Bio-engineering and cellular imaging of silver nanoparticles as weaponry against multidrug resistant human pathogens

'Go green' has also been implied to nanotechnology by harbouring eco-benign principle for a cleaner production of silver nanoparticles (AgNPs). This was achieved using a nitrate reducing Bacillus subtilis L1 (KT266579.1) inhabiting rhizosphere soil under optimized laboratory conditions, highlighting on its antibacterial modus operandi. Nano-characteristics and antimicrobial mechanism were investigated using spectroscopic and electron microscopic studies. Spectroscopic and microscopic characterization revealed typical surface plasmon resonance (SPR) with λ_max 420 nm showing mean particle size of ~28.30 nm and spherical shaped nanoparticles. Antimicrobial susceptibility pattern of clinically important pathogens (n = 15) exposed to AgNPs at 10 μg, 15 μg and 20 μg/mL for 18 h was found significant in a dose dependent fashion. Electron and atomic force microscopic (AFM) studies have demonstrated the typical bactericidal effect of AgNPs (<25 μg/mL) associated with 'pitting effect', cell shrinkage and increase in surface roughness. The EDX spectrum of the control and treated bacteria showed the intrusion of AgNPs inside the bacterial cells endorsing the event of bacterial paralysis. DNA fragmentation assay demonstrated significant DNA damage in the form of smear, indicative of genotoxicity at ≤32 μg and ≤16 μg/mL of AgNPs respectively for Gram positive and negative strains in <12 h. These results suggest that AgNPs possess excellent antimicrobial activity, providing a potential lead for developing a broad spectrum antibacterial agent and extending its therapeutic modalities targeting antibiotic resistant strains at gene level.