Does a dog's mouth have more bacteria than a toilet seat?

Actually, yes. Some truly nasty bacteria such as streptococcus (the bacteria that causes strep throat, among other things) is one of many that can be found on toilet seats. A dog's mouth on the other hand, can house colonies of bacteria. Now, just to put that in perspective, the human mouth also houses colonies of bacteria but a dog's mouth has been shown to house significantly more colonies than those of a human. For more information on both bacteria found on toilet seats and bacteria found in a dog's mouth, see the related links.