Murraya koenigii-mediated synthesis of silver nanoparticles and its activity against three human pathogenic bacteria

Synthesis of silver nanoparticles (Ag NPs) by the leaf extract of Murraya koenigii (Indian curry leaf tree) is reported in this study. The colour of the leaf extract prepared by grinding turned from green to brown after treatment with AgNO3 (1 mM). The UV–visible spectroscopic analysis showed the absorbance peak at about 420 nm, which indicates the synthesis of Ag NPs. Further characterisation by Fourier transform infrared spectroscopy showed the presence of proteins as capping agents, which increase the stability of Ag NPs in the colloids. Scanning electron microscopy demonstrated the presence of spherical Ag NPs in the range of 40–80 nm. The bactericidal activity of the standard antibiotics was significantly increased in the presence of Ag NPs against pathogenic bacteria, viz., Escherichia coli-JM-103 (ATCC 39403), Staphylococcus aureus (ATCC 25923) and Pseudomonas aeruginosa (MTCC 424). Ag NPs in combination with gentamicin showed the maximum activity against E. coli (increase in fold area −4.06), followed by P. aeruginosa (1.11) and S. aureus (0.09), while tetracycline showed maximum activity against S. aureus (2.16) followed by P. aeruginosa (0.24) and E. coli (0.21). The Ag NPs thus obtained demonstrated remarkable antibacterial activity against three human pathogenic bacteria when used in combination with commercially available antibiotics.