Mechanisem of Antibacterial Activity of Methanolic Extract of Myrtus communis L. on E.coli K12 HB101

Myrtus Communis, L. is a medicinal herb, which has antibacterial activity and is used against many pathogens. The present study was conducted to investigate the mechanism of antibacterial activity of the methanolic extract of this herb against E.coli K12 HB101. E.coli K12 HB101 containing plasmid pBR322 was cultured in Muler Hinton agar under different concentration (1.56-6.25 mg/ml) of Myrtus communis air-dried extract. The cells were lysed by repeated sonication and freeze -thawing. The catalase, and superoxide dismutase(SOD) activities, total antioxidant (TAS) and malondialdehyde determination were performed on the cell lysate. Plasmid DNA was purified and the electrophoretic behavior of the purified DNA grown under different concentration of the extract were compared. Various Concentrations (SIC) of the extract did not show any changes in the DNA topology. When the extract concentration in the culture increased from 1.56 to 6.25 mg/ml the catalase specific activity of the cell extract reduced from 20.47 ± 0.7 to 5.1 ± 2.9 unit/mg protein. Under the same condition, SOD activity was decreased from 63.86 ± 5.2 to 20.04 ± 1.6 units/mg protein. Total antioxidant capacity in the cell lysate significantly decreased in the test samples compared to the control cultures (18.07 ± 3.1 vs 6.19 ± 2.1 mmole/L). Malondialedhyde concentration was elevated from 23.09 ± 7.6 to 49.92 ± 3.4 m g/mg protein of the cell lysate. The extract of Myrtus communis persumabably does not change the DNA topology of E.coli as judged by excision of plasmid pBR322. The results however showed that, Free radicals are one of the major causes of the antibacterial action of this medicinal herb.