In vitro antimicrobial and antioxidant activity of black thyme (Thymbra spicata L.) essential oils

Abstract

In order to study antimicrobial effects of essential oils of Wild Thyme (Thymbra spicata L.) on two Gram positive bacteria (Streptococcus agalactiae RJTTC1978 and Staphylococcus aureus RJTTC1885) and two Gram negative bacteria (Escherichia coli RJTTC2409 and Klebsiella pneumoniae RJTTC1097), the research carried out with five concentrations (0.2, 2, 4, 10 and 20 microl) using disk diffusion and microbroth dilution (to determine MIC and MBC) methods at Ilam University during 2010. Tetracycline and Gentamicin discs were used as control. Chemical composition of the EOs was analyzed by GC-MS. Antioxidant activity of the essential oils (EOs) was measured following DPPH assay. Results showed that Carvacrol (60.36%), gamma-Terpinene (15.09%), beta-Myrcene (2.15%), trans-Caryophyllene (1.78%) and alpha-Thujene (1.54%) were the main components of the oils. Evaluation of antimicrobial activity revealed that the oils were active against both Gram positive and Gram negative bacteria. However, the biggest growth inhibitory zone (33.34 +/- 0.5 mm) was recorded on Streptococcus agalactiae at 20 microl/ml concentration. The lowest MIC (3.12 microl/ml) observed for Klebsiella pneumoniae and Streptococcus agalactiae, while minimum MBC (6.25 microl/ml) recorded on Klebsiella pneumoniae. Radical-scavenging ability of the EOs and BHT ranged from 9.93 +/- 2.57 to 77.81 +/- 1.3% and 80.48 +/- 0.56 to 10.66 +/- 1.11%, respectively. The inhibiting effect of Thymbra oils was stronger than the synthetic BHT, particularly at lower concentrations, as IC50 concentration of EOs for the reduction of DPPH radicals was 1.28 microl/ml which was lower than IC50 calculated for BHT (1.31 microl/ml). The total phenolic content, determined according to the Folin-Ciocalteu method, was 1.52 +/- 0.15 mg PyE/ml EOs.