Characterization of Pseudomonas aeruginosa ghost and evaluation of its immune proficiency in Nile tilapia (Oreochromis niloticus)

Pseudomonas aeruginosa is known to be multidrug-resistant organisms so its infection is challenging. This study aimed to use the sponge-like reduced protocol in preparation of P. aeruginosa ghosts (PAGs) as a vaccine alternative and evaluate its competency in stimulating the immune response in Nile tilapia. Characterization of PAGs was done using the light, fluorescent and transmission electron microscope. 240 fish have been divided into four groups (60 fish each; three groups were injected with a high, medium, or low dose of PAGs, and a control group. Total and differential leukocyte count, phagocytic activity, lysozyme activity, and gene expression of some immune-related genes were done after the first and booster ghost dose injection. All fish groups were challenged intraperitoneally with P. aeruginosa (1 × 10 7 CFU ml −1 ); the mean percent mortality was calculated. Significant immunization potency of the large dose of PAGs was prominent. It is associated with a significant increased number of WBCs, heterophile, lymphocytes, and monocytes. Also the phagocytic activity and indexes were significantly increased by the high and moderate dose of PAGs. Additionally, significant upregulation of immune-related gene ( MHC-II) and inflammatory-related gene ( IL8 ) and maintained expression level of TLR7 were recorded . We conclude that chemically prepared P. aeruginosa ghosts maintained both the 3D structure and surface molecules of live bacteria and also are capable of inducing specific immune responses in Nile Tilapia, and reduced mortalities in challenged fish . Our results indicate the advantage of this procedure for production of bacterial ghost, which can be used in wide a range of hosts.