Antimicrobial resistance is a major health concern worldwide. A narrowing of the antibiotic development pipeline and a resurgence in public opinion towards 'natural' therapies have renewed the interest in using essential oils as antimicrobial agents. The drawbacks of bulk dosing of essential oils can be mitigated by formulating them as micro- and nanoemulsions. These emulsions have an added advantage as they are in the nanometre size range whose thermodynamic properties enable them to be used as an effective drug delivery system. This review describes the current work on the antimicrobial activities of essential oil micro- and nanoemulsions and their role as drug delivery vehicles.

Amitava Mukherjee

Centre for Nanobiotechnology

Vellore Campus

Chandra Sekaran N

Franklyne J.S

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Letters in Applied Microbiology

Antibiotic resistance is one of the most important public health concerns worldwide. Essential oils especially as micro- and nanoemulsion formulations are emerging as potential agents to target resistant pathogens and as drug delivery vehicles. Cinnamon and clove oils were formulated into nanoemulsions using Brij 35 or Tween 20. Based on the physicochemical characteristics and stability, CiB-3, ClB-3, CiT20-5 and ClT20-5 were identified as optimised emulsions and their anti-Staphylococcal properties were determined. Hydrodynamic diameter of the oil droplets was &lt; 15 nm. The emulsions have only 5% of oil, and there was an 83–166-fold improvement in static MIC over the bulk oil. Inocula ranging from 105 to 107 CFU mL−1 of both MSSA and VISA strains did not significantly affect the activity of all four nanoemulsions. Tween 20 containing nanoemulsions had higher anti-biofilm activity (66–76%) and the activity was comparable between MSSA and VISA. ClT20-5 decreased the viable counts of both strains below detectable limits by 24 h. There was a statistically significant difference in leakage of 260-nm-absorbing cellular components between MSSA and VISA at 30 min (CiB-3: P = 4.67e−013, ClB-3: P = 2.49e−010, CiT20-5: P = 0.00028, ClT20-5: P = 0.00056) and at 60 min (CiB-3: P = 1.37e−014, ClB-3: P = 4.14e−014, CiT20-5: P = 5.30e−012, ClT20-5: P = 2.82e−009). The SEM images of the treated and untreated cells show significant damage and alteration in the morphology of the emulsion treated cells. This study demonstrates the significant anti-Staphylococcal activity of cinnamon and clove oil against MSSA and VISA strains. © 2019, King Abdulaziz City for Science and Technology.

Applied Nanoscience

Cinnamon and clove oil nanoemulsions: novel therapeutic options against vancomycin intermediate susceptible Staphylococcus aureus

Staphyloccocus aureus causes wide range of infections from being mild to crucial problems. Azithromycin macrolide have been in use for many years solving the severity of these infections. But, aqueous insolubility and resistance developed is the question of focus. Considering the need for improvement of the drug properties, we used conventional clove oil based microemulsion drug delivery system for its effective antimicrobial activity and stability of the formulation. This optimized system is prepared using clove oil, tween 20 and water (5:30:65 v/v) by gentle mixing at laboratory environment. The dynamic light scattering technique reports the droplet size range in the nanometer scale with low polydispersity index value. The better quality antibacterial action was further quantified by the liberation of UV absorbing substances at 260 nm confirming structural damage of the treated pathogen. Copyright © 2014 American Scientific Publishers

Journal of Bionanoscience

Microencapsulation of Azithromycin Shows Improved Anti-Bacterial Efficacy

The plant derived essential oil nanoemulsion was prepared using a mixture of components containing eucalyptus oil as organic phase, water as continuous phase, and non ionic surfactant, Tween 80, as emulsifier at a particular proportion of 1:1 v/v%. The ultrasonication was applied for varied processing time from 0 to 30 min to study the effect of time on the formation of nanoemulsion and physical stability of formulation by this method. The transparency and stability of emulsion was enhanced when the sonication time was increased compared to hand blender emulsion. The most stable nanoemulsion was obtained in 30 min sonication having the mean droplet diameter of 3.8 nm. The antibacterial studies of nanoemulsion against Staphylococcus aureus by time kill analysis showed complete loss of viability within 15 min of interaction. Observations from scanning electron microscopy of treated bacterial cells confirmed the membrane damage compared to control bacteria. Furthermore, the wound healing potential and skin irritation activity of the formulated nanoemulsion in Wistar rats, suggested non-irritant and higher wound contraction rate with respect to control and neomycin treated rats. These results proposed that the formulated system could be favourable for topical application in pharmaceutical industries. © 2013 Elsevier B.V. All rights reserved.

