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- C. albicans: the most important Candida species.
- Colonizer/commensal of GI and GU tracts and skin.
- This species accounts for nearly all mucosal candidiasis and is the most common cause of invasive disease.
- Epidemiology does vary by geographical region, extent of antifungal (esp. azole class) exposure and local hospital epidemiology.
- Fungal organism has multiple morphologies (depending upon environmental conditions):
- Yeast: spherical single cells with ability to bud.
- Usually about 3-6µm in diameter.
- Likely important in facilitating dissemination through fluids (e.g. saliva, urine, water, bloodstream) to distant sites.
- Pseudohyphae: filamentous structures composed of elongated yeast cells in chains and have constrictions at septal junctions (rather than true septa).
- True hyphae: filamentous structures composed of cells with uniform in width.
- Have true septa and facilitate invasion of tissues.
- Germ tube: when incubated in serum, C. albicans and C. dubliniensis form an early hyphal structure called the germ tube (although ~5% may be initially called germ-tube negative).
- For this reason preliminary identification reports from the microbiology laboratory will often read "C. albicans/C. dubliniensis.
- Because it is much more common than C. dubliniensis, almost invariably the actual species in such circumstances is C. albicans.
- Chlamydospores: rounded, thick walled structures, several times the size of the yeast, typically found at ends of hyphae.
- Seen with C. albicans and C. dubliniensis.
- Diagnostic tests:
- Stains: organisms may be visualized via KOH, Gram stain, calcofluor white, Grocott-Gomori’s methenamine silver (GMS) and periodic-acid-Schiff (PAS).
- Culture: grows aerobically in a range of media including blood culture broth, blood agar, Sabouraud agar and Mueller Hinton agar.
- Blood cultures, continuous monitoring systems: these modern systems are as good as lysis centrifugation ("fungal isolator") method.
- False-negative blood cultures: common in candidemia and with any blood culture technique.
- Identification of individual species: facilitated microscopic morphology, biochemical tests, chromatogenic agar and PNA FISH techniques.
- Serum beta D glucan (BDG): non-specific test for fungal infections.
- Levels >60-80 pg/ml suggest invasive disease.
- Causes of false positives include severe burns, extensive gauze packing, other fungal infections.
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