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Updated: Jun 3, 2026
Clarifying and Imaging Candida albicans Biofilms
Published on: March 6, 2020
Pellicle associated adherence film above incubation broth surface - an inexpensive adjunct to recognizing Candida
Jacob Fleischmann1, Elia M Sripuntanagoon
1Research Division Greater Los Angeles VA Healthcare System, 16111 Plummer St, North Hills, California, 91343, USA. jfl@ucla.edu.
Background:
Candida species including Candida krusei have become common pathogens, especially in immune-compromised patients. Pellicle on the surface of incubating nutrient broth extending with an adherent film above the broth has been described as a feature of this organism. We investigated whether this easily observable adherent film could be useful in the identification of this yeast. We also wanted to see if this process involved any morphological changes from the yeast form on the part of C. krusei.
Findings:
Common and less frequently isolated species of Candida were inoculated into YPD broth and observed for pellicle formation. For C. krusei different inoculum sizes and time periods were studied to establish earliest period and the smallest number of organisms needed for this process. A cover-slip assay was established to observe the architecture of the film formed by this organism. Among the clinically common Candida species, only C. krusei formed a visible film, requiring 106 organisms to produce it at 24 hours post inoculation. Film formation also differentiated C. krusei from C. inconspicua usually reported as a complex by carbohydrate assimilation assays. Rarely isolated C. famata and C. norvegensis also formed pellicles and film but less robustly. Microscopic observations of the film showed only yeast forms, no hypha or pseudohypha were seen.
Conclusions:
Pellicle formation following inoculation of a clinical specimen into liquid culture, is a useful alert to the probable presence of C. krusei and likely fluconazole resistance, while awaiting the results of more definitive identification assays. Pellicle and adherence film formation are not a result of polymorphic changes on the part of C. krusei as only yeast forms were present.
Insights
Pellicle formation in liquid culture can quickly alert clinicians to the likely presence of Candida krusei, a yeast often resistant to fluconazole. This observable film consists only of yeast cells, not hyphae or pseudohyphae.
Area of Science:
- Medical Mycology
- Clinical Microbiology
Background:
- Candida species, including Candida krusei, are significant pathogens, particularly in immunocompromised individuals.
- Pellicle formation, an adherent film on liquid culture surfaces, has been described as a characteristic of Candida krusei.
- The study aimed to evaluate the diagnostic utility of pellicle formation for identifying Candida krusei and to investigate associated morphological changes.
Purpose of the Study:
- To determine if pellicle formation is a reliable indicator for identifying Candida krusei.
- To assess if Candida krusei undergoes morphological changes during pellicle formation.
- To explore the potential of pellicle formation as an early alert for probable fluconazole resistance.
Main Methods:
- Various Candida species were inoculated into YPD broth to observe pellicle formation.
- Specific parameters for Candida krusei, including inoculum size and incubation time, were optimized.
- Cover-slip assays were used to examine the microstructure of the formed film.
Main Results:
- Only Candida krusei consistently formed a visible pellicle and adherent film, requiring 10^6 organisms at 24 hours.
- Pellicle formation distinguished Candida krusei from Candida inconspicua.
- Microscopic examination revealed only yeast forms in the film, with no evidence of hyphae or pseudohyphae.
Conclusions:
- Pellicle formation serves as a valuable preliminary indicator for the presence of Candida krusei in clinical specimens.
- This observation can suggest likely fluconazole resistance, prompting further definitive identification.
- The formation of pellicle and adherent films by Candida krusei does not involve polymorphic changes, as only yeast cells are present.
