Green synthesis of gamma rays-induced melanin-based bismuth oxide nanoparticles for evaluation of the antibacterial and anti-virulence activities against extra-intestinal pathogenic bacteria.

The rise of microorganisms that are resistant to drugs is one of the significant challenges facing the health sector. The need to identify effective alternatives facing bacterial diseases is significantly highlighted. Nanomaterials have the potential to be a game-changing weapon in the battle against infectious diseases. Melanin, with the assistance of different doses of gamma rays, successfully produced highly stable Bi2O3 NPs. The most effective dose was 40 kGy. Bi2O3 NPs were characterized using FTIR, XRD, DLS/zeta potential, and TEM. In this study, the antibacterial efficacy of Bi2O3 NPs versus the extra-intestinal bacteria Citrobacter freundii and Enterobacter aerogenes was evaluated. Bi2O3 NPs at 200 µL generate inhibition zone diameters of 35.26 ± 0.305 and 38.42 ± 0.570 mm for C. freundii and E. aerogenes, respectively. Bi2O3 NPs at 200 µL caused significant biofilm reduction of 81.05 and 88.25% also, registered a significant decline in the colony count of (0.29 × 108) for C. freundii and (0.15 × 108) for E. aerogenes. The Bi2O3 NPs greatly decreased catalase activity, displaying 1.5 ± 0.62 and 6.0 ± 0.91 U/mL, and lipase activity exhibiting 12.13 ± 0.34 and 6.7 ± 0.26 U/mL for C. freundii and E. aerogenes, respectively. SEM observations indicated that the bacterial cell membrane was disrupted, resulting in significant ultrastructure alterations. Bi2O3 NPs reported a moderate cytotoxic effect on normal kidney epithelial cells with IC50 value of 513.9 ± 2.71 µg/mL. In conclusion, Bi2O3 NPs exhibited potential antibacterial activity, suggesting recommended usage in medical fields. The novelty of this study is the use of low-dose gamma irradiation to synthesize highly stable Bi2O3 NPs.