Increase in antibiotic resistant Helicobacter pylori in a University Hospital in Japan Chihiro Kageyama,1 Mayu Sato,1 Hiroyuki Sakae,2 Yuka Obayashi,2 Yoshiro Kawahara,2 Takehiko Mima,3 Osamu Matsushita,3 Kenji Yokota,1 Motowo Mizuno,4 Hiroyuki Okada2 1Graduate School of Health Science, Medical Technology, Okayama University, Okayama 700-8558, Japan; 2Gastroenterology and Hepatology, Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-8558, Japan; 3Bacteriology, Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-8558, Japan; 4Department of Gastroenterology and Hepatology, Kurashiki Central Hospital, 710-8602, Japan Background: Eradication effectively prevents Helicobacter pylori-associated diseases; however, H. pylori antibiotic resistance has increased throughout Japan and worldwide. This study aimed to assess rates of resistance to antibiotics; amoxicillin, clarithromycin and metronidazole in a University Hospital in Japan. Materials and methods: H. pylori (208 strains) were isolated from patients at the Okayama University Hospital in Japan. The minimum inhibitory concentrations (MIC) were determined using the mean values of the E-test to determine the antimicrobial susceptibilities of the strains. Sequencing and gene analysis were performed to analyze resistance genes to clarithromycin and amoxicillin. Results: Rates of amoxicillin, clarithromycin, and metronidazole resistance were 13%, 48%, and 49%, respectively. Genetic analysis indicated that the A2143G point mutation in 23S rDNA is closely associated with the MIC of clarithromycin. The MIC in amoxicillin-resistant strains increased with an increase in the number of PBP1A amino acids mutations. Conclusion: Genetic analysis for resistant strains is not clinically effective in cases of amoxicillin resistance. Numerous bacteria with already high antibiotic resistance rates have been isolated in large hospitals such as a University Hospital. For effective eradication therapy, MIC measurement should be considered via several methods. Keywords: Helicobacter pylori, resistance, clarithromycin, amoxicillin, University Hospital, genotype