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Published on: October 29, 2020
Tetracyclines at subinhibitory concentrations are lethal for NADH peroxidase-deficient mutants of Enterococcus
Valentin Wasselin1, Aurélie Budin-Verneuil1, Isabelle Rincé1
1CBSA UR 4312, Université de Caen Normandie, Univ Rouen Normandie, Normandie Univ, Caen F-14 000, France.
Objectives:
Tigecycline is a bacteriostatic antibiotic member of the glycylcycline family that inhibits protein synthesis. Tigecycline is a last-line treatment for infections caused by MDR pathogens like vancomycin-resistant Enterococcus faecium (VR-Efm). We recently explored oxidative stress defences in E. faecium and we here aimed to assess their role in antibiotic resistance.
Methods:
Antibiotic susceptibility was evaluated in mutants deficient in primary oxidative stress defences by monitoring bacterial survival after a 24 h treatment. Hydrogen peroxide (H2O2) levels were quantified to link bacterial survival to oxidative stress.
Results:
Unexpectedly, tigecycline and other tetracyclines were lethal for VR-Efm AUS0004 mutants deficient in NADH peroxidase (Npr) at concentrations below their MICs. Lethality seemed to correlate with increased H2O2 accumulation in the Δnpr mutant. H2O2 production in Efm AUS0004 was mainly mediated by lactate oxidase Lox1, whereas Lox2 and pyruvate oxidase (Pox) had minor or no roles. Tigecycline was not lethal for a ΔnprΔlox1 double mutant, suggesting lethality results from both antibiotic effect and peroxide accumulation.
Conclusions:
This study might pave the way to develop strategies aimed at potentiating tigecycline action by increasing endogenous H2O2 production and/or impairing H2O2 detoxification, potentially improving treatment efficiencies for VR-Efm infections with this last-line antibiotic.
Insights
Vancomycin-resistant Enterococcus faecium (VR-Efm) antibiotic resistance can be overcome by targeting oxidative stress defenses. Impairing hydrogen peroxide (H2O2) detoxification potentiates tigecycline efficacy against these difficult-to-treat infections.
Area of Science:
- Microbiology
- Molecular Biology
- Drug Discovery
Background:
- Tigecycline is a critical last-line antibiotic for treating infections caused by multidrug-resistant (MDR) pathogens, including vancomycin-resistant Enterococcus faecium (VR-Efm).
- Oxidative stress plays a role in bacterial physiology and antibiotic resistance mechanisms.
- Understanding the interplay between oxidative stress and antibiotic efficacy is crucial for developing new therapeutic strategies.
Purpose of the Study:
- To investigate the role of oxidative stress defense mechanisms in VR-Efm's resistance to tigecycline.
- To determine if targeting specific oxidative stress pathways can re-sensitize VR-Efm to tigecycline.
Main Methods:
- Evaluated antibiotic susceptibility of VR-Efm mutants lacking key oxidative stress defense proteins.
- Quantified intracellular hydrogen peroxide (H2O2) levels in bacterial mutants.
- Assessed the contribution of different enzymes (NADH peroxidase, lactate oxidase, pyruvate oxidase) to H2O2 metabolism.
Main Results:
- Mutants deficient in NADH peroxidase (Npr) exhibited unexpected lethality when exposed to sub-inhibitory concentrations of tigecycline and other tetracyclines.
- This tigecycline lethality correlated with increased intracellular H2O2 accumulation in the Δnpr mutant.
- Lactate oxidase (Lox1) was identified as the primary enzyme responsible for H2O2 production in VR-Efm, with minor contributions from Lox2 and pyruvate oxidase (Pox).
- A ΔnprΔlox1 double mutant was not killed by tigecycline, indicating that the combined effect of the antibiotic and peroxide accumulation drives lethality.
Conclusions:
- Targeting NADH peroxidase and modulating hydrogen peroxide levels represent a potential strategy to enhance tigecycline's effectiveness against VR-Efm.
- Increasing endogenous H2O2 production or impairing its detoxification could improve treatment outcomes for infections caused by this challenging pathogen.
- This research opens avenues for novel therapeutic approaches to combat antibiotic resistance.
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