Combatting biofilm formation of Klebsiella pneumoniae and Bacillus subtilis clinical strains from the oral cavity using biogenic Se-NPs: molecular docking simulation and cytotoxic effects on HepG2 cancer cells

Bacterial biofilms are one of the primary causes of pathogenic activity in the oral environment; they adhere to both natural and artificial oral surfaces, causing cariogenic processes that result in dental decay and significantly reducing the lifespan of dental restoratives and prostheses; they can also affect the tissues surrounding teeth, causing gingival inflammation; persistent biofilms can cause damage to the alveolar bone, which in extreme cases may result in tooth loss; our study aims to isolate clinical isolates that are resistant to multiple drugs, before disarming them by suppressing the formation of biofilms. Klebsiella pneumoniae A11(K. pneumoniae) and Bacillus subtilis A33 (B. subtilis) clinical isolates were determined, and the most potent clinical isolates were identified as the most virulent strains for further investigations using 16 S rDNA PCR sequencing, with accession numbers PP995146 and PP995148 respectively. Synthesized selenium nanoparticles (Se-NPs) were analyzed using FTIR Spectroscopy, UV-Vis Spectroscopy, zeta potential, dynamic light scattering (DLS), X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX) of the [Se-NPs] solution revealed that it contained 88.49% selenium and 11.51% carbon, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). According to TEM images, the average size of Se-NPs was 45.4 nm, and their shape was nearly spherical. The minimum inhibitory concentration (MICs) of biogenic Se-NPs were 0.25 mg/mL for K. pneumoniaeA11 and 0.125 mg/mL for B. subtilisA33, with inhibition zones of 11-14 mm. Se-NPs significantly reduced biofilm formation at 0.125 and 0.25 mg/mL (p < 0.05), by 85.08% in K. pneumoniae A11 and 75.45% in B. subtilis A33. A synergistic effect with azithromycin was observed, with fractional inhibitory concentration (FIC) values of 0.502 and 0.253, respectively. Molecular interactions showed Se-NPs forming hydrophobic contacts in K. pneumoniae LuxS Synthase (Asp52, Asp132; binding energy - 3.9020 kcal/mol) and B. subtilis AbbA (His3, Met4, Arg5; -4.2489 kcal/mol). Se-NPs had an IC₅₀ of 2.12 ± 0.02 µg/mL on HepG2 cells.