Iraj Rasooli

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.

Acinetobacter baumannii is known for its ability to invade and persist within eukaryotic cells, impacting infection outcomes and disease progression. This study investigates the role of Omp34, a key outer membrane protein (Omp), in A. baumannii interaction with epithelial cells and the protective effects of anti‐Omp34 antibodies (Abs). Omp34 is a key regulator of A. baumannii epithelial cell invasion, influencing bacterial adherence, internalization, and intracellular proliferation. The presence of anti‐Omp34 Abs mitigates A. baumannii ‐induced cellular damage and enhances bacterial clearance. The process involved the expression and purification of Omp34, which in turn induced Abs in BALB/c mice against Omp34. The acute toxicity of Omp34 was studied through a histological analysis conducted on six distinct organs in mice. HeLa cells were infected by A. baumannii ATCC 19606 and a clinical strain. Various aspects of A. baumannii behavior with HeLa cells, including HeLa cell viability, adherence, serum resistance, cell internalization, and intracellular proliferation with and without anti‐Omp34 sera. Cytoskeleton inhibitors were used to study the potential roles played in the process of A. baumannii invasion by microfilaments and microtubules. Omp34 effectively triggered Ab production in mice without resulting in any toxicity. The assay for serum resistance revealed potent bactericidal and antibiofilm effects on both A. baumannii strains. Bacterial internalization was constrained when actin polymerization was inhibited. Examination under the microscope revealed instances of adherence, alterations in the cell membrane, apoptosis, vacuolization, and cell damage. HeLa cells exposed to anti‐Omp34 serum showed decreased cell damage. The results provide substantial evidence of the adherence capacity of A. baumannii to proliferate in the epithelial cells. In conclusion, Omp34 plays a substantial role in regulating interactions between epithelial cells and A. baumannii , the multifaceted nature of which intricately modifies the trajectory of infection within host cells by A. baumannii .

Acinetobacter baumannii, a common nosocomial pathogen, is known for its rapid acquisition of antimicrobial resistance, underscoring the urgent need to develop an effective vaccine against this pathogen. Outer membrane protein 22 (Omp22) regulates the biogenesis of outer membrane vesicles to transport virulence-promoting factors into the host cells and facilitates the progression of A. baumannii infection. In this study, we used a mouse model to assess a vaccine’s immunogenicity and protective efficacy using recombinant Omp22 protein within the hypervariable region of flagellin (FliC-Omp22). FliC-Omp22 demonstrated superior protection following challenge with a lethal dose of multidrug-resistant (MDR) A. baumannii strain 58ST compared to Omp22 alone. In addition, it elicited increased IgG1/IgG2a and IL-4/IFN-γ ratios, indicating a predominant Th2 immune response. Furthermore, the FliC-Omp22 vaccination elicited strong specific antibodies that inhibited the adhesion and invasion of A. baumannii 58ST and enhanced the opsonic killing activity against the pathogen. FliC-Omp22 immunization significantly reduced bacterial loads in infected mice’s spleen, lungs, and liver, thereby improving their survival against the lethal infection caused by MDR A. baumannii 58ST. This study suggests that integrating Omp22 into the hypervariable domain of flagellin holds promise for developing an effective vaccine against A. baumannii infections.

Acinetobacter baumannii thrives within eukaryotic cells, influencing persistence, treatment approaches, and progression of disease. We probed epithelial cell invasion by A. baumannii and the influence of antibodies raised to outer membrane protein 34 (Omp34) on epithelial interactions. We expressed and purified recombinant Omp34 and induced anti-Omp34 antibodies in Bagg albino or BALB/c mice. Omp34 was evaluated for acute toxicity in mice through histological analysis of six organs. The host cell line, A549, was exposed to both A. baumannii 19606 and a clinical isolate. The study also investigated serum resistance, adherence, internalization, and proliferation of A. baumannii in A549 cells, with and without anti-Omp34 sera, utilizing cell culture techniques and light microscopy. A549 cell viability was evaluated by A. baumannii challenge and exposure to anti-Omp34 sera. Actin disruption experiments using cytochalasin D probed microfilament and microtubule roles in A. baumannii invasion. Omp34 prompted antibody production without toxicity in mice. The serum showed bactericidal effects on both strains. Additionally, both A. baumannii strains were found to form biofilms. Omp34 serum was observed to decrease biofilm formation, bacterial adherence, internalization, and proliferation in A549 cells. Furthermore, the use of anti-Omp34 serum enhanced the post-infection survival of the host cell. Pre-exposure of A549 cells to cytochalasin D reduced bacterial internalization, highlighting the role of actin polymerization in the invasion process. Microscopic analysis revealed various interactions, such as adherence, membrane alterations, vacuolization, apoptosis, and cellular damage. Anti-Omp34 serum-exposed A549 cells were protected and showed reduced damage. The findings reveal that A. baumannii can significantly multiply intracellularly within host cells. This suggests the bacterium’s ability to establish an environment conducive to its replication by preventing fusion with degradative lysosomes and inhibiting acidification. This finding contributes to the understanding of A. baumannii’s intracellular persistence and highlights the role of Omp34 in influencing apoptosis, autophagy, and bacterial adherence, which may impact the development of effective treatments against A. baumannii infections.

BamA, an Omp85 superfamily member, is universally conserved and essential for cell viability. Using anti‐Oma87 antibodies, we focus on understanding the effect of Oma87 of Acinetobacter baumannii on pathogenicity. Oma87 was expressed, purified, and used to induce anti‐Oma87 antibodies in BALB/c mice. Acute toxicity of the protein was evaluated in mice. HeLa cells were infected with both live and killed A. baumannii 19606 and a clinical isolate. The effects of anti‐Oma87 sera on A. baumannii adherence, internalization, and proliferation in HeLa cells were studied. The roles of microfilaments and microtubules in A. baumannii invasion were demonstrated by Actin disruption. Reduced bacterial population and biofilm formation were noted. The ability of A. baumannii to provoke autophagy through Oma87 induction leads to incomplete autophagy and potentially facilitates bacterial replication. Actin‐mediated uptake, attachment, and invasion demonstrated A. baumannii survival and multiplication within vacuoles in the host cell. The findings underscore the potential of Oma87 as a therapeutic intervention target in infections caused by A. baumannii. This comprehensive analysis contributes valuable information for understanding the virulence mechanisms of A. baumannii, potentially guiding future strategies to combat infections caused by this pathogen.