Antimicrobial and cytotoxic activity of silver nanoparticles synthesized from two haloalkaliphilic actinobacterial strains alone and in combination with antibiotics.

AIMS: Presently, the effective antimicrobial agents have been limited by the emergence of microbial strains with multidrug resistance and biofilm formation potential. In the present study, we report remarkable antimicrobial activity of silver nanoparticles (AgNPs) synthesized from Streptomyces calidiresistens IF11 and IF17 strains, including inhibition of biofilm formation and synergistic effect of AgNPs and antibiotics against selected bacteria and yeasts. Cytotoxic effect of AgNPs on mammalian cell lines was also evaluated. METHODS AND RESULTS: Analysis of biosynthesized AgNPs by Fourier Transform Infrared Spectroscopy and transmission electron microscopy revealed their spherical shape, small size in the range of 5-50 and 5-20 nm, respectively, as well as the presence of capping agents. Study of antimicrobial activity of AgNPs against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Candida albicans and Malassezia furfur evaluated by minimum inhibitory concentration (MIC) and minimum biocidal concentration (MBC) assays revealed that MICs of AgNPs from IF11 and IF17 strains against bacteria and yeasts were found to be in the range of 16-128 and 8-256 µg ml-1 , while MBCs were in the range of 48-192 and 32-256 µg ml-1 respectively. AgNPs inhibited biofilm formation of microbial strains, which was tested by using crystal violet stain. The highest synergistic effect determined by fractional inhibitory index of AgNPs with antibiotic (kanamycin or tetracycline) was found against Staph. aureus; while in case of yeasts, M. furfur showed highest sensitivity to AgNPs-ketoconazole combination (FIC = 0·12). The cytotoxic activity of AgNPs towards HeLa and 3T3 cell lines was studied by MTT assay. The IC50 of AgNPs estimated against mouse fibroblasts was found to be 8·3 and 28·3 µg ml-1 and, against HeLa cell line, 28·5 and 53·8 µg ml-1 respectively. CONCLUSIONS: It can be concluded that AgNPs synthesized from S. calidiresistens IF11 and IF17 strains have potential as an effective antimicrobial and cytotoxic agent, especially when used in combination with antibiotics/antifungal agents. SIGNIFICANCE AND IMPACT OF THE STUDY: This study indicates potential application of biogenic silver nanoparticles as an antimicrobial agent in nanomedicine.

Study of silver nanoparticles synthesized by acidophilic strain of Actinobacteria isolated from the of Picea sitchensis forest soil.

AIMS: In the present work the acidophilic actinobacteria strain was used as a novel reducing agent for the cheap, green and single-step synthesis of nanostructure silver particles. Structural, morphological and optical properties of the synthesized nanoparticles have been characterized by spectroscopy, dynamic light scattering and electron microscopy approach. The antimicrobial activity of silver nanoparticles against clinical strains such as Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Proteus mirabilis and Salmonella infantis alone and in combination with antibiotics were studied. METHODS AND RESULTS: The crystalline and stable biosynthesized silver nanoparticles ranged in size from 4 to 45 nm and were mostly spherical in shape being characterized evolving several analytical techniques. The bioAgNPs inhibited growth of most bacterial strains. The highest antimicrobial activity was observed against Ps. aeruginosa (10 mm), followed by Staph. aureus, B. subtilis and Pr. mirabilis (all 8 mm). The lower activity was noticed for E. coli and Kl. pneumoniae (6 and 2 mm, respectively). Moreover, the synergistic effect of bio(AgNPs) with various commercially available antibiotics was also evaluated. The most significant results were observed for bio(AgNPs) combined with tetracycline, kanamycin, ampicillin and neomycin, followed by streptomycin and gentamycin against E. coli, Salm. infantis and Kl. pneumoniae. The most resistant bacteria to commercial antibiotics was Pr. mirabilis. CONCLUSION: The Streptacidiphilus sp. strain CGG11n isolated from acidic soil can be used to efficiently synthesize the bioactive nanoparticles using inexpensive substances in an eco-friendly and nontoxic manner. The present work provides helpful insight into the development of new antimicrobial agents with the synergistic enhancement of the antibacterial mechanism against pathogenic micro-organisms. SIGNIFICANCE AND IMPACT OF THE STUDY: The synthesized silver bionanoparticles from Streptacidiphilus sp. strain CGG11n possess potent inhibitory effect that offers valuable contribution to pharmaceutical associations.

Acidophilic actinobacteria synthesised silver nanoparticles showed remarkable activity against fungi-causing superficial mycoses in humans.

Superficial mycoses are limited to the most external part of the skin and hair and caused by Malassezia sp., Trichophyton sp. and Candida sp. We report extracellular biosynthesis of silver nanoparticles (AgNPs) by acidophilic actinobacteria (SF23, C9) and its in vitro antifungal activity against fungi-causing superficial mycoses. The phylogenetic analysis based on the 16S rRNA gene sequence of strains SF23 and C9 showed that they are most closely related to Pilimelia columellifera subsp. pallida GU269552(T). The detection of AgNPs was confirmed by visual observation of colour changes from colourless to brown, and UV-vis spectrophotometer analysis, which showed peaks at 432 and 427 nm, respectively. These AgNPs were further characterised by nanoparticle tracking analysis (NTA), Zeta potential, Fourier-transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The FTIR analysis exhibited the presence of proteins as capping agents. The TEM analysis revealed the formation of spherical and polydispersed nanoparticles in the size range of 4-36 nm and 8-60 nm, respectively. The biosynthesised AgNPs were screened against fungi-causing superficial mycoses viz., Malassezia furfur, Trichophyton rubrum, Candida albicans and C. tropicalis. The highest antifungal activity of AgNPs from SF23 and C9 against T. rubrum and the least against M. furfur and C. albicans was observed as compared to other tested fungi. The biosynthesised AgNPs were found to be potential anti-antifungal agent against fungi-causing superficial mycoses.