Variability in chemical composition and antimicrobial activity of Tagetes minuta L. essential oil collected from different locations of Himalaya

Tagetes minuta L. is an annual herb used in flavoring, perfumery, food and pharmacological industry. In the recent past, bioactivities and therapeutic properties of T. minuta against a wide range of plant, human and animal pathogens remain the focus of considerable scientific studies. So in this study chemical and antimicrobial activity profiles of T. minuta grown in 16 altitudinal locations of three states in India were explored. Fresh plant material was subjected to hydrodistillation using a Clevenger-type apparatus. The essential oil content ranged from 0.37 to 0.79% (v/w). Nine volatile compounds were identified by GC and GC-MS analysis. Range of major compounds in sixteen locations were Z-beta-ocimene (56.34 - 39.32%), dihydrotagetone (28.07 - 7.66%), E-ocimenone (25.06 - 0.00%) and Z-tagetone (14.46 - 5.29%). Comparison of the relative concentrations of essential oil compounds showed a significant altitudinal impact with higher Z-beta-ocimene from high altitudes; while reverse was seen in case of dihydrotagetone. Antimicrobial activity of the essential oils (EOs) was investigated against two Gram-positive bacteria viz. Micrococcus luteus, and Staphylococcus aureus, and two gram-negative bacteria viz. Klebsiella pneumoniae and Pseudomonas aeruginosa using agar well-diffusion and microdilution methods. The agar well diffusion method demonstrated better activity of T. minuta EOs in gram positive bacteria as compared to gram negative bacteria. Best activity was demonstrated against S. aureus with zone of inhibition above 9 mm. Best potential EOs (three locations of HP and one location of Manipur) demonstrated an MIC of 25-30% (v/v). Based on the current study, EOs of T. minuta from Indian Himalayas may be regarded as potential antibacterial agents against S. aureus and selected EOs may have potential application as bactericidal agents.