Front Microbiol 2020 15;11:409. Epub 2020 Apr 15.
Institute of Food Sciences, CNR-ISA, Italian National Research Council, Avellino, Italy.
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 chemotype "Variety B" and , native to Australia. Geranyl acetate, γ-terpinene, geraniol, terpinolene, α-pinene, -cimene, and linalool were the main components in EO, confirming also the existence of several chemotypes in such taxa; on the other hand, 1,8-cineole, -sabinene hydrate acetate, globulol, longicyclene, terpinolene, and camphene were present in major amounts in the EO. Chemical analysis of revealed that it belongs to the variety "B." EO showed good antibacterial activity, with an MIC of 0.5 and 2 μg/mL against , and , respectively. The activity of EO was stronger than EO, whose maximum MIC reached 5 μg/mL. and EOs were particularly effective in inhibiting the biofilm formation by , 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 was recorded for 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 . In addition, even though EO 0.1 μg/mL was unable to inhibit biofilm formation by , 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, EO 0.5 μg/mL induced a 79.88% inhibition of biofilm, maintaining a high metabolic activity (90.89%) compared to the control. Moreover, this EO showed inhibitory activity against radical elongation of and the germination of radish. On the contrary, EO showed no phytotoxic activity.