Different penicillin-binding protein profiles in amoxicillin-resistant Helicobacter pylori

Background. The beta-lactam group of antibiotics kills bacteria by inhibiti ng the terminal stages of peptidoglycan metabolism. We have recently identi fied amoxicillin-resistant Helicobacter pylori, none of which expressed bet a-lactamase. Penicillin-binding proteins (PBPs) represent a group of target enzymes for the beta-lactam antibiotic family, and alterations in PBPs hav e been described in other penicillin-resistant bacteria. The amoxicillin-re sistant phenotype characteristically was lost after freezing but could be r estored by consecutive transfers into gradient plates. Materials and Methods. To determine whether amoxicillin resistance in H. py lori was related to alterations in any of the H. pylori PBPs, five H. pylor i strains resistant to amoxicillin and three amoxicillin-sensitive strains were tested. PBPs were extracted from bacteria grown to logarithmic phase, labeled in vivo with H-3-benzylpenicillin, and analyzed by sodium dodecyl s ulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and fluorography. Four main PBPs were separated from all amoxicillin-sensitive H. pylori strains. Results. Only three of the four main PBPs were found in the amoxicillin-res istant H. pylori strains. The differentially detectable PBP (PBP D) had an apparent molecular weight of 30 to 32 kD. Conclusion. These results suggest that PBP D might play a role in the amoxi cillin-resistant phenotype of H. pylori strains lacking beta-lactamase acti vity.