Characterization of rifampicin-resistant clinical Helicobacter pylori isolates from Germany.

OBJECTIVES The aim of this study was to assess the rate of rifampicin resistance in Helicobacter pylori isolated from patients in Germany, to detect rifampicin resistance-associated mutations and to identify non-resistance-associated genetic variants in the rpoB gene. METHODS Susceptibility to rifampicin in a total of 1585 clinical isolates obtained between January 2003 and July 2006 was tested by disc diffusion and/or by the Etest method. The rpoB genes of a selection of both resistant (n=17) and susceptible (n=100) clinical isolates were sequenced in order to distinguish between resistance- and non-resistance-associated genetic alterations. In vitro mutagenesis experiments such as site-directed mutagenesis were carried out to demonstrate the pivotal role of rpoB mutations in rifampicin resistance. RESULTS From 1585 clinical isolates examined, 22 (1.4%) showed phenotypic resistance to rifampicin (MIC>4 mg/L). The majority of the resistant strains harboured point mutations in their rpoB genes at codons 530, 540 and 545 and showed cross-resistance to rifabutin. Four clinical isolates with moderate rifampicin resistance (8 mg/L) showed a rifabutin-susceptible phenotype and did not harbour any mutation in the sequenced rpoB fragments. Sequence analysis of 100 rifampicin-susceptible isolates revealed numerous novel silent mutations in the rpoB genes resulting in amino acid exchanges, but not in resistance. CONCLUSIONS Resistance to rifampicin/rifabutin in H. pylori strains isolated in Germany is still low and is associated with mutations in the rpoB gene. Further surveillance studies analysing the use of rifabutin in H. pylori eradication and its association with the occurrence of rifabutin-resistant strains are required.