Identification, characterization and pathogenicity of aeromonas schubertii isolated from diseased striped snakehead fish (Channa Striata)

Abstract

Striped snakehead fish (Channa striata) is one of the popular cultivated fish in Thailand. However, it is inevitable to be susceptible to abundant pathogens, especially Aeromonas schubertii. In July 2020, an unknown outbreak was occurred on striped snakehead fish nursery farm in Nakhon Pathom province, Thailand. Suspected six isolates were A. schubertii yielded from the fish as the main causative agent. This research aimed to characterize and examine pathogenicity of A. schubertii isolated from diseased striped snakehead fish. Characterization was performed based on combination of biochemical assay, PCR and DNA sequencing (based on 16S rRNA and gyrB), and MALDI-TOF MS. The results showed the A. schubertii isolates can be distinguished from other bacterial pathogens by its biochemical characteristics, DNA fingerprints (16S rRNA and gyrB), and protein mass fingerprints. The experimental challenge of A. schubertii, using intra-peritoneal (IP) injection on C. striata, showed 80% mortality on high dose (1.2x108) and median lethal dose (LD50) of 3.9x105. A significant manifestation of skin ulceration, internal organ hemorrhage and white nodules on the fish internal organs (liver, kid-ney, and spleen) was progressively seen on 7-, 14-, and 21-days of post injection (dpi). The white nodules significantly appeared at the liver, spleen, and kidney, respectively. Likewise, granulomas, melano-macrophage centers (MMCs) and necrotic cells were also observed in histopathology analysis. Moreover, it was discovered that white nodules on kidney and spleen were strongly correlated with granulomas observed on kidney and spleen histopathology.