Candida parapsilosis Colony Morphotype Forecasts Biofilm Formation of Clinical Isolates

Abstract

Candida parapsilosis is a frequent cause of fungal bloodstream infections, especially in critically ill neonates or immunocompromised patients. Due to the formation of biofilms, the use of indwelling catheters and other medical devices increases the risk of infection and complicates treatment, as cells embedded in biofilms display reduced drug susceptibility. Therefore, biofilm formation may be a significant clinical parameter, guiding downstream therapeutic choices. Here, we phenotypically characterized 120 selected isolates out of a prospective collection of 215 clinical C. parapsilosis isolates, determining biofilm formation, major emerging colony morphotype, and antifungal drug susceptibility of the isolates and their biofilms. In our isolate set, increased biofilm formation capacity was independent of body site of isolation and not predictable using standard or modified European Committee on Antimicrobial Susceptibility Testing (EUCAST) drug susceptibility testing protocols. In contrast, biofilm formation was strongly correlated with the appearance of non-smooth colony morphotypes and invasiveness into agar plates. Our data suggest that the observation of non-smooth colony morphotypes in cultures of C. parapsilosis may help as an indicator to consider the initiation of anti-biofilm-active therapy, such as the switch from azole- to echinocandin- or polyene-based strategies, especially in case of infections by potent biofilm-forming strains.

High Biofilm Formation of Non-Smooth Candida parapsilosis Correlates with Increased Incorporation of GPI-Modified Wall Adhesins

“…C. parapsilosis strains used in this study were part of a previously described strain collection [12]. Strains were maintained on YPD (1% yeast extract, 2% peptone, and 2% glucose) or Sabouraud (Oxoid GmbH, Wesel, Germany) agar.…”

“…Biofilm production of C. parapsilosis strains to plastic (polystyrene) was determined in microtiter plates with the crystal violet (CV, Sigma) assay after 24 h of incubation in YPD at 37 • C in a moist environment, as detailed in [12].…”

“…Agar invasion capacity of C. parapsilosis strains was tested as previously described by [12,13]. Cells were plated on YPD agar supplemented with 5 mg/mL of Phloxine B and allowed to grow for ten days.…”

“…Agar invasion was scored by gently scraping colonies with an inoculation loop while washing off the cells under running water at day ten of incubation. Agar invasion was defined on a rating scale from low (1) to high (5) invasion as described [12].…”

“…parapsilosis isolates have been shown to produce colonies with different shapes, which roughly can be divided into smooth and various non-smooth morphotypes, such as crepe and concentric. Most isolates present stable dominant phenotypes, but occasional morphotype switching has been observed [12,13]. Furthermore, isolates with irregular non-smooth morphotypes show elongated cellular morphologies (pseudohyphae) and have a higher capacity to form biofilms [12,13].…”