Antibacterial and Anti-Quorum Sensing Studies of Extracellularly Synthesized Silver Nanoparticles from Azadirachta indica (Neem) Leaf Extract

Abstract

Azadirachta indica (Neem ) is an important medicinal plant with proven strong antiseptic, antiviral, antifungal and antibacterial properties. The study here presents the antibacterial and QS (Quorum Sensing) inhibitory potential of biogenic Silver nanopaticles (AgNPs) from Azadirachta indica leaf extracts. The nanoparticles were synthesized using an aqueous extract of Azadirachta indica leaves and silver nitrate solution. The size, crystal structure, elemental composition and other physical properties of nanoparticles were determined using different microscopic and spectroscopic techniques. The average diameter of the nanoparticles was found to be between 20-43 nm with crystalline morphology. These extracellularly synthesized AgNPs strongly inhibited Gram negative pathogenic species and exhibited demonstrable anti- Quorum Sensing (QS) activity as evident from pigment inhibition and 75- 80% decrease in biofilm mass on AgNPs treatment in a dose dependent manner.

Botanicals as Quorum Quenching Molecules and Their Effect in Plant Growth Promoting Traits in Pantoea, Paenibacillus, and Rhizobium

“…A mechanism that involves disrupting these AHL molecules is called quorum quenching [6]. These molecules may be chemicals like salicylic acid [7] and gallic acid [8], enzymes like lactonase, acylase, and oxidoreductase [9], physical parameters like pH and temperature [10] botanicals like neem leaf extract [11] and turmeric extract. These quorum-quenching molecules inhibit IAA production [12], extracellular polymeric substances (EPS) synthesis, and biofilm formation [13] and also adversely affect their symbiotic relationship with their eukaryotic hosts [14]…”