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Background  In 1957, Tunisia introduced 117 species of  Eucalyptus ; they have been used as fire wood, for the production of mine wood and to fight erosion. Actually,  Eucalyptus  essential oil is traditionally used to treat respiratory tract disorders such as pharyngitis, bronchitis, and sinusitis. A few investigations were reported on the biological activities of  Eucalyptus  oils worldwide. In Tunisia, our previous works conducted in 2010 and 2011 had been the first reports to study the antibacterial activities against reference strains. At that time it was not possible to evaluate their antimicrobial activities against clinical bacterial strains and other pathogens such as virus and fungi.    Methods  The essential oils of eight  Eucalyptus  species harvested from the Jbel Abderrahman, Korbous (North East Tunisia) and Souinet arboreta (North of Tunisia) were evaluated for their antimicrobial activities by disc diffusion and microbroth dilution methods against seven bacterial isolates:  Haemophilus influenzae ,  Klebsiella pneumoniae ,  Pseudomonas aeruginosa ,  Staphylococcus aureus ,  Streptococcus agalactiae ,  Streptococcus pneumoniae  and  Streptococcus pyogenes . In addition, the bactericidal, fungicidal and the antiviral activities of the tested oils were carried out.    Results  Twenty five components were identified by GC/FID and GC/MS. These components were used to correlate with the biological activities of the tested oils. The chemical principal component analysis identified three groups, each of them constituted a chemotype. According to the values of zone diameter and percentage of the inhibition (zdi, % I, respectively), four groups and subgroups of bacterial strains and three groups of fungal strains were characterized by their sensitivity levels to  Eucalyptus  oils. The cytotoxic effect and the antiviral activity varied significantly within  Eucalyptus  species oils.    Conclusions   E. odorata  showed the strongest activity against  S. aureus ,  H. influenzae ,  S. agalactiae ,  S. pyogenes ,  S. pneumoniae  and against all the tested fungal strains. In addition,  E. odorata  oil showed the most cytotoxic effect. However, the best antiviral activity appeared with  E. bicostata . Virus pretreatment with  E. bicostata  essential oil showed better antiviral activity (IC 50  = 0.7 mg/ml, SI = 22.8) than cell-pretreatment (IC 50  = 4.8 mg/ml, SI = 3.33). The essential oil of  E. astringens  showed antiviral activity only when incubated with virus prior to cell infection. This activity was dose-dependent and the antiviral activity diminished with the decreasing essential oil concentration.

Chemical composition of 8 eucalyptus species' essential oils and the evaluation of their antibacterial, antifungal and antiviral activities