Your teammates can do as much damage as they want.
I think this achievment is easiest with biological, they have a great DOT build and they have crystalize, so you can take a fireclaw out of the picture while you kill the other enemies
I tried to finish it with bio but i find it extremely boring. After i've finished it with both hydro and psycho this seems to be logical. Now i am on a heroic - hydro run, that's why i asked. Anyway, thanks everyone.