Phenotypic and genotypic correlation as expressed in Helicobacter pylori resistance to clarithromycin and fluoroquinolones

Helicobacter pylori susceptibility to clarithromycin and fluoroquinolone can be determined through Etest or molecular assays. We examined the correlation between phenotypic susceptibility (MIC results) and genotypic susceptibility in H. pylori strains isolated from gastric biopsies. Out of 85 duplicate biopsies obtained from patients from northern Israel who underwent endoscopy, 70 were positive for H. pylori using the CUTest (urease test). These biopsies were cultured for H. pylori and Etest breakpoints were determined for levofloxacin and clarithromycin. H. pylori detection, characterization of wild type (WT) or mutant alleles, and antibiotic resistance were determined molecularly using GenoType HelicoDR kit. Phenotypic and genotype results were compared. The molecular method had higher sensitivity for detection of H. pylori than culture (94.3% vs. 77.1%). Resistance to clarithromycin was higher than to levofloxacin by both methods. Levofloxacin resistance was found in 21.2 and 0% using genotypic and phenotypic methods, respectively. Clarithromycin resistance was found in 66.7 and 62.9% by genotypic and phenotypic methods, respectively. Some samples were found susceptible by Etest and resistant by GenoType HelicoDR (13/53 samples) and some vice versa (10/53 samples). GenoType HelicoDR kit has high sensitivity rate for H. pylori detection. It has the ability to detect many mutations and can help to determine initial antibiotic treatment at the beginning of therapy. However, there were a few cases where there was a phenotype-genotype mismatch result that could derive from possible causes. For example, a resistance mechanism that is not tested in the kit.