Helicobacter pylori amoxicillin heteroresistance due to point mutations in PBP-1A in isogenic isolates.
OBJECTIVE
To investigate the Helicobacter pylori amoxicillin resistance rate, the occurrence of heteroresistance, and their related molecular mechanisms.


METHODS
Eighty-seven H. pylori-positive patients were included: 45/87 with single biopsy and 42/87 with multiple biopsies. MICs were determined, and sequencing analysis of pbp1A gene and the variable regions of seven hop porins was performed in resistant and susceptible isolates. Clonal relationships were determined by lspA-glmM-RFLP and by random amplification of polymorphic DNA-PCR. An isogenic amoxicillin-susceptible isolate was transformed with pbp1A PCR products from the resistant isolates.


RESULTS
Amoxicillin-resistant (MIC 2 mg/L) and amoxicillin-susceptible (MIC 0.06 mg/L) isolates, belonging to the same strain, were observed in different biopsies in one patient (inter-niche heteroresistance). Isolates from the remaining patients were amoxicillin-susceptible. Sequencing analysis of the pbp1A of two amoxicillin-resistant isolates and their susceptible partners revealed the same two point mutations: (i) in the third PBP motif of the resistant isolates (C1667G); (ii) a nonsense mutation at the 3' end of the gene. Replacement of pbp1A of a susceptible isolate by pbp1A from a resistant isolate increased the transformants MICs (2 mg/L). A similar MIC was observed when a pbp1A DNA fragment including both point mutations was transformed. Transfer of the smallest fragment (C1667G region only) yielded slightly lower MICs (0.5-1 mg/L). Identical hop gene sequences were observed in paired susceptible and resistant isolates.


CONCLUSIONS
A low resistance rate was observed. However, inter-niche heteroresistance could hinder amoxicillin resistance detection when only one biopsy is obtained. Alteration in PBP-1A seems to be enough to reach an MIC of 2 mg/L in our resistant isolates.
Matteo
Mario José
MJ
Departamento de Microbiología, Parasitología e Inmunología, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina.
Granados
Gabriela
G
Olmos
Martín
M
Wonaga
Andrés
A
Catalano
Mariana
M
D000595:Amino Acid Sequence; D000658:Amoxicillin / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D016480:Helicobacter pylori / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification*; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D008969:Molecular Sequence Data; D010403:Penicillin Resistance / Q000235:genetics*; D010458:Peptidyl Transferases / Q000235:genetics*; D017354:Point Mutation / Q000235:genetics*
D001426:Bacterial Proteins; D000658:Amoxicillin; C480727:PBP1a protein, Streptococcus pneumoniae; D010458:Peptidyl Transferases