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Amoxycillin tolerance in Helicobacter pylori
M P Dore1, M S Osato, G Realdi
1VA Medical Center and Baylor College of Medicine, Houston, TX 77030, USA.
Abstract:
Resistance to amoxycillin in Helicobacter pylori has only recently been reported. To demonstrate the existence of resistance, and to test for the presence of tolerance, 17 amoxycillin-resistant strains of H. pylori, first isolated in Sardinia (Italy) and the USA, were studied. Four amoxycillin-sensitive strains were used as controls. Primary isolates of all test strains exhibited amoxycillin resistance; beta-lactamase activity was not detected. Amoxycillin resistance was lost after storage of strains at -80 degrees C but could be rescued by plating these strains on to amoxycillin gradient plates. MICs and MBCs from rescued isolates ranged from 0.5 to 32 mg/L and from 32 to > 1024 mg/L, respectively. MBC/MIC ratios > or = 32 are characteristic of antibiotic tolerance. The ratios of MBC/MIC of amoxycillin ranged from 32 to > 1024 for the test strains, indicating that these strains were tolerant to the antibiotic. Amoxycillin resistance does occur in H. pylori. Amoxycillin susceptibility testing of H. pylori isolates in patients who fail therapy should include determination of the MBC to detect tolerance.
Insights
Amoxycillin resistance in Helicobacter pylori is confirmed, with strains showing tolerance to the antibiotic. Testing minimum bactericidal concentration (MBC) is crucial for identifying tolerance in treatment failures.
Area of Science:
- Microbiology
- Antimicrobial Resistance
Background:
- Recent reports indicate emerging amoxycillin resistance in Helicobacter pylori.
- Understanding amoxycillin resistance and tolerance is critical for effective H. pylori eradication therapy.
Purpose of the Study:
- To demonstrate amoxycillin resistance in H. pylori.
- To investigate amoxycillin tolerance in resistant H. pylori strains.
Main Methods:
- Studied 17 amoxycillin-resistant and 4 amoxycillin-sensitive H. pylori strains.
- Assessed amoxycillin resistance and tolerance using Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) assays.
- Investigated the stability of amoxycillin resistance through strain storage and rescue experiments.
Main Results:
- Primary H. pylori isolates exhibited amoxycillin resistance without detectable beta-lactamase activity.
- Amoxycillin resistance was lost upon storage but could be restored.
- MBC/MIC ratios ranged from 32 to >1024, indicating significant amoxycillin tolerance.
Conclusions:
- Amoxycillin resistance is a validated phenomenon in H. pylori.
- H. pylori strains can exhibit tolerance to amoxycillin, characterized by high MBC/MIC ratios.
- Determination of MBC alongside MIC is recommended for H. pylori susceptibility testing in patients with treatment failure to detect tolerance.