Background: Candida auris, an emerging nosocomial pathogen, exhibits phenotypic variation. Non-aggregating C. auris isolates display greater biofilm-forming capacity and virulence than aggregate-forming isolates. Most of the studies till date have focused on clinical isolates. The biofilm-forming capacity of colonising isolates remains uninvestigated.

Objectives: The present study aimed to elucidate the biofilm-forming capacity of the colonising isolates of C. auris, correlate it with their aggregation behaviour and antifungal susceptibility, and compare it with that of the isolates from blood-stream infection.

Methods: Colonising and clinical (candidemia) isolates of C. auris were screened for aggregation behaviour, biofilm-forming capacity and antifungal susceptibility testing. Aggregation behaviour was assessed microscopically. Biofilm-forming capacity was determined on 96-well flat-bottomed microtitre plates. Antifungal susceptibility testing was performed by broth microdilution assay.

Results: Aggregative and non-aggregative phenotypes were found to be predominantly associated with colonising and clinical isolates, respectively, with the former ones being stronger biofilm producers in the colonising group. Non-aggregative isolates in the colonising group showed lower susceptibility to amphotericin B and fluconazole than aggregative isolates. In contrast, no association was noted between biofilm formation, aggregation behaviour and antifungal susceptibility amongst the clinical isolates.

Conclusion: Biofilm formation is a strain-dependent trait in C. auris, strongly associated with the type and phenotypic behaviour of the isolates. Colonising isolates of this fungus were found to be predominantly aggregative in nature, with a higher biofilm-forming capacity than non-aggregative ones.