Hopefully when you saw your doctor about your UTI, they asked for a urine sample
and did what Twopack mentioned, a culture
and sensitivity. What that means is that they send it to a lab, where the urine is put on special plates that enhance the growth of organisms. It takes at least 16-18 hours for the organism to grow, and if there is something there, it takes another 8-10 or so to get an antibiotic sensitivity.