FIG 10.

Transformation assay in the absence and presence of bacitracin. S. mutans was cultured in TSBg containing the pDL278 plasmid carrying a spectinomycin resistance gene. Bacitracin was added at the concentration at which each strain most strongly induced biofilm formation (bac+, 0.5 U/ml [1/8× MIC for the WT strain] and 0.0625 U/ml [1/2× MIC for the mbr mutant strains]). After culture for 5 h, the cells were cultured on a mitis salivarius agar plate with or without spectinomycin for 36 h. We measured the number of CFU and determined the transformation efficiency. The data are the mean ± SD of three independent experiments. The asterisks indicate a significant difference between two groups (Student's t test; *, P < 0.05, versus bac−).