The Immune Response and Passive Protective Abilities of the Outer Membrane Lipoprotein Slp of Aeromonas hydrophila against the Major Pathogenic Bacteria of Freshwater Aquaculture in Fish
The Immune Response and Passive Protective Abilities of the Outer Membrane Lipoprotein Slp of Aeromonas hydrophila against the Major Pathogenic Bacteria of Freshwater Aquaculture in Fish
Sijie Jian1,2,3,4, Wei Sun1,3, Jia Chao1,2, Na Rong1,4, Xiang Liu1,2,3,4* and Chen Chen1,2,3,4*
ABSTRACT
Aeromonas hydrophila and Pseudomonas fluorescens are major pathogenic bacteria in freshwater aquaculture and cause huge economic losses. The outer membrane lipoprotein Slp of A. hydrophila has potential applications in fish vaccines. Slp bioinformatics analysis showed that anti-Slp serum might provide cross-protection to resist bacterial infection in fish. Slp was obtained by molecular cloning, expression and purification, and the expression conditions were optimized. In mice immunized with Slp, the immune-related factors of LZM and AKP were enhanced (p < 0.05), and a specific antiserum titer (1: 3200) was obtained that had immune recognition effects for A. hydrophila and P. fluorescens. Passive immunization of Carassius auratus with Slp mouse serum and challenging with bacteria showed a passive protection rate of Slp serum against A. hydrophila infection of 42.5 % (p < 0.05) and a passive cross-protection rate against P. fluorescens of 18.6 %; the immune-related factors of LZM, AKP and ACP and the leukocyte phagocytosis of phagocytic percentage (PP) and phagocytic index (PI) increased (p < 0.05); the inflammation-related genes expression of IL-6, IL-8, IL-1β and TNF-α decreased (p < 0.05) in kidneys and spleens after challenging with A. hydrophila and P. fluorescens; and reduced injury to the kidneys, spleens and intestines; there was no significant change in the antioxidant-related factors of MDA, SOD, CAT and GSH-PX. Therefore, Slp has passive protection (A. hydrophila) and passive cross-protection (P. fluorescens) abilities and it can boost resistance to infection using major freshwater aquaculture etiologic agent of fish.
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