Characterization of Biofilm Formation and the Role of BCR1 in Clinical Isolates of Candida parapsilosis

InCandida parapsilosis , biofilm formation is considered to be a major virulence factor. Previously, we determined the ability of 33 clinical isolates causing bloodstream infection to form biofilms and identified three distinct groups of biofilm-forming strains (negative, low, and high). Here, we establish two different biofilm structures among strains forming large amounts of biofilm in which strains with complex spider-like structures formed robust biofilms on different surface materials with increased resistance to fluconazole. Surprisingly, the transcription factor Bcr1, required for biofilm formation inCandida albicans andC. parapsilosis , has an essential role only in strains with low capacity for biofilm formation. AlthoughBCR1 leads to the formation of more and longer pseudohyphae, it was not required for initial adhesion and formation of mature biofilms in strains with a high level of biofilm formation. Furthermore, an additional phenotype affected byBCR1 was the switch in colony morphology from rough to crepe, but only in strains forming high levels of biofilm. Allbcr1 Δ/Δ mutants showed increased proteolytic activity and increased susceptibility to the antimicrobial peptides protamine and RP-1 compared to corresponding wild-type and complemented strains. Taken together, our results demonstrate that biofilm formation in clinical isolates ofC. parapsilosis is both dependent and independent ofBCR1 , but even in strains which showed aBCR1 -independent biofilm phenotype,BCR1 has alternative physiological functions.