Antimicrobial activity of essential oil and extracts of Eucalyptus camaldulensis Dehnh. on Pseudomonas tolaasii under In vitro & In vivo conditions

One of the modern methods for biological control of button mushroom (Agaricus bisporus) brown blotch disease is using plant's essential oil. Therefore, antimicrobial properties of essential oil and extracts obtained from Eucalyptus camaldulensis Dehnh. leaves were evaluated against the plant pathogenic bacterium Pseudomonas tolaasii both In vitro and In vivo conditions. 0.3 g/ml of each leaf samples was macerated in water and organic solvents (acetone, methanol and ethanol) to obtain the relevant extracts. The extraction of essential oil from leaves was performed Hydro-distillation method using Clevenger apparatus. Bioassays for inhibition activities of EO were carried out in five concentrations (0/1, 0/01, 0/001, 0/0001 and pure mg/ml) on two agar media of NA and KB. According to the isolation and identification of the main components in essential oils by gas chromatography (GC-MS), Cineol (58.1%) and α-phellandrene (6%) were identified as the main components. The most efficient In vitro results obtained by pure essential oil of Eucalyptus with 17 mm inhibition zone on KB and methanol extract with 8mm on NA. These were more pronounced when compared to inhibition effects of antibiotics erythromycin, penicillin and gentamycin and not with tetracycline in both concentrations of 0.1 and 0.01 mg/ml. This was reversed by subsequent increase of the antibiotics tetracycline and gentamicin to the level of 1, 5 and 10 mg/ml. In vivo assays were conducted in order to evaluate the efficacy of essential oil and methanol extract in two dilutions of 0/1 and 0/01 mg/ml. 20µl of each plant extracts was pre-treated on mushroom caps and after 24 h, the bacterial suspension at ca 105 cfu/ml was inoculated the same pre-treated sites. After a two day incubation period at 25°C, the 0/01 concentration of both extracts showed a satisfactory result.