2.4. Antibiofilm assay
2.4.1. Inhibition of biofilm formation
The effect of P. betle extract on biofilm formation of each representative
strain, S. mutans ATCC 25175 and A. actinomycetemcomitans
ATCC 33384, was examined by using the modified microdilution
method.16 Briefly, two-fold serial dilutions of P. betle extract were
prepared, with final concentration ranged from 0.02 to 25 mg/mL. A
cell suspension of the tested strainswas prepared as described in the
MIC assay, and 100 mL (1 106 CFU/mL) were inoculated in each of a
96-wellplate.A0.1%CHX, phosphate bufferedsaline (PBS) and extractfree medium were used as the positive controls, non-treated and
blank controls, respectively. After incubation at 37 C for 24 h, supernatants
were discarded and washed 3 times with PBS. Biofilm
formation was quantified by using a 3-[4,5-dimethyl-2-thiazolyl]-2,
5-diphenyl-2H-tetrazolium-bromide (MTT) assay. The numbers of
surviving bacteria were determined by measuring their ability to
reduce the yellow tetrazolium salt to a purple formazan product at
570 nm. Higher OD values indicate an increased number of surviving
microorganisms in the biofilm. Percentage inhibition was calculated
by using the equation [1 (A570 of the test/A570 of non-treated
control)] 100. The minimum biofilm inhibition concentration
(MBIC)was defined as the lowest concentration that showed 50% and
90% inhibition of biofilm formation (MBIC50 and MBIC90).