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| Anti-biofilm nanoemulsions Nano-Emulsion Technology 1. Microemulsion Microemulsions are spontaneously forming, fluid, oil and water dispersions stabilized by a surfactant and typically a cosurfactant. The size of the nanodroplets in a microemulsion is typically in the range 10-100nm. To date microemulsions have found application in drug delivery, particle engineering, food and beverages and chemical synthesis. They believe that microemulsions offer an exciting (but as yet untested) alternative to disinfectants and biocides (e.g. formaldehyde, phenols and sodium hypochlorite) as agents both to prevent the formation of bioflims and to facilitate the formation of an anti-bacterial film. However there are only a few studies exploring the potential of microemulsion as an effective anti-microbial agent for use as an anti-biofilm agent for industrial and environmental applications. For example microemulsions containing ethyl oleate, Tween® 80 and n-pentanol have been shown to decrease the viability of the two cultures of bacterial cells, Pseudomonas aeruginosa ATCC 9027 and Staphylococcus aureus ATCC 6538, from 106 cell/mL to zero in a minute or a 5 log reduction in bacterial titre within 45 mins. The viability of biofilm culture of Pseudomonas aeruginosa PAO1 was reduced to 3 log-cycle after incubation for 4 hours. The effect of microemulsions on the bacteria was cytoplasmic membrane dysfunction and cell death. Recently TiO2 films have been prepared on stainless steel by dip-coating in a microemulsion containing a TiO2 solution. 2. Nanoemulsion Nanoemulsions, in common with microemulsions, are stable systems that contain small droplets (typically 100-300nm) of one immiscible phase in another but, unlike microemulsions, are formed by the input of a high amount of energy. The group believe that nanoemulsions (a relatively new tool in nanotechnology), like microemulsions, offer potential as anti-biofilm agents. For example the sporicidal and anti-microbial activities of nanoemulsion have been reported. The water-in-oil nanoemulsions used were made from soybean oil, tri-n-butyl phosphate, Triton X-100 and water. The average size of the nanodroplets was about 200-800 nm. A 3-log reduction in the bacterial count of most Gram-positive bacteria, Bacillus subtilis, Bacillus cereus and Streptococcus pneumonia, and some Gram-nagative bacteria, Haemophilus influenzae, Neisseria gonorrhoeae, and Vibrio cholerae, was observed after incubation of bacteria with 1% nanoemulsions5. The resistance of most Gram-negative bacteria (e.g. Escherichia coli, Salmonella typhimurium) was thought to be due to the repulsive interaction of nanoemulsions and the bacterial cell wall. Electron microscopy studies showed a disruption of the spore coat and cortex with distortion and loss of core components of Bacillus cereus after exposure to nanoemulsions diluted 1:100 in the growth medium for 4 hours. The in vivo toxicity and sporicidal activity test of nanoemulsions were done in CD-1 mice. The injection of nanoemulsions diluted 1:10 in normal saline showed no signs of inflammatory reaction. After injection of Bacillus cereus premixed with nanoemulsions, the mice did not develop edema, necrotic lesion or inflammation and the size of necrotic lesion was smaller than that in nanoemulsion-untreated mice. The mechanism of sporicidal activity is unclear but is thought to be mediated by Triton-X-100 and tri-n-butyl phosphate. Nanoemulsions have also been reported to exhibit anti-viral activity against some viruses, namely, Herpes simplex, influenza A, vaccinia and Ebola (strain Zaire) viruses after 15-minute treatment with 1% nanoemulsions by destroying the viral envelope. Additionally, nanoemulsions have been reported to decrease the growth rate of Candida albicans and yeast. |
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