Introduction: Understanding drug resistance is important in drug selection for Helicobacter pylori  (H. pylori ) eradication, and drug resistance data are lacking in Beijing.
Purpose: This cross-sectional study aimed to isolate H. pylori  from patients with gastroduodenal diseases and to analyze drug resistance to clarithromycin (CLA) and levofloxacin (LEV), which are used frequently in China.
Patients and Methods: One hundred and seventy-six patients with gastroduodenal diseases undergoing gastroduodenoscopy were selected by convenient sampling. Gastric mucosa samples were cultured and sub-cultured using a new medium broth. Active H. pylori  strains were confirmed by microscopy observation as Gram-negative curved bacilli with positive test results for urease, oxidase, and catalase, and H. pylori 16S rRNA  amplification by polymerase chain reaction (PCR). CLA and LEV resistance was identified by minimum inhibitory concentration (MIC) tests and sequencing of 23S rRNA, gyrA , and gyrB  genes.
Results: From the 176 clinical samples, 112 (112/176, 63.6%) were confirmed with H. pylori  infection and 65 (65/176, 36.9%) active H. pylori  strains were obtained and further confirmed by MIC assay. Overall, the rates of CLA-resistant and LEV-resistant mutations in the 112 samples were 50.9% and 33.0%, respectively. Mutation related to CLA resistance was A2143G in the 23S rRNA  gene and mutations associated with LEV resistance were N87K, D91G, and D91Y in the gyrA  gene. Of 112 samples, 22 (19.6%) presented dual resistance to CLA and LEV. Resistance of the H. pylori  strains to CLA (r =0.846, P < 0.001) and LEV (r =0.936, P < 0.001) had a strong correlation in phenotypic and genotypic level.
Conclusion: The results indicated that resistance of CLA and LEV is severe among patients with gastroduodenitis. A good consistency could be found as to drug resistance between genotypic or phenotypic assay, suggested extending the detection of H. pylori  drug resistance from the MIC method to a genotypic assay.
Keywords: Helicobacter pylori , clarithromycin, levofloxacin, antibiotic resistance