Fulltext

Ultrasonics Sonochemistry

Ultrasonic emulsification of eucalyptus oil nanoemulsion: Antibacterial activity against Staphylococcus aureus and wound healing activity in Wistar rats

Candida albicans is a common fungal pathogen that causes systemic and superficial infections in most immunocompromised patients. Fluconazole, a synthetic triazole antifungal agent, is the most prescribed drug used in treating this pathogen. But because of its poor solubilization in water and the emergence of resistant strains against this antimycotic drug, we aimed at devising a unique microemulsion drug delivery system for fluconazole against candidiasis. A clear oil-in-water microemulsion system, consisting of clove oil as oil phase, Tween 20 as surfactant, and water as aqueous phase was developed using a ternary phase diagram. Physicochemical characterization was done to understand the internal physicochemical state. The bulk drug, fluconazole, that measured several microns in length was reduced to a 10-65 nm range with no means of high-energy methods as confirmed by transmission electron microscopy. The very small and uniform spherical structure of the drug-loaded microemulsion system could be of high impact to the biological system as the efficacy of fluconazole is greatly improved when compared with its conventional bulk form. The optimized microemulsion exhibited significantly higher antifungal activity at a minimum concentration (8 μg/ml) of fluconazole as examined by fluorescence and scanning electron microscopy. Thus, our report discloses an excellent oral drug delivery system. © 2013 International Union of Biochemistry and Molecular Biology, Inc.

Biotechnology and Applied Biochemistry

Improved efficacy of fluconazole against candidiasis using bio-based microemulsion technique

Cinnamon oil (extracted from Cinnamomum zeylanicum) nanoemulsion was formulated using Tween 80 and water by ultrasonic emulsification. Process of nanoemulsion formulation was optimized for parameters such as surfactant concentration, oil-surfactant mixing ratio and emulsification time. Surfactant concentration was found to be inversely related to droplet size and directly related to stability. Increase in emulsification time resulted in decrease in droplet diameter. Stable cinnamon oil formulation (CF3) having droplet diameter of 65 nm was formulated after sonication for 30 min. Formulated nanoemulsion was evaluated for bactericidal efficacy against Bacillus cereus. Time and concentration dependent killing of B. cereus cells was observed upon treatment with nanoemulsion. Even at a higher dilution of CF3, significant reduction in bacterial population was observed. Alteration in membrane permeability of interacted samples was suggested by quantifying the release of UV absorbing materials. Bacterial staining with acridine orange/ethidium bromide supported kinetics of killing data and also substantiated the above findings of alteration in membrane permeability. FTIR illustrated disappearance of peak corresponding phosphate vibration at 1078 cm-1 and 536 cm-1, and peak associated with vibration of acyl chains of lipid at 2852 cm-1 was shifted to 2854 cm-1 which suggested deformation of membrane phospholipids in nanoemulsion treated cells. SEM observations demonstrated membrane distortion leading to cell lysis. These results propose the potential use of cinnamon oil nanoemulsion for preservation of minimally processed food. Copyright © 2013 American Scientific Publishers All rights reserved.

Journal of Nanoscience and Nanotechnology

Cinnamon Oil Nanoemulsion Formulation by Ultrasonic Emulsification: Investigation of Its Bactericidal Activity

Basil oil (Ocimum basilicum) nanoemulsion was formulated using non-ionic surfactant Tween80 and water by ultrasonic emulsification method. Process of nanoemulsion development was optimized for parameters such as surfactant concentration and emulsification time to achieve minimum droplet diameter with high physical stability. Surfactant concentration was found to have a negative correlation with droplet diameter, whereas emulsification time had a positive correlation with droplet diameter and also with intrinsic stability of the emulsion. Stable basil oil nanoemulsion with droplet diameter 29.3 nm was formulated by ultrasonic emulsification for 15 min. Formulated nanoemulsion was evaluated for antibacterial activity against Escherichia coli by kinetics of killing experiment. Fluorescence microscopy and FT-IR results showed that nanoemulsion treatment resulted alteration in permeability and surface features of bacterial cell membrane. © 2012 Elsevier B.V. All rights reserved.

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ISSN	0266-8254
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