FimH (the adhesion fragment of type 1 fimbriae) is implicated in uropathogenic Escherichia coli (UPEC) attachment to epithelial cells through interaction with mannose. Recently, some studies have found that UPEC can thrive intracellularly causing recurrent urinary tract infection (UTI). Almost all vaccines have been designed to induce antibodies against UPEC. Yet, the humoral immune response is not potent enough to overcome neither the primary UTI nor recurrent infections. However, DNA vaccines offer the possibility of inducing cell mediated immune responses and may be a promising preventive tool.

In this study, we employed two different open reading frames within mammalian (mam) and wild type (wt) codons of fim H gene. Optimized fragments were cloned in pVAX-1. Expression of the protein in COS-7 was confirmed by western blot analysis after assessing pVAX/ fim H(mam) and pVAX/ fim H(wt). The constructs were injected to BALB/c mice at plantar surface of feet followed by electroporation.

The mice immunized with both constructs following booster injection with recombinant FimH showed increased interferon-γ and interleukin-12 responses significantly higher than non-immunized ones (p<0.05). The immunized mice were challenged with UPEC and then the number of bacteria recovered from the immunized mice was compared with the non-immunized ones. Decreased colony count in immunized mice along with cytokine responses confirmed the promising immune response by the DNA vaccines developed in this study.

In conclusion, DNA vaccines of UPEC proteins may confer some levels of protection which can be improved by multiple constructs or boosters.