Candida albicans

Shmuel Shoham, M.D.
Candida albicans is a topic covered in the Johns Hopkins ABX Guide.

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MICROBIOLOGY

  • 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, the 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 the ability to bud [Fig 1].
      • 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) [Fig 2].
    • True hyphae: filamentous structures composed of cells uniform in width [Fig 3].
      • 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 the ends of hyphae [Fig 4].
      • 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 the 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, chromogenic 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.
    • T2Candida: Nano diagnostic tool that utilizes T2 magnetic resonance and a dedicated instrument to detect Candida directly in a whole blood sample.
      • Time to positivity and initiation of antifungal therapy significantly shorter compared to traditional blood cultures
      • Sensitivity is generaly as good and even better than standard blood culture techniques. Sensitivity is superior to blood cultures in cases of prior antifungal therapy, neutropenia, and C. albicans candidemia.

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MICROBIOLOGY

  • 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, the 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 the ability to bud [Fig 1].
      • 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) [Fig 2].
    • True hyphae: filamentous structures composed of cells uniform in width [Fig 3].
      • 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 the ends of hyphae [Fig 4].
      • 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 the 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, chromogenic 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.
    • T2Candida: Nano diagnostic tool that utilizes T2 magnetic resonance and a dedicated instrument to detect Candida directly in a whole blood sample.
      • Time to positivity and initiation of antifungal therapy significantly shorter compared to traditional blood cultures
      • Sensitivity is generaly as good and even better than standard blood culture techniques. Sensitivity is superior to blood cultures in cases of prior antifungal therapy, neutropenia, and C. albicans candidemia.

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Last updated: October 10, 2021