Antimicrobial sensing coupled with cell membrane remodeling mediates antibiotic resistance and virulence in Enterococcus faecalis

Abstract

Bacteria have developed several evolutionary strategies to protect their cell membranes (CMs) from the attack of antibiotics and antimicrobial peptides (AMPs) produced by the innate immune system, including remodeling of phospholipid content and localization. Multidrug-resistantEnterococcus faecalis,an opportunistic human pathogen, evolves resistance to the lipopeptide daptomycin and AMPs by diverting the antibiotic away from critical septal targets using CM anionic phospholipid redistribution. The LiaFSR stress response system regulates this CM remodeling via the LiaR response regulator by a previously unknown mechanism. Here, we characterize a LiaR-regulated protein, LiaX, that senses daptomycin or AMPs and triggers protective CM remodeling. LiaX is surface exposed, and in daptomycin-resistant clinical strains, both LiaX and the N-terminal domain alone are released into the extracellular milieu. The N-terminal domain of LiaX binds daptomycin and AMPs (such as human LL-37) and functions as an extracellular sentinel that activates the cell envelope stress response. The C-terminal domain of LiaX plays a role in inhibiting the LiaFSR system, and when this domain is absent, it leads to activation of anionic phospholipid redistribution. Strains that exhibit LiaX-mediated CM remodeling and AMP resistance show enhanced virulence in theCaenorhabditis elegansmodel, an effect that is abolished in animals lacking an innate immune pathway crucial for producing AMPs. In conclusion, we report a mechanism of antibiotic and AMP resistance that couples bacterial stress sensing to major changes in CM architecture, ultimately also affecting host–pathogen interactions.

Exposure of Mycobacterium abscessus to Environmental Stress and Clinically Used Antibiotics Reveals Common Proteome Response among Pathogenic Mycobacteria

“…The activation of the peptidoglycan and fatty acid biosynthesis indicates MAB and MAH attempt to modify the cell surface, influencing bacterial susceptibility to antibiotics, as previously seen in Mycobacterium avium subsp. paratuberculosis and Enterococcus faecalis [47,48].…”

ExPortal and the LiaFSR Regulatory System Coordinate the Response to Cell Membrane Stress in Streptococcus pyogenes

“…LiaFSR is a critical component of the cell envelope stress response and is activated following exposure to antimicrobials targeting the cell envelope (e.g., bacitracin [BAC] or daptomycin) or AMPs (e.g., LL-37) ( 16 ). Interest in the LiaFSR TCS is rooted in the association between antimicrobial resistance and mutations within the individual TCS components or its downstream effectors ( 17 , 18 ). While much is known regarding LiaFSR and the development of resistance to antimicrobials, the external host stimuli, mechanisms of signaling, and downstream effects of LiaFSR activation in pathogenic Gram-positive bacteria are largely unresolved.…”

Synergies with and Resistance to Membrane-Active Peptides

“…Studying the effects of genetic mutation on its coding region showed that the protein LiaX, a previously unknown mediator to this response pathway, leads to hypersensitivity to daptomycin and other membrane targeting MAP-like peptides. The authors concluded that “LiaX functions as a modulator of the [cell membrane] stress response linking membrane adaptation, antibiotic resistance, and pathogenesis” [ 74 ]. The LiaX protein can mediate this important cellular function with its carboxy domain in intracellular space and responsible for activating the response.…”

“…It appears there is cooperativity in the binding of MAPs to extracellular N-terminus of the peptide. It is hypothesized that this is only one of a family of proteins that contributes to the stress response cascade of cell membrane remodeling [ 74 ]. Thus, there may be a widespread, broad-spectrum resistance mediating mechanism that MAPs will need to overcome in future mutant microbial strains.…”