Volatile Terpenoids from Water Pepper (Polygonum punctatum) Against Pseudomonas aeruginosa and Staphylococcus aureus Virulence Strategies

Abstract

Polygonum punctatum Elliot (water pepper) is a pungent herb ancestrally employed as a disinfectant in traditional medicine by Toba Indians of the north-eastern region of Argentina and also commonly used as spice in Japanese cuisine. GC-MS of whole diethyl ether extract (EE) from aerial parts allowed to identify 14 volatile terpenoids such as sesquiterpenes: α-bisabolol (3.4 %), polygodial and isotadeonal (34.0%); various methylated phenol like α-tocopherol or vitamin E (3.6 %), and phytosterols: stigmasterol (2.1%) and β-sitosterol (29.9 %). Thus, water pepper is a promising source of drimane sesquiterpenes and phytoestrogens with important bioactivities. Following a taste- guided fractionation by CC and HPLC, drimane-type sesquiterpenes, polygodial (1) and its stereoisomer isotadeonal (2) were isolated as main compounds from the EE. The antipathogenic effects on the bacterial growth, biofilm formation, and elastase activity of both pure compounds and EE were evaluated against two Staphylococcus aureus and two Pseudomonas aeruginosa strains at 10 and 100 µg/mL. The highest effects were observed for the non pungent drimane isotadeonal (2) which was able to reduce about 75 % the bacterial growth of all tested microorganisms and to inhibit Gram-positive biofilm formation (85 % mean) at 100 µg/mL. In addition, elastase activity of P. aeruginosa, another virulence strategy, was attenuated more than 50 % at 100 µg/mL by 2. These results provide evidence that support the antimicrobial use of P. punctatum against P. aeruginosa and S. aureus, as well as, demonstrating that isotadeonal (2), despite it has been suggested to lack biological properties, is a bioactive compound able to control biofilm formation and bacterial growth of both human pathogens.