Enhanced biocidal activities of Citrullus colocynthis aqueous extracts by green nanotechnology

Abstract

Summary. Synthesis of metal nanoparticles is an attractive research area for their divers and potential implications in the field of nanomedicine. Recently, production of nanoparticles by biosynthetic method employing live plant or plant extract has emerged a simple and viable alternative to traditional methods. In the present study the biocidal; antibacterial, antifungal, antiviral and larvicidal activities of greenly synthesized silver nanoparticles (SNPs) in aqueous extracts (AEs) of Citrullus colocynthis were investigated. SNPs Formed in C. colocynthis AEs were spherical and homogenous and their average mean sizes were 19.267 nm, 16.578 nm, 13.376.nm and 7.398 nm in AEs of fruits, seeds, leaves and roots respectively. The biosynthesized SNPs greatly enhanced the activities of C. colocynthis AEs. It showed  a significant inhibitory action against different bacterial species; Escherichia coli, Neisseria gonorrhoeae, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pyogenes ; antifungal activity against Aspergillus fumigatus, Candida albicans, Geotricum candidum and Trichophyton mentagrophyte s, with inhibition zones ranging from 15.1 ± 0.44 to 25.2 ± 0.37 mm. Transmitted electron microscopic (TEM) analysis of the morphological changes in S. aureus and E. coli cells revealed SNPs aggregated and located non-specifically on the cell wall, also, SNPs were seen within the cell wall or the cell of bacteria. The cells became severely distorted and disrupted showing a bactericidal action. Interestingly, a size dependence of SNPs' antiviral activity was observed. We found that the SNPs/ C. colocynthis roots AEs showed the strongest antiviral activity causing 70%, 73% and 75% reduction of the Cytopathic effect (CPE) of hepatitis A virus, Herpes simplex virus type I and Herpes simplex virus type II respectively. Also, the SNPs /C. colocynthis showed a significant larvicidal activity against the 3 rd instars larvae of Culex pipens mosquito. Comparing LD 50 of different AEs versus their corresponding SNPs/AEs showed a significant enhancement of the larvicidal activity after SNPs synthesis. Greenly synthesized SNPs using C. colocynthis aqueous extracts is a potential candidate to develop into a broad spectrum biocidal agent. Industrial relevance. Various microorganisms have evolved resistance to conventional chemical antimicrobial agents over many generations. Greenly synthesized SNPs using C. colocynthis AEs, which has been found to be effective against many viruses and bacterial species, can provide a cheap broad-active alternative that can be used against a variety of pathogens. Keywords . green synthesis; silver nanoparticles; Citrullus colocynthis; antiviral; antimicrobial; larvicidal