Green Synthesis of Silver Nanoparticle from Anadenanthera colubrina Extract and Its Antimicrobial Action against ESKAPEE Group Bacteria

Abstract

Given the urgent need for novel methods to control the spread of multidrug-resistant microorganisms, this study presents a green synthesis approach to produce silver nanoparticles (AgNPs) using the bark extract from Anadenanthera colubrina (Vell.) Brenan var. colubrina. The methodology included obtaining the extract and characterizing the AgNPs, which revealed antimicrobial activity against MDR bacteria. A. colubrina species is valued in indigenous and traditional medicine for its medicinal properties. Herein, it was employed to synthesize AgNPs with effective antibacterial activity (MIC = 19.53-78.12 μM) against clinical isolates from the ESKAPEE group, known for causing high hospitalization costs and mortality rates. Despite its complexity, AgNP synthesis is an affordable method with minimal environmental impacts and risks. Plant-synthesized AgNPs possess unique characteristics that affect their biological activity and cytotoxicity. In this work, A. colubrina bark extract resulted in the synthesis of nanoparticles measuring 75.62 nm in diameter, with a polydispersity index of 0.17 and an average zeta potential of -29 mV, as well as low toxicity for human erythrocytes, with a CC₅₀ value in the range of 961 μM. This synthesis underscores its innovative potential owing to its low toxicity, suggesting applicability across several areas and paving the way for future research.

Keywords: biogenic Bio-AgNPs; multidrug-resistant bacteria; white angico.

Figure 1

Comparison between the Bio-AgNPs biosynthesized using A. colubrina extract (A) and the extract without silver nitrate (B). Visualization of the Tyndall effect in the Bio-AgNPs solution (C), and absence of the Tyndall effect in the control extract sample (D).

Figure 2

Histogram of the average size distribution of Bio-AgNPs (nm). The average diameter is 75.62 ± 0.38.

Figure 3

UV–Vis plasmonic spectrum of Bio-AgNPs and extract control.

Figure 4

Comparison of Fourier transform infrared spectroscopy (FT-IR) spectra of the biosynthesized Bio-AgNPs and the control.

Figure 5

X-ray diffraction (XRD) of the control sample with A. colubrina bark extract.

Figure 6

X-ray diffraction (XRD) of the Bio-AgNPs sample biosynthesized with A. colubrina.

Figure 7

Morphology of Bio-AgNPs observed using scanning electron microscopy (SEM). Spherical morphology of isolated Bio-AgNPs (A). Organic structures from the A. colubrina extract (B). Aggregated arrangements of Bio-AgNPs and larger structures (C).

Figure 8

Morphological characterization of the Bio-AgNPs synthesized from A. colubrina with transmission electron microscopy (TEM). The micrograph shows spherical nanoparticles of Bio-AgNPs.

Figure 9

Growth kinetics and activity of Bio-AgNPs against E. coli ATCC 25922 at concentrations of MIC (78.12 µM). C (control) indicates the bacterial growth without antimicrobial.

Figure 10

Hemolytic activity of Bio-AgNPs biosynthesized for A. colubrina through human erythrocytes. Values of hemolysis percentage are the mean ± standard deviation. The linear model equation used to predict the CC₅₀ was y = 50.03x + 1.914 and the R-squared (R²).