Chemical composition and antimicrobial activity of the essential oils of Micromeria thymifolia, M. dalmatica and Satureja cuneifolia

Plant material of Micromeria thymifolia (Scop.) Fritsch., M. dalmatica Benth. and Satureja cuneifolia Ten. was collected on Orien mountain, Montenegro in July 2006. Essential oils were obtained by steamdistillation using a Clevenger-type apparatus, according to procedure I of the Yugoslav Pharmacopoeia IV. Light yellow oils were obtained in 1.33%, 0.75% and 0.24% yield from the aerial parts of M. thymifolia, M. dalmatica and S. cuneifolia, respectively. The oils were subjected to qualitative and quantitative analysis by GC and GC/MS and antimicrobial activity of the oils (diluted 1:10 in DMSO) was tested. A variety of microorganisms: Escherichia coli (ATCC 25922), Salmonella typhimurium (ATCC 14028), Enterobacter cloacae (ATCC 13883), Pseudomonas aeruginosa (ATCC 27853), P. tolaasii (NCTC 387), Proteus mirabilis (ATCC 14273), Staphylococcus aureus (ATCC 25923), S. epidermidis (ATCC 12228), Streptococcus faecalis (ATCC 12952), Bacillus subtilis (ATCC 6051), Micrococcus luteus (ATCC 10240), M. flavus (ATCC 14452), Sarcina lutea (ATCC 10054), Listeria monocytogenes (ATCC 15313) and Candida albicans were used in the antimicrobial assay. The MIC (minimum inhibitory concentrations) values were determined using the broth microdilution method in 96-hole plates according to NCCLS [1]. Serial dilutions of the stock solutions of tested oils in broth medium (Muller-Hinton broth or Sabouraud broth) were prepared in a microtiter plate. The microbial suspensions were added in the microwells at the concentration of 5×105 organisms/mL. Streptomycin was used to control the sensitivity of tested bacteria, whereas nystatin was used as a control against the fungi. Each assay was repeated two times. Piperitenone, pipertitenone oxide and pulegone were among the dominant compounds in essential oils of M. thymifolia and M. dalmatica while S. cuneifolia oil did not contain thymol or carvacrol. Antimicrobial activity was noticed in all examined essential oils with MIC values ranging from 5.6–54µg/ml. The most active was essential oil of S. cuneifolia.

Reference: 1. NCCLS (2000) Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically; Approved Standard – Fifth Edition. NCCLSocument M7-A5. NCCLS: Wayne, PA, USA.