Virulence genes contributing to Aeromonas veronii pathogenicity in Nile tilapia (Oreochromis niloticus): approaching the development of live and inactivated vaccines

Abstract

This study aimed to develop and evaluate live and inactivated vaccines to Aeromonas veronii pathogenicity in Nile tilapia. Therefore, five well-identified Aeromonas veronii isolates, including A (HY1), A (HY2), A (HY3), A (HY4), and A (HY6) isolated from diseased Nile tilapia (Oreochromis niloticus), were used for vaccine preparation. Virulence genes detected by a polymerase chain reaction (PCR) and lethal dose determination were conducted. Nile tilapia, each with a body weight of 25 ± 0.5 g were divided into six experimental groups (each of 20): T1 group (control), fish were injected with saline as a negative control, T2 group (formalin-killed vaccine) for the A (HY2) strain, T3 group ( formalized killed vaccine) for the A (HY4), T4 group (autoclaved vaccine) for the A (HY2), T5 group (autoclaved vaccine) for A (HY4), and T6 (live vaccine) for A (HY1), triplicate. At the end of the immunization period, all groups were challenged by A. veronii, A (HY2). Blood samples were drawn 21 days post-immunization and 3 days after the challenge test for antibody titer assay. The results showed that the pathogenicity of strains A (HY2) and A (HY4) was the strongest, as the lethality rates (LR) were 100% and 90%, respectively, whereas the pathogenicity was moderate for strains A (HY3) and A (HY6) (LR 60% for each). A (AY1) was the weakest strain as no dead fish was found for this strain. The presence of alt, act, aerolysin, lipase, and fla genes as the main cause of the pathogenesis. The best protective efficacy was obtained from the live vaccine, A (HY1) with a protective rate of about 94.12% (relative percentage of survival, RPS), compared to autoclaved killed vaccines and formalin-killed vaccines. Based on immunoglobulin estimation (IgM) and RPS%, our data concluded that A (HY1) live vaccine had the best vaccine prophylactic effect against the highly pathogenic strain A(HY2).

Silica nanoparticles alleviate the immunosuppression, oxidative stress, biochemical, behavioral, and histopathological alterations induced by Aeromonas veronii infection in African catfish (Clarias gariepinus)

“…It is assumed that the virulence genes of A. veronii plus its toxic products are responsible for its pathogenicity, which negatively affects the health and performance of fish, resulting in these abnormalities. As reported by Youssef et al ( 2023 ), A. veronii has alt, fla, lipase, aerolysin, and act genes, identifying them as the primary cause of its pathogenicity. Another document verified virulence factors for A. veronii , including outer membrane proteins, proteases, toxins, secretory enzymes, and hemolytic and cytotoxic activities (Chen et al 2019 ).…”

Detection of Virulence Genes, Antimicrobial Susceptibility and Pathogenicity of Aeromonas veronii Isolates from Labeo rohita and Catla catla

“…sobria from frozen fish. Tyagi et al (2022) and Youssef et al (2022) discovered a lipase gene in A. veronii isolated from L. rohita and tilapia. Lipases are essential for bacterial feeding (Pemberton et al, 1997), although some studies have found that A. hydrophila with mutant lipase gene lowers lethality, which shows that the role of lipase as virulence factor (Merino et al, 1999).…”

Pathogenicity of <em>Aeromonas veronii</em> from Nile Tilapia (<em>Oreochromis niloticus</em>) and Efficacy of Fish Oral Vaccine against Motile Aeromonad Septicemia in Tank Trials

“…The potency of the vaccine could be dependent on many levels including bacterial strain and virulence factors present. Virulence genes in other A. veronii strains such as aerolysin (aerA), lipase, cytotoxic enterotoxin (alt) among others (Youssef et al, 2023) showed 90-100% mortality in pathogenicity tests. The virulence of the isolate was estimated from the lethal dose concentration determined for the isolate.…”

“…The virulence of the isolate was estimated from the lethal dose concentration determined for the isolate. The application of the isolate as an oral vaccine in aquaculture farms is possible as suspected cross protection between Aeromonas species due to common virulence factors shared by the aeromonads (Youssef et al, 2023).…”