A-028. High-Level Amoxicillin-Resistance Mediated by β-Lactamase in Clinical Isolate of Helicobacter pylori

L-L. Chang1, Y-S. Tseng1, C-H. Kuo2, D-C. Wu2;
1Kaohsiung Med. Univ., Kaohsiung, TAIWAN, 2Kaohsiung Med. Univ. Hosp., Kaohsiung, TAIWAN.

The isolation of amoxicillin- resistant Helicobacter pylori are increasing, which may cause serious problems in therapy. Six clinical H. pylori with amoxicillin resistance range from 0.5 to >256 mg/L were isolated in Kaohsiung Medical University Hospital, Taiwan. The mechanism of amoxicillin resistance of H. pylori was investigated. β-lactamase was detected by means of nitrocefin sticks and characterized by PCR for bla gene and further sequencing. Results indicated that β-lactamase activity was detected in one of the 6 isolates which provide high level (>256 mg/L) resistance to amoxicillin. The β-lactamase producing isolate carried β-lactamase belonged to blaTEM-1. PCR and DNA sequences analyses of the gene encoding penicillin binding protein 1A (PBP1A) of amoxicillin resistant isolates showed nucleotide mutations and amino acid substitution, resulting in decreased affinity of PBP1 for amoxicillin and penicillin. Low-level resistance was transferable to susceptible H. pylori by natural transformation using PCR fragments of pbp1 gene from clinical resistant isolates. In conclusion, these results demonstrate that high level amoxicillin resistance in clinical H. pylori is mediated by β-lactamase production, while pbp1 mutations contributed to low level amoxicillin resistance. Furthermore, decreased labeling of PBP1 in the amoxicillin resistant strain might be provided by diffusional barrier or possible antibiotic efflux mechanism.