Chemical Composition and Biological Activities of the Essential Oils of Leptospermum petersonii and Eucalyptus gunnii

Abstract

The aim of this study was to characterize the chemical composition and to evaluate the antimicrobial and phytotoxic properties of the essential oils (EOs) obtained from leaves of Leptospermum petersonii chemotype "Variety B" and Eucalyptus gunnii, native to Australia. Geranyl acetate, γ-terpinene, geraniol, terpinolene, α-pinene, p-cimene, and linalool were the main components in L. petersonii EO, confirming also the existence of several chemotypes in such taxa; on the other hand, 1,8-cineole, trans-sabinene hydrate acetate, globulol, longicyclene, terpinolene, and camphene were present in major amounts in the E. gunnii EO. Chemical analysis of L. petersonii revealed that it belongs to the variety "B." E. gunnii EO showed good antibacterial activity, with an MIC of 0.5 and 2 µg/mL against Staphylococcus aureus, and Pectobacterium carotovorum, respectively. The activity of E. gunnii EO was stronger than L. petersonii EO, whose maximum MIC reached 5 µg/mL. E. gunnii and L. petersonii EOs were particularly effective in inhibiting the biofilm formation by S. aureus, already at a concentration of 0.01 µg/mL. The other strains were resistant to both EOs up to a dose of 0.05 µg/mL. The maximum inhibition on biofilm formed by P. carotovorum was recorded for E. gunnii EO, reaching a value of 93.12% at 1.0 µg/mL. This is the first manuscript which studies the biofilm inhibition by EOs and evaluates their effects on biofilm metabolism. Both EOs were more effective against P. carotovorum. In addition, even though L. petersonii EO 0.1 µg/mL was unable to inhibit biofilm formation by Escherichia coli, it decreased the metabolic activity of the biofilm to 78.55% compared to control; furthermore, despite it inducing a relatively low inhibition (66.67%) on biofilm formation, it markedly affected metabolic activity, which decreased to 16.09% with respect to the control. On the contrary, L. petersonii EO 0.5 µg/mL induced a 79.88% inhibition of S. aureus

Eucalyptus gunnii and Eucalyptus pulverulenta ‘Baby Blue’ Essential Oils as Potential Natural Herbicides

“…Even though volatile allelochemicals derived from Eucalyptus EOs are probably among the most investigated for their herbicidal properties, no studies are currently available on the possible phytotoxic activity of EP EO. Regarding EG, our previous study on EO from Sardinia showed no phytotoxic activity against several tested seeds [35].…”

“…1,8-Cineole was reported as the main constituent of EG EO also in the samples from Argentina (17.9%); Serbia (67.8%); and Sardinia, Italy (33.0%), even if with a different percentage on total EO [33][34][35]. Regarding the other constituents, the Argentinian EO presented high percentages of p-cymene (12.3%), spathulenol (12.3%), and α-phellandrene (7.0%) [33], as well as from the Sardinian EO that showed high amounts of trans-sabinene hydrate acetate (15%), globulol (10.3%), and longicyclene (9.1%) [35]. Only the EO from Serbia presented α-pinene as the second major compound with a percentage of 14.1%, similar to that of the sample here presented [34].…”

Chemical Characterization and Antibiofilm Activities of Bulbs and Leaves of Two Aglione (Allium ampeloprasum var. holmense Asch. et Graebn.) Landraces Grown in Southern Italy

“…The effect of the extracts to inhibit the bacterial adhesion ability was evaluated in flat-bottomed 96-well microtiter plates following the methods of O’ Toole and Kolter [ 33 ] and Caputo et al [ 34 ], using doses ranging from 0.4 to 2 mg/mL. In each well, the overnight bacterial cultures were adjusted to 0.5 McFarland (1.5 × 10 7 cells/mL, Densitometer cell density turbidity 0.3–15.0 McFarland, CAMLAB, Cambridge, United Kingdom) with fresh culture broth.…”

Synthesis and Technology of Nanoemulsion-Based Pesticide Formulation

“…The dissolution of oil in nanoemulsion could enhance the cytotoxicity, genotoxicity and antimicrobial activity against pathogens as the oil constituents are rich with biologic properties. Different phytochemical composition in essential oils will affect the biologic behaviors towards the pathogens [38].…”