Preparation and properties of films loaded with cellulose nanocrystals stabilized Thymus vulgaris essential oil Pickering emulsion based on modified tapioca starch/polyvinyl alcohol

Pickering emulsions were prepared by stabilizing thymus vulgaris essential oil (TEVO) with cellulose nanocrystals (CNCs), which formed composite films by loading the emulsions into modified tapioca/polyvinyl alcohol (PVA)-based films. The results showed that the 1.0 % CNCs-15 % TEVO emulsion had optimal stability and smaller particle size. The emulsion increased the thickness of the composite film in the form of solid material additions (thickness, 0.062-0.099 mm), which opacity given the laminating film's superior UV-blocking ability compared to blank film. The emulsion plasticizing effect enhanced the film's elongation at break (EAB, 123-159 %). In addition, due to the hydrophobicity and influencing the diffusion path of water molecules in the emulsion, the denser microstructure composite film had a lower water vapor transmission coefficient (WVP, 6.22 × 10-11-5.35 × 10-11g∙cm/cm2∙s∙Pa) to impede moisture penetration. Meanwhile, the composite film can effectively maintain the color and inhibit the growth of microorganisms to extend the storage time of fish fillets.

Thymus vulgaris essential oil + tobramycin within nanostructured archaeolipid carriers: A new approach against Pseudomonas aeruginosa biofilms

BACKGROUND

Pseudomonas aeruginosa biofilms in the respiratory tract of patients with an excessive inflammatory context are difficult to eradicate. New medicines that simultaneously target biofilms and inflammation should be developed.

HYPOTHESIS

Co-delivery of Thymus vulgaris essential oil (EOT) and tobramycin (TB) by nanostructured archaeolipids carriers (NAC) could support nebulization as well as improve EOT and TB antioxidant, anti-inflammatory and antibiofilm activity.

METHODS

NAC_(EOT+TB) were prepared by loading EOT and TB in NAC having a compritol and miglyol core, covered with a shell of archaeolipids, extracted from the hyperhalophylic archaebacteria Halorubrum tebenquichense, and Tween 80. NAC_(EOT+TB) were structurally characterized, including DSC thermograms, Raman spectra, TB release profile, EOT volatilization and in vitro antioxidant activity. In addition, stability upon nebulization, autoclaving and storage were assessed. The antibiofilm activity on P. aeruginosa PAO1 established biofilm of NAC_(EOT+TB) and the cytotoxicity on human lung epithelial cells and macrophage were determined, as well as intracellular reactive oxygen species (ROS) production and cytokines release on LPS stimulated cells.

RESULTS

NAC_(EOT+TB) showed a size of 197 ± 16 nm with PdI of 0.3 ± 0.1 and ζ Potential of -38 ± 3 mV. Structural characterization suggested that EOT was trapped in the compritol-miglyol core and TB was distributed between the surface of nanoparticles and free in solution. NAC_(EOT+TB) displayed a dual release profile of TB, a delayed release of EOT and improved EOTs in vitro antioxidant activity. While NAC_(EOT+TB) preserved its structural features after nebulization, autoclaving and 18 months of storage, carriers without archaeolipids gelled at room temperature and showed a significant increase of size after the same storage time. Below cytotoxic concentration, NAC_(EOT+TB) decreased bacteria viability and enhanced the disruption of established PAO1 biofilms compared to free TB and EOT. Also, the strong entrapment of EOT in NAC_(EOT+TB) delayed its volatilization, decreased intracellular ROS production and maintained its anti-inflammatory activity in LPS stimulated cells.

CONCLUSION

Combination of EOT + TB within NAC_(EOT+TB) result in a stable and nebulizable formulation that enhanced the antioxidant and anti-biofilm activity of free ingredients, improved their ability to decrease intracellular ROS and provided anti-inflammatory activity, at non-cytotoxic concentrations on eukaryotic cells.

Fully dilutable Thymus vulgaris essential oil:acetic or propionic acid microemulsions are potent fruit disinfecting solutions

The aim of this study was to evaluate the effect of acetic (AA) or propionic (PA) acid as a cosurfactant on the microemulsion (ME) characteristics of Thymus vulgaris essential oil (TVO). The results showed that addition of propylene glycol to TVO/AA or PA:T80/water MEs gave dilutable systems with particles ~59 nm in diameter. Plain TVO showed the highest antimicrobial activity against E. coli, S. aureus, and S. typhi in in vitro antimicrobial tests, followed closely by AA/PA-MEs. The antimicrobial activity of AA/PA-MEs used as a washing solution on cucumber and strawberry samples was remarkably greater than those of free TVO, TVO nanoemulsions, and chlorhexidine solutions against E. coli and S. aureus. The sensory properties of the samples were not changed by the use of AA/PA-MEs at 0.05 or 0.1% TVO. The results introduce dilutable TVO:AA/PA-MEs for incorporation of TVO in aqueous systems for use as a fruit/vegetable disinfecting agent.

The anti MRSA biofilm activity of Thymus vulgaris essential oil in nanovesicles

BACKGROUND

Thymus vulgaris essential oil (T) could be an alternative to classical antibiotics against bacterial biofilms, which show increased tolerance to antibiotics and host defence systems and contribute to the persistence of chronic bacterial infections.

HYPOTHESIS

A nanovesicular formulation of T may chemically protect the structure and relative composition of its multiple components, potentially improving its antibacterial and antibiofilm activity.

STUDY DESIGN

We prepared and structurally characterized T in two types of nanovesicles: nanoliposomes (L80-T) made of Soybean phosphatidylcholine (SPC) and Polysorbate 80 (P80) [SPC:P80:T 1:0.75:0.3 w:w], and nanoarchaeosomes (A80-T) made of SPC, P80 and total polar archaeolipids (TPA) extracted from archaebacteria Halorubrum tebenquichense [SPC:TPA:P80:T 0.5:0.50.75:0.7 w:w]. We determined the macrophage cytotoxicity and the antibacterial activity against Staphylococcus aureus ATCC 25,923 and four MRSA clinical strains.

RESULTS

L80-T (Z potential -4.1 ± 0.6 mV, ∼ 115 nm, ∼ 22 mg/ml T) and A80-T (Z potential -6.6 ± 1.5 mV, ∼ 130 nm, ∼ 42 mg/ml T) were colloidally and chemically stable, maintaining size, PDI, Z potential and T concentration for at least 90 days. While MIC₉₀ of L80-T was > 4 mg/ml T, MIC₉₀ of A80-T was 2 mg/ml T for all S. aureus strains. The antibiofilm formation activity was maximal for A80-T, while L80-T did not inhibit biofilm formation compared to untreated control. A80-T significantly decreased the biomass of preformed biofilms of S. aureus ATCC 25,923 strain and of 3 of the 4 clinical MRSA isolates at 4 mg/ml T. It was found that the viability of J774A.1 macrophages was decreased significantly upon 24 h incubation with A80-T, L80-T and T emulsion at 0.4 mg/ml T. These results show that from 0.4 mg/ml T, a value lower than MIC₉₀ and the one displaying antibiofilm activity, with independence of its formulation, T significantly decreased the macrophages viability.

CONCLUSION

Overall, because of its lower MIC₉₀ against planktonic bacteria, higher antibiofilm formation capacity and stability during storage, A80-T resulted better antibacterial agent than T emulsion and L80-T. These results open new avenues to explode the A80-T antimicrobial intracellular activity.