Bismuth nanoparticles obtained by a facile synthesis method exhibit antimicrobial activity against Staphylococcus aureus and Candida albicans

Abstract

Background: Bismuth compounds are known for their activity against multiple microorganisms; yet, the antibiotic properties of bismuth nanoparticles (BiNPs) remain poorly explored. The objective of this work is to further the research of BiNPs for nanomedicine-related applications. Stable Polyvinylpyrrolidone (PVP)-coated BiNPs were produced by a chemical reduction process, in less than 30 min.

Results: We produced stable, small, spheroid PVP-coated BiNPs with a crystalline organization. The PVP-BiNPs showed potent antibacterial activity against the pathogenic bacterium Staphylococcus aureus and antifungal activity against the opportunistic pathogenic yeast Candida albicans, both under planktonic and biofilm growing conditions.

Conclusions: Our results indicate that BiNPs represent promising antimicrobial nanomaterials, and this facile synthetic method may allow for further investigation of their activity against a variety of pathogenic microorganisms.

Keywords: Antimicrobial nanomaterials; Bacteria; Biofilms; Bismuth nanoparticles; Fungi; Nanoantibiotics.

Fig. 1

Research of BiNPs in recent literature. BiNPs as antimicrobial agents remain barely researched. According to Web of Science, approximately 300 studies on BiNPs have been published in the last 20 years, from which only 12 are related to their antimicrobial activity. “The search parameter in the Web of Science (WoS) search was: “Bismuth nanoparticles” in title, abstract, and keywords. Then, the results were filtered by “antimicrobial” OR “antibacterial” OR and “antifungal””

Fig. 2

Characterization of the BAL-mediated PVP-BiNPs. a Our HR-TEM analysis from a single particle confirms their crystalline organization, whereas the (b) Electron Diffraction Pattern reveals their crystalline lattice as a cubic and hexagonal organization

Fig. 3

Proposed mechanism of synthesis for the formation of BiNPs. Bismuth (III) ions, solubilized in a glycine solution (a), interact with BAL, leading to the formation of the bismuth-BAL complex (b). Finally, NaBH₄ induces the generation of PVP-BiNPs (c). Hydrogens atoms were not included in the molecular models for clarity. Molecules were built using the GLmol engine at http://molview.org/

Fig. 4

Antimicrobial activity of the BiNPs. Dose-response curves of the BiNPs antimicrobial activity against the bacterium S. aureus and the yeast C. albicans. Planktonic cells (green line) and Biofilms formation stage (red lines)

Fig. 5

BiNPs inhibit biofilm formation by S. aureus. Untreated controls (a, d), as well as BiNPs-treated samples exposed to a low concentration of nanoparticles (b), form biofilms, but the cells from on the BiNPs-treated samples, display changes in morphology (e), from changes in size (yellow and blue-colored cells), and in shape (red-colored cells). Samples treated with a higher concentration of BiNPs do not form biofilms, but the cell morphology changes were less common (f). Scale bars: white = 20 μm, yellow = 2 μm

Fig. 6

BiNPs affect the dimorphic transition and inhibit biofilm formation in C. albicans. Untreated controls (a, d) show the typical filamentous C. albicans biofilms; however, in samples treated with a low concentration of BiNPs, the dimorphic transition is affected. b, e In samples treated with a high concentration of BiNPs, biofilm formation is mostly inhibited, and the cells show aberrant morphologies (c, f). Yeast-like (in red) and pseudohyphae-like (in blue) cells were observed. Scale bars: white = 40 μm, yellow = 4 μm