Pathogenicity of Aeromonas veronii from Nile tilapia (Oreochromis niloticus) and efficacy of fish oral vaccine against motile aeromonad septicemia in tank trials

Abstract

Download Supplementary MaterialMotile aeromonad septicemia (MAS), caused by the Aeromonas species, has been a serious problem in fish health management, particularly in Nile tilapia (Oreochromis niloticus). This study characterized an Aeromonas species isolated from farmed tilapia fingerlings in Binangonan, Rizal, Philippines, and tested for its pathogenicity in tank trials. The isolate, designated as Aeromonas veronii DFR01 (Diseased Fish Rizal), was identified based on 16S rRNA phylogenetic analysis, 16S rRNA homology, and MALDI-TOF mass spectrometry. Its biochemical profile was generated from API and Biolog Gen III systems. A median lethal dose of A. veronii DFR01 was determined to be 107 CFU/mL in tank trials and was utilized as a whole-cell inactivated antigen for oral vaccine development. The immunized tilapia fingerlings produced elevated levels of immunoglobulin M (IgM) in the blood as determined by an enzyme-linked immunosorbent assay (ELISA). There was a significant increase in IgM levels 14 days post-vaccination. A quantitative polymerase chain reaction (qPCR) showed increasing levels of IgM gene expression after vaccination until 38 days of culture. Vaccinated fish showed 25–35% cumulative mortality after the challenge, while non-vaccinated-challenged fish showed 75% mortality. The findings of this research suggest that the fish oral vaccine may prove beneficial for farmed tilapia populations. The vaccine elicited improved immune responses in the fish and resulted in higher survival rates.Financial support for this study came from a research grant to AMA from the Department of Science and Technology (DOST) Philippine Council for Aquatic and Marine Research and Development (PCAMRD), now the Philippine Council for Agriculture, Aquatic, and Natural Resources Research and Development (PCAARRD; Program Code: 2021-01-A1-CRADLE-3042; approved 3 November 2021). Many thanks to the Trinity University of Asia and Santeh Feeds Corporation for the support and counterpart funding