The effect of arachidonic acid on lipid metabolism and biofilm formation of two closely related Candida species

English: Candida albicans and C. dubliniensis are two closely related pathogenic yeast species, sharing many phenotypic characteristics which make it difficult to differentiate them, especially in clinical samples. As a result of the similarities between these species, identification techniques, based on phenotypic characteristics, have been developed. In this study some of these techniques and virulence factors were used to characterise strains belonging to these species and to select phenotypically dissimilar strains for further study. This was performed to evaluate if the effect of arachidonic acid (20:4) on these strains were the same, even though they are phenotypically different. Candida albicans and C. dubliniensis can form biofilms which play an important role during infection. During C. albicans infection, 20:4, a long-chain polyunsaturated fatty acid (PUFA), derived from the phospholipids (PLs) of the infected host cell membrane, serves as carbon source and precursor for eicosanoid production. Conflicting results are presented in literature regarding the effect of 20:4 on morphogenesis in C. albicans. In addition, the effect of 20:4 on growth and morphology of C. dubliniensis is unknown. Microscopic examination and enzyme activity assay indicated that 1 mM 20:4 had little to no effect on growth and metabolic activity of planktonic cells and biofilms, as well as on the morphology and viability of the cells in the biofilms. The uptake of PUFAs by yeasts is necessary for utilisation as metabolic fuels, cellular building blocks and the production of signalling molecules. However, there are no definitive studies regarding the uptake and cellular metabolism of 20:4 by these pathogenic yeasts. The uptake and incorporation of 20:4 by planktonic cells and biofilms of selected strains of C. albicans and C. dubliniensis were evaluated by subjecting residual and cellular lipids from planktonic cells and biofilms, grown in the presence and absence of 20:4, to gas chromatography and gas chromatography-mass spectrometry. Strain specific variation in 20:4 uptake and incorporation into different lipid fractions of planktonic cells and biofilms were found. In addition, eicosanoids produced by biofilms in the presence of 20:4 were extracted and it was found that biofilms of these strains were capable of producing 3-hydroxy fatty acids from 20:4. Arachidonic acid can be incorporated into the PLs of yeasts, influencing saturation in cell membranes. It is suggested that the effectiveness of antifungals may depend upon the level of unsaturation and ergosterol content of the membrane, therefore the effect of 20:4 on the cell membrane and susceptibility of C. albicans and C. dubliniensis biofilms towards amphotericin Band clotrimazole were also determined. This was performed by confocal laser scanning microscopy, determination of mitochondrial metabolism, unsaturation index of the PL fractions and ergosterol content of the membranes of biofilms grown in the presence and absence of 20:4. The results indicated that 20:4 influences PL unsaturation and ergosterol content of both C. albicans and C. dubliniensis type strains, increasing susceptibility to the antifungals. Pre-treatment of biofilms with PUFAs may result in the reduction in antifungal dose needed to inhibit biofilms.