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

Abstract

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.

Keywords: Citrobacter freundii; Enterobacter aerogenes; Antibacterial; Antibiofilm; Bi2O3 NPs; Gamma radiation.

Fig. 1

The schematic diagram of melanin-based Bi₂O₃ NPs synthesis

Fig. 2

Characterization of melanin-based Bi₂O₃ NPs (a) UV–Vis spectrophotometer, (b) FTIR and, (c) XRD patterns

Fig. 3

Characterization of melanin-based Bi₂O₃ NPs (a) DLS, (b) Zeta potential, and (c) TEM images

Fig. 4

The antibacterial activity of melanin-based Bi₂O₃ NPs on C. freundii and E. aerogenes (a) The antibiotic susceptibility test, (b) Well diffusion assay at a concentration of 200 µL

Fig. 5

The killing mechanism of Bi₂O₃ NPs on bacterial cell

Fig. 6

Effect of melanin-based Bi₂O₃ NPs at concentrations of 25, 50, 100, and 200 µL on (a) Biofilm formation inhibition %, (b) CFU/mL, and (a) Log₁₀

Fig. 7

Effect of melanin-based Bi₂O₃ NPs at concentrations of 25, 50, 100, and 200 µL on (a) catalase and (b) lipase activities (U/mL) of C. freundii and E. aerogenes

Fig. 8

SEM images of (a) Untreated C. freundii cells, (b) C. freundii treated with melanin-based Bi₂O₃ NPs, (c) Untreated E. aerogenes, and (d) E. aerogenes treated with melanin-based Bi₂O₃ NPs

Fig. 9

Cytotoxicity of melanin-based Bi₂O₃ NPs on the Vero cells