Preparation and evaluation of the exotoxin A nano-gold conjugate as a vaccine candidate for Pseudomonas aeruginosa infections

Pseudomonas aeruginosa is an opportunistic pathogen that is an important cause of nosocomial infections. This bacterium produces various virulence factors, among which exotoxin A is significantly involved in mortality and morbidity. In this study, we evaluated the immunogenicity of native exotoxin A extracted from the P. aeruginosa and its conjugation with gold nanoparticles in the animal model. Exotoxin A was first extracted and purified from the culture medium of P. aeruginosa PAO1 by selective precipitation and dialysis. The gold nanoparticles were prepared using the Turkevich method and conjugated to the prepared exotoxin A by electrostatic force. The size and conjugation were confirmed using electron microscopy and Fourier transform infrared spectrometry (FTIR), respectively. The immunogenicity of prepared ExoA-gold nanoparticles was investigated in the mice model. The results indicated that nano-gold particles can be conjugated to the native exotoxin A with high efficiency. Immunogenicity investigation demonstrated that antibody titers produced against native exotoxin A and its conjugate to nano-gold particles are significant in a mouse model (P<0.005). Moreover, significant protection against 2×LD50 P. aeruginosa infection was observed in animals immunized with nano-gold-exotoxin A as compared with control groups (P=0.00). Our study indicated that exotoxin A can be produced with acceptable purity in the laboratory, and conjugated to gold nanoparticles. Based on these results nano-gold-exotoxin A conjugate is highly immunogenic and can be considered a potential vaccine candidate for P. aeruginosa infections.