Mohammed Alissa
Cephalosporin-resistant Escherichia coli and Klebsiella pneumoniae increasingly limit therapeutic options, necessitating novel antimicrobial strategies. This study investigated the antibacterial and immunomodulatory potential of a bioactive Streptomyces isolate (SGM-12) and its silver nanoparticle (AgNP) formulations using integrated experimental and computational approaches. In silico docking and ADME profiling predicted metabolite-target interactions, while molecular dynamics simulations evaluated AgNP-bacterial membrane interactions. The isolate was cultured, extracted, and fractionated into six fractions (F1-F6), and tested against resistant pathogens using agar-diffusion, MIC/MBC, and time-kill assays. AgNPs synthesized from crude-extract and active-fractions (F3, F4) were characterized by UV-Vis, DLS, TEM, and FTIR, with ion release behavior assessed via quantum chemical analysis. Bioactivity assays included biofilm inhibition, membrane permeability, ROS generation, intracellular leakage, cytotoxicity, hemolysis, and macrophage -profiling. In vivo efficacy was assessed in a murine systemic-infection model. F3 exhibited the strongest antibacterial activity, producing inhibition zones of 22.6 mm against E. coli and 20.9 mm against Klebsiella. F3-AgNP reduced MICs to 16 and 32 μg/mL, respectively, representing a 4-16-fold improvement. Docking revealed strong binding of a F3-derived polyketide (m/z 345.17) to RNA polymerase (-8.2 kcal/mol), outperforming fluoroquinolones. F3-AgNP inhibited biofilm formation by 88% and reduced bacterial burden by 3.8 log10 CFU in vivo, comparable to imipenem. It also modulated host immunity by reducing TNF-α and IL-6 while increasing IL-10, with low cytotoxicity and hemolysis. Pharmacokinetic analysis showed rapid systemic exposure with a 4.1 h half-life. F3-AgNP demonstrated potent antibacterial, antibiofilm, and immunomodulatory effects, supporting its potential as a translational candidate against resistant Gram-negative infections.