Abstract
Francisella noatunensis subsp. orientalis (Fno), an intracellular bacterium, causes systemic granulomatous diseases, resulting in high mortality and huge economic losses in Taiwanese tilapia farming. In this study, we tested the efficacy of a formalin-killed Fno vaccine in cultured tilapia. Fno was isolated from diseased tilapia, inactivated with formalin, and mixed with the mineral oil base adjuvant (MontanideTM ISA 763 AVG). A total of 300 tilapia were divided into two groups. The experimental group was intraperitoneally injected with 0.1 mL of vaccine, which was substituted with phosphate-buffered saline (PBS) in the control group. A booster was administered at 2 weeks post-immunization. Tilapia were challenged at 6 weeks post primary immunization by intraperitoneal (IP) injection and immersion methods. Mortality was recorded at 21 and 60 days. The results revealed that the vaccine induced a greater antibody titer and led to 71% and 76% of relative percent survival (RPS) after the IP and immersion challenge. The transcripts of proinflammatory cytokines and immune-related genes, including interleukin-1β (IL-1β), tumor necrosis factor alpha (TNFα), C-X-C motif chemokine ligand 8 (CXCL8), and interleukin-17C (IL-17C), were significantly upregulated after vaccination. Additionally, vaccinated fish had lower bacterial loads in the blood and lower granuloma intensities in the kidney, spleen, liver, and gill than control fish. The results in this study demonstrate that the inactivated Fno vaccine could be an essential resource in Taiwanese tilapia farming.
Highlights
Francisella noatunensis subsp. orientalis, known as F. asiatica, is a Gram-negative intracellular pathogenic bacterium that has a coccobacillus shape and fastidious nature
Tilapia francisellosis was initially reported in Taiwan in 2005 as a Francisella-like bacterium in cultured tilapia [4] and is still considered a major threat in Taiwanese tilapia farming [5] along with other bacterial diseases like streptococcosis [6,7]
The results revealed that the vaccinated fish challenged with the homologous isolate showed high protection, whereas fish challenged with the two heterologous isolates showed relative percent survival (RPS) of 69.8% and 65.9%
Summary
Francisella noatunensis subsp. orientalis, known as F. asiatica, is a Gram-negative intracellular pathogenic bacterium that has a coccobacillus shape and fastidious nature. Orientalis, known as F. asiatica, is a Gram-negative intracellular pathogenic bacterium that has a coccobacillus shape and fastidious nature Tilapia francisellosis was initially reported in Taiwan in 2005 as a Francisella-like bacterium in cultured tilapia [4] and is still considered a major threat in Taiwanese tilapia farming [5] along with other bacterial diseases like streptococcosis [6,7]. Streptococcosis usually occurs in the summer season, while Fno generally causes disease outbreaks in the winter season. Both of the two diseases have a huge economic impact on the tilapia farming industry worldwide.
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