This study aims to provide an updated analysis of the resistance patterns of H. pylori in the Nanjing region, with a focus on characterizing the current status of phenotypic and genotypic resistance to these six antimicrobial agents. The findings are expected to offer a scientific basis for the rapid diagnosis and personalized treatment of H. pylori infection.

Since its discovery, Helicobacter pylori has become one of the most prevalent microorganisms globally, with an estimated worldwide infection rate of 44.3%. The burden is notably higher in developing countries (50.8%) compared to developed nations (34.7%). Beyond its established role in chronic active gastritis and peptic ulcer disease, H. pylori is now recognized as a primary risk factor for gastric cancer and mucosa-associated lymphoid tissue lymphoma. This is particularly significant in China, where gastric cancer ranks as a leading malignancy. Consequently, H. pylori infection constitutes a major public health challenge. The escalating threat of antimicrobial resistance further underscores the urgent need to improve eradication strategies. The Maastricht VI/Florence Consensus Report recommends routine antibiotic susceptibility testing to guide the selection of precise treatment regimens prior to H. pylori eradication. Currently, only a limited number of antibiotics-including amoxicillin, clarithromycin, metronidazole, levofloxacin, tetracycline, and furazolidone-remain effective. However, their widespread use has accelerated the emergence of resistance. China, with its high burden of infection, faces a particularly complex landscape of antibiotic resistance.

Regimens containing clarithromycin and levofloxacin are effective strategies for both first-line and salvage therapy. A meta-analysis highlighted that a 14-day levofloxacin-based sequential therapy is one of the most effective regimens worldwide. However, levofloxacin susceptibility shows significant geographic variation, with primary resistance rates in China having risen considerably in recent years. Faced with continuously rising resistance rates to these antibiotics, it is crucial to delineate the dynamic trends in phenotypic resistance and the characteristics of associated gene mutations.

The increasingly severe resistance situation necessitates the establishment of continuous surveillance and the accumulation of local data. Our center has previously published cross-sectional studies analyzing H. pylori resistance in Nanjing. However, data on resistance trends for other antimicrobials and their potential mechanisms remain limited. Therefore, this study systematically reviews the evolution of phenotypic and genotypic resistance rates of H. pylori to six commonly used antibiotics over the past seven years.

Beyond phenotypic analysis, this study investigates the genotypic resistance mechanisms for these antibiotics. Resistance in H. pylori primarily results from mutations in genes encoding drug targets, leading to reduced efficacy. Evidence indicates that susceptibility can be effectively assessed by detecting specific mutations: in the 23S rRNA gene (e.g., A2143G, A2142G) for clarithromycin resistance; the gyrA gene for quinolone resistance; penicillin-binding protein genes for amoxicillin resistance; the 16S rRNA gene for tetracycline resistance; and the rdxA and frxA genes for metronidazole resistance.

Objective and Methods This retrospective, single-center, cross-sectional epidemiological study aims to provide an updated analysis of H. pylori resistance patterns in the Nanjing region. It focuses on characterizing the current status of phenotypic and genotypic resistance to amoxicillin, clarithromycin, metronidazole, levofloxacin, tetracycline, and furazolidone. The findings are intended to provide a scientific basis for the rapid diagnosis and personalized treatment of H. pylori infection. The study involves a retrospective review of medical records from the electronic medical record system and laboratory information system of Nanjing First Hospital. It will identify all outpatients who underwent H. pylori culture and genetic testing at the gastroenterology clinic between January 1, 2018, and December 31, 2025.

Study Procedures Cohort Identification: An initial cohort of approximately 7,228 records of H. pylori testing will be retrieved from the hospital information system for the specified period.

Case Screening: Two researchers will independently screen the cases according to pre-defined inclusion and exclusion criteria. Discrepancies will be resolved by a third senior researcher.

Data Extraction: Using a pre-designed electronic Case Report Form, data will be extracted, including patient demographics, endoscopic diagnosis, H. pylori culture results, phenotypic antimicrobial susceptibility testing (AST) results for the six antibiotics (using agar dilution or E-test, interpreted per CLSI/EUCAST standards), and mutation detection results for resistance-related genes (e.g., 23S rRNA, gyrA, PBP1A, 16S rRNA, rdxA, frxA via multiplex PCR or sequencing).

Data Analysis: Statistical analysis will be performed using SPSS. Descriptive statistics will be used to calculate resistance rates. The Kappa consistency test will be used to evaluate the agreement between antibiotic resistance phenotypes and genotypes.

Ethics and Data Management This study will be conducted in accordance with the Declaration of Helsinki. The protocol has been approved by the ethics committee. As this is a retrospective data-based study analyzing existing laboratory results from gastric mucosal biopsy samples stored in the hospital database, no new biological samples were collected. All patient personal information will be replaced with a unique study ID to ensure complete data anonymization. The requirement for individual informed consent may be waived by the ethics committee given the retrospective nature of the study.

Inclusion Criteria:

1. Patients who visited the Gastroenterology Department of Nanjing First Hospital and underwent gastroscopy with H. pylori culture and genetic testing between 2018 and 2024.
2. Positive for H. pylori by at least one diagnostic method (13C-urea breath test, rapid urease test, or histopathology).
3. Provision of general written informed consent for the use of gastroscopy and specimen data in research.
4. Availability of complete medical records and laboratory test results.

Exclusion Criteria:

1. Withdrawal of informed consent; use of antibiotics, proton pump inhibitors, H2-receptor antagonists, or bismuth agents within four weeks prior to gastroscopy.
2. History of gastric surgery.
3. Incomplete medical records or test results precluding evaluation.
4. Other factors deemed by the investigator to render the participant unsuitable for inclusion.

Patient records were retrieved from the electronic medical record system and laboratory information system of Nanjing First Hospital. The search identified all outpatients who underwent H. pylori culture and genetic testing at the gastroenterology clinic between January 1, 2018, and December 31, 2024, according to pre-defined inclusion and exclusion criteria.