The minimum inhibitory concentration (MIC) of the green tea extract was determined by agar dilution method. MHA plates that contained various concentrations of green tea extract (0, 2.5, 3.0, 3.5, and 4.0 mg/ml) were prepared. Suspensions of 0.5 McFarland standard dilutions (equal to 1.5 × 108 cells/ml) were prepared from bacterial cultures grown overnight in LB broth. A 10-4 dilution of these suspensions was prepared, and 100 μl of dilution per plate was inoculated using a spread plate technique (plated concentration equals 1.5 × 103 cells). Inoculated plates were incubated at 37° C for 48 h, and on the basis of colony counts, the MIC was determined as the lowest concentration of green tea extract to show an inhibitory effect on growth of the bacteria (no colonies detected). Each strain was tested three times.