Xylitol Inhibition of S. mutans Adhesion to Hydroxyapatite

We are characterizing the efficacy of xylitol in the presence of other sugars to inhibit the adherence of S. mutans (SM) to pure hydroxyapatite (HA), and to cause the dissociation of SM from monolayer SM already adhered to HA (SM.HA). 

Objective: 1. Exposure of HA to xylitol will inhibit SM adherence.  2. Exposure of SM to xylitol will inhibit HA adherence.   3. Exposure of SM.HA to xylitol will cause SM to dissociate. 

Method: Our model comprises commercial SM (UA159) and 20 μm spheres of HA.  SM.HA is made by incubating excess SM in the presence of HA in phosphate buffer and washing away excess SM. Preparations of HA, SM and SM.HA are exposed to 0 – 1.3 M xylitol for 0 – 90 minutes, and SM adherence is assayed by fluorescence microscopy after adding SYTO-9.

Result: The [xylitol] dependence was measured for 60’ exposure.  Exposure of SM or HA to xylitol and washing before mixing inhibits monolayer binding.  Decreased binding is seen at 0.3 M (~5%) and no binding is seen above 0.7 M (~10%) xylitol.  The time dependence was measured for 0.3 M xylitol.  Reduced binding begins at 30’ and no binding is seen 90’ after addition of 0.3M xylitol. Adding xylitol to SM.HA induced dissociation. For 60’ exposure, partial dissociation is observed at 0.3 M xylitol and complete dissociation at 0.7 M xylitol.

Conclusion: Xylitol inhibits and reverses the first step in bilayer formation by SM and HA.  For our conditions, inhibition is complete for 60 minute exposure to ~0.3 M xylitol.  Reversal is complete for 60 minute exposure to ~0.6 M xylitol.