A change in PBP1 is involved in amoxicillin resistance of clinical isolates of Helicobacter pylori

Abstract

Reports on the isolation of amoxicillin-resistant Helicobacter pylori are increasing worldwide, which may cause serious problems in eradication therapy. To elucidate the mechanism of amoxicillin resistance of H. pylori, penicillin-binding proteins (PBPs) of amoxicillin-resistant strains isolated in Korea were analysed. Three PBPs (66, 63 and 60 kDa) were identified in both amoxicillin-resistant and -susceptible strains using biotinylated ampicillin, and the PBP profiles were very similar irrespective of the difference in amoxicillin susceptibility. We obtained clones with moderate resistance from an amoxicillin-susceptible strain, HPK5, by transformation with genomic DNA from an amoxicillin-resistant strain, HPA116. In a resistance-induced clone, HPO1, the affinity of PBP1 for amoxicillin was reduced. The pbp1 genes from HPA116, HPO1 and HPK5 were cloned and sequenced. The nucleotide sequences of pbp1 from HPA116 and HPO1 were almost identical, whereas that of HPK5 was quite different. Both the ORFs of HPA116 and HPO1 pbp1 have four substitutions and one insertion of amino acid residues compared with those of HPK5 and other sensitive strains. All the mutations, except one, are in the C-terminal half of the 659-amino-acid sequence containing the penicillin-binding modules. DNA fragments containing either full-length or a C-terminal half of pbp1 could transform HPK5 to have resistance, indicating that changes in the penicillin-binding core of PBP1 are involved in the amoxicillin resistance of H. pylori isolated in Korea.