Bactericidal and In-Vitro Cytotoxic Efficacy of Silver Nanoparticles (Ag-NPs) Fabricated by Endophytic Actinomycetes and Their Use as Coating for the Textile Fabrics

Abstract

An endophytic strain of Streptomyces antimycoticus L-1 was isolated from healthy medicinal plant leaves of Mentha longifolia L. and used for the green synthesis of silver nanoparticles (Ag-NPs), through the use of secreted enzymes and proteins. UV-vis spectroscopy, Fourier-transform infrared (FT-IR), transmission electron microscopy (TEM), X-ray diffraction (XRD), and dynamic light scattering (DLS) analyses of the Ag-NPs were carried out. The XRD, TEM, and FT-IR analysis results demonstrated the successful biosynthesis of crystalline, spherical Ag-NPs with a particle size of 13-40 nm. Further, the stability of the Ag-NPs was assessed by detecting the surface Plasmon resonance (SPR) at 415 nm for one month or by measuring the NPs surface charge (-19.2 mV) by zeta potential analysis (ζ). The green-synthesized Ag-NPs exhibited broad-spectrum antibacterial activity at different concentrations (6.25-100 ppm) against the pathogens Staphylococcus aureus, Bacillus subtilis Pseudomonas aeruginosa, Escherichia coli, and Salmonella typhimurium with a clear inhibition zone ranging from (9.5 ± 0.4) nm to (21.7 ± 1.0) mm. Furthermore, the green-synthesized Ag-NPs displayed high efficacy against the Caco-2 cancerous cell line (the half maximal inhibitory concentration (IC₅₀) = 5.7 ± 0.2 ppm). With respect to antibacterial and in-vitro cytotoxicity analyses, the Ag-NPs concentration of 100 ppm was selected as a safe dose for loading onto cotton fabrics. The scanning electron microscopy connected with energy-dispersive X-ray spectroscopy (SEM-EDX) for the nano-finished fabrics showed the distribution of Ag-NPs as 2% of the total fabric elements. Moreover, the nano-finished fabrics exhibited more activity against pathogenic Gram-positive and Gram-negative bacteria, even after 10 washing cycles, indicating the stability of the treated fabrics.

Keywords: Ag-NPs; antibacterial and cytotoxicity activities; cotton fabrics; endophytic actinomycetes; green synthesis; streptomyces spp..

Figure 1

Phylogenetic tree of Streptomyces antimycoticus based on 16S rRNA sequences analysis. The symbol◆ indicates to 16S rRNA fragments of the endophytic actinomycetes strain obtained in the current study. The analysis was completed with MEGA 6 using the neighbor-joining method.

Figure 2

UV–vis spectroscopic analysis and color change of silver nanoparticles (Ag-NPs) synthesized by endophytic S. antimycoticus L-1: (A) UV–Vis spectra of Ag-NPs at different interval times; (B) biomass filtrate color; (C) silver nitrate solution; (D) yellowish-brown color of Ag-NPs synthesized by S. antimycoticus L-1.

Figure 3

FT-IR spectrum of the Ag-NPs derived from endophytic S. antimycoticus L-1.

Figure 4

Characterization of Ag-NPs synthesized by Streptomyces antimycoticus L-1: (A) transmission electron microscopy (TEM) image; (B) X-ray diffraction (XRD) analysis; (C) dynamic light scattering (DLS) analysis.

Figure 5

Antibacterial activities and minimum inhibitory concentrations (MICs) for Ag-NPs synthesized by S. antimycoticus L-1 against pathogenic S. aureus, B. subtilis, P. aeruginosa, E. coli, and S. typhimurium. # indicates MIC value.

Figure 6

Cytotoxic activity of Ag-NPs derived from S. antimycoticus L-1 against Vero and Caco-2 cell lines.

Figure 7

Scanning electron microscopy results for cotton fabrics; (A) cotton fabric without any treatment, and showing smooth surface; (B) cotton fabrics treated with Ag-NPs (100 ppm), showing the deposited NPs on the cotton surface; (C) mapping picture of treated fabrics with Ag-NPs, showing qualitative elemental analysis; (D) EDX of the treated sample with elemental analysis of the Ag-NPs contents.