What are Candida albicans and non‑albicans Candida species?

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Candida Species Classification

Candida albicans and non-albicans Candida (NAC) species represent distinct taxonomic groups of yeasts with different epidemiological patterns, virulence characteristics, and antifungal susceptibility profiles that are critical for clinical management.

Candida albicans

C. albicans is the most common Candida species causing both mucocutaneous and invasive infections, historically accounting for the majority of candidiasis cases 1, 2. This species:

  • Remains the predominant pathogen in both superficial and invasive candidiasis, though its relative proportion has decreased over recent decades 3, 1
  • Is the primary colonizer of the digestive tract in humans and warm-blooded animals, with limited environmental distribution 4
  • Generally demonstrates predictable susceptibility to most antifungal agents, with resistance remaining uncommon in most settings 1
  • Exhibits susceptibility to fluconazole (≤2 mg/L), amphotericin B (≤1 mg/L), echinocandins, and other azoles according to standardized breakpoints 5

Non-Albicans Candida (NAC) Species

NAC species have emerged as increasingly important pathogens, now accounting for 35-65% of all candidemias and demonstrating distinct resistance patterns 6, 7, 8. The major NAC species include:

The Four Most Common NAC Species

  • C. glabrata: Accounts for 5-40% of candidemias, demonstrates intrinsically reduced azole susceptibility with no established fluconazole susceptibility breakpoint, and shows increasing resistance to triazoles (15% fluconazole-resistant, 46% itraconazole-resistant) 6, 1, 5

  • C. tropicalis: Represents 10-30% of candidemias, particularly common in neutropenic patients and bone marrow transplant recipients, with 10-25% showing fluconazole resistance and 18.6% itraconazole resistance 6, 8, 9

  • C. parapsilosis: Causes 20-40% of candidemias, associated with foreign body insertion, neonates, and hyperalimentation, generally susceptible to azoles but with higher echinocandin MICs (≤2 mg/L for caspofungin) 6, 5, 8, 9

  • C. krusei: Accounts for 10-35% of infections, intrinsically resistant to fluconazole, associated with azole prophylaxis and neutropenia, with reduced amphotericin B susceptibility 6, 5, 10

Emerging NAC Species

  • C. auris (Candidozyma auris): Classified as an urgent public health threat by the CDC due to pan-drug resistance potential, hospital transmission capability, and tripling of echinocandin-resistant cases in recent years 7, 2

  • C. lusitaniae: Causes 2-8% of infections, associated with prior polyene use, with 5-20% showing amphotericin B resistance 6, 8

  • C. guilliermondii: Represents 1-5% of infections, linked to previous polyene exposure, with 5-10% amphotericin B resistance 8

Key Clinical Distinctions

Epidemiological Differences

NAC species demonstrate distinct habitat and transmission patterns compared to C. albicans 4:

  • C. albicans survives poorly on dry surfaces and has restricted natural distribution primarily in association with humans and animals 4
  • Many NAC species are ubiquitously distributed in the environment (soil, plants, foods) and are more resistant to environmental influences 4
  • NAC species are more likely to cause exogenous infections, while C. albicans infections are predominantly endogenous 4

Antifungal Susceptibility Patterns

The susceptibility profiles differ significantly between C. albicans and NAC species, necessitating species-directed therapy 6, 1, 10:

  • C. albicans: Generally susceptible to all major antifungal classes with resistance remaining uncommon 1
  • C. glabrata: Susceptible-dose dependent or resistant to azoles, requiring higher doses or alternative agents 1, 5
  • C. krusei: Intrinsically resistant to fluconazole, intermediate to resistant for itraconazole 6, 5
  • C. parapsilosis: Susceptible to azoles but considered a poor target for anidulafungin therapy 5

Clinical Impact

Mortality rates vary by species, with some NAC species demonstrating equal or greater virulence than C. albicans 8:

  • Overall mortality for NAC species ranges from 15-35%, similar to C. albicans 8
  • C. tropicalis and C. glabrata show highest mortality (40-70%) 8
  • C. parapsilosis demonstrates lowest mortality among NAC species 8
  • Attributable mortality for C. glabrata is higher than C. albicans despite similar crude mortality 8

Important Clinical Caveats

Susceptibility testing is strongly recommended for all bloodstream and clinically relevant Candida isolates, particularly for patients with prior azole exposure, treatment failure, or infections with NAC species 1, 5. The increasing prevalence of NAC species (from 10-40% pre-1990 to 35-65% in 1991-1998 and beyond) underscores the importance of species identification for optimal management 11, 8.

References

10
Guideline

guidelines for treatment of candidiasis.

Clinical Infectious Diseases, 2004

11
Research

Non-albicans Candida Infection: An Emerging Threat.

Interdisciplinary perspectives on infectious diseases, 2014

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