A Novel Anti-Virulence Approach For Attenuating Acinetobacter Baumannii Outer Membrane Protein A Using Biogenic Silver Nanoparticles: In Vitro and In Silico Docking

Abstract

Purpose: Outer membrane protein A (OmpA) of Acinetobacter baumannii as the major virulence factor coupled with efflux pump systems mediates resistance to various antibiotics. Methods: Silver nanoparticles (AgNPs) are explored as novel multi-functional therapeutic agents that would effectively suppress multidrug-resistant bacterial strains and mitigate inflammatory responses, resulting from bacterial infections. Aqueous leaf extract of E. camaldulensis was profiled and used as a reducing and capping agent during the biosynthesis of AgNPs. Moreover, chromatography profiled data of extract were docked to understand the in silico therapeutic potential for antibacterial, antioxidant, and anti-inflammatory activity. Furthermore, synthesized AgNPs were investigated as a novel approach to reduce OmpA of A. baumannii. Results: Liquid chromatography coupled with a mass spectrophotometer (LC–MS) indicated that E. camaldulensis aqueous leaf extract is a plethora of phenolic bioactive reservoirs. Molecular docking results revealed that the major phytochemicals identified from Eucalyptus camaldulensis exhibited superior binding modes, indicating favorable orientation and interactions within the active site and stronger binding affinities (more negative docking scores) to the outer membrane protein A (OmpA) of Acinetobacter baumannii (PDB ID: 5F19), compared to the standard antibiotic ciprofloxacin. The synthesized AgNPs demonstrated surface plasmon resonance peak at 411 nm, and the size of nanoparticles (NPs) was in the range of 16.67 to 24.85 nm with insignificant change in vibration infra-red intensity. Antibacterial activity of AgNPs showed that minimum inhibitory concentration ranged between 2.70 and 5.40 µg/mL against tested bacterial isolates. Moreover, AgNPs considerably reduced A. baumannii OmpA expression by up to 70% (p < 0.001). Additionally, compared to the positive control, AgNPs at 5.40 µg/mL decreased the production of nitric oxide by 15.68 µM, thereby reducing OmpA-mediated inflammatory responses (p < 0.001). Conclusions: This pioneering work suggested that biosynthesized AgNPs are an effective anti-virulence agent against antibiotic-resistant A. baumannii. Lay Summary: The aqueous leaf extract of Eucalyptus camaldulensis, which is rich in bioactive phenolic compounds, was used to reduce silver nitrate into biogenic silver nanoparticles (AgNPs). In silico molecular docking results suggested that these phytochemicals contribute to the extract’s antibacterial potential. The biosynthesized AgNPs demonstrated strong antibacterial activity and effectively targeted the key virulence factor OmpA in Acinetobacter baumannii, highlighting their promise as a novel strategy to combat drug-resistant infections.