Biofilm formation by Candida dubliniensis

Candida dubliniensis is an opportunistic yeast closely related to Candida a lbicans that has been recently implicated in oropharyngeal candidiasis in h uman immunodeficiency virus-infected patients. Most manifestations of candi diasis are associated with biofilm formation, with cells in biofilms displa ying properties dramatically different from free-living cells grown under n ormal laboratory conditions. Here, we report on the development of in vitro models of C. dabliniensis biofilms on the surfaces of biomaterials (polyst yrene and acrylic) and on the characteristics associated with biofilm forma tion by this newly described species. Time course analysis using a formazan salt reduction assay to monitor metabolic activities of cells within the b iofilm, together with microscopy studies, revealed that biofilm formation b y C. dubliniensis occurred after initial focal adherence, followed by growt h, proliferation, and maturation over 24 to 48 h. Serum and saliva precondi tioning films enhanced the initial attachment of C. dubliniensis and subseq uent biofilm formation. Scanning electron microscopy and confocal scanning laser microscopy were used to further characterize C. dubliniensis biofilms . Mature C. dubliniensis biofilms consisted of a dense network of yeasts ce lls and hyphal elements embedded within exopolymeric material. C. dublinien sis biofilms displayed spatial heterogeneity and an architecture showing mi crocolonies with ramifying water channels. Antifungal susceptibility testin g demonstrated the increased resistance of sessile C. dubliniensis cells, i ncluding the type strain and eight different clinical isolates, against flu conazole and amphotericin B compared to their planktonic counterparts. C. d ubliniensis biofilm formation may allow this species to maintain its ecolog ical niche as a commensal and during infection with important clinical repe rcussions.