Trimethoprim resistance in enterococci: microbiological and biochemical aspects

Area of Science:

• Microbiology
• Antimicrobial Resistance
• Molecular Biology

Background:

• Enterococci exhibit resistance to multiple antibiotics, including trimethoprim.
• Understanding the genetic basis of trimethoprim resistance is crucial for effective treatment strategies.

Purpose of the Study:

• To investigate the synergistic effects of sulphonamide and trimethoprim against enterococci.
• To elucidate the genetic mechanisms underlying trimethoprim resistance in enterococci.

Main Methods:

• Testing synergistic activity of sulphonamide and trimethoprim in various ratios against trimethoprim-sensitive and -resistant enterococci.
• Plasmid analysis and curing experiments to assess the role of plasmids in antibiotic resistance.
• Conjugation experiments to evaluate the transferability of trimethoprim resistance.
• Enzyme inhibition assays to compare dihydrofolate reductase activity in sensitive and resistant strains.

Main Results:

• Synergistic activity was observed between sulphonamide and trimethoprim against both sensitive and resistant enterococcal strains.
• Trimethoprim resistance in some strains was associated with a 35-45 Md plasmid, which, upon elimination, also conferred loss of kanamycin resistance.
• Trimethoprim resistance was transferable via plasmids from highly resistant strains but not from low-grade resistant strains.
• Dihydrofolate reductase from resistant strains showed significantly reduced susceptibility to trimethoprim inhibition compared to the sensitive strains' enzyme.

Conclusions:

• Trimethoprim resistance in enterococci can be plasmid-encoded, potentially involving transposons.
• Plasmid-mediated trimethoprim resistance may be linked to resistance to other antibiotics like kanamycin.
• The reduced susceptibility of dihydrofolate reductase to trimethoprim is a key factor in trimethoprim resistance.