I've not heard of Publish America, but I wouldn't worry overly about having put a book out through them. Before I started self-publishing, I hadn't heard of Author Solutions and all their aliases either. Even now that I do know about them, seeing their name on a book listing doesn't put me off buying the book, it just makes me feel slightly sad that the author probably got a bad deal
I wouldn't mention it. If you're asked about it, be honest - you made a mistake. It looked like a good deal, and you only found out the truth when it was too late.