Comparison of antibacterial activity of four cultivars of olive (Olea europaea) leaf extract on Bacillus cereus

In recent years, plant extracts have been used as antimicrobial agents. One of these extracts is olive leaf extract, which has antimicrobial properties due to its phenolic compounds. In current study the leaf extract of four olive (Olea europaea) cultivars (Shiraz, Zard, Roghani and Dezfool) was extracted by different solvents (acetone, methanol and ethanol) using microwave-assisted extraction method. Then the antibacterial activity of the extracts was assessed on Bacillus cereus. The antibacterial activity of the extracts was determined using the standard and micro broth-dilution methods. All experiments were carried out in triplicate. Minimum inhibitory concentration (MIC) of eleven extracts was estimated as 20 mg/ml, and only MIC of the methanolic extract of Roghani cultivar was 10 mg/ml. Bacterial growth curve of B. cereus in the presence of olive leaf extracts was drawn after 24 h incubation at 37 °C and the mean percentage of growth inhibition of each extract was measured after 24 hours. The results showed that in comparison with the other cultivars, the methanolic extract of Roghani cultivar with the percentage of growth inhibition of 91.3% and 87.8% (in the concentrations of 10 and 20 mg/ml, respectively), demonstrated stronger antibacterial effect on B. cereus. This study indicated that olive leaf extract from inexpensive agricultural waste might be a valuable bioactive source with antibacterial activity, and seem to be applicable as a safe food additive.