title: Human serum inhibits adhesion and biofilm formation in Candida albicans.
abstract: BACKGROUND
  Candida albicans can form biofilms on intravenous catheters; this process plays a key role in the pathogenesis of catheter infections. This study evaluated the effect of human serum (HS) on C. albicans biofilm formation and the expression of adhesion-related genes in vitro. A C. albicans laboratory strain (ATCC90028) and three clinical strains were grown for 24 h in RPMI 1640 supplemented with HS or RPMI 1640 alone (as a control). The growth of biofilm cells of four strains was monitored by a Live Cell Movie Analyzer, and by XTT reduction assay. The expression of the adhesion-related genes BCR1, ALS1, ALS3, HWP1 and ECE1 was analyzed by RT-PCR at three time points (60 min, 90 min, and 24 h).
  
  
  RESULTS
  In the adhesion phase, C. albicans cells kept a Brownian movement in RPMI medium containing HS until a large number of germ tubes were formed. In the control group, C. albicans cells quickly adhered to the bottom of the reaction plate. Compared with RPMI 1640, medium supplemented with 3-50% HS caused a significant decrease in biofilm development (all p < 0.001). However, the presence of HS had no significant inhibitory effect on the pre-adhered biofilms (all p > 0.05). Biofilm formation was also inhibited by heat-inactivated and proteinase K pre-treated HS. The presence of 50% HS did not significantly affect the planktonic growth of C. albicans (p > 0.05). At three time points, HS inhibited expression of the ALS1 and ALS3 genes and promoted expression of the HWP1 and ECE1 genes. Significant up-regulation of BCR1 was observed only at the 90-min point.
  
  
  CONCLUSIONS
  Human serum reduces biofilm formation by inhibiting the adhesion of C. albicans cells. This response may be associated with the down-regulation of adhesion-related genes ALS1, ALS3 and BCR1. The inhibitory serum component is protease-resistant and heat stable.
authors.forename: Xiurong
authors.initials: X
authors.lastname: Ding
authors.forename: Zhizhong
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Clinical Laboratory Center, Beijing Friendship Hospital, Capital Medical University, Beijing 100050, China. sujianrongyy@126.com.
authors.forename: Jianrong
authors.initials: J
authors.lastname: Su
authors.forename: Donghui
authors.initials: D
authors.lastname: Yan
mesh_terms: D018441:Biofilms / Q000187:drug effects*; D002176:Candida albicans / Q000235:genetics / Q000276:immunology* / Q000502:physiology*; D002448:Cell Adhesion / Q000187:drug effects*; D005656:Fungal Proteins / Q000096:biosynthesis; D020869:Gene Expression Profiling; D005800:Genes, Fungal; D006801:Humans; D020133:Reverse Transcriptase Polymerase Chain Reaction; D044967:Serum / Q000276:immunology*
chemical_list: C093538:ALS1 protein, Candida albicans; C113620:ALS3 protein, Candida albicans; D005656:Fungal Proteins