Adaptive cell wall thickening in Enterococcus faecalis is associated with decreased vancomycin susceptibility

Theresa Maria Wagner; Anna K Pöntinen; Mushtaq Al Rubaye; Arnfinn Sundsfjord; Kristin Hegstad

doi:10.1016/j.cmi.2023.12.002

Adaptive cell wall thickening in Enterococcus faecalis is associated with decreased vancomycin susceptibility

Clin Microbiol Infect. 2024 Mar;30(3):396.e1-396.e5. doi: 10.1016/j.cmi.2023.12.002. Epub 2023 Dec 6.

Authors

Theresa Maria Wagner¹, Anna K Pöntinen², Mushtaq Al Rubaye¹, Arnfinn Sundsfjord³, Kristin Hegstad⁴

Affiliations

¹ Research Group for Host-Microbe Interactions, Department of Medical Biology, Faculty of Health Sciences, UiT The Arctic University of Norway, Tromsø, Norway.
² Norwegian National Advisory Unit on Detection of Antimicrobial Resistance, Department of Microbiology and Infection Control, University Hospital of North Norway, Tromsø, Norway; Department of Biostatistics, Faculty of Medicine, University of Oslo, Oslo, Norway.
³ Research Group for Host-Microbe Interactions, Department of Medical Biology, Faculty of Health Sciences, UiT The Arctic University of Norway, Tromsø, Norway; Norwegian National Advisory Unit on Detection of Antimicrobial Resistance, Department of Microbiology and Infection Control, University Hospital of North Norway, Tromsø, Norway.
⁴ Research Group for Host-Microbe Interactions, Department of Medical Biology, Faculty of Health Sciences, UiT The Arctic University of Norway, Tromsø, Norway; Norwegian National Advisory Unit on Detection of Antimicrobial Resistance, Department of Microbiology and Infection Control, University Hospital of North Norway, Tromsø, Norway. Electronic address: kristin.hegstad@uit.no.

PMID: 38065364
DOI: 10.1016/j.cmi.2023.12.002

Abstract

Objectives: Enterococcus faecalis can adopt both a commensal and a nosocomial lifestyle, resisting numerous antibiotics. In this study, we aim to investigate the relationship between the cell wall (CW) thickness and decreased susceptibility to vancomycin (VD) in van-gene negative clinical isolates of E. faecalis (n_{MIC 8} = 2, n_{MIC 4} = 3, ST30, ST40, and ST59).

Methods: The CW thickness was assessed in VD strains and compared with vancomycin susceptible isolates of the same sequence type (ST) (Vancomycin susceptible [VS]; n_MIC 2 = 5). The VD and VS strains were subjected to serial passage (evolved [ev]) with and without vancomycin selection. Subsequent measurements of CW thickness and vancomycin MICs were performed.

Results: The VD strains exhibited increased CW thickness when compared with ST-related VS strains (ΔCW thickness VD vs. VS ST30 25 nm, ST59 15 nm, and ST40 1 nm). Serial passages without vancomycin selection led to a decrease in CW thickness and vancomycin MIC in VD strains (ΔCW thickness VD vs. evVD ST30 22 nm, ST59 3 nm, and ST40 2 nm). Serial passages with vancomycin selection caused an increase in CW thickness and vancomycin MIC in ST-related VS strains (ΔCW thickness VS vs. evVS ST30 22 nm, ST59 16 nm, and ST40 1 nm).

Discussion: Adaptive changes in CW thickness were observed in response to vancomycin exposure. Increased CW thickness correlated with decreased vancomycin susceptibility, whereas decreased CW thickness correlated with increased vancomycin susceptibility. Core single nucleotide polymorphisms in the evolved mutants were mostly found in genes encoding proteins associated with the cytoplasm or the cytoplasmic membrane. The potential relevance of these adaptive changes is underlined by the observed phenotypes in clinical isolates. Our findings emphasize the importance of monitoring adaptive changes, as vancomycin-resistant enterococci infections are a growing concern.

Keywords: Adaption; Cellular structures; Electron microscopy; Enterococci; Glycopeptides.

MeSH terms

Anti-Bacterial Agents / pharmacology
Cell Wall
Enterococcus faecalis / genetics
Enterococcus faecium* / genetics
Gram-Positive Bacterial Infections* / microbiology
Humans
Microbial Sensitivity Tests
Vancomycin / pharmacology

Substances

Vancomycin
Anti-Bacterial Agents