Blocking of Candida albicans biofilm formation by cis-2-dodecenoic acid and trans-2-dodecenoic acid

Candida is an important opportunistic human fungal pathogen. Infections caused by Candida albicans are related to the formation of a biofilm. The biofilm enhances the resistance of the C. albicans defence system, increases its resistance to antifungal drugs and induces increased drug tolerance, making clinical care more challenging. The in vitro activity of cis-2-dodecenoic acid (BDSF; a diffusible signal factor from Burkholderia cenocepacia) and trans-2-dodecenoic acid (trans-BDSF) against C. albicans growth, germ-tube germination and biofilm formation was estimated by absorbance measurements and microscopic assessments. C. albicans biofilms were prepared using a static microtitre plate model. Quantitative analysis of biofilm formation was performed using a 2,3-bis(2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide reduction assay to evaluate the effect of different concentrations of BDSF and trans-BDSF at different stages of biofilm formation. Reductions in biofilm structure and formation were visualized by inverted microscopy. Real-time RT-PCR was employed to estimate the mRNA expression levels of the hyphae-specific genes HWP1 and ALS3. It was found that 30 mu M of either BDSF or trans-BDSF reduced germ-tube formation by approximately 70% without inhibiting yeast growth. Yeast growth was strongly repressed by the exogenous addition of 300 mu M BDSF and trans-BDSF at 0 and 1 h after cell attachment, with biofilm formation being reduced by approximately 90 and 60%, respectively. BDSF and trans-BDSF were more effective against biofilm formation than farnesol and the diffusible signal factor cis-11-methy1-2-dodecenoic acid. None of the four drugs was able to destroy pre-formed biofilms. Real-time RT-PCR analysis showed that HWP1 was downregulated by approximately 90% and ALS3 was downregulated by 70-80 % by 60 mu M BDSF and trans-BDSF, implying that BDSF and trans-BDSF block C. albicans biofilm formation by interfering with the morphological switch. These results suggest that BDSF and trans-BDSF are potentially useful therapeutic agents worthy of further study.