Loop 3 Repeats in Omp34 is a Promising Immunogen for Vaccine Development Against Acinetobacter baumannii Infections.

The overuse of antibiotics has led to antibiotic-resistant Acinetobacter baumannii. This study evaluated the protective effect of a recombinant protein, derived from Omp34's loop 3 repeats, as a potential vaccine candidate against A. baumannii in a murine sepsis model. Recombinant Omp34 and L3 × 5 proteins were expressed in E. coli BL21 using the autoinduction method. The proteins were then purified and verified. To assess their protective efficacy, the proteins were injected into BALB/c mice, and the vaccine's effectiveness in both prevention and treatment stages was evaluated in a murine sepsis model against an infection caused by a clinical strain of A. baumannii. The study shows that recombinant proteins Omp34 and Omp34L3 × 5 have protective and immunogenic properties against A. baumannii. Using the immunogen loop 3, rather than the mature Omp34 protein, to stimulate the immune system yielded promising results. Omp34 offered superior protection, likely through B- and T-cell activation, while L3 × 5, though less protective, induced significant antibody production and recognized the clinical strain, warranting further research. The study highlights the potential of recombinant proteins Omp34 and Omp34L3 × 5 as vaccine candidates against A. baumannii. Omp34 provided stronger protection in mouse sepsis models, likely due to its activation of both B- and T-cell responses. While Omp34L3 × 5 was less protective, it still produced significant antibodies and recognized clinical strains. The results emphasize the need for further research into these proteins to develop vaccines or treatments against A. baumannii infections.