Human gingival fibroblasts were cultured in Dulbecco’s modified Eagle’s medium (DMEM)(Life Technologies, Carlsbad, CA, USA)
supplemented with 10% newborn calf serum (Life Technologies)
and 1% penicillin–streptomycin (Life Technologies) as previously
described [26]. Passage 6 cells were used for the following studies.
HGFs were seeded at 2 × 103 cells per well in 96-well plates
or 1 × 105 cells per well in 12-well plates. After being cultured for
48 h, the cells were exposed to Bac8c at the concentration of 32, 64,
or 128 g/ml for 5 min, 60 min, or 240 min. Cells that were exposed
to medium alone served as controls. The cell viability and levels
of extracellular lactate dehydrogenase (LDH) were evaluated as we
did previously [26].