Extracellular synthesis of silver nanoparticles using entomopathogenic fungus: characterization and antibacterial potential

Abstract

Present study involves the simple, rapid, non-toxic and in vitro method of extracellular silver nanoparticles synthesis using Entomopathogenic fungus (Beauveria bassiana). The development of silver nanoparticle in fungal supernatant was confirmed by the absorbance peak at 450 nm in UV–Vis spectrophotometer. Further, presence of AgNPs and its crystal lattice was confirmed by EDS and XRD, respectively. TEM micrograph confirmed the presence of differently shaped (triangular, circular, hexagonal) nanoparticles with size ranging from 10 to 50 nm. Variable shape and size of fungal assisted AgNps was also confirmed in SEM study. The optimal pH and temperature for biosynthesis of nanoparticles was found to be 6.0 and 25 °C, respectively. The continuous effects of AgNPs against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus in time dependent manner was confirmed in growth kinetic studies. During 36 h of growth study, maximum reduction in O.D560 was found in E. coli (67.2%) followed by P. aeruginosa (63.3%) and S. aureus (56.8%) at 30 °C. The MIC values of fungal assisted AgNPs against E. coli, P. aeruginosa and S. aureus was found to be 2.5, 3 and 4.5 ppm, respectively. The MIC values of Ciprofloxacin was observed to be 0.5, 0.5 and 0.7 ppm, whereas MICs of AgNPs + Ciprofloxacin showed 0.4, 0.4, 0.5 ppm against E. coli, P. aeruginosa and S. aureus, respectively, clearly highlighting the synergistic effect of AgNPs in combination with Ciprofloxacin. In the view of challenges for developing antimicrobial nanoparticles of variable shape and size by various other methods, tuning nanoparticles synthesis via fungi can be a wonderful approach to resolve existing hurdles.