Not sure why you're asking, as the same system should apply as you've used to highlight the words "italics" and "bold" in your question - it works happily for me.

Just in case there's some sort of wibble going on, try finding someone else's comment which has italics or bold text, open it up as a quote and check how they've done it. (As an admin, you could post the quote to see it sitting on the page, and then quickly delete it before anyone spots it ....)