Abstract
We report synthesis of silver nanoparticles (AgNPs) from Streptomyces xinghaiensis OF1 strain, which were characterised by UV–Vis and Fourier transform infrared spectroscopy, Zeta sizer, Nano tracking analyser, and Transmission electron microscopy. The antimicrobial activity of AgNPs alone, and in combination with antibiotics was evaluated against bacteria, namely Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis, and yeasts viz., Candida albicans and Malassezia furfur by using micro-dilution method. The minimum inhibitory concentration (MIC) and minimum biocidal concentration of AgNPs against bacterial and yeast strains were determined. Synergistic effect of AgNPs in combination with antibacterial and antifungal antibiotics was determined by FIC index. In addition, MTT assay was performed to study cytotoxicity of AgNPs alone and in combination with antibiotics against mouse fibroblasts and HeLa cell line. Biogenic AgNPs were stable, spherical, small, polydispersed and capped with organic compounds. The variable antimicrobial activity of AgNPs was observed against tested bacteria and yeasts. The lowest MIC (16 µg ml−1) of AgNPs was found against P. aeruginosa, followed by C. albicans and M. furfur (both 32 µg ml−1), B. subtilis and E. coli (both 64 µg ml−1), and then S. aureus and Klebsiella pneumoniae (256 µg ml−1). The high synergistic effect of antibiotics in combination with AgNPs against tested strains was found. The in vitro cytotoxicity of AgNPs against mouse fibroblasts and cancer HeLa cell lines revealed a dose dependent potential. The IC50 value of AgNPs was found in concentrations of 4 and 3.8 µg ml−1, respectively. Combination of AgNPs and antibiotics significantly decreased concentrations of both antimicrobials used and retained their high antibacterial and antifungal activity. The synthesis of AgNPs using S. xinghaiensis OF1 strain is an eco-friendly, cheap and nontoxic method. The antimicrobial activity of AgNPs could result from their small size. Remarkable synergistic effect of antibiotics and AgNPs offer their valuable potential in nanomedicine for clinical application as a combined therapy in the future.
Highlights
Due to the extensive application of nanomaterials in medicine, food, agriculture, electronics, energy, etc. their global demand is growing significantly
TEM analysis of AgNPs synthesized from S. xinghaiensis OF1 strain revealed the presence of spherical and polydispersed nanoparticles in the size range of 5–20 nm
Physico‐chemical characterization of AgNPs synthesized from S. xinghaiensis OF1 strain
Summary
Due to the extensive application of nanomaterials in medicine, food, agriculture, electronics, energy, etc. their global demand is growing significantly. The biogenic nanoparticles have been found to be active against a wide range of Gram-negative and Gram-positive bacteria such as Escherichia coli, Vibrio cholerae, Pseudomonas aeruginosa, Salmonella typhi, Listeria monocytogenes, Staphylococcus aureus and Bacillus cereus as well as against fungi including Candida albicans, Candida tropicalis, Malassezia furfur and Trichophyton rubrum (Morones et al 2005; Birla et al 2009; Priyaragini et al 2013; Anasane et al 2016; Wypij et al 2017). The enhanced antimicrobial activity of antibiotics in combination with biogenic AgNPs against E. coli, P. aeruginosa and S. aureus and fungi such as C. albicans, C. tropicalis and dermatophytes causing superficial mycoses, namely M. furfur and T. rubrum was observed (Birla et al 2009; Anasane et al 2016; Wypij et al 2017). We selected actinobacterial strain for synthesis of biogenic nanoparticles as these microorganisms are known to be important producers of most natural bioactive compounds, mainly antibiotics and antimetabolites (Bérdy 2005; Newman and Cragg 2007; Olano et al 2009a, b)
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