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Removal of peptidoglycan and inhibition of active cellular processes leads to daptomycin tolerance in Enterococcus
Rachel D Johnston1, Brittni M Woodall2, Johnathan Harrison3
1UT-ORNL Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN, United States of America.
Abstract:
Daptomycin is a cyclic lipopeptide antibiotic used in the clinic for treatment of severe enterococcal infections. Recent reports indicate that daptomycin targets active cellular processes, specifically, peptidoglycan biosynthesis. Within, we examined the efficacy of daptomycin against Enterococcus faecalis under a range of environmental growth conditions including inhibitors that target active cellular processes. Daptomycin was far less effective against cells in late stationary phase compared to cells in exponential phase, and this was independent of cellular ATP levels. Further, the addition of either the de novo protein synthesis inhibitor chloramphenicol or the fatty acid biosynthesis inhibitor cerulenin induced survival against daptomycin far better than controls. Alterations in metabolites associated with peptidoglycan synthesis correlated with protection against daptomycin. This was further supported as removal of peptidoglycan induced physiological daptomycin tolerance, a synergistic relation between daptomycin and fosfomycin, an inhibitor of the fist committed step peptidoglycan synthesis, was observed, as well as an additive effect when daptomycin was combined with ampicillin, which targets crosslinking of peptidoglycan strands. Removal of the peptidoglycan of Enterococcus faecium, Staphylococcus aureus, and Bacillus subtilis also resulted in significant protection against daptomycin in comparison to whole cells with intact cell walls. Based on these observations, we conclude that bacterial growth phase and metabolic activity, as well as the presence/absence of peptidoglycan are major contributors to the efficacy of daptomycin.
Insights
Daptomycin efficacy decreases in stationary phase bacteria and is influenced by cell wall integrity. Peptidoglycan presence significantly impacts daptomycin effectiveness against various bacterial species.
Area of Science:
- Microbiology
- Antibiotic Research
- Bacterial Pathogenesis
Background:
- Daptomycin is a crucial antibiotic for treating severe enterococcal infections.
- Emerging evidence suggests daptomycin targets active cellular processes, particularly peptidoglycan biosynthesis.
- Understanding daptomycin's mechanisms of action is vital for optimizing its clinical use.
Purpose of the Study:
- To investigate the efficacy of daptomycin against Enterococcus faecalis under diverse environmental conditions.
- To explore the role of active cellular processes and peptidoglycan integrity in daptomycin's effectiveness.
- To identify factors influencing bacterial susceptibility to daptomycin.
Main Methods:
- Testing daptomycin efficacy against Enterococcus faecalis in different growth phases (exponential vs. late stationary).
- Evaluating the impact of inhibitors targeting protein synthesis (chloramphenicol) and fatty acid biosynthesis (cerulenin) on daptomycin activity.
- Analyzing metabolic alterations related to peptidoglycan synthesis and their correlation with daptomycin protection.
- Assessing the effect of peptidoglycan removal on daptomycin tolerance in multiple bacterial species (E. faecalis, E. faecium, S. aureus, B. subtilis).
- Examining synergistic and additive effects of daptomycin in combination with other antibiotics (fosfomycin, ampicillin).
Main Results:
- Daptomycin was significantly less effective against bacteria in late stationary phase compared to exponential phase, irrespective of ATP levels.
- Inhibitors of protein and fatty acid synthesis enhanced bacterial survival against daptomycin.
- Metabolite changes linked to peptidoglycan synthesis correlated with protection.
- Removal of peptidoglycan conferred significant tolerance to daptomycin across multiple bacterial species.
- Synergistic activity was observed between daptomycin and fosfomycin, with an additive effect when combined with ampicillin.
Conclusions:
- Bacterial growth phase and metabolic activity are key determinants of daptomycin efficacy.
- The presence or absence of intact peptidoglycan is a major factor influencing daptomycin's effectiveness.
- These findings highlight the importance of bacterial physiological state and cell wall structure in daptomycin treatment outcomes.
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