Nobile et al.[30] found that the expression of Hwp1 in Saccharomyces cerevisiae permits adherence to wild-type C. albicans but not an als1Δ/als1Δ als3Δ/als3Δ double RAD001 mutant. In addition, a TDH3-HWP1 hybrid gene could not promote biofilm formation in the als1Δ/als1Δ als3Δ/als3Δ background in vitro or in vivo. Our study revealed that human serum decreased the expression level

of ALS1 and ALS3, so overexpression of HWP1 failed to save the adhesion and biofilm formation of C. albicans. ECE1 was regarded as a hyphal-induced gene, although its mechanism of action is uncertain. Our study showed that hyphae were significantly greater in the presence of serum than in the control group, especially in the mature biofilm stage (data not shown). This may be due to the increase of ECE1 and HWP1[23]. In this study, we also tested the expression of adhesion-related genes in biofilms grown for 24 h and found that the expression trend of related genes at this time was similar to the adhesion phase, both in the reduction of ALS1 and ALS3 and the up-regulation of HWP1 and ECE1. The expression of the BCR1 gene, however, was significantly inhibited. 5-Fluoracil in vitro Its level was far lower than that of the control group. All in all, the serum reduces BCR1 gene expression,

and that might be a reason for biofilm inhibition. Conclusion In summary, our study demonstrated that human serum may reduce the biofilm formation of C. albicans by inhibiting the adhesion. This inhibition is partly due to the down-regulation of adhesion-related genes, including ALS1, ALS3 and BCR1. Meanwhile, the inhibitory effect of human serum is caused by non-protein

components in the serum. Therefore, biofilm formation in vivo may be “selected for” (possibly by immune pressure and sheer forces) rather than “induced” by serum at the level of transcription. Methods Ethics Statement This study was approved by the Medical Ethics Committee of Beijing Friendship Hospital, Capital Medical University, Beijing, China (approval #BJFH-EC/2013-014), and individual informed consent was waived. Organisms Four Candida albicans strains (laboratory strain ATCC90028 and three clinical isolates of C. albicans: 9079, y2991, 31448) were tested in this study. The three C. albicans bloodstream isolates were collected from three different intensive care patients admitted to the Beijing Friendship Hospital and were confirmed according to standard mycological methods, such as the germ tube test in serum, growth on CHROMagar Candida medium, and API testing methods. All isolates were stored in skim milk at -80°C until use. Medium and growth conditions Prior to each experiment, C. albicans strains were subcultured on Sabouraud’s Agar (SDA) at 35°C for 24 h.