FIG. 3.

Activity of mPE against S. mutans in a biofilm. Bacteria (1 × 10⁵ CFU) were seeded in wells of a 96-well plate in the presence of 1% sucrose. (A) Activity against growing biofilm. After formation of a biofilm, mPE was added at increasing concentrations. Growth in the biofilm was quantified by reading the absorbance at 595 nm, and results are presented as the change in absorbance from day 2 cultures prior to the addition of compound. Controls included no mPE (0) and 500 μg/ml tetracycline. The experiment was performed in triplicate. Error bars equal 1 standard deviation. (B) Bactericidal activity against bacteria in a biofilm. Bacteria were plated in sucrose for 2 days, followed by the addition of mPE. After 24 h, biofilms were disrupted by sonication and plated to measure the remaining viable bacteria. Error bars equal 1 standard deviation. (C) Confocal microscopy analysis of biofilm viability. Biofilms were treated for 24 h with 0 or 50 μg/ml mPE and stained using the LIVE/DEAD kit. Cultures were observed using a confocal laser scanning microscope at 488 nm and 543 nm. Merged images were produced using Zeiss LSM Image Browser software. Cultures are visualized from the side (left panel) and the top (right panel).