Passive protective ability of the outer membrane protein PF1380 of Pseudomonas fluorescens against the major pathogenic bacteria of freshwater aquaculture in fish

The outer membrane lipoprotein PF1380 of Pseudomonas fluorescens is located in the outermost layer of the cell, and its immune function is unclear. PF1380 was obtained by molecular cloning, prokaryotic expression and purification. Mice immunized with PF1380 had a significantly increased spleen index (p < 0.05), leukocyte phagocytic percentage (PP), and phagocytic index (PI). A specific antiserum was obtained, which had an immune recognition effect on P. fluorescens and Aeromonas hydrophila in vitro. In addition, PF1380 bioinformatics analysis has revealed that the relationship between P. fluorescens and A. hydrophila is closer than others and anti-PF1380 serum might provide cross-protective ability to help resist these two kinds of bacterial infection in fish. Passive immunization of Carassius auratus with PF1380 mouse serum showed that PF1380 serum can enhance the PP (p < 0.05) and PI (p < 0.05) indexes. The passive protective rate of PF1380 serum against P. fluorescens infection was 57% (p < 0.05) and the passive cross-protective rate against A. hydrophila infection was 50% (p < 0.05). The expression of inflammation-related genes il-6, il-8, il-1β, and tnf-α decreased (p < 0.05) in the kidneys, spleens, and gills in C. auratus challenged with P. fluorescens and A. hydrophila, reducing injury in the kidney, spleen and intestine. These results suggest that PF1380 has a passive protective (P. fluorescens) and passive cross-protective (A. hydrophila) immune function and that it can boost resistance to infection with major freshwater aquaculture etiologic agents in fish.