Antibiotic resistance is specific to the antibiotic as well as the strain of infectious organism. Broad spectrum antibiotics are the doctors' big guns, superantibiotics for treating superbugs resistant to, say, penicillin, resistance to which is, as you've
said, well-established. But if the superbugs become resistant to the superantibiotics, humans will be superduperbuggered.
A fuckload of azithromycin might indiscriminately annihilate chlamydia and gonorrhea as they're both gram-negative, but if a dude has a less specific urinary tract infection like staphylococcus, then he should be taking something that is more effective against