Biosynthesis of modified peptidoglycan precursors by vancomycin-resistant Enterococcus faecium

Area of Science:

• Microbiology
• Biochemistry
• Molecular Biology

Background:

• Vancomycin resistance in Enterococcus faecium is a significant clinical challenge.
• Enterococcus faecium with the vanA phenotype exhibits resistance to vancomycin.
• Bacitracin interferes with bacterial cell wall synthesis by inhibiting lipid carrier recycling.

Purpose of the Study:

• To investigate the effect of bacitracin on peptidoglycan precursor accumulation in vancomycin-resistant Enterococcus faecium (VRE).
• To characterize the structure of the accumulated peptidoglycan precursors.
• To determine if these modified precursors can support peptidoglycan polymerization and confer vancomycin resistance.

Main Methods:

• Utilizing vancomycin-resistant Enterococcus faecium (vanA phenotype) strains.
• Employing in vitro peptidoglycan polymerization assays.
• Analyzing accumulated UDP-N-acetylmuramyl(UDP-MurNAc)-tetrapeptide and UDP-MurNAc-depsipentapeptide precursors in the presence of bacitracin.

Main Results:

• Bacitracin treatment led to the accumulation of UDP-N-acetylmuramyl(UDP-MurNAc)-tetrapeptide.
• A novel UDP-MurNAc-depsipentapeptide, with lactate replacing D-alanine, was also accumulated.
• These modified precursors were found to be functional in peptidoglycan polymerization assays.
• The modified precursors conferred resistance to vancomycin.

Conclusions:

• Bacitracin induces the accumulation of specific modified peptidoglycan precursors in vancomycin-resistant Enterococcus faecium.
• The presence of lactate in the depsipentapeptide precursor is a key modification.
• These modified precursors can bypass the vancomycin inhibition mechanism, contributing to vancomycin resistance.