Effect of drought stress on antibacterial activity of Thymus daenensis subsp. daenensis Celak.

Abstract

Thymus daenensis subsp. daenensis is an endemic aromatic and medicinal plant of Iran. An experiment was conducted to study the effect of drought stress on growth and on antibacterial activity of T. daenensis subsp. daenensis Celak in pot experimental of field, Shahrekord, Southwest Iran. Plants were exposed to three drought treatments at before flowering (75 days after sowing): (1) well-watered at 100% field capacity (control), (2) severe drought stress at 20% field capacity, (3) mild drought stress at 40% field capacity, and (4) hard drought stress at 60% field capacity, until complete flowering (120 days after sowing). The antibacterial activity of the ethanol extract was assayed against four pathogens (Staphylococcus aureus, Bacillus cereus, Salmonella typhimurium and Streptococcus agalactiae) by agar disc diffusion method. The results of showed that the ethanol extracts from the different treatments studied showed antibacterial ‎activities, with the diameters of the inhibition zone ranging from 8 to 31 mm. There were no significant differences in the antibacterial activity of the extracts from the different treatments in almost concentrations against four pathogens. But, the highest level of antibacterial activities against S. aureus, B. cereus, S. typhimurium and S. agalactiae were demonstrated by the extract (1000 µg/ml) of drought stress at 60% field capacity (IZ = 26 mm), drought stress at 20% field capacity (IZ = 18.7 mm), drought stress at 20% field capacity (IZ = 20.2 mm) and drought stress at 20% field capacity (IZ = 23.7 mm), respectively. Increased drought levels did not significant reduce antibacterial activity as compared with controls. Key words: Thymus daenensis subsp. daenensis, drought stress, antibacterial activity, ethanol extract.