FYI there are two ticket machine types in Italy, the older type which has a flat front and IIRC a non-touch screen and new types with touch screens, and plastic fronts. The older ones do not take US credit cards, the ones do. I'm not sure of the prevelence of new ones, but they do exist at FCO, Roma-Termini (not all machines are new) and plenty of other stations. I did not have any problems using my credit card each of the four times I had to buy tickets.