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

BACKGROUND

The beta-lactam group of antibiotics kills bacteria by inhibiting the terminal stages of peptidoglycan metabolism. We have recently identified amoxicillin-resistant Helicobacter pylori, none of which expressed beta-lactamase. Penicillin-binding proteins (PBPs) represent a group of target enzymes for the beta-lactam antibiotic family, and alterations in PBPs have been described in other penicillin-resistant bacteria. The amoxicillin-resistant phenotype characteristically was lost after freezing but could be restored by consecutive transfers into gradient plates.

MATERIALS AND METHODS

To determine whether amoxicillin resistance in H. pylori was related to alterations in any of the H. pylori PBPs, five H. pylori strains resistant to amoxicillin and three amoxicillin-sensitive strains were tested. PBPs were extracted from bacteria grown to logarithmic phase, labeled in vivo with 3H-benzylpenicillin, and analyzed by sodium dodecyl sulfate-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-resistant 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 amoxicillin-resistant phenotype of H. pylori strains lacking beta-lactamase activity.