Correlation between chemical composition and antibacterial activity of essential oils from fifteen Eucalyptus species growing in the Korbous and Jbel Abderrahman arboreta (North East Tunisia)

Abstract

The essential oils of fifteen Eucalyptus species harvested from the Jbel Abderrahman and Korbous arboreta (North East Tunisia) were screened for their antibacterial activities by the agar disc diffusion method. Eighteen major components as identified by GC/FID and GC/MS were selected for a study of the chemical and biological activity variability. The main one was 1,8-cineole, followed by spathulenol, trans-pinocarveol, α-pinene, p-cymene, globulol, cryptone, β-phellandrene, viridiflorol, borneol, limonene and isospathulenol. The chemical principal component analysis identified five species groups and subgroups, where each group constituted a chemotype, however that of the values of zone diameter of the inhibition (zdi) identified six groups of Eucalyptus oils, characterized by their antibacterial inhibition ability. The strongest activity was shown by E. platypus oil against Enterococcus faecalis and by E. lamannii oil against Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli. A correlation between the levels of some major components and the antibacterial activities was observed.

Figure 1

Principal component analysis of 18 major compounds of leaf essential oils of 15 Eucalyptus species. For the abbreviation of the Eucalyptus species () and the compounds ( ), see Table 1.

Figure 2

Dendrogram obtained by hierarchical cluster analysis based on the Euclidean distance between groups of the leaf essential oils of fifteen Tunisian Eucalyptus species. Components that characterize the major subgroups, considered as chemotypes, are indicated. For the abbreviation of the Eucalyptus species, see Table 1.

Figure 3

Principal component analysis of the antibacterial activity of 15 Eucalyptus species oils against four bacteria model. Gen: gentamicine; for the abbreviation for the Eucalyptus species () see Table 1.

Figure 4

Dendrogram obtained by hierarchical cluster analysis (HCA) based on the Euclidean distance between groups of the leaf essential oils of fifteen Tunisian Eucalyptus species and their antibacterial activities against four model strains.