Induction of Daptomycin Tolerance in Enterococcus faecalis by Fatty Acid Combinations

Enterococcus faecium: evolution, adaptation, pathogenesis and emerging therapeutics

The opportunistic pathogen Enterococcus faecium colonizes humans and a wide range of animals, endures numerous stresses, resists antibiotic treatment and stubbornly persists in clinical environments. The widespread application of antibiotics in hospitals and agriculture has contributed to the emergence of vancomycin-resistant E. faecium, which causes many hospital-acquired infections. In this Review, we explore recent discoveries about the evolutionary history, the environmental adaptation and the colonization and dissemination mechanisms of E. faecium and vancomycin-resistant E. faecium. These studies provide critical insights necessary for developing novel preventive and therapeutic approaches against vancomycin-resistant E. faecium and also reveal the intricate interrelationships between the environment, the microorganism and the host, providing knowledge that is broadly relevant to how antibiotic-resistant pathogens emerge and endure.

Emerging mechanisms by which endocannabinoids and their derivatives modulate bacterial populations within the gut microbiome

Bioactive lipids such as endocannabinoids serve as important modulators of host health and disease through their effects on various host functions including central metabolism, gut physiology, and immunity. Furthermore, changes to the gut microbiome caused by external factors such as diet or by disease development have been associated with altered endocannabinoid tone and disease outcomes. These observations suggest the existence of reciprocal relationships between host lipid signaling networks and bacterial populations that reside within the gut. Indeed, endocannabinoids and their congeners such as N-acylethanolamides have been recently shown to alter bacterial growth, functions, physiology, and behaviors, therefore introducing putative mechanisms by which these bioactive lipids directly modulate the gut microbiome. Moreover, these potential interactions add another layer of complexity to the regulation of host health and disease pathogenesis that may be mediated by endocannabinoids and their derivatives. This mini review will summarize recent literature that exemplifies how N-acylethanolamides and monoacylglycerols including endocannabinoids can impact bacterial populations in vitro and within the gut microbiome. We also highlight exciting preclinical studies that have engineered gut bacteria to synthesize host N-acylethanolamides or their precursors as potential strategies to treat diseases that are in part driven by aberrant lipid signaling, including obesity and inflammatory bowel diseases.

Daptomycin as an option for lock therapy: a systematic literature review

Aim: To review preclinical and clinical data relevant to daptomycin lock therapy in catheter-related bloodstream infection (CRBSI). Methods: Systematic review in PubMed, Scopus and clinical trial registries. Results: Preclinical data demonstrate daptomycin lock solution stability and compatibility with heparin, good biofilm penetration, bactericidal activity against biofilm-embedded bacteria, and high efficacy in vitro and in animal catheter infection models. Clinical data remain limited (two case reports and five case series totaling n = 65 CRBSI episodes), albeit promising (successful catheter salvage in about 80% of cases). Conclusion: Despite theoretical advantages of daptomycin, clinical data remain scarce. Comparative studies versus alternative lock solutions are needed, as well as studies to define optimal daptomycin lock regimen (including optimal concentration, dwell time and lock duration).

Dual stable isotopes enhance lipidomic studies in bacterial model organism Enterococcus faecalis

Dual stable isotope probes of deuterium oxide and 13C fatty acid were demonstrated to probe the lipid biosynthesis cycle of a Gram-positive bacterium Enterococcus faecalis. As external nutrients and carbon sources often interact with metabolic processes, the use of dual-labeled isotope pools allowed for the simultaneous investigation of both exogenous nutrient incorporation or modification and de novo biosynthesis. Deuterium was utilized to trace de novo fatty acid biosynthesis through solvent-mediated proton transfer during elongation of the carbon chain while 13C-fatty acids were utilized to trace exogenous nutrient metabolism and modification through lipid synthesis. Ultra-high-performance liquid chromatography high-resolution mass spectrometry identified 30 lipid species which incorporated deuterium and/or 13C fatty acid into the membrane. Additionally, MS2 fragments of isolated lipids identified acyl tail position confirming enzymatic activity of PlsY in the incorporation of the 13C fatty acid into membrane lipids.

