Extracellular and Intracellular Bacterial Compounds in the Synthesis of Inorganic Particles: Silver Nanoparticles

The primary objective of this study was to compare the contribution of cellular and cell-free filtrates of Serratia marcescens ATCC 9986 to the synthesis of silver nanoparticles, followed by a determination of the inhibitory activity on growth of S. marcescens and E. coli of the obtained biogenic silver nanoparticles. The synthesized silver nanoparticles exhibited maximum absorption at 257 nm and 262 nm when analyzed by ultraviolet–visible spectroscopy (UV–Vis). Energy-dispersive X-ray spectroscopy (EDX) analysis revealed a peak at 3 keV, corresponding to silver nanocrystals. Characterization by TEM, EDX, and IR spectroscopy demonstrated the presence of organic compounds in the nanoparticles. IR analysis revealed the presence of proteins, carbohydrates, carboxylic acids, and other compounds with saturated and unsaturated C-C bonds in the nanoparticles. Silver nanoparticles synthesized using cell-free and cellular filtrates inhibited growth of antibiotic-resistant bacteria E. coli. Moreover, cell-free filtrate of S. marcescens exerted inhibitory activity against E. coli, but not against its source, S. marcescens bacteria.