Arch Clin Infect Dis. 2019 February; 14(1):e55015. Published online 2019 February 26. doi: 10.5812/archcid.55015. Research Article Antibiotic Resistance Among Helicobacter pylori Strains Isolated from Patients with Histopathological Changes of the Gastric Tissue Towards Metronidazole, Clarithromycin, and Ciprofloxacin Saeed Bayati 1 , Nour Amirmozafari 1, * , Masoud Alebouyeh 2, 3, ** , Nastaran Farzi 2 , Nasser Ebrahimi Daryani 4 and Mohammad Reza Zali 5 1 Department of Microbiology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran 2 Foodborne and Waterborne Diseases Research Center, Research Institute for Gastroenterology and Liver Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran 3 Pediatric Infections Research Center (PIRC), Research Institute for Children Health, Shahid Beheshti University of Medical Sciences, Tehran, Iran 4 Department of Gastroenterology and Hepatology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran 5 Gastroenterology and Liver Diseases Research Center, Research Institute for Gastroenterology and Liver Diseases, Shahid Beheshti University of Medical Science, Tehran, Iran * Corresponding author: Professor, Department of Microbiology, School of Medicine, Iran University of Medical Sciences, Tehran,Iran. Email: amirmozafari@iums.ac.ir ** Corresponding author: Assistant Professor, Foodborne and Waterborne Diseases Research Center, Research Institute for Gastroenterology and Liver Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Tel: +982122432518, Fax: +982122432518, Email: masoud.alebouyeh@gmail.com Received 2017 June 14; Revised 2018 October 09; Accepted 2018 October 28. Abstract Background: The extent of antibiotic resistance among Helicobacter pylori strains influences current clinical therapeutic regimens in each region. Objectives: This cross-sectional study aimed to determine the resistance property and minimum inhibitory concentration (MIC50-90) of Helicobacter pylori strains toward metronidazole, clarithromycin, and ciprofloxacin in patients with distinct gastric histopathological changes in Tehran, Iran. Methods: This study was conducted on 170 patients suffering from gastric complications in three hospitals in Tehran from October 2014 until March 2015. Two separate biopsy samples were collected from each patient and used for pathological and microbiolog- ical examinations. Antimicrobial susceptibility tests were performed by agar dilution method according to the CLSI guidelines. The MIC values and susceptibility to varying concentrations of metronidazole (4 to 64 μg/mL), ciprofloxacin (0.5 to 16 μg/mL), and clarithromycin (0.25 to 16 μg/mL) were determined based on EUCAST recommendations. Results: Our results indicated the infection with H. pylori in a frequency of 32% (55/170) among the study patients (female, 51% and male, 49%). Endoscopic findings indicated that 42% of the patients suffered from peptic ulcers, 33% from duodenal ulcers, and 25% with a non-ulcer disease. Pathological findings indicated 58% of the patients had chronic gastritis, 33% had active chronic gastritis, and 9% suffered from intestinal metaplasia. In terms of antibiotic susceptibility, nearly 76.3%, 49%, and 45.5% of the strains were resistant to metronidazole, clarithromycin, and ciprofloxacin, respectively. The MIC values at which the growth of 50% and 90% of the strains was inhibited (MIC50-90) were 32 - 64 μg/mL for metronidazole, 0.5 - 16 μg/mL for clarithromycin, and 2 - 16 μg/mL for ciprofloxacin. Conclusions: The overall resistance levels were relatively high among the study patients. Accordingly, the administration of other anti-Helicobacter drugs, as well as more appropriate therapeutic regimens based on laboratory results, is recommended in patients with a history of treatment failure. Keywords: Helicobacter pylori, Antimicrobial Resistance, Histopathological Changes, Minimum Inhibitory Concentration 1. Background Helicobacter pylori is a microaerophilic Gram-negative bacterium that resides within gastric mucosa. It is respon- sible for a variety of gastric and extra-gastrointestinal dis- eases (1, 2). Although in some developing countries, its prevalence is as high as 80% - 90%, lower rates of infection are reported from developed countries (3). Many different therapeutic regimens are used in order to eradicate H. py- lori infection and prevent the development of drug resis- tance. The standard triple therapy includes amoxicillin in combination with either metronidazole or clarithromycin and a proton pump inhibitor (4). Resistance to antimi- crobial drugs is a major cause of treatment failure and Copyright © 2019, Archives of Clinical Infectious Diseases. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (http://creativecommons.org/licenses/by-nc/4.0/) which permits copy and redistribute the material just in noncommercial usages, provided the original work is properly cited.