For many years in the United Kingdom, people with urinary tract infections have been treated with sulfonamide antibiotics. These antibiotics used to be very effective against the common pathogen of the urinary tract, E. coli, but in the late 1990s, increased resistance among the E. coli strains was documented. In the meantime, worrisome side effects of these drugs were documented as well, so doctors curtailed their use. Which of the following statements is TRUE about the evolution of resistance to the sulfonamides in the last decade?