BACKGROUND AND OBJECTIVES: The rise in antibiotic resistance and the increasing prevalence of infectious diseases have a significant impact on global health. To address this problem, combinatorial on medications can be used to improve antibiotic efficacy and decrease inhibitory concentrations. Due to their small size and high surface-to-volume ratio, metallic nanoparticles are being investigated broadly to achieve this purpose and improve their compatibility, solubility, and multifunctionality. The purpose of this research is to find out the potential synergy between Fe2O3- NPs (NPs) that are synthesized biologically and standard antibiotics in fighting resistant bacterial strains. MATERIALS AND METHODS: The Fe2O3-NPs were synthesized using Bacillus sp. GMS10 culture and the iron sulfate precursor, FeSO4.7H2O. Various techniques were used to characterize the properties of the nanoparticles postsynthesis, including UV-visible spectrometry, field emission scanning electron microscopy (FESEM), X-ray energy dispersion spectroscopy, dynamic light scattering (DLS), zeta potential measurement, and Fourier transform infrared spectroscopy (FTIR). RESULTS AND DISCUSSION: Based on results, the Fe2O3-NPs exhibits respectable antibacterial activity (MICs were between 2.5 and 50 µg.ml-1 and MBCs were between 5 and 100 µg.ml-1). Additionally, the studied Fe2O3-NPs were able to affect most of the bacterial virulence factors at sub-MIC concentrations. These factors included the inhibition of biofilm formation at MIC/2 concentration, the inhibition of motility for motile bacteria at MIC/2 concentration, the synergistic interaction with cefixime and penicillin antibiotics, and the inhibition of the S. aureus efflux pump. Based on the observed data, it can be stated that the green method's nanoparticles can inhibit the tested bacteria, which could lead to their application as useful antibacterial substances in the future. The successful synthesis of Fe2O3-NPs was confirmed, with UV-visible spectrometry revealing a strong absorption peak at 228 nm. The nanoparticles were primarily spherical, averaging 30 nm in size. DLS analysis indicated an average nanoparticle size of 36.3 nm with
