FIG. 1.

Action of 2% xylitol on viridans group streptococcus ultrastructure as revealed by differential Gram-staining imaged with the same magnification. (a) Planktonic viridans group streptococcus cells cultured in BHI medium and 0% xylitol anaerobically for 24 h prior to growth in xylitol. The titer has been reduced 10,000-fold to ensure that all bacteria attain log-phase growth in the presence of the xylitol. (b) Gram-stained viridans group streptococci cultured in BHI medium and 2% xylitol anaerobically for 24 h. The xylitol-exposed (2% or higher) bacterial population demonstrated a remarkable change; 50% of them stained pink, appearing like Gram-negative or dead bacteria instead of purple.