en ميکروب شناسي Microbiology Research Article Research Article <div style="text-align: justify;"><span style="font-family:Times New Roman;"><span style="font-size:12px;"><b>Background:</b> Antibiotic resistance in <i>Helicobacter pylori</i> infections can lead to treatment failure. This study aims to evaluate the antibiotic resistance to metronidazole, clarithromycin, and fluoroquinolone in <i>H. pylori</i> strains isolated from gastric biopsy specimens.<br> <b>Methods:</b> This study was conducted between 2016 and 2017 on 80 biopsy specimens obtained from Golestan province. Resistance to metronidazole (<i>rdxA</i>) and fluoroquinolones (<i>gyrA</i>) was determined using PCR. Mutations in the loci of the 23S rRNA gene associated with clarithromycin resistance were analyzed using PCR-RFLP with the BsaI and BbsI enzymes.<br> <b>Results:</b> In this study, 25% of <i>H. pylori</i> strains showed resistance to clarithromycin. Mutations in the A2143G locus (65%) and the A2142G locus (35%) were detected in these strains. Resistance to fluoroquinolones (27.5%) was observed, with the most common mutations being at the 91 amino acid position of aspartate (63.63%) and the 87 amino acid position of asparagine (36.36%). Resistance to metronidazole was not observed in any of the strains of this study, and concomitant resistance to clarithromycin and fluoroquinolones was observed in 13.75% of <i>H. pylori</i> strains.<br> <b>Conclusion</b>: According to our study, in Iran, the resistance of <i>H. pylori</i> to clarithromycin is increasing, which may lead to treatment failure. The mechanism of clarithromycin resistance is related to mutations in the A2143G and A2142G positions, and a mutation in the gyrA gene causes resistance to fluoroquinolones, which often occurs in the 91 amino acid position.</span></span><br> &nbsp;</div> Helicobacter pylori,Drug resistance, Microbial, Polymerase Chain Reaction, Polymorphism, Restriction Fragment Length 41 45 http://mlj.goums.ac.ir/browse.php?a_code=A-10-1444-1&slc_lang=en&sid=1 Azam Shareh Azamshareh780254198@gmail.com 100319475328460030908 100319475328460030908 No Laboratory Sciences Research Center, Golestan University of Medical Sciences, Gorgan, Iran Behnoush Khasheii bh_kh@yahoo.com 100319475328460030909 100319475328460030909 No Department of Pathobiology, Faculty of Veterinary Sciences, Bu-Ali Sina University, Hamedan, Iran Tayebeh Faraji tayebefaraji@gmail.com 100319475328460030910 100319475328460030910 No Department of Microbiology, Faculty of Medical Sciences, Golestan University of Medical Sciences, Gorgan, Iran Masoud Khoshnia khoshniamd@gmail.com 100319475328460030911 100319475328460030911 No Golestan Research Center of Gastroenterology and Hepatology, Golestan University of Medical Sciences, Gorgan, Iran Shaghayegh Anvari shaghayeghanvari@yahoo.com 100319475328460030912 100319475328460030912 No Laboratory Sciences Research Center, Golestan University of Medical Sciences, Gorgan, Iran Ailar Jamalli jamali@goums.ac.ir 100319475328460030913 100319475328460030913 Yes Laboratory Sciences Research Center, Golestan University of Medical Sciences, Gorgan, Iran