Biofilm formation of Candida spp. isolates from patients at a cardiothoracic intensive care unit

Invasive Candida infections in seriously ill patients are rare but associated with high mortality, while Candida colonization of the mucocuteneous surfaces is common in patients admitted to intensive care units. To investigate biofilm formation as a possible virulence factor, we analyzed the biofilm formation of 128 non-invasive isolates from long-term ICU patients and that of 106 invasive bloodstream isolates. Candida biofilms were quantified by the percent transmittance (%Tbloc) method. Crystal Violet (CV) staining was used as marker of biofilm thickness, and XTT assay was used as a marker of the metabolic activity of Candida cells. The ability of biofilm formation was 99.2% in the non-invasive isolates versus 96.2% in the bloodstream isolates (%Tbloc vs.%Tbloc not significant). However, high biofilm production (%Tbloc, ≥35) was more frequent among the non-invasive isolates compared to the bloodstream isolates (78.1 vs. 72.5, p<0.001).