Bacterial Mediated Rapid and Facile Synthesis of Silver Nanoparticles and Their Antimicrobial Efficacy against Pathogenic Microorganisms

Abstract

In the present study, silver nanoparticles (AgNPs), biosynthesized using culture supernatant of bacterial strain Paenarthrobacter nicotinovorans MAHUQ-43, were characterized and their antimicrobial activity was investigated against both Gram-positive Bacillus cereus and Gram-negative bacteria Pseudomonas aeruginosa. Bacterial-mediated synthesized AgNPs were characterized by UV-Visible (UV-Vis) spectrophotometer, field emission-transmission electron microscopy (FE-TEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and dynamic light scattering (DLS) analysis. The UV-Vis spectral analysis showed the absorption maxima at 466 nm which assured the synthesis of AgNPs. The FE-TEM analysis revealed the spherical shape of nanoparticles with the size range from 13 to 27 nm. The EDX and XRD analysis ensured the crystalline nature of biosynthesized AgNPs. The FTIR analysis revealed the involvement of different biomolecules for the synthesis of AgNPs as reducing and capping agents. The bacterial-mediated synthesized AgNPs inhibited the growth of pathogenic strains B. cereus and P. aeruginosa and developed a clear zone of inhibition (ZOI). The MIC and MBC for both pathogens were 12.5 µg/mL and 25 µg/mL, respectively. Moreover, field emission scanning electron microscopy analysis revealed that the synthesized AgNPs can destroy the outer membrane and alter the cell morphology of treated pathogens, leading to the death of cells. This study concludes the eco-friendly, facile and rapid synthesis of AgNPs using P. nicotinovorans MAHUQ-43 and synthesized AgNPs showed excellent antimicrobial activity against both Gram-positive and Gram-negative pathogens.

Keywords: AgNPs; Bacillus cereus; Paenarthrobacter nicotinovorans MAHUQ-43; Pseudomonas aeruginosa; antimicrobial activity; extracellular synthesis.

Figure 1

The neighbor-joining (NJ) tree based on 16S rRNA gene sequence analysis showing phylogenetic relationships of strain MAHUQ-43^T and the related type strains. Bootstrap values more than 70% based on 1000 replications are shown at branching points. Scale bar, 0.02 substitutions per nucleotide position.

Figure 2

R2A broth with AgNO₃ as control (A), P. nicotinovorans MAHUQ-43-mediated synthesized AgNPs (B), UV–vis spectra (C), and FE-TEM images of synthesized AgNPs (D,E).

Figure 3

EDX spectrum P. nicotinovorans MAHUQ-43-mediated synthesized AgNPs (A), TEM image used for mapping (B) and distribution of silver in elemental mapping (C).

Figure 4

X-ray diffraction pattern (A) and SAED pattern (B) of P. nicotinovorans MAHUQ-43-mediated synthesized AgNPs.

Figure 5

FT-IR spectra of P. nicotinovorans MAHUQ-43-mediated synthesized AgNPs.

Figure 6

Particles size distribution of P. nicotinovorans MAHUQ-43-mediated synthesized AgNPs according to intensity (A), number (B) and volume (C).

Figure 7

Zones of inhibition of P. nicotinovorans MAHUQ-43-mediated synthesized AgNPs (30 μL and 60 μL at 1000 ppm concentrations in water) and commercial antibiotics against P. aeruginosa and B. cereus. Abbreviation: P (penicillin, G 10 μg/disc), MY (lincomycin, 15 μg/disc), and VA (vancomycin, 30 μg/disc).

Figure 8

Growth curves of P. aeruginosa (A) and B.cereus (B) cultured in MHB with different concentrations of P. nicotinovorans MAHUQ-43-mediated synthesized AgNPs to determine MIC.

Figure 8

Growth curves of P. aeruginosa (A) and B.cereus (B) cultured in MHB with different concentrations of P. nicotinovorans MAHUQ-43-mediated synthesized AgNPs to determine MIC.

Figure 9

MBC of P. nicotinovorans MAHUQ-43-mediated synthesized AgNPs against P. aeruginosa (A) and B. cereus (B).

Figure 10

SEM images of normal P. aeruginosa cells (A), 1 × MBC AgNPs-treated P. aeruginosa cells (B), normal B. cereus cells (C), 1 × MBC AgNPs-treated B. cereus cells (D).