Glycopeptide-resistant enterococci: a decade of experience

Area of Science:

• Microbiology and Infectious Diseases
• Molecular Biology and Genetics
• Epidemiology and Public Health

Background:

• Glycopeptide-resistant enterococci (GRE) have emerged as a major cause of hospital-acquired infections globally since their initial identification in 1988.
• Two primary acquired resistance mechanisms, VanA and VanB, exist alongside intrinsic (VanC) and a rarer acquired form (VanD), all altering peptidoglycan precursors to reduce glycopeptide antibiotic binding.

Discussion:

• Clinical detection of VanA resistance is reliable, but variable vancomycin resistance levels in other phenotypes, particularly VanB, lead to under-reporting and potentially skewed prevalence data.
• The epidemiology of GRE is complex, with evidence of transferable resistance genes on transposons and plasmids, genetic linkage to aminoglycoside resistance, and the emergence of epidemic strains of Enterococcus faecium.
• The origins of GRE resistance remain unclear, with limited homology to known resistant bacteria or glycopeptide producers, suggesting a distant evolutionary relationship.

Key Insights:

• VanA resistance is frequently observed in clinical isolates, while VanB resistance may be under-detected due to diagnostic limitations.
• The gene clusters for VanA and VanB resistance are located on transposable elements, facilitating their spread via transposition and plasmid transfer across diverse enterococcal species.
• Community and animal reservoirs (e.g., sewage, meat) for VanA resistance suggest non-hospital origins, potentially linked to avoparcin use in livestock, contrasting with the USA where avoparcin is not licensed.

Outlook:

• Further research is needed to fully elucidate the evolutionary origins and precise epidemiological drivers of glycopeptide resistance in enterococci.
• Improved diagnostic methods are crucial for accurate detection and surveillance of all GRE phenotypes, especially VanB.
• Understanding the complex global dissemination patterns of GRE is essential for developing effective strategies to combat these challenging nosocomial pathogens.