Population dynamics in colonizing vancomycin-resistant Enterococcus faecium isolated from immunosuppressed patients

Area of Science:

• Microbiology
• Infectious Diseases
• Genomics

Background:

• Vancomycin-resistant Enterococcus faecium and Enterococcus faecalis (VRE) are significant causes of healthcare-associated infections.
• Whole genome sequencing (WGS) offers high discriminatory power for hospital outbreak surveillance.

Purpose of the Study:

• To analyze the clonal composition and population dynamics of enteric VRE in at-risk patients over several weeks.
• To characterize VRE population diversity and identify mechanisms driving these changes within individual patients.

Main Methods:

• Core genome multi-locus sequence typing (cgMLST) and van-element typing were performed on VRE isolates from rectal swabs of five bone marrow transplant recipients.
• Multiple isolates (14 per swab) were analyzed over several weeks to capture population dynamics.

Main Results:

• VRE populations exhibited clonal diversity and dynamic changes in three out of five patients.
• Evidence of horizontal gene transfer, via shared van-elements on plasmids between clonally distinct isolates, contributed to VRE diversity within patients.

Conclusions:

• Analyzing a single VRE isolate per patient is insufficient for accurate outbreak surveillance in vulnerable populations.
• VRE population heterogeneity and horizontal gene transfer of resistance elements must be considered for effective hospital infection control.