The Outer Membrane Proteins and Their Synergy Triggered the Protective Effects against Pathogenic Escherichia coli

Colibacillosis caused by pathogenic Escherichia coli (E. coli) is one of the most serious infectious diseases, causing an extensive burden on animal husbandry and the human healthcare system. Vaccination is one of the ideal ways to prevent E. coli infection. In this work, recombinant outer membrane protein A (rOmpA), outer membrane protein C (rOmpC) and BamA (rBamA) from E. coli O78 (CVCC CAU0768) were expressed in a prokaryotic expression system with the concentration of 1–2 mg/mL after purification. Considerable immune responses could be triggered in mice that were immunized with these recombinant proteins, high antibody titers, high total IgG level and various antibody isotypes were detected in antisera after booster immunizations. Moreover, mice immunized with several recombinant proteins in combination showed a higher survival rate with the challenge of homologous strain E. coli O78 and a more significant cross-protection effect against heterologous strain E. coli O157:H7 (CICC 21530) in vivo than those of immunized alone. The antisera from immunized mice showed high affinity to multiple strains of Escherichia, Shigella and Salmonella in vitro, indicating that recombinant outer membrane proteins from E. coli O78 had the potential to be developed into universal antigenic substances against not only E. coli but also a variety of Gram-negative bacteria. rOmpA was considered as the most immunogenic protein in this work and the combination of different proteins could further enhance the immune response of immunized mice, which provided the reference for the construction of novel antigens with higher efficiency.