Antibacterial activity of chrysanthemum cinerariaefolium (pyrethrum) secondary metabolites and green synthesized silver nanoparticles

Abstract

The development of resistance to antibacterial agents by bacteria, drive efforts in bio prospecting for new novel compounds that can be used to target these resistant microorganisms. Plants are among natural sources of novel compounds with medicinal importance due to their desirable potency. Besides, plant phytochemicals can reduce metal ions to metal nanoparticles hence play important role in the green synthesis of nanoparticles. In the current study, bioactive compounds against selected bacteria were isolated from pyrethrum plant Chrysanthemum cinerariaefolium by carrying out bioassay-guided fractionation. The isolated compounds were characterized using 1D and 2D Nuclear Magnetic Resonance (NMR). Extracts of organic solvents and aqueous of C. cinerariaefolium were also used in the green synthesis of silver nanoparticles (Ag NPs) via reduction of silver ions present in silver nitrate. Synthesis involved mixing a fixed ratio of plant crude extracts with silver ions and storing the mixture in the dark. Observation of a color change to brown signified the formation of the nanoparticles. The nanoparticles were characterized using UV-Vis, Scanning Electron Microscopy, Transmission Electron Microscopy, EDX (energy dispersive X-ray analysis), and Fourier-Transfonn Infrared Spectroscopy (FTIR). The compounds isolated were (Z)-2 methyl-4-oxo-3-(pent-Z-en-1- yl)cyclopent-2-en-l-yl2,2-dimethyl-3-(2-methylprop-1-en-1-yl) cyclopropane- l -carboxylate (jasmolin I), 2-methyl-4-oxo-3(Z)-penta-2,4-diene-1-yl)cyclopent-2-en-l-yl3-(E)-3 -methoxy- 2-methyl-3-oxoprop-1-en-yl-2,2-dimethylcyclopropane-l-carboxylate (pyrethrin II), and (Z)- 2-(but-2-en-1-yl)-4-hydroxy-3-methylcycl0pent-2-en-1-one (cinerolonc). The compounds showed more activity on the bacteria as a mixture in the ratio of l:l:1 than individual compounds, with MIC of 25 mg/ml against Pseudomonas aeruginosa. The compounds can therefore be used as lead compounds in drug discovery against bacteria. All the nanoparticles fonned were generally spherical in shape. The smallest and largest nanoparticles had sizes of 22.81 17.5 nm and 75.3i 19.7 nm and they belonged to dichloromethane-Ag NPs and ethyl acetate-Ag NPs respectively. The particles exhibited size-dependent activity on the selected bacteria. Safety studies on the nanoparticles and pyrethrum extracts on Vero cells showed that they were not cytotoxic hence safe for utilization in drug discovery. Pyrethrum plant therefore possesses phytochemicals that can be used in green synthesis nanoparticles. Other plants should be exploited to ascertain their ability to synthesis nanoparticles