In vitro AFM evaluation of Streptococcus mutans membrane exposed to two mouthwashes.

Streptococcus mutans is the primary microorganism of the dental plaque, which causes the caries disease. In addition to tooth brushing, oral care products are usually recommended by dentists to reduce and prevent the plaque formation. The objective of this work was to assess via atomic force microscopy the Streptococcus mutans membrane exposed to two mouthwashes, one containing triclosan, and the other, phenolic essential oils. S. mutans were cultured in brain and heart infusion during 48 hours at 37C. The pellets were harvested by centrifugation (2500 rpm, 3 min), and re-suspended in 4 mL mouthwash. One minute later, the bacterial cells were washed twice times by centrifugation (2500 rpm, 3 min) using saline solution (0.9% NaCl). The cell mass was gently spread over clean glass coverslip and evaluated by atomic force microscopy, in dynamic mode. For microorganisms not exposed to mouthwashes, images showed clustered microcolonies with round-shaped cells in typical string arrangement. Measured mean diameter varied between 0.6 μm and 1.0 μm. Exposure to phenolic essential oils caused no perceptible alterations in the bacterial cells. However, after exposure to triclosan, cell membranes were slightly wrinkled, probably due to the structural perturbations caused in the membrane permeability.