It’s a fact that bacteria can grow on toothbrushes after they’ve been used, especially if wet toothbrushes are kept in closed, dark places. Wet toothbrush bristles should not be covered. They should air dry.
The Centers for Disease Control and Prevention (CDC) Recommends:
After brushing, it’s best to rinse toothbrushes with water to clean off remaining toothpaste and small pieces of food. Then the toothbrushes should be stored in an upright position to air dry. If several toothbrushes are stored in the same holder, make sure there is enough space between the toothbrushes so that they do not touch each other. Remember to label each toothbrush with the child’s name.
Do not soak toothbrushes in bleach water or other disinfecting solutions. And toothbrushes do not need to be placed in dishwashers, microwaves, or ultraviolet devices to disinfect them. These methods may damage the toothbrushes.