Rhamnolipids as emulsifying agents for essential oil formulations: antimicrobial effect against Candida albicans and methicillin-resistant Staphylococcus aureus.

This work examines the influence of essential oil composition on emulsification with rhamnolipids and their use as therapeutic antimicrobial agents against two opportunistic pathogens, methicillin-resistant Staphylococcus aureus (MRSA) and Candida albicans. Rhamnolipids, produced by Pseudomonas aeruginosa, with waste frying oil as the carbon source, were composed of eight rhamnolipid homologues. The rhamnolipid mixture was used to produce emulsions containing essential oils (EOs) of Melaleuca alternifolia, Cinnamomum verum, Origanum compactum and Lavandula angustifolia using the titration method. Ternary phase diagrams were designed to evaluate emulsion stability, which differed depending on the essential oil. The in vitro antimicrobial activity of the EOs alone and the emulsions was evaluated. The antimicrobial activity presented by the essential oils alone increased with emulsification. The surface properties of rhamnolipids contribute to the positive dispersion of EOs and thus increase their availability and antimicrobial activity against C. albicans and S. aureus. Therefore, rhamnolipid-based emulsions represent a promising approach to the development of EO delivery systems.

Hydroxy-fatty acid production in a Pseudomonas aeruginosa 42A2 PHA synthase mutant generated by directed mutagenesis.

Pseudomonas aeruginosa 42A2 growing on waste frying oils is capable to synthesize polyhydroxyalkanoic acids (PHAs) and hydroxy-fatty acids as a result of several enzymatic conversions. In order to study the physiological role of PHA biosynthesis in P. aeruginosa with respect to the synthesis of hydroxy-fatty acids, an unmarked deletion mutant deficient for PHA biosynthesis was generated in P. aeruginosa 42A2. A combination of the sacB-based negative selection system with a cre-lox antibiotic marker recycling method was used for mutant isolation. Electron microscopy, nuclear magnetic resonance analysis, and transmission electron microscopy confirmed that PHA accumulation was completely abolished in the mutant strain. Interestingly, the new mutant strain showed higher carbon and oxygen uptake rate than the wild-type strain and higher efficiency in the conversion of oleic acid into (E)-10-hydroxy-8-octadecenic acid-octadecenoic acid.