Hello and welcome to HCM. Thank you for your query. Let me first shed light on the rules of treating an infection, more specifically a urinary tract infection. As you experienced a return or relapse of symptoms as soon as you got off your antibiotics the reasons for the same could be the following: -Inadequate dosage used to treat the infection (a stronger dosage should have been advised) -Inadequate duration of use (should have been continued for a longer duration as infection was clearly still prevalent) -Inappropriate antibiotic used (the antibiotic used was not good enough to treat the infection) In such cases, a urine culture should be conducted (which was done) and one of the most effective antibiotics should be selected to treat the condition, for an adequate amount of time with an appropriate dosage. Now coming to the presence of a colony of 50,000. If you are not on the antibiotic, this colony count is only going to multiply and increase which would most certainly result in an infection again. If the antibiotic used was effective, the urine culture should have not reported any colonies or infection-causing organisms at all. I hope all this is clear. It is quite evident what has to be done. Please re-visit your doctor or another one, and select an antibiotic which is susceptible to your infection, and re-initiate a course of at least 7-10 days, and discontinue only once a repeat urine test has reported the absence of an infection. I hope I have succeeded in providing the information you were looking for. Please feel free to write back to me for any further clarifications at: http://doctor.healthcaremagic.com/doctors/dr-shoaib-khan/64581 . I would gladly help you. Best wishes.