Molecular characterization of Helicobacter pylori resistance to rifamycins

Antibiotic resistance is a major contributing factor in treatment failure of Helicobacter pylori eradication. Rifabutin ( RB ) is a rescue treatment and rifampicin ( RP ) is used to screen RB resistance in vitro. The aim of this study was to evaluate the rate of rifamycins resistance and to determine the mutations in the rpo B gene conferring resistance to discuss the current break point. Methods Antimicrobial susceptibility to RP was first determined by E ‐test for 1015 H. pylori isolates. RP and RB MIC s were then determined by agar dilution method for strains with MIC of RP  > 1 mg/L, and the rpo B gene was sequenced. Results Overall, 54 of 1015 strains exhibited a RP MIC  > 1 mg/L by agar dilution method. Among these 54 strains, 10 had MIC s of RP  > 4 mg/L and RB  ≥ 1 mg/L. They all carried at least one mutation in the rpo B gene at codons 530, 538, 540, 525 in the RP resistance‐determining region ( RRDR ). Implication of the mutation L547F was confirmed by site‐directed mutagenesis experiment. In contrast, among the 44 H. pylori isolates with a MIC of RP comprised between 2 and 4 mg/L, only 4 of 44 (9%) strains exhibited a mutation in rpoB , but outside RRDR (codons 470, 499, 636, or 657). For 31 of 44 tested strains, the RB MIC s were ≤0.064 mg/L. Conclusion These results suggest that H. pylori isolates should be classified as resistant to RP for MIC s > 4 mg/L. We considered that the optimal cut off for RB was ≥0.125 mg/L. We report a new mutation responsible for rifamycins, resistance, L547F.