Human serum induces daptomycin tolerance in Enterococcus faecalis and viridans group streptococci

Daptomycin is a membrane-targeting lipopeptide antibiotic used in the treatment of infective endocarditis caused by multidrug-resistant Gram-positive bacteria such as Staphylococcus aureus, enterococci and viridans group streptococci. Despite demonstrating excellent in vitro activity and a low prevalence of resistant isolates, treatment failure is a significant concern, particularly for enterococcal infection. We have shown recently that human serum triggers daptomycin tolerance in S. aureus, but it was not clear if a similar phenotype occurred in other major infective endocarditis pathogens. We found that Enterococcus faecalis, Streptococcus gordonii or Streptococcus mutans grown under standard laboratory conditions were efficiently killed by daptomycin, whereas bacteria pre-incubated in human serum survived exposure to the antibiotic, with >99 % cells remaining viable. Incubation of enterococci or streptococci in serum led to peptidoglycan accumulation, as shown by increased incorporation of the fluorescent d-amino acid analogue HADA. Inhibition of peptidoglycan accumulation using the antibiotic fosfomycin resulted in a >tenfold reduction in serum-induced daptomycin tolerance, demonstrating the important contribution of the cell wall to the phenotype. We also identified a small contribution to daptomycin tolerance in E. faecalis from cardiolipin synthases, although this may reflect the inherent increased susceptibility of cardiolipin-deficient mutants. In summary, serum-induced daptomycin tolerance is a consistent phenomenon between Gram-positive infective endocarditis pathogens, but it may be mitigated using currently available antibiotic combination therapy.

Bacterial cell membranes and their role in daptomycin resistance: A review

Lipids play a major role in bacterial cells. Foremost, lipids are the primary constituents of the cell membrane bilayer, providing structure and separating the cell from the surrounding environment. This makes the lipid bilayer a prime target for antimicrobial peptides and membrane-acting antibiotics such as daptomycin. In response, bacteria have evolved mechanisms by which the membrane can be adapted to resist attack by these antimicrobial compounds. In this review, we focus on the membrane phospholipid changes associated with daptomycin resistance in enterococci, Staphylococcus aureus, and the Viridans group streptococci.

Antimicrobial tolerance and its role in the development of resistance: Lessons from enterococci

Bacteria have developed resistance against every antimicrobial in clinical use at an alarming rate. There is a critical need for more effective use of antimicrobials to both extend their shelf life and prevent resistance from arising. Significantly, antimicrobial tolerance, i.e., the ability to survive but not proliferate during antimicrobial exposure, has been shown to precede the development of bona fide antimicrobial resistance (AMR), sparking a renewed and rapidly increasing interest in this field. As a consequence, problematic infections for the first time are now being investigated for antimicrobial tolerance, with increasing reports demonstrating in-host evolution of antimicrobial tolerance. Tolerance has been identified in a wide array of bacterial species to all bactericidal antimicrobials. Of particular interest are enterococci, which contain the opportunistic bacterial pathogens Enterococcus faecalis and Enterococcus faecium. Enterococci are one of the leading causes of hospital-acquired infection and possess intrinsic tolerance to a number of antimicrobial classes. Persistence of these infections in the clinic is of growing concern, particularly for the immunocompromised. Here, we review current known mechanisms of antimicrobial tolerance, and include an in-depth analysis of those identified in enterococci with implications for both the development and prevention of AMR.

Bacterial adaptation strategies to host-derived fatty acids

Fatty acids (FAs) are potent antimicrobials which hold great promise as viable alternatives or complements to conventional antibiotics. Intriguingly, bacteria are well equipped to use environmental FAs as energy sources and/or building blocks for their membrane lipids. Furthermore, these microbes display a wide array of mechanisms to prevent or mitigate FA toxicity. In this review we discuss strategies that bacteria use to thrive despite extensive exposure to host-derived antimicrobial FAs. We also highlight the altered response of these FA-adapted bacteria to antibiotics. Given the ubiquitous nature of FAs in various host environments, deciphering bacterial adaptation strategies to FAs is of prime importance. This knowledge may pave the way for a rational design of FA-based combination therapies with antibiotics.

Enterococcus faecalis Readily Adapts Membrane Phospholipid Composition to Environmental and Genetic Perturbation

The bacterial lipid membrane, consisting both of fatty acid (acyl) tails and polar head groups, responds to changing conditions through alteration of either the acyl tails and/or head groups. This plasticity is critical for cell survival as it allows maintenance of both the protective nature of the membrane as well as functioning membrane protein complexes. Bacteria that live in fatty-acid rich environments, such as those found in the human host, can exploit host fatty acids to synthesize their own membranes, in turn, altering their physiology. Enterococcus faecalis is such an organism: it is a commensal of the mammalian intestine where it is exposed to fatty-acid rich bile, as well as a major cause of hospital infections during which it is exposed to fatty acid containing-serum. Within, we employed an untargeted approach to detect the most common phospholipid species of E. faecalis OG1RF via ultra-high performance liquid chromatography high-resolution mass spectrometry (UHPLC-HRMS). We examined not only how the composition responds upon exposure to host fatty acids but also how deletion of genes predicted to synthesize major polar head groups impact lipid composition. Regardless of genetic background and differing basal lipid composition, all strains were able to alter their lipid composition upon exposure to individual host fatty acids. Specific gene deletion strains, however, had altered survival to membrane damaging agents. Combined, the enterococcal lipidome is highly resilient in response to both genetic and environmental perturbation, likely contributing to stress survival.