Objectives: Trichosporon species are the second most common etiological agent in catheter-related fungemia, followed by Candida species. The clinical outcome of disseminated trichosporonosis is poorer than that of disseminated candidiasis, and the mortality rate is over 70 %. Trichosporon asahii is the major causative agent of disseminated or deep-seated trichosporonosis. The microorganism can form biofilm on substrates, which can be a cause of fungemia. Assimilation of essential nutrient from their hosts is critical ability for pathogenic microorganisms to proliferate and to form and maintain biofilms.To identify metal cation which affect biofilm formation, we evaluated the effect of cation chelators on biofilm formation in T. asahii. Also T. asahii can change various morphology from yeast to hyphae and arthroconidia. The effect of trace metal on morphology of T. asahii was also investigated. 
Methods: 1) Biofilm formation assays were performed on cells under incubation with a variety of diavalent cation chelators, named EDTA, Deferoxamine, Triethylenetetramine (TETA) and N, N, N’, N’-Tetrakis(2-pyridylmethyl) ethylenediamine (TPEN) by using XTT reduction assay. 2) Biofilm formation was evaluated in the presence of zinc and TPEN. 3) The effects of zinc and TPEN on cell morphology were assessed by light microscopy. 
Results: 1) EDTA, TETA and TPEN inhibited biofilm formation in concentration-dependent manner, and TPEN was most effective (90 % inhibition; 0.5 μM, TPEN; 0.5 mM, EDTA, 5mM, TETA). While deferoxamine did not show inhibitory effect on biofilm formation by 50 mM. 2)  Adding 0.1 μM zinc complemented the biofilm formation which was inhibited by TPEN. 1 μM of zinc promoted biofilm formation compared with TPEN-free medium control. 3) TPEN decresed hyphae formation. While zinc elongated hyphal form conversely.
Conclusion: Our data showed that TPEN, zinc chelator was the most effective for inhibition of biofilm formation by T. asahii. The effect of TPEN on biofilm formation is derived from zinc depletion. TPEN may inhibits biofilm formation through reducing hyphae formation. These results suggest that zinc is essential factor for biofilm formation of T. asahii. Also, the data indicated that hyphal form might be one of the important morphologies for the process of forming biofilms in T. asahii.

TPEN, zinc chelator, inhibits biofilm and hyphae formation by Trichosporon asahii