en Infectious diseases and public health Infectious diseases and public health Original article Original article <strong>Introduction: </strong>Antibiotic resistance, especially in Gram-negative uropathogens such as <em>Escherichia coli</em>, is the main barrier to treat urinary tract infection (UTI). In recent years, the dramatically increased resistance of <em>E. coli </em>to quinolones, a group of widely used antibiotics, has become a significant concern<strong>. Methods: </strong>In this descriptive cross-sectional study, we collected 261 <em>E. coli </em>isolates from the urine and stool samples of patients, referred to or hospitalized at Loghman hospital in Tehran, Iran, with either acute or recurrent UTI. The susceptibility testing for quinolones was performed by the disk diffusion method according to the recent protocols. <strong>Results: </strong>The frequency of resistant <em>E. coli</em> isolates was higher against nalidixic acid than ciprofloxacin and norfloxacin (67.8% <em>vs.</em> 48.7% and 44.1% respectively). When comparing acute and recurrent phases of UTI, in the urine samples, no significant difference was seen in the frequency of resistant isolates against nalidixic acid and norfloxacin, while this frequency against ciprofloxacin was significantly higher in recurrent UTI (68% <em>vs.</em> 48.2%). However, in the stool samples, the frequency of resistant isolates against nalidixic acid was higher in recurrent UTI (77.1% <em>vs.</em> 55.7%), while no significant difference was seen against ciprofloxacin and norfloxacin in these phases. <strong>Conclusion: </strong>Regarding the antibiotic type and frequency of the administration, the resistance pattern of <em>E. coli </em>to quinolones seems to differ in acute and recurrent phases of UTI. Urinary Tract Infection, Uropathogenic Escherichia coli, Antimicrobial Susceptibility, Quinolones, Acute Disease 120 126 http://jommid.pasteur.ac.ir/browse.php?a_code=A-10-71-2&slc_lang=en&sid=1 Hossein Norouzian norozihossin@yahoo.com 0000-0002-6496-543X No Molecular Biology Department, Pasteur Institute of Iran, Tehran, Iran Nader Shahrokhi nader.shahrokhi@gmail.com 0000000164510374 No Molecular Biology Department, Pasteur Institute of Iran, Tehran, Iran Shahram Sabeti sabeti_shahram@yahoo.com 0000-0002-8682-7070 No Pathology Ward, Loghman Hakim Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran Saeid Bouzari saeidbouzari@yahoo.com 0000000188353801 No Molecular Biology Department, Pasteur Institute of Iran, Tehran, Iran Mohammad Pooya mpooyamd@gmail.com 0000000329765915 Yes Molecular Biology Department, Pasteur Institute of Iran, Tehran, Iran