Evaluation of the Effect of Promoter Type on the Immunogenicity of the Live Recombinant Salmonella Vaccines Expressing Escherichia Coli HeatlabileEnterotoxins (LTB)

Enterotoxigenic escherichia coli (etec)-induced diarrhoea is the second most common cause of death in children in the developing countries. heat labile toxin (lt) is responsible for etec-induced diarrhoea. in the present study, a novel live etec vaccine based on subunit b of lt (ltb) expression in attenuated phop^c salmonella strain was developed. herein, we aimed to compare the in-vitro activity of promoters including constitutive tac, iptg inducible trc, and in-vivo-inducible (nirb and nirb78-23) in phop^c. additionally, the ability of these recombinant phop^c/pltbs to induce ltb-specific antibody responses in balb/c mice after nasal immunization was evaluated. in-vitro studies demonstrated that phop^c has the ability to produce rltb. furthermore, nirb promoter directed significantly more ltb expression in phop^c/pnirbltb under anaerobic condition without induction compared to the amount of rltb secreted by phop^c/ptrcltb in bacterial soup under uninduced condition (6.06 ± 0.05 vs. 1.4 ±0.46 µg/109 cfu, p < 0.01). in addition, the constitutive rltb expression from tac promoter was more than its expression from uninduced trc promoter in bacterial soup (4.2 ± 0.92 vs. 1.4 ± 0.46 (µg/109 cfu)) and pellet (27.4 ± 0.89 vs. 13.4 ± 1.42 (µg/109 cfu), p < 0.0001). however, the mice immunized with phop^c/ptrcltb elicited the superior anti-ltb responses among the phop^c containing the examined prompters, which were significantly higher than those induced by phop^c/pnirb78-23ltb and phop^c/pnirb, 6 weeks after the first immunization. totally, it could be concluded that in-vitro analysis of promoters for ltb expression in phop^c may not necessarily predict the recombinant phop^c immunogenicity.