Antibacterial effects of olive leaf extract

A single colony of L. monocytogenes F2365 was inoculated in 5 ml Brain Heart Infusion (BHI) broth and incubated overnight at 37°C with controlled agitation at 200 rpm. A 1:1000 dilution of the overnight culture with BHI broth was used for the inhibition study. The inhibitory activities of OLE against L. monocytogenes F2365 were assessed by a two-fold serial broth dilution method using 96-well microtiter plates, as described previously [3 (link)]. Briefly, eight OLE concentrations (128.0, 64.0, 32.0, 16.0, 8.0, 4.0, 2.0, and 1.0 mg/ml) were generated by two-fold serial dilutions using BHI broth. Fifty microliters (50 μL) of OLE at each concentration and 50 μL of diluted L. monocytogenes F2365 overnight culture, total 100 μL, were mixed into each well of the plate. After 24 h incubation, the OD₆₀₀ was measured using a spectrophotometric microplate reader (BioTek Instruments, Inc., Winooski, VT) at 37°C with 0.05 linear agitation, as programed by the Gen 5 software (v. 3.00.19). Eight replicates (on the plate) were set up for each OLE concentration condition.