Candida species

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

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MICROBIOLOGY

  • The most important species is C. albicans, which causes nearly all mucosal candidiasis and is generally the most common cause of invasive disease. However, epidemiology varies by geographical region, the extent of antifungal (esp. azole class) exposure and local hospital epidemiology.
    • Other species of importance are C. glabrata (also known as Nakaseomyces glabrata), C. parapsilosis (especially in association with implanted devices), C. tropicalis, C. krusei (also known as Pichia kudriavzevii), C. guilliermondii, C. kefyr, C. lusitaniae and C. auris (which is associated with multidrug resistance and healthcare facility outbreaks)
    • See separate module for Candida albicans.
  • Multiple morphologies (depending upon species and environmental conditions)
    • Yeast: spherical single cells with the ability to bud. Usually about 3-6 µm in diameter [Fig 1].
      • Likely important in facilitating dissemination through fluids (e.g. saliva, urine, water, bloodstream) to distant sites.
      • The yeast forms of C. glabrata tend to be smaller at about 2-5 µm.
    • Pseudohyphae: filamentous structures composed of elongated yeast cells in chains and have constrictions at septal junctions (rather than true septa, Fig 2).
      • Pseudohyphae are NOT seen with C. glabrata
    • True hyphae: filamentous structures composed of cells uniform in width [Fig 3]. Have true septa.
      • Typically seen with C. albicans, C. dubliniensis and C. tropicalis. Facilitate invasion of tissues
      • Germ tube: when incubated in serum, C. albicans and C. dubliniensis form an early hyphal structure called the germ tube. This can be used for rapid and preliminary identification of these species.
    • Chlamydospores: rounded, thick-walled structures, several times the size of the yeast, typically found at 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.
      • For blood cultures, continuous monitoring systems are as good as the lysis centrifugation ("fungal isolator") method.
      • False negatives are common in candidemia with any blood culture technique.
    • Identification of individual species facilitated by microscopic morphology, biochemical tests, chromogenic agar, multiplex PCR, MALDI-TOF and PNA FISH techniques.
    • Serum beta D glucan (BDG): Levels >60-80 pg/ml suggest invasive disease. Causes of false positives include severe burns, extensive gauze packing, other fungal infections.
    • T2: A nano diagnostic assay using magnetic resonance to detect Candida directly from blood samples: High sensitivity and negative predictive value.
  • Candida auris
    • May be misidentified as other Candida species including C. haemulonii, C. duobushaemulonii, C. guilliermondii, C. lusitaniae, C. parapsilosis and C. famata
    • MALDI-TOF and PCR can be useful for accurate identification and updated versions of commercial yeast identification platforms are increasingly evolving to be able to identify C. auris.

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MICROBIOLOGY

  • The most important species is C. albicans, which causes nearly all mucosal candidiasis and is generally the most common cause of invasive disease. However, epidemiology varies by geographical region, the extent of antifungal (esp. azole class) exposure and local hospital epidemiology.
    • Other species of importance are C. glabrata (also known as Nakaseomyces glabrata), C. parapsilosis (especially in association with implanted devices), C. tropicalis, C. krusei (also known as Pichia kudriavzevii), C. guilliermondii, C. kefyr, C. lusitaniae and C. auris (which is associated with multidrug resistance and healthcare facility outbreaks)
    • See separate module for Candida albicans.
  • Multiple morphologies (depending upon species and environmental conditions)
    • Yeast: spherical single cells with the ability to bud. Usually about 3-6 µm in diameter [Fig 1].
      • Likely important in facilitating dissemination through fluids (e.g. saliva, urine, water, bloodstream) to distant sites.
      • The yeast forms of C. glabrata tend to be smaller at about 2-5 µm.
    • Pseudohyphae: filamentous structures composed of elongated yeast cells in chains and have constrictions at septal junctions (rather than true septa, Fig 2).
      • Pseudohyphae are NOT seen with C. glabrata
    • True hyphae: filamentous structures composed of cells uniform in width [Fig 3]. Have true septa.
      • Typically seen with C. albicans, C. dubliniensis and C. tropicalis. Facilitate invasion of tissues
      • Germ tube: when incubated in serum, C. albicans and C. dubliniensis form an early hyphal structure called the germ tube. This can be used for rapid and preliminary identification of these species.
    • Chlamydospores: rounded, thick-walled structures, several times the size of the yeast, typically found at 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.
      • For blood cultures, continuous monitoring systems are as good as the lysis centrifugation ("fungal isolator") method.
      • False negatives are common in candidemia with any blood culture technique.
    • Identification of individual species facilitated by microscopic morphology, biochemical tests, chromogenic agar, multiplex PCR, MALDI-TOF and PNA FISH techniques.
    • Serum beta D glucan (BDG): Levels >60-80 pg/ml suggest invasive disease. Causes of false positives include severe burns, extensive gauze packing, other fungal infections.
    • T2: A nano diagnostic assay using magnetic resonance to detect Candida directly from blood samples: High sensitivity and negative predictive value.
  • Candida auris
    • May be misidentified as other Candida species including C. haemulonii, C. duobushaemulonii, C. guilliermondii, C. lusitaniae, C. parapsilosis and C. famata
    • MALDI-TOF and PCR can be useful for accurate identification and updated versions of commercial yeast identification platforms are increasingly evolving to be able to identify C. auris.

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Last updated: October 10, 2021