USMLE

Candida albicans

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Fungi
  1. Histoplasma
  2. Blastomyces
  3. Coccidioides
  4. Paracoccidioides
  5. Tinea (Dermatophytes)
  6. Malassezia
  7. Candida albicans
  8. Aspergillis fumigatus
  9. Cryptococcus neoformans
  10. Mucor and Rhizopus
  11. Pneumocystis jirovecii
  12. Sporothrix schenckii

Summary

Candida albicans is a fungus that acts as an opportunistic pathogen to cause various infections in people. Candida exists as a single cell budding yeast with pseudohyphae that forms colonies with a distinctive white color. In the presence of food, the fungus can also generate hyphal germ tubes. 

As an opportunistic pathogen, Candida is a component of our normal skin and mucosal flora, and infections are seen mainly in immunocompromised patients or patients with a history of antibiotic use.

Clinically candida infections can present as thrush in the mouth and esophagus, vaginitis, or intertrigo in skin folds.  Most mild candida infections are treated with conazole antifungals, like fluconazole. Oral and esophageal thrush may be treated with Nystatin in a swish and swallow formulation. Finally, for severe disseminated infections, echinocandins, like caspofungin, should be administered.

Key Points

  • Candida albicans
    • Characteristics
      • Single-celled budding yeast with pseudohyphae
        • Pseudohyphae are not true hyphae but elongated yeast cells
      • Forms hyphal germ tubes  when food is readily available
      • Creamy white color of fungus and colonies
        • Candida is from Latin candidus (meaning white)
        • Albicans is from Latin albico (meaning becoming white)
    • Transmission
      • Opportunistic
        • Component of normal flora; rarely infects healthy people
        • Seen in immunocompromised patients
          • E.g. obesity, diabetes, steroids, chemo, HIV/AIDS, BMT, chemotherapy, neonates, elderly
          • Patients with impaired T-cells (or neutrophils) are particularly susceptible
            • Candida skin test
              • Small candida extract injected into skin
              • Used to test for Type 4 (delayed cellular) hypersensitivity
              • Reaction indicates normal functioning T-cells
        • Associated with antibiotic use
          • Kills other microorganisms (e.g. lactobacilli in vagina), opening niche for candida overgrowth
    • Presentation
      • Oral and esophageal thrush
        • Most common cause of HIV esophagitis
        • Presents with odynophagia
        • Endoscopy reveals white plaques on erythematous skin or mucosa
      • Vaginitis
        • Most common cause of fungal vaginitis
        • Presents with itchiness, redness, and white curd-like discharge
      • Candida intertrigo
        • Erythematous (red) plaques with satellite papules
        • Seen in skin folds with increased moisture and friction
          • E.g. axillae, groin, web spaces of fingers/toes, etc.
        • Responsible for diaper rash in neonates
      • Disseminated candidemia is rare
        • Usually seen in IV drug users
        • Endocarditis, renal or bladder abscesses, may be seen
    • Diagnosis
      • Diagnosis is primarily clinical
      • Yeasts and pseudohyphae seen on microscopy, with positive germ tube test
    • Treatment
      • Fluconazole for uncomplicated vaginitis or oral/esophageal infections
        • Boric acid, nystatin, amphotericin B, and flucytosine may be added for complicated vaginitis
        • Itraconazole, posaconazole, or voriconazole also used for oral/esophageal candidiasis
      • Nystatin also used for oropharyngeal infections
      • Echinocandins (caspofungin) used for severe disseminated infections
        • Fluconazole and amphotericin are second-line