Nikki P
It depends on the type.
The real inexpensive ones tend to loose bristles so they may end up in your food.
Some of the synthetic ones can melt at higher temperatures so if you are basting on a hot piece of meat the bristles may start to melt. And do not leave the brush in the sauce if it is on a burner keeping warm.
If it is all you have for the moment use it but then I would toss it.
A paint brush has a metal ring that helps keeps the bristles attached it is possible that you will not be able to clean well enough under the metal band and that could allow bacteria to grow.
Next time you are out pick up a silicone basting brush they are inexpensive and can easily be washed and can be used at higher temperatures.
Marduk
Yes, but better than that is the new silicone basting brushes. The paint brushes tend to loose hairs and you don't want to eat that.
οικος
I do. Obviously, they never get used for anything else.
RockIt
Use the ones made of horse hair for a more earthy musky flavor
Phade3
Or should you use a pastry brush!