Evaluation of the biological activities of Bacillus cereus-synthesized titanium dioxide nanoparticles

The emergence of multidrug-resistant pathogens and the growing burden of cancer worldwide demand novel therapeutic approaches. This study evaluated the biological activities of green-synthesized titanium dioxide nanoparticles (TiO₂ NPs) using Bacillus cereus cell-free supernatant and titanium tetra-isopropoxide precursor. Nanoparticles were analyzed and standard methods were employed to evaluate the antimicrobial, antibiofilm, and cell cytotoxicity. UV-Vis spectroscopy confirmed the synthesis of TiO₂ NPs with a characteristic peak at 360 nm. Transmission electron microscopy (TEM) revealed roughly spherical particles (8.8 ± 3 nm diameter). A Z-average hydrodynamic diameter of 328.1 nm (PDI, 0.439) was revealed by dynamic light scattering (DLS). According to the energy-dispersive X-ray spectroscopy (EDX) results, oxygen was 42.39% and titanium was 45.93%. The X-ray diffraction (XRD) measurement confirmed a crystalline anatase structure, with a prominent peak at 25.3° 2θ. Fourier transform infrared (FTIR) detected the characteristic Ti-O-Ti and vibrational band at 403.31 cm⁻¹. The nanoparticles demonstrated broad-spectrum antimicrobial activity with MICs of 78 μg/mL (E. coli), 156 μg/mL (C. albicans), 625 μg/mL (E. faecalis), and 2500 μg/mL (S. aureus and P. aeruginosa). At sub-MIC concentrations, TiO₂ NPs reduced biofilm formation in S. aureus by roughly 65.72% ± 0.01, in E. faecalis by 50.91% ± 0.02, and in P. aeruginosa by 38.4% ± 0.1. Cytotoxicity investigations revealed IC₅₀ values of 212.15 μg/mL (Caco-2) and 342.96 μg/mL (Vero cells), with a selectivity index of 1.62. Strong antiviral activity against HSV-1 was observed (74.74% inhibition at 60 µg/mL, EC₅₀ = 17.41 µg/mL, selectivity index = 19.7). Biogenic synthesis using B. cereus successfully produced highly crystalline, small-sized anatase TiO₂ nanoparticles demonstrating multifunctional biological activities including antimicrobial, antibiofilm, anticancer selectivity, and antiviral properties. KEY POINTS: • Green synthesis via B. cereus yielded crystalline anatase TiO₂ NPs with nanoscale dimensions. • TiO₂ NPs demonstrated broad antimicrobial/antibiofilm effects and selective anticancer activity. • Strong antiviral potency against HSV-1 with excellent selectivity was observed.