Essential Oil Compounds in Combination with Conventional Antibiotics for Dermatology.

Antimicrobial resistance has emerged as a significant threat to public health, prompting novel combinations comprising of natural sources such as essential oil compounds with conventional antibiotics. This study aimed to determine the possible interactions between six essential oil compounds with eight antibiotics/antifungals against six pathogens (Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, Acinetobacter baumannii, Cutibacterium acnes, and Candida albicans) commonly implicated in skin infections. The minimum inhibitory concentrations (MICs) for the antibiotics and essential oil compounds were evaluated singularly and in combination using the broth microdilution assay. The fractional inhibitory concentrations (FIC) were calculated to determine the interactive profile of the combinations. The synergistic interactions (FIC ≤ 0.5) were further analysed at varying ratios and depicted on isobolograms. The toxicity of the synergistic combinations was determined using the brine shrimp lethality assay. Eight synergistic interactions were identified against the selected Gram-positive and P. aeruginosa pathogens, and the combinations also demonstrated a reduced toxicity. The combination of amoxicillin and eugenol demonstrated the lowest toxicity (LC50 = 1081 µg/mL) and the highest selectivity index (14.41) when in a 70:30 ratio. This study provides insight into the in vitro antimicrobial interactions of essential oil compounds and conventional antibiotics that can form a basis for newer therapies.

Commercially Available Viola odorata Oil, Chemical Variability and Antimicrobial Activity.

Viola odorata L. oil is frequently recommended in the aromatherapeutic literature for treating respiratory, urinary, and skin infections; however, antimicrobial evidence is lacking. In addition, in aromatherapy, combinations of essential oils are predominantly utilized with the goal of achieving therapeutic synergy, yet no studies investigating the interaction of essential oil combinations with V. odorata oil exists. This study thus aimed to address these gaps by investigating the antimicrobial activity of three Viola odorata oil samples, sourced from different suppliers, independently and in combination with 20 different commercial essential oils, against micro-organisms involved in respiratory, skin, and urinary tract infections associated with global resistance trends. These pathogens include several of the ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) The chemical profile of the oils was determined using gas chromatography coupled with mass spectrometry. The minimum inhibitory concentrations (MIC) were determined using the broth micro-dilution method. The interactive profiles for the combinations were assessed by calculating the fractional inhibitory concentration index (ΣFIC). The main compounds varied across the three samples, and included phenethyl alcohol, isopropyl myristate, 2-nonynoic acid, methyl ester, α-terpineol, α-cetone, and benzyl acetate. The V. odorata oil samples displayed overall poor antimicrobial activity when tested alone; however, the antimicrobial activity of the combinations resulted in 55 synergistic interactions where the combination with Santalum austrocaledonicum resulted in the lowest MIC values as low as 0.13 mg/mL. The frequency of the synergistic interactions predominantly occurred against Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Enterococcus faecium with noteworthy MIC values ranging from 0.25-1.00 mg/mL. This study also reports on the variability of V. odorata oils sold commercially. While this warrants caution, the antimicrobial benefit in combination provides an impetus for further studies to investigate the therapeutic potential.

Headspace analysis and characterisation of South African propolis volatile compounds using GCxGC-ToF-MS

ABSTRACT Propolis also known as "bee glue or bee resin" is a resinous mixture of bee saliva or bee wax and exudate from tree trunks and flowers, produced by honeybees. The composition of propolis varies depending on the vegetation the bees can access. It is therefore expected that propolis obtained from various localities may have different chemical profiles. In this study, the headspace volatiles of propolis (n = 39) collected from various locations in South Africa (Gauteng, Northern Cape and Western Cape Provinces) were explored for the first time using GCxGC-ToF-MS. Several GCxGC parameters were optimised including; incubation time, temperature and modulation period. Multivariate data analysis techniques (principal component and hierarchical cluster analyses) were applied on the GCxGC-ToF-MS data to investigate trends and clustering patterns within propolis samples. The results demonstrated that headspace volatiles of propolis varied between locations. The volatile profiles were dominated by monoterpenes such as α-pinene (1.2-46.5%), β-pinene (2.0-21.8%), dihydrosabinene (trace-17.8%), limonene (trace-11.6%), p-cymene (0.1-5.3%), 1,8-cineole (0.1-11.0%), 2,7-dimethyl-3-octen-5-yne (trace-11.7%), E-β-ocimene (trace-17.8%), octanal (trace-12.9%), styrene (trace-13.5%) and α-thujene (trace-11.0%). Principal component analysis revealed chemical variation within propolis from the various locations. The heatmap of the averages revealed dehydrosabinene, isopropentyltoluene, p-cymene, acetophenone and α-thujene as chemical markers for the Northern Cape propolis, while λ-terpinene, propanoic acid, furfural, 2-methoxy benzyl alcohol and hexanoic acid methylester were filtered out as markers for Gauteng propolis. The propolis samples originating from the Western Cape Province were dominated by prenal, cinnamaldehyde styrene, 1,8-cineole, decanal, prenyl acetate and butanoic acid. Using GCxGC-ToF-MS in combination with chemometrics, it was possible to profile headspace volatile constituents of propolis and further identify marker compounds that differentiate propolis from various provinces in South Africa.