Constituents and antimicrobial activity of the essential oils of six Himalayan Nepeta species

Abstract

The essential oils from six Himalayan Nepeta species, viz. Nepeta leucophylla Benth., Nepeta discolor Royle ex Benth., Nepeta govaniana Benth., Nepeta clarkei Hook. f., Nepeta elliptica Royle ex Benth. and Nepeta erecta Benth., were tested for their in vitro antimicrobial activity against six pathogenic bacterial and two fungal strains. The results showed that Pseudomonas aeruginosa was the most sensitive strain tested to the essential oils of Nepeta species. The essential oils of N. elliptica and N. erecta exhibited the highest activity against P. aeruginosa, followed by the essential oils of N. leucophylla and N. clarkei. The essential oils from N. elliptica and N. erecta were also found to be very effective against Serratia marcescens; while the essential oil from N. leucophylla displayed significant activity against Proteus vulgaris and Staphylococcus aureus. Other bacterial strains displayed variable degree of susceptibility against one or more of the tested essential oils. The essential oil from N. leucophylla also showed the highest antifungal activity against both tested fungal strains, viz. Candida albicans and Trichophyton rubrum, followed by the essential oils from N. clarkei, N. govaniana and N. erecta. Iridodial derivatives, viz. iridodial β-monoenol acetate (25.4 %), dihydroiridodial diacetate (18.2 %) and iridodial dienol diacetate (7.8 %) were identified as the major constituents of N. leucophylla, while the essential oils from N. elliptica and N. erecta were dominated by (7R)-trans,trans nepetalactone (83.4 %) and isoiridomyrmecin (66.7 %), respectively. The essential oil of N. discolor was characterized by 1,8-cineole (25.5 %) and β-caryophyllene (18.6 %), while N. clarkei was dominated by β-sesquiphellandrene (22.0 %) and germacrene D (13.0 %). Isoiridomyrmecin (35.2 %) and pregeijerene (20.7 %) were identified as the major constituents of N. govaniana. In general the Nepeta species containing constituents with an iridoid or lactone skeleton were found to have the 740 BISHT et al. greater antagonistic activity against most of the microbial strains as compared to those containing regular terpene constituents.

In vitro inhibition activity of essential oils from some Lamiaceae species against phytopathogenic fungi

“…Chemical composition of essential oils determined by combined GC and GC/MS analyses confirmed presence of marker constituents previously recorded in N. leucophylla and N. clarkei [9,14] except quantitative changes. Iridodial b-monoenol acetate (1) and caryophyllene oxide (2) were the major constituents of the N. leucophylla oil besides sesquiphellandrene among other minor constituents.…”

“…The essential oils of Lamiaceae species are accredited with antioxidant, antiseptic, anti-inflammatory, antimicrobial and fungicidal properties [8][9][10][11][12][13]. Himalayan Nepeta leucophylla and Nepeta clarkei are known to possess iridoids and actinidine (a volatile terpene-alkaloid) besides mono-and sesquiterpenoids [13,14].…”

Anticandidal Activity of the Essential Oil of Nepeta transcaucasicaGrossh.

“…For example, the essential oil of N. erecta [24], Figure. Chemical structures of the compounds with contents higher than 1.0% in the essential oil isolated from the aerial parts of Nepeta transcaucasica [15] [19] containing nepetalactones (84%), has shown moderate antifungal activity against C. albicans with a MIC value of 1.5 ml/ml, a value that is in good agreement with our results. It could be worthwhile to test nepetalactones against several Candida strains.…”

Himalayan Aromatic Medicinal Plants: A Review of their Ethnopharmacology, Volatile Phytochemistry, and Biological Activities

“…In addition, 1,8-cineole has demonstrated ulcer-healing and gastroprotective properties in rats [435] as well as antispasmodic effects on isolated mouse ileum [436]. Several other Nepeta samples have been rich in sesquiterpenoids such as β-caryophyllene [200,204,209,214,218], caryophyllene oxide [201,214,218], and germacrene D [200,204,209,218] (see Table 1). β-Caryophyllene has shown anesthetic [437], anti-inflammatory activity [438], but not analgesic activity [439], in animal models.…”