Selective concentrations for trimethoprim resistance in aquatic environments

Area of Science:

• Environmental microbiology
• Antimicrobial resistance
• Ecotoxicology

Background:

• Antibiotic resistance is a growing global health threat.
• Environmental exposure levels triggering antibiotic resistance are largely unknown.
• Trimethoprim is a widely used antibiotic with potential environmental impacts.

Purpose of the Study:

• To determine trimethoprim concentrations that select for antibiotic resistance in aquatic environments.
• To evaluate experimental approaches for identifying resistance selection thresholds.
• To propose a protective environmental exposure limit for trimethoprim.

Main Methods:

• Biofilm and planktonic co-culturing experiments with E. coli strains.
• Pairwise competition experiments with engineered E. coli strains.
• Analysis of trimethoprim resistance gene (dfr) selection dynamics.

Main Results:

• Trimethoprim selection for resistant E. coli was observed at 100 µg/L in biofilms and planktonic cultures.
• Fitness costs associated with trimethoprim resistance genes were reduced at 10 µg/L.
• A novel method for defining lowest effect concentrations was proposed, considering fitness advantages.

Conclusions:

• Environmental trimethoprim concentrations of 100 µg/L promote the selection of resistant E. coli.
• A proposed protective environmental exposure limit for trimethoprim in aquatic environments is 1 µg/L.
• The study highlights the importance of context-specific fitness costs in determining antibiotic resistance selection.