Immunodominant Epitopes Identified on the LPS from Different Enterobacteria Using Phage Display

Background: Escherichia coli and Salmonella are etiologic agents of intestinal infections. A previous
study showed the presence of shared epitopes between lipopolysaccharides (LPSs) of E. coli O157
and Salmonella.
Aim: Using phage display, the aim of this study was to identify mimotopes of shared epitopes in
different enterobacterial LPSs.
Methods: We use anti-LPS IgG from E. coli O157 and Salmonella to select peptide mimotopes of the
M13 phage. The amino acid sequence of the mimotopes were used to synthesize peptides which
were in turn used to immunize rabbits. The antibody response of the resulting sera against the LPSs
and synthetic peptides (SPs) was analyzed by ELISA and by Western blot assays, indicating LPS
sites were recognized by the same antibody. In a complementary test, the reactions of human serum
samples obtained from the general population against the SPs and LPSs were also analyzed.
Results: From the last biopanning, sixty phagotopes were selected. The analysis of the peptide
mimotope amino acid sequences showed that in 4 of them the S/N/A/PF motif was a common
sequence. Antibodies from the sera of immunized rabbits with SP287/3, SP459/1, SP308/3, and
SP073/14 react against both their own peptide and the different LPSs. The Western blot test shows a
sera reaction against both the lateral chains and the cores of the LPSs. The analysis of the human
sera shows a response against the SPs and LPSs.
Conclusion: The study’s conclusion is that the response of antibodies against S. typhi, S. urbana, S.
arizonae, and E. coli O157 LPS obtained from immunized rabbits with SP287/3, SP459/1, SP308/3,
and SP073/14 confirms that synthetic peptides are immunogenic mimotopes of the evaluated LPSs
and that is feasible to consider them as an alternative system to protect against infections caused by
Salmonella and E. coli O157, however, prior studies with animal models are necessary to confirm
their protective capacity. The designed synthetic peptides are mimotopes of LPS epitopes of
Salmonella and E. coli that possess immunogenic capacity. These mimotopes could be considered for
use in the design of vaccines against both enterobacteria.