Abstract
Objectives: Previous research from this group has identified significant antimicrobial activity associated with oil-in-water (O/W) microemulsions. This activity has been exhibited against both bacteria and fungi (including yeasts) and bacterial biofilms and is dependent upon the position of the microemulsion within its stability zone. This novel work aims to identify antimicrobial activity of water-in-oil (W/O) microemulsions. Materials & Methods: A simple, thermodynamically stable water-in-oil microemulsion was tested for its time-related antimicrobial activity against a selected panel of test microorganisms (i.e.: Pseudomonas aeruginosa ATCC 9027, Escherichia coli ATCC 8739, Candida albicans ATCC 10231 and Staphylococcus aureus ATCC 6538P) and its effectiveness as a self-preserving system against a similar panel (Pseudomonas aeruginosa ATCC 9027, Candida albicans ATCC 10231, Staphylococcus aureus ATCC 6538P and Aspergillus niger ATCC 16404). Results: The microemulsion exhibited significant antimicrobial activity against all the selected microorganisms. Decreases in the viability of cultures (P. aeruginosa, C. albicans, E. coli and S. aureus) were observed over a short period of time after exposure to a known concentration of the first microemulsion. The results for the four samplings in the preservative effectiveness test according to the European Pharmacopeia requires a significant reduction in bacterial count, and this requirement was achieved in all samplings. Conclusions: Thermodynamically stable water-in-oil microemulsions are antimicrobially active, self-preserving systems, as are their oil-in-water counterparts.
Highlights
In recent years there has been a dramatic increase in the utilization of microemulsion systems in pharmaceutical systems, largely as carrier and delivery systems
According to the European Pharmacopeia, the results of the preservative effectiveness test require a significant reduction in bacterial count, and this requirement was achieved against all test microorganisms
This work [2] concluded that microemulsions are stable, selfpreserving antimicrobial agents with highly effective killing rates against Staphylococcus aureus and the resistant bacterial species Pseudomonas aeruginosa, and that microemulsions have an effect on the structure and performance of the microbial cytoplasmic membrane
Summary
In recent years there has been a dramatic increase in the utilization of microemulsion systems in pharmaceutical systems, largely as carrier and delivery systems. There are few studies on their antimicrobial activity per se, but researchers have shown an increased interest in this field. The possibility of microemulsions having an antimicrobial action was suggested by Friberg [1], who observed that bacteria cannot survive in pure fat or oil and that water is necessary for their growth and reproduction. Friberg’s comments suggested the hypothesis that the chemical structure of thermodynamically stable microemulsions is harmful to microbial cells. This work [2] concluded that microemulsions are stable, selfpreserving antimicrobial agents with highly effective killing rates against Staphylococcus aureus and the resistant bacterial species Pseudomonas aeruginosa, and that microemulsions have an effect on the structure and performance of the microbial cytoplasmic membrane
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