This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Di Bonaventura, G. Articles by Piccolomini, R. Search for Related Content PubMed PubMed Citation Articles by Di Bonaventura, G. Articles by Piccolomini, R.

 Previous Article  |  Next Article 

Antimicrobial Agents and Chemotherapy, October 2006, p. 3269-3276, Vol. 50, No. 10
0066-4804/06/$08.00+0     doi:10.1128/AAC.00556-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Biofilm Formation by the Emerging Fungal Pathogen Trichosporon asahii: Development, Architecture, and Antifungal Resistance

Laboratory of Clinical Microbiology, Department of Biomedical Sciences, "G. d'Annunzio" University of Chieti-Pescara,¹ Aging Research Center, CeSI, "Gabriele d'Annunzio" University Foundation, Chieti-Pescara, Italy,² Clinical Microbiology Service, Department of Hematology and Oncology, "Santo Spirito" Hospital, Pescara, Italy³

Received 5 May 2006/ Returned for modification 6 June 2006/ Accepted 11 July 2006

Trichosporon asahii is the most common cause of fatal disseminated trichosporonosis, frequently associated with indwelling medical devices. Despite the use of antifungal drugs to treat trichosporonosis, infection is often persistent and is associated with high mortality. This drove our interest in evaluating the capability of T. asahii to form a biofilm on biomaterial-representative polystyrene surfaces through the development and optimization of a reproducible T. asahii-associated biofilm model. Time course analyses of viable counts and a formazan salt reduction assay, as well as microscopy studies, revealed that biofilm formation by T. asahii occurred in an organized fashion through four distinct developmental phases: initial adherence of yeast cells (0 to 2 h), germination and microcolony formation (2 to 4 h), filamentation (4 to 6 h), and proliferation and maturation (24 to 72 h). Scanning electron microscopy and confocal scanning laser microscopy revealed that mature T. asahii biofilms (72-h) displayed a complex, heterogeneous three-dimensional structure, consisting of a dense network of metabolically active yeast cells and hyphal elements completely embedded within exopolymeric material. Antifungal susceptibility testing demonstrated a remarkable rise in the MICs of sessile T. asahii cells against clinically used amphotericin B, caspofungin, voriconazole, and fluconazole compared to their planktonic counterparts. In particular, T. asahii biofilms were up to 16,000 times more resistant to voriconazole, the most active agent against planktonic cells (MIC, 0.06 µg/ml). Our results suggest that the ability of T. asahii to form a biofilm may be a major factor in determining persistence of the infection in spite of in vitro susceptibility of clinical isolates.