The present work focuses on a low-cost, simple, and green synthesis of silver nanoparticles (AgNPs) by mixing AgNO solution with the extract of Spirulina platensis (SP) without any chemical reducing and/or capping agents. The green synthesis of AgNPs was confirmed by the color change from colorless to yellowish brown. The biosynthesis of AgNPs was further confirmed by UV-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), biological transmission electron microscopy (Bio-TEM), and energy dispersive X-ray analysis (EDX). The UV-vis spectroscopy results showed the surface plasmon resonance (SPR) of AgNPs around 450 nm. Bio-TEM analysis revealed that the Ag nanoparticles were well dispersed with average range of 5-50 nm. XRD results indicated that the green synthetic process produced face-centered cubic structure of AgNPs. FT-IR spectroscopy analysis showed that the bioactive molecules from the SP extract believed to be the responsible for the reduction of Ag ions. Furthermore, the synthesized AgNPs were evaluated against pathogens such as Staphylococcus sp. and Klebsiella sp. The AgNPs (1-4 mM) extensively reduced the growth rate of the pathogens.

Multi resistance to antibiotics is a serious and disseminated clinical problem, common to several new compounds that block the resistance mechanism. The present study aimed at the comparative study of silver nanoparticles synthesized through actinomycetes and their antimicrobial metabolites with standard antibiotic. Marine actinomycetes collected from Gulf mannar costal region, Kayalpatnam, located at Tuticorin district, Tamil nadu, India. Totally, five actinomycetes were isolated and identified based on their spore formation and biochemical studies. Three isolates belonged to the genera of Streptomyces sp and two were Micromonospora sp. Streptomyces sp KPMS3 showed potent antibacterial activity against Gram negative pathogens. Gram positive isolates are sensitive to Micromonospora sp (KPMM2). Among the five isolates, isolate Micromonospora sp (KPMM2) was found to be an effective silver nanoparticle synthesizer. The obtained silver nanoparticles were characterized using UV-Vis spectroscopy, FTIR and TEM. The morphology of nanoparticle is found to be spherical and an average size of ranges between 38 to 52 nm. The antimicrobial activities of silver ion against test pathogens were found to be superior to cephalosporin antibiotic. The in vitro hemolytic assessment of silver nanoparticles were found to be non-hemolytic at maximum of 20 µg/ml. It was found that smaller silver nanoparticles synthesized by microbial route had a greater antibacterial activity and less hemolytic in nature.