Abstract
Bacteria are the causative agents of numerous diseases. Ever increasing number of bacterial infections has generated the need to find new antibiotic materials and new ways to combat bacterial infections. Our study investigated Azadirachta indica (AI) as an alternate source of antibiotic compounds. Phytochemical and GC-MS analysis revealed presence of flavonoids, phenolic compounds, terpenoids and terpenes. Aqueous extracts of leaves were used to synthesize silver nanoparticles (AI-AgNPs), as established by colorimetric confirmation with maximum absorbance peak at 400 nm. Optimized reaction parameters produced high yield of stable AI-AgNPs, which were characterized by UV-Vis spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and transmission electron microscopy. Results confirmed particle diameter of 33 nm and spherical shape of AI-AgNPs. Fourier transform infrared spectroscopy inferred the presence of functional groups in bioactive constituents involved in conversion of silver ions into elemental silver by acting as capping and reducing agents during formation of AI-AgNPs. X-ray diffraction revealed their crystalline nature. Toxicity studies on Drosophila validated normal egg laying capacity and eclosion of F1 generation on AI-AgNPs (100 μg/mL). DPPH (65.17%) and ABTS (66.20%) assays affirmed strong radical scavenging effect of AI-AgNPs (500 μg/mL). The antibacterial activity of AI-AgNPs (1,000 μg/mL) was confirmed by disc diffusion assay with zone of inhibition against Bacillus cereus (17.7 mm), Escherichia coli (18.7 mm), Pseudomonas aeruginosa (10.3 mm), and Staphylococcus aureus (17.7 mm). Minimum inhibitory concentration and minimum bactericidal concentration values for AI-AgNPs ranged between 390 and 780 μg/mL. Higher bacterial suppression by AI-AgNPs in comparison with AI-extract was further divulged by prominent damage to the bacterial cell walls, disintegration of cell membranes and outflow of intercellular content as evident in SEM images. AI-AgNPs were loaded on PF127 (biocompatible-biodegradable polymer) to form a viscous, spreadable, hydrogel that demonstrated enhanced antibacterial properties in disc diffusion assay (13–18.7 mm). When topically applied on mice, AI-AgNPs-PF127 hydrogel did not show symptoms of skin irritation. Application of AI-AgNPs-PF127 hydrogel on wound sites in mice, significantly increased the wound contraction rate. Our studies present a simple green route to synthesize AI-AgNPs with enhanced antibacterial and free-radical scavenging efficacy; and AI-AgNPs-PF127 hydrogel as a low-toxic, eco-friendly delivery vehicle with potential in wound healing.
Highlights
Bacteria are the causative agents of numerous diseases often leading to death and disruption due to damaged crops, spoiled food products, and contaminated equipment (Baranwal et al, 2018)
Synthesized drugs have many side effects; medicinal plants are being evaluated for curative role owing to their easy availability and non-toxicity for therapeutic use while being effective in curbing bacterial infections (Chinnasamy et al, 2019)
Silver nanoparticles synthesized from plants that are ubiquitous in secondary metabolites, have been documented for their intrinsic property of antibacterial inhibition in foodborne pathogens and antibiotic resistant bacteria (Jain and Mehata, 2017; Loo et al, 2018)
Summary
Bacteria are the causative agents of numerous diseases often leading to death and disruption due to damaged crops, spoiled food products, and contaminated equipment (Baranwal et al, 2018). Synthesized drugs have many side effects; medicinal plants are being evaluated for curative role owing to their easy availability and non-toxicity for therapeutic use while being effective in curbing bacterial infections (Chinnasamy et al, 2019). United Nations acknowledged the importance of this tree and entitled it as “Tree of the 21st century.” It is a revered home remedy and find multiple uses as leaf juice to kill intestinal worms, twigs for cleaning teeth, bark paste, and gum for topical application to treat leprosy and skin ailments, seed oil as mosquito repellent and leaves are known for anti-inflammatory, antipyretic, antimalarial, anticancer and antidiabetic properties (Kumar and Navaratnam, 2013; Sarah et al, 2019). Thermo-sensitive hydrophilic PF127 was used as a non-toxic biocompatible hydrogel carrier for AI-AgNPs in topical applications on mice skin towards wound healing
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