Biogenic Silver Nanoparticles Synthesized by Lysinibacillus xylanilyticus MAHUQ-40 to Control Antibiotic-Resistant Human Pathogens Vibrio parahaemolyticus and Salmonella Typhimurium

Abstract

The present study highlights a simple and eco-friendly method for the biosynthesis of silver nanoparticles (AgNPs) using Lysinibacillus xylanilyticus strain MAHUQ-40. Also, the synthesized AgNPs were used to investigate their antibacterial activity and mechanisms against antibiotic-resistant pathogens. Biosynthesis of AgNPs was confirmed by ultraviolet-visible spectroscopy, and then, they were characterized by field emission-transmission electron microscopy (FE-TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), and fourier transform-infrared (FTIR). The toxicity of AgNPs against two pathogenic bacteria was evaluated. The UV-vis spectral scanning showed the peak for synthesized AgNPs at 438 nm. Under FE-TEM, the synthesized AgNPs were spherical with diameter ranges from 8 to 30 nm. The XRD analysis revealed the crystallinity of synthesized AgNPs. FTIR data showed various biomolecules including proteins and polysaccharides that may be involved in the synthesis and stabilization of AgNPs. The resultant AgNPs showed significant antibacterial activity against tested pathogens. The MICs (minimum inhibitory concentrations) and MBCs (minimum bactericidal concentrations) of the AgNPs synthesized by strain MAHUQ-40 were 3.12 and 12.5 μg/ml, respectively, against Vibrio parahaemolyticus and 6.25 and 25 μg/ml, respectively, against Salmonella Typhimurium. FE-TEM analysis showed that the biogenic AgNPs generated structural and morphological changes and damaged the membrane integrity of pathogenic bacteria. Our findings showed the potentiality of L. xylanilyticus MAHUQ-40 to synthesis AgNPs that acted as potent antibacterial material against pathogenic bacterial strains.

Keywords: AgNPs; Lysinibacillus xylanilyticus MAHUQ-40; antimicrobial activity; eco-friendly synthesis; human pathogens.

FIGURE 1

The phylogenetic tree constructed by neighbor-joining (NJ) algorithm on the basis of 16S rRNA gene sequences, showing phylogenetic relationships of strain MAHUQ-40^T and members of genus Lysinibacillus. Bootstrap values more than 70% based on 1,000 replications are shown at branching points. Scale bar, 0.05 substitutions per nucleotide position.

FIGURE 2

R2A broth with AgNO₃ as control (A), synthesized AgNPs (B), UV–vis spectra (C), and FE-TEM images of synthesized silver nanoparticles (D,E).

FIGURE 3

EDX spectrum of synthesized AgNPs (A), FE-TEM image used for elemental mapping (B), and distribution of silver in elemental mapping (C).

FIGURE 4

X-ray diffraction pattern (A) and SAED (B) pattern of synthesized AgNPs.

FIGURE 5

FT-IR spectrum of synthesized AgNPs.

FIGURE 6

Particle size distribution of biogenic AgNPs on the basis of intensity (A), number (B), and volume (C).

FIGURE 7

Inhibition zones of biogenic AgNPs (30 μl) at 500 and 1,000 ppm against V. parahaemolyticus and S. Typhimurium.

FIGURE 8

Inhibition zones of some commercial antibiotics against V. parahaemolyticus and S. Typhimurium. Abbreviation: E (erythromycin, 15 μg/disc), OL (oleandomycin, 15 μg/disc), P (penicillin, G 10 μg/disc), MY (lincomycin, 15 μg/disc), and VA (vancomycin, 30 μg/disc).

FIGURE 9

Growth curves of V. parahaemolyticus (A) and S. Typhimurium (B) cultured in NB with 3% NaCl and MHB, respectively, with different concentrations of the synthesized AgNPs to determine MIC.

FIGURE 10

MBC of biosynthesized AgNPs against V. parahaemolyticus (A) and S. Typhimurium (B).

FIGURE 11

FE-SEM images of normal V. parahaemolyticus cells (A), 1× MBC AgNP-treated V. parahaemolyticus cells (B), normal S. Typhimurium cells (C), 1× MBC AgNP-treated S. Typhimurium cells (D).