Antibacterial activity of Tagetes minuta L. (Asteraceae) essential oil with different chemical composition

The essential oils from aerial parts of Tagetes minuta L. grown in Egypt, South Africa and the UK were obtained by hydrodistillation. Although they had similar constituents, the oils had different percentage compositions. Dihydrotagetone was the most abundant component of the oils from the UK (34.3 and 54.1%), while the oils from South Africa and Egypt were characterized by a high content of cis-β-ocimene (50.9 and 32.0%, respectively). The oils exhibited antibacterial activity, especially against Gram-positive bacteria. Antimicrobial activity was greater in oils from the UK than in oils from Egypt or South Africa, irrespective of whether the UK plants had been grown in a greenhouse or in the field. The minimum inhibitory concentrations (MIC) for the oil from UK greenhouse-grown plants were 6.25-25 μg/mL for Gram-positive bacteria and 25-50 μg/mL for Gram-negative bacteria, with the lowest MIC of 6.25 μg/mL against Streptococcus faecalis. Oil from plants from South Africa had MICs of 50-100 μg/mL against Gram-positive and Gram-negative bacteria. The MICs of oil from plants from Egypt against all tested bacteria except Pseudomonas aeruginosa and Salmonella typhi were half of the MICs of oil from plants from South Africa.