Overview
Yeasts are unicellular fungi that typically reproduce by budding. In clinical mycology they are recognized by microscopic morphology and creamy colony growth, then identified by institutional pathways.
Classification
| Group cue | Laboratory hint | Caution |
|---|---|---|
| Candida-like | Budding yeast ± pseudohyphae | Not species from smear alone |
| Cryptococcus-like | Capsule prep halo when used | Follow local biosafety/ID SOP |
| Other yeasts | Diverse genera possible | Confirm with validated method |
| Sterile-site yeast | High interpretive priority | Notify per protocol |
Morphologic Features
Round-to-oval budding cells; some form pseudohyphae. Capsule-associated organisms may show a halo on India ink or equivalent preps when performed. Size and budding pattern support yeast recognition, not final speciation.
Laboratory Characteristics
- Often grow on routine bacteriology media at 35–37°C
- Also recovered on fungal media when ordered
- Faster than most molds in many cases
- Species ID requires validated phenotypic or instrument methods
Reference Intervals
No numeric reference interval applies. Interpret recovered/not recovered with site comments. Colony-count thresholds for urine yeast significance, if used, are institutional, verify local policy.
Clinical and Laboratory Significance
Blood and CSF yeast are typically significant pending ID. Mucosal, sputum, and catheter urine recoveries frequently need colonization-versus-infection framing.
Differential Considerations
Distinguish yeast from large Gram-positive cocci, stain precipitate, and artifact. Differentiate colonization from infection using site, quantity, and clinical data, not colony creaminess.
Comparison Tables
Yeast vs mold (lab framing)
| Feature | Yeasts | Molds |
|---|---|---|
| Growth form | Unicellular budding | Filamentous hyphae |
| Colony look | Creamy/opaque | Fuzzy/woolly/powdery often |
| Typical speed | Often faster | Often slower |
| Temp emphasis | Often 35–37°C | Often room temp ± dual |
Classification Frameworks
Not applicable, laboratory morphologic frame, not a WHO disease list.
Laboratory Notes
- Do not finalize species from colony color alone
- Hedge chromogenic and biochemical interpretive charts as local
- No antifungal recommendations in report comments
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- Forbes BA, Sahm DF, Weissfeld AS. Bailey & Scott's Diagnostic Microbiology. 15th ed. Elsevier; 2020.
- Mahon CR, Lehman DC, Manuselis G. Textbook of Diagnostic Microbiology. 6th ed. Elsevier; 2018.
- Carroll KC, Hobden JA, Miller S, et al. Jawetz, Melnick, & Adelberg's Medical Microbiology. 28th ed. McGraw-Hill; 2019.
- Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. 9th ed. Elsevier; 2021.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial Susceptibility Testing. CLSI document M100 (verify current edition and institutional adoption).
- Centers for Disease Control and Prevention / NIH. Biosafety in Microbiological and Biomedical Laboratories (BMBL). Current edition (verify institutional adoption).
Frequently Asked Questions
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