Actually, I wasn't clear before. The infections are worse because of mutations that create new bacteria. For instance, MRSA isn't known to have existed before the early 1960s and didn't become widespread until the late 1990s.
But you are correct, they aren't actually stronger, they are just more resistant to what we have available.
Probably another nit. But MRSA is not a "new bacteria." It's simply a new strain of
Staphylococcus aureus, which has been around a very long time.
Now that it's resistant, it can go back to doing to people what Staph infections did before penicillin. Which isn't pretty.