Microemulsions are membrane-active, antimicrobial, self-preserving systems

Microemulsions are physically stable oil/water systems that have potential use as delivery systems for many pharmaceuticals which are normally of limi ted use due to their hydrophobicity, toxicity or inability to access the si te of action. It has been suggested that microemulsions are self-preserving antimicrobials in their own right, although there is little evidence to su pport this. In this experiment, microemulsions of various compositions were formulated and tested for their stability and antimicrobial action. The ph ysical stability of the different microemulsions was assessed by centrifuga tion at 4000 g and by storage in a water bath at 37 degrees C for one month , during which no phase separation was observed. The antimicrobial activity of the microemulsions was tested using the compendial method, observation of the kinetics of killing, and transmission electron microscopy (TEM) of m icroemulsion-exposed cultures of Pseudomonas aeruginosa PA01. These latter experiments on Ps. aeruginosa indicated distinct signs of membrane disrupti on. The results indicated that the microemulsions are self-preserved, and t hat their killing of microbial cultures is very rapid and may be the result of membrane activity.