Comparative evaluation of the E-test and the broth microdilution method in antimicrobial susceptibility testing of Helicobacter pylori

Abstract

The increasing prevalence of antimicrobial-resistant Helicobacter pylori has become a major concern for eradication therapy. However, standardized methods for antimicrobial susceptibility testing (AST) of H. pylori have not been fully established in Japan, and different methodologies are currently used across laboratories. Standardization of AST is therefore essential for accurate evaluation of eradication efficacy. In this study, we compared AST results obtained using different testing methods and pre-culture conditions.

Four H. pylori strains (JSHR3, JSHR6, JSHR31, and ATCC 43504) were subjected to AST using the E-test and broth microdilution methods. Pre-culture conditions included liquid culture and agar plate culture. Four experimental combinations were evaluated, and the obtained minimum inhibitory concentrations (MICs) were compared with reference values reported by the Japanese Society for Helicobacter Research.

For clarithromycin, susceptibility results were consistent across all experimental conditions for all strains tested. In contrast, discrepancies were observed for metronidazole only in the broth microdilution method using agar-grown bacteria. For amoxicillin, discordant results were observed for the non-susceptible strain JSHR31 specifically in the broth microdilution method using agar-grown bacteria. In this case, results from the other three conditions diverged, whereas only this condition was concordant with the reference values.

These findings suggest that differences in testing methods and pre-culture conditions may influence AST results for H. pylori. Standardization of AST procedures, along with the establishment of appropriate quality control systems, is warranted to ensure reliable antimicrobial susceptibility assessment.