Re-assessment of the disk diffusion technique for routine antimicrobial susceptibility testing for Helicobacter pylori

Background The aim of this study was to assess the disk diffusion technique against E-test as a routine antibiotic susceptibility testing method for Helicobacter pylori. Materials and methods Susceptibilities of 301 H pylori clinical isolates were simultaneously profiled by E-test and disk diffusion method for levofloxacin (5-mu g disk), clarithromycin (15-mu g disk), metronidazole (5-mu g disk), amoxicillin (10-mu g disk), and tetracycline (30-mu g disk). Furazolidone susceptibility was evaluated using a 100-mu g disk only. The correlation between MICs by E-test and inhibition zone diameters by disk diffusion was assessed by linear regression analysis. Results Correlation between inhibition zone diameters and MICs was found for levofloxacin (r = -.932), clarithromycin (r = -.894), and to a minor extent metronidazole (r = -.820). Using the linear regression analysis, the inhibition zone diameter breakpoints were calculated to be 29 mm for levofloxacin, 41 mm for clarithromycin, and 15 mm for metronidazole corresponding to the EUCAST-recommended MIC breakpoints. The susceptibility agreement between E-test and disk diffusion for levofloxacin, clarithromycin, and metronidazole was 98.6%, 96.0%, and 96.7%, respectively. The inhibition zone diameters recorded for the amoxicillin, tetracycline, and furazolidone were large (approximately 60 mm in mean), and a poor correlation was found between inhibition zone diameters and MICs for amoxicillin (r = -.594) and tetracycline (r = -.490). Conclusions The disk diffusion can be used as a routine H pylori susceptibility testing method for levofloxacin, clarithromycin, and metronidazole in clinical practice under the described technical conditions. The use of disk diffusion for amoxicillin, tetracycline, and furazolidone susceptibility testing needs to be further studied.