Abstract:
With the emergence of microbial resistance to currently employed antimicrobial
agents, the recent trend is to search for novel antimicrobial substances from nature.
The traditional applications of plants and plant based products as well as metals and
metalloids suggest the potential of these sources for the discovery of new
antimicrobial compounds with diverse chemical structures and novel mechanisms of
action. Moreover, it is reasonable to hypothesize that the metal nano-preparations
produced from these plant extracts could offer highly potent antimicrobial properties
due to the synergistic effect of the plant extract and the metal nanoparticles. Thus the
aims of the present investigation are to evaluate the antimicrobial potential of
pharmacologically underexplored Plectranthus zeylanicus (Iruveriya), a plant
claimed as an antimicrobial remedy in traditional medicine and the green synthesis
of silver and zinc oxide nanoparticles as effective herbal disinfectants. The
antimicrobial activity of the n-hexane, dichloromethane, ethyl acetate and methanol
extracts of P. zeylanicus was determined by disc diffusion and broth microdilution
methods against Enterococcus faecalis, Staphylococcus aureus and Staphylococcus
saprophyticus. The dichloromethane extract displayed a MIC value of 31.25 μg/mL
against S. saprophyticus and S. aureus while a MIC of 250 μg/mL against E. faecalis.
Therefore this potent extract was then utilized for the green synthesis of silver and
zinc oxide nanoparticles by treating with AgNO3 and ZnSO4 aqueous solutions
respectively. The formation of metal nanoparticles was monitored by the
measurement of the absorbance of the reaction mixture within the range of 200-600
nm using an ultraviolet-visible spectrophotometer at different time intervals for a
period of three days. The silver nano-preparation displayed high absorbance in the
range of 240-260 nm and 420- 440 nm and the absorbance of the reaction mixture
increased with time. Similarly, the Zinc oxide nano-preparation has shown a high
absorbance at 350-370 nm. Products of the green synthesis were evaporated in hot
air oven. The scanning electron microscopy was employed to study the morphology
of the nanoparticles. The antimicrobial potential of the nano-preparations will be
studied in detail for the development of potent and eco-friendly herbal disinfectant/s.
