LiaX Is a Surrogate Marker for Cell Envelope Stress and Daptomycin Non-susceptibility In Enterococcus faecium

Authors

Dierdre B Axell-House
Shelby R Simar
Diana Panesso
Sandra Rincon
William R Miller
Ayesha Khan
Orville A Pemberton
Lizbet Valdez
April H Nguyen
Kara S Hood
Kirsten Rydell
Andrea M DeTranaltes
Mary N Jones
Rachel Atterstrom
Jinnethe Reyes
Pranoti V Sahasrabhojane
Geehan Suleyman
Marcus Zervos
Samuel A Shelburne
Kavindra V Singh
Yousif Shamoo
Blake M Hanson
Truc T Tran
Cesar A Arias

Publication Date

3-6-2024

Journal

Antimicrobial Agents and Chemotherapy

Abstract

Daptomycin (DAP) is often used as a first-line therapy to treat vancomycin-resistant Enterococcus faecium infections, but emergence of DAP non-susceptibility threatens the effectiveness of this antibiotic. Moreover, current methods to determine DAP minimum inhibitory concentrations (MICs) have poor reproducibility and accuracy. In enterococci, DAP resistance is mediated by the LiaFSR cell membrane stress response system, and deletion of liaR encoding the response regulator results in hypersusceptibility to DAP and antimicrobial peptides. The main genes regulated by LiaR are a cluster of three genes, designated liaXYZ. In Enterococcus faecalis, LiaX is surface-exposed with a C-terminus that functions as a negative regulator of cell membrane remodeling and an N-terminal domain that is released to the extracellular medium where it binds DAP. Thus, in E. faecalis, LiaX functions as a sentinel molecule recognizing DAP and controlling the cell membrane response, but less is known about LiaX in E. faecium. Here, we found that liaX is essential in E. faecium with an activated LiaFSR system. Unlike E. faecalis, E. faecium LiaX is not detected in the extracellular milieu and does not appear to alter phospholipid architecture. We further postulated that LiaX could be used as a surrogate marker for cell envelope activation and non-susceptibility to DAP. For this purpose, we developed and optimized a LiaX enzyme-linked immunosorbent assay (ELISA). We then assessed 86 clinical E. faecium bloodstream isolates for DAP MICs and used whole genome sequencing to assess for substitutions in LiaX. All DAP-resistant clinical strains of E. faecium exhibited elevated LiaX levels. Strikingly, 73% of DAP-susceptible isolates by standard MIC determination also had elevated LiaX ELISAs compared to a well-characterized DAP-susceptible strain. Phylogenetic analyses of predicted amino acid substitutions showed 12 different variants of LiaX without a specific association with DAP MIC or LiaX ELISA values. Our findings also suggest that many E. faecium isolates that test DAP susceptible by standard MIC determination are likely to have an activated cell stress response that may predispose to DAP failure. As LiaX appears to be essential for the cell envelope response to DAP, its detection could prove useful to improve the accuracy of susceptibility testing by anticipating therapeutic failure.

Keywords

Humans, Anti-Bacterial Agents, Biomarkers, Cell Membrane, Daptomycin, Drug Resistance, Bacterial, Enterococcus faecalis, Enterococcus faecium, Gram-Positive Bacterial Infections, Microbial Sensitivity Tests, Phylogeny, Reproducibility of Results, Enterococcus faecium, antibiotic resistance, daptomycin

DOI

10.1128/aac.01069-23

PMID

38289081

PMCID

PMC10916372

PubMedCentral® Posted Date

1-30-2024

PubMedCentral® Full Text Version

Post-print

Published Open-Access

yes