Effect of Lipid and Fatty Acid Composition of Phospholipid Vesicles on Long-Term Stability and Their Response to Staphylococcus aureus and Pseudomonas aeruginosa Supernatants

Abstract

Phospholipid vesicles have been the focus of attention as potential vehicles for drug delivery, as they are biomimetic, easy to produce, and contain an aqueous compartment which can be used to carry hydrophilic material, such as drugs or dyes. Lipid vesicles used for this purpose present a particular challenge, as they are not especially stable and can rapidly break down and release their contents away from the target area, especially at physiological temperatures/environments. This study aims to investigate optimum methods for vesicle stabilization where the vesicles are employed as part of a system or technology that signals the presence of pathogenic bacteria via the effect of secreted cytolytic virulence factors on a sensor interface. A number of approaches have been investigated and are presented here as a systematic study of the long-term (14 day) stability at 37 °C, and at various pHs. The response of vesicles, both in suspension and within hydrogels, to Staphylococcus aureus (RN 4282) and Pseudomonas aeruginosa (PAO1) whole bacteria, and supernatants from overnight cultures of both (containing secreted proteins but free of cells), was measured via a sensitive encapsulated carboxyfluorescein release assay. The results showed that lipid chain length, cholesterol concentration, and stabilization via photopolymer stable components were critical in achieving stability. Finally, dispersion of the optimum vesicle formulation in hydrogel matrixes was investigated, culminating in the in vivo demonstration of a simple prototype wound dressing.

A new assay for rhamnolipid detection—important virulence factors of Pseudomonas aeruginosa

“…Here we present a new methodology in detecting and quantifying RL using carboxylfluorescein encapsulated phospholipid vesicles. We have previously shown that these vesicles are stable under various conditions (Marshall et al 2013) and are susceptible to a suite of Stapylococcus aureus toxins that have surfactant-like properties (Laabei et al 2014b). In this report we confirm that RL can be detected and semi-quantified directly from pure overnight culture supernatants of P. aeruginosa using the vesicle-lysis assay, decreasing preparation time, hazardous extraction techniques or expert analysis.…”

Prototype Development of the Intelligent Hydrogel Wound Dressing and Its Efficacy in the Detection of Model Pathogenic Wound Biofilms

“…22,23 This is accomplished through the use of synthetic lipid vesicles loaded with fluorescent self-quenching dye, which are sensitive to the key population-density regulated cytotoxic virulence factors produced by major wound pathogens 19,24,25 . These vesicles were found to be stable under conditions reflective of the un-infected wound environment, 26 but production of cytotoxins by bacterial pathogens results in lysis and dye release, which may be used to provide a clear signal that the CCT has been reached, and clinically relevant infection has been intiated. 19,24 The natural evolution of this technology is now the incorporation of vesicles directly within wound dressings, to produce "intelligent", infection-responsive, theranostic devices that can notify clinicians of the need to intervene directly at point of care.…”

Advanced dextran based nanogels for fightingStaphylococcus aureusinfections by sustained zinc release

“…16 In addition, phospholipid vesicles contained within a hydrogel matrix have been demonstrated as potential antimicrobial delivery vehicles. 17 Potential opening mechanisms for the drug delivery systems include swelling of hydrogels, 18,19 environmental pH changes, 20 membrane lytic action of secretion toxins from the infecting bacteria, which open phospholipid vesicles, [21][22][23] or polymer degradation by extracellular enzymes. 24 Accordingly, biodegradable/compatible materials like polysaccharides seem very promising for such drug-delivery systems at the nanoscale as they can oen be degraded specically by bacterial enzymes.…”