Antibacterial activity of essential oils in disc diffusion assays. A) Example of disc diffusion assay plate showing the halos in the bacterial lawn resulting from the antibacterial activity of lemon balm and coriander oils against E. coli DH5α. B) Graph of mean halo diameters from three disc diffusion assays showing the effect of essential oils on the growth of E. coli, +/- SEM. C) Graph of mean halo diameters from four replicates of a single disc diffusion assay showing the effect of essential oils or antibiotics on the growth of E. coli, +/- SEM. t tests were carried out to determine whether the halos produced by rifaximin were significantly different from the solvents, essential oils or other antibiotics. Significance levels obtained from two-tailed t tests are denoted by stars: * = significant (P < 0.05); ** = highly significant (P < 0.01); *** = very highly significant (P < 0.001).