease outcomes in tilapia.
Using a multiomics approach, the first paper compared the genomes of four S. agalactiae strains, revealing distinct evolutionary patterns, virulence factors, and zoonotic potential. The second paper analysed the fish brain’s transcriptome after infection, showing that serotype Ib activated strong immune and tissue repair responses, while serotype III caused early mortality and more pronounced behavioral effects. The third paper examined DNA methylation in the kidney, identifying strain-specific epigenetic changes in immune-related genes and regulatory regions.
The results demonstrate that bacterial serotype variation shapes immune and epigenetic responses in Nile tilapia. These findings can guide the development of targeted vaccines, selective breeding for disease resistance, and improved monitoring of zoonotic bacterial strains, contributing to more sustainable aquaculture and better protection of fish and public health.
