I wouldn't bite back. (In fact, I had a biter and I didn't bite back. . .) I think it's a very unmerciful way to deal with a child. (And I say that not to offend other parents who have responded but bc I know J920 and I have similar beliefs--that comment will make sense to her.

)
Anyhow I agree with mcmama that sometimes their emotions just take over. While certainly you should speak about the biting, really, the teacher needs to give a consequence (like time out--just like mcmama suggested) because by the time you arrive the situation is over and long forgotten (esp. at that age.) I would work with the teacher to encourage an appropriate and immediate consequence for biting. If it happens in your presence. . .still take swift and immediate consequences. With Emily--my only biter--I just would pick her up, make my "I'm not happy face" and very quietly but calmly tell her that we don't bite. Then we'd sit in time out. . .or the stroller. She did bite a few more times after that but I think the twinness has something to do with it. (She would bite in response to something darling sister did--like pulling hair.)
Anyways, my point is that if you're consistent and deal with it swiftly--whatever manner you choose--you won't have a full blown biting issue.

The trick is to nip it in the bud!