Demonstration of the interactions between aromatic compound-loaded lipid nanocapsules and Acinetobacter baumannii bacterial membrane.

Acinetobacter baumannii is an important nosocomial pathogen that is resistant to many commonly-used antibiotics. One strategy for treatment is the use of aromatic compounds (carvacrol, cinnamaldehyde) against A. baumannii. The aim of this study was to determine the interactions between bacteria and lipid nanocapsules (LNCs) over time based on the fluorescence of 3,3'-Dioctadecyloxacarbocyanine Perchlorate-LNCs (DiO-LNCs) and the properties of trypan blue to analyse the physicochemical mechanisms occurring at the level of the biological membrane. The results demonstrated the capacity of carvacrol-loaded LNCs to interact with and penetrate the bacterial membrane in comparison with cinnamaldehyde-loaded LNCs and unloaded LNCs. Modifications of carvacrol after substitution of hydroxyl functional groups by fatty acids demonstrated the crucial role of hydroxyl functions in antibacterial activity. Finally, after contact with the efflux pump inhibitor, carbonylcyanide-3-chlorophenyl hydrazine (CCCP), the results indicated the total synergistic antibacterial effect with Car-LNCs, showing that CCCP is associated with the action mechanism of carvacrol, especially at the level of the efflux pump mechanism.

Synergistic interactions between doxycycline and terpenic components of essential oils encapsulated within lipid nanocapsules against gram negative bacteria.

The combination of essential oils (EOs) with antibiotics provides a promising strategy towards combating resistant bacteria. We have selected a mixture of 3 major components extracted from EOs: carvacrol (oregano oil), eugenol (clove oil) and cinnamaldehyde (cinnamon oil). These compounds were successfully encapsulated within lipid nanocapsules (LNCs). The EOs-loaded LNCs were characterised by a noticeably high drug loading of 20% and a very small particle diameter of 114nm. The in vitro interactions between EOs-loaded LNCs and doxycycline were examined via checkerboard titration and time-kill assay against 5 Gram-negative strains: Acinetobacter baumannii SAN, A. baumannii RCH, Klebsiella pneumoniae, Escherichia coli and Pseudomonas aeruginosa. No growth inhibition interactions were found between EOs-loaded LNCs and doxycycline (FIC index between 0.7 and 1.30). However, when bactericidal effects were considered, a synergistic interaction was observed (FBC index equal to 0.5) against all tested strains. A synergistic effect was also observed in time-kill assay (a difference of at least 3 log between the combination and the most active agent alone). Scanning electron microscopy (SEM) was used to visualise the changes in the bacterial membrane. The holes in bacterial envelope and leakage of cellular contents were observed in SE micrographs after exposure to the EOs-LNCs and the doxycycline combination.

[Antibacterial activity against 224 clinical bacterial strains of JCA 250 and JCA 251 compounds containing essential oils provided from Aroma Technologies research]. / Étude de la sensibilité de 224 bactéries isolées d'infections hospitalières vis-à-vis des composés JCA 250 et JCA 251 à base d'huiles essentielles issus de la recherche Aroma Technologies.

OBJECTIVE: It was to determine the antibacterial spectrum of JCA 250 and JCA 251, two naturally occurring compounds from Aroma Technologies research, on a bacterial population isolated from clinical infections. METHOD: Two hundred and twenty-four bacterial strains were tested. The minimum inhibitory concentrations (MIC) of JCA 250 and JCA 251 were determined by agar dilution method. Tests were performed in triplicate. RESULTS: The mean MIC was 0.20% for JCA 250 and 0.15% for JCA 251. JCA 251 regularly exhibited greater activity. All Enterobacteriaceae were inhibited at concentrations less or equal to 0.15% for JCA 250 or JCA 251. For strict aerobes, the MIC values were more spread out. Two Pseudomonas aeruginosa strains differed from the population with JCA 251 MIC of 0.25 and 0.40%. Concerning Gram-positive cocci, all the strains were inhibited with less or equal to 0.25% of compound. The most resistant population were the Enterococci and the Lactobacilli, with MIC more or equal to 0.2% for JCA 250 or JCA 251. Anaerobes showed MIC closely grouped for a heterogeneous bacterial group. One Propionibacterium sp. strain came apart from the group and was inhibited with a MIC of 0.5%. CONCLUSION: The overall results showed an interesting antibacterial activity on bacteria isolated from clinical samples. Most of the bacterial strains were inhibited at a concentration of 0.2%. The highest mean values were obtained for commensal bacteria from the flora, which is of particular interest in this study.