What I found is that most acne cases requiring antibiotic therapy, the acne is of gram negative origin and a high percentage are enteric in origin. E coli and klebsiella especially. These two have the plasmids to confer lateral transfer of resistance genes to other bacteria's, including each other. With subsequent exposure to changing and long term use of antibiotics, this is how the breeding of superbugs occur.
Someone mentioned E coli in their bloodstream. If an injury whether slight or not were to occur, the resistant bacteria can get there. If in the GI tract and leaky gut, or the medical term called bacterial translocation occur, then the bacteria can go into the mesenteric lymph, to the capillaries, to the portal vein, and become systemic as well. The urinary tract, is usually confined, unless there is reflux into the kidneys. You will find with the enterics, the liver and kidneys are both highly correlated with cystic masses of these bacteria.
The epithelial tissues have many tiny blood vessels in which the bacteria can access when they attach to epithelial cells. Kidney, skin, mucous membranes, intestinal walls, etc. It is what makes these areas so tough to treat with antibiotics, as the vessels are small and exposure must be high enough to the antibiotic to be bacteriocidal, but with tiny vasculature, is next to impossible due to these tiny vessels. A good example would be chronic sinus infections.
It is difficult to get at the gram negatives that produce the polysaccharide capsules and copious thick biofilm. E coli produces certain types of pili for attachment, and they are motile as well. You could stay on antibiotics for years, and still not get them all. All it would take is one tiny niche to start the process all over again, and is why many find themselves going on and off antibiotics for years. Since the same infection comes back, they change the antibiotic because they think it isn't working, and the process just keeps going.
Brief, but I hope this helps.
So perhaps its not the antibiotics per se, albeit a contributor...
Lauriel