Plate dilution method was used for determination of the
minimum inhibitory concentration (MIC) and minimum bactericidal
concentration (MBC) of herbal medicine extracts on
five kinds of oral bacterial strains. For MIC and MBC, the
bacteria was incubated for 20 hours at 37 ◦C in 5% CO2. To
determine MIC, the extract concentration was diluted twofold
from 5000 g/mL to 78 g/mL and the inoculum of 1
×
104
CFU/mL was used. The lowest concentration of the herbal
medicine extracts that inhibited the growth of the organism,
corresponding to an inhibition of 99% of the inoculum, was
considered as the MIC. To determine MBC, we used a variant
on the agar dilution method. The inoculation spots with no
visible growth were cut and top down 3 L of bacterial culture
broth on BHI agar plate. The lowest concentration of herbal
medicine extract that yielded no growth on the agar (99.9%
kill) was defined as MBC.