Study on the Effect of the Recombinant OmpA Protein Fragments Protect Mice from Death Caused by E. coli Induced Bacteremia

Although the mortality rates have decreased over the past few decades, neonatal meningitis is still a severe disease with high morbidity. Moreover, approximately 40% of survivors exhibit neurological sequelae. Escherichia coli is the major gram-negative bacterial pathogen in neonatal meningitis. The N-terminal -barrel domain of the outer membrane protein A (OmpA) of E. coli is essential for effective protein conformation and function and contains 4 surface-exposed hydrophilic loops. We expressed different fragments of the 4 ring structures of the N-terminal domain (loop 1－2, loop 1－3, loop 1－4, loop 2－3, loop 2－4, and loop 3－4), and investigated whether these recombinant OmpA fragments can protect mice from death after E. coli infection. We have demonstrated and published in Journal of Microbiology, Immunology and Infection, that the recombinant loop 1－3, loop 2－3, and loop 2－4 can protect mice from death after E. coli infection. In this study, we want to elucidate the mechanisms of the protective effects of the recombinant loop 1－3, loop 2－3, and loop 2－4. Furthermore, we want to look for the shorter protective peptide. In bacterial meningitis, although antibiotic therapy is the first choice for management, neurological complications can be seldom averted. Based on the results of the present study, we intend to establish an effective therapeutic application for E. coli meningitis. This project includes: (A) To check whether the recombinant OmpA protein fragments (L1－3, L2－3, and L2－4) can inhibit E. coli attachment and then invasion of C6 cells, regulation of GFAP, COX-2 and NOS-2 expression, and the molecular mechanisms involved. (B) In experiments with mice, to check whether the recombinant OmpA protein fragments (L1－3, L2－3, and L2－4) can inhibit E. coli infection caused the COX-2 and NOS-2 expression in the mouse brain, as well as leukocyte infiltration, the ability to protect mice from death caused by E. coli infection. (C) Expression of the shorter recombinant OmpA protein fragments (L1, L2, L3, and L4). (D) To check whether these shorter recombinant OmpA protein fragments (L1, L2, L3, and L4) can inhibit E. coli attachment and then invasion of C6 cells, regulation of GFAP, COX-2 and NOS-2 expression, and the molecular mechanisms involved. In addition, to check whether these shorter recombinant OmpA protein fragments (L1, L2, L3, and L4) can inhibit E. coli infection caused the COX-2 and NOS-2 expression in the mouse brain, as well as leukocyte infiltration, the ability to protect mice from death caused by E. coli infection. (E) To build up a simulation model of ascending infection from bloodstream to the central nervous system. Mice were infected with E. coli, after different time intervals, give different recombinant OmpA protein fragments, then check whether the inhibition of E. coli infection in mice brain caused COX-2 and NOS-2 expression, and the infiltration of leukocyte, the ability to protect mice from death caused by E. coli infection.