Analysis Of Fitness Costs Associated With Metronidazole And Amoxicillin Resistance Inhelicobacter Pylori

Background Increasing rates of antibiotic resistance are a major concern for all pathogens, includingH. pylori. However, increased resistance often coincides with a decrease in relative fitness of the pathogen in the absence of the antibiotic, raising the possibility that increased resistance can be mitigated for some antibiotics by improved antibiotic husbandry. Therefore, a greater understanding of which types of antibiotic resistance create fitness defects inH. pylorimay aid rational treatment strategies. Materials and Methods While a wealth ofH. pyloriliterature reports mutations that correlate with increased resistance, few studies demonstrate causation for these same mutations. Herein, we examined fitness costs associated with metronidazole and amoxicillin resistance. Isogenic strains bearing literature reported point mutations in therdxAandpbp1genes were engineered and tested in in vitro competition assays to assess relative fitness. Results None of the metronidazole resistance mutations resulted in a fitness cost under the tested conditions. In contrast, amoxicillin-resistant mutant strains demonstrated a defect in competition by 24 hours. This change in fitness was further enhanced by moderate osmotic stress. However, under extreme osmotic stress, the amoxicillin-resistant N562Y PBP1 mutant strain showed enhanced fitness, suggesting that there are somepbp1mutations that can give a conditional fitness advantage. Conclusions Our results demonstrate the role of specific point mutations inrdxAandpbp1in antibiotic resistance and suggest that amoxicillin-resistant strains ofH. pylorishow environmentally dictated changes in fitness. These later finding may be responsible for the relatively low rates of amoxicillin resistance seen in the United States.