AUTHOR=Caputo Lucia , Smeriglio Antonella , Trombetta Domenico , Cornara Laura , Trevena Greg , Valussi Marco , Fratianni Florinda , De Feo Vincenzo , Nazzaro Filomena 

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

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.00409

DOI=10.3389/fmicb.2020.00409

ISSN=1664-302X

ABSTRACT=<p>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 <italic>Leptospermum petersonii</italic> chemotype “Variety B” and <italic>Eucalyptus gunnii</italic>, native to Australia. Geranyl acetate, γ-terpinene, geraniol, terpinolene, α-pinene, <italic>p</italic>-cimene, and linalool were the main components in <italic>L. petersonii</italic> EO, confirming also the existence of several chemotypes in such taxa; on the other hand, 1,8-cineole, <italic>trans</italic>-sabinene hydrate acetate, globulol, longicyclene, terpinolene, and camphene were present in major amounts in the <italic>E. gunnii</italic> EO. Chemical analysis of <italic>L. petersonii</italic> revealed that it belongs to the variety “B.” <italic>E. gunnii</italic> EO showed good antibacterial activity, with an MIC of 0.5 and 2 μg/mL against <italic>Staphylococcus aureus</italic>, and <italic>Pectobacterium carotovorum</italic>, respectively. The activity of <italic>E. gunnii</italic> EO was stronger than <italic>L. petersonii</italic> EO, whose maximum MIC reached 5 μg/mL. <italic>E. gunnii</italic> and <italic>L. petersonii</italic> EOs were particularly effective in inhibiting the biofilm formation by <italic>S. aureus</italic>, 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 <italic>P. carotovorum</italic> was recorded for <italic>E. gunnii</italic> 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 <italic>P. carotovorum</italic>. In addition, even though <italic>L. petersonii</italic> EO 0.1 μg/mL was unable to inhibit biofilm formation by <italic>Escherichia coli</italic>, 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, <italic>L. petersonii</italic> EO 0.5 μg/mL induced a 79.88% inhibition of <italic>S. aureus</italic> biofilm, maintaining a high metabolic activity (90.89%) compared to the control. Moreover, this EO showed inhibitory activity against radical elongation of <italic>Solanum lycopersicum</italic> and the germination of radish. On the contrary, <italic>E. gunnii</italic> EO showed no phytotoxic activity.</p>