Comparative Evaluation of Modified Agar Dilution and Standard Agar Dilution Methods for Antimicrobial Susceptibility...

The increasing challenge of antibiotic resistance in Helicobacter pylori highlights the urgent need for susceptibility-guided treatment strategies. However, current susceptibility testing methods often lack the combination of accuracy, efficiency, and practicality required for routine clinical use. This study aimed to evaluate the feasibility of a cost-effective modified agar dilution method for H. pylori antimicrobial susceptibility testing.

A total of 139 clinical H. pylori isolates were tested for amoxicillin, clarithromycin, levofloxacin, metronidazole, tetracycline, and furazolidone susceptibility, simultaneously using both modified and standard agar dilution methods. The correlation of minimum inhibitory concentrations (MICs) was analyzed by linear regression, and resistance classification agreement was assessed using the chi-square test.

MIC values obtained by 2 methods showed strong correlation (r > 0.78 for most antibiotics). High susceptibility agreement was observed for amoxicillin (97.1%), clarithromycin (97.8%), levofloxacin (98.3%), and furazolidone (98.6%). Using the modified agar dilution method, the false susceptible rates were 2.1% for amoxicillin, 1.5% for clarithromycin, and 0.9% for levofloxacin, while no false susceptible result were found for furazolidone. The false resistance rates were low for amoxicillin (0.7%), clarithromycin (0.7%), and levofloxacin (0.9%), with a minor false resistance rate of 0.9% for furazolidone. In contrast, lower agreement were observed for metronidazole (88.2%) and tetracycline (88.5%), with false susceptible rates of 5.9% and 7.2%, as well as false resistance rate of 5.9% and 4.3%, respectively.

The modified agar dilution method offers a potentially cost-effective and reliable alternative to the standard method for H. pylori antimicrobial susceptibility testing.