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Background Amoxicillin-resistant  Helicobacter pylori  ( H. pylori ) strains seem to have increased over time in Vietnam. This threatens the effectiveness of  H. pylori  eradication therapies with this antibiotic. This study aimed to investigate the prevalence of primary resistance of  H. pylori  to amoxicillin and to assess its association with  pbp1A  point mutations in Vietnamese patients. Materials and methods Naive patients who presented with dyspepsia undergoing upper gastrointestinal endoscopy were recruited. Rapid urease tests and PCR assays were used to diagnose  H. pylori  infection. Amoxicillin susceptibility was examined by E-tests. Molecular detection of the mutant  pbp1A  gene conferring amoxicillin resistance was carried out by real-time PCR followed by direct sequencing of the PCR products. Phylogenetic analyses were performed using the Tamura-Nei genetic distance model and the neighbor-joining tree building method. Results There were 308 patients (46.1% men and 53.9% women,  p  = 0.190) with  H. pylori  infection. The mean age of the patients was 40.5 ± 11.4 years, ranging from 18 to 74 years old. The E-test was used to determine the susceptibility to amoxicillin (minimum inhibitory concentration (MIC) ≤ 0.125 μg/ml) in 101 isolates, among which the rate of primarily resistant strains to amoxicillin was 25.7%. Then, 270 sequences of  pbp1A  gene fragments were analysed. There were 77 amino acid substitution positions investigated, spanning amino acids 310–596, with the proportion varying from 0.4 to 100%. Seven amino acid changes were significantly different between amoxicillin-sensitive (Amox S ) and amoxicillin-resistant (Amox R ) samples, including Phe 366  to Leu ( p  &lt;  0.001), Ser 414  to Arg ( p  &lt;  0.001), Glu/Asn 464–465  ( p  = 0.009), Val 469  to Met ( p  = 0.021), Phe 473  to Val ( p  &lt;  0.001), Asp 479  to Glu ( p  = 0.044), and Ser/Ala/Gly 595–596  ( p  = 0.001). Phylogenetic analyses suggested that other molecular mechanisms might contribute to amoxicillin resistance in  H. pylori  in addition to the alterations in PBP1A. Conclusions We reported the emergence of amoxicillin-resistant  Helicobacter pylori  strains in Vietnam and new mutations statistically associated with this antimicrobial resistance. Additional studies are necessary to identify the mechanisms contributing to this resistance in Vietnam.

Emergence of amoxicillin resistance and identification of novel mutations of the pbp1A gene in Helicobacter pylori in Vietnam