Candida Albicans

Candida spp. are normal flora found in the gastrointestinal tract, mucous membranes, and skin. Invasive candidiasis is typically an opportunistic infection with the patient’s own, endogenous flora. Although it can be normal skin flora, the growth of Candida spp. from a blood culture should be presumed to be pathogenic; treatment should be initiated, and attempts made to identify the source. Typically, invasive candidiasis arises from one of three sources:

 1) Colonization and biofilm formation on an indwelling intravenous catheter

 2) Dissemination from a deep nidus of infection, often urinary tract

 3) Translocation from the gastrointestinal tract. 

Patients who are at greatest risk for developing invasive candidiasis include:

• Patients with a prolonged stay in intensive care
• Presence of central venous catheters
• Patients with hematologic or solid organ malignancy
• Patients with neutropenia
• Pre-term infancy with very low birth weight 
• Use of broad spectrum antibiotics
• Patients with GI tract perforation or anastomotic leaks post-operatively
• Renal failure or hemodialysis
• Injection drug use

C. albicans has historically been the most common species of yeast causing invasive disease. However, non-albicans species (C. glabrata, C. parapsilosis, C. tropicalis and C. krusei) now cause almost 50% of invasive candidiasis. This changing epidemiology is relevant because the different species demonstrate different susceptibility profiles to anti-fungal agents. C. auris is another recently emerging species that shows resistance to multiple anti-fungal agents and has been described as causing outbreaks of healthcare-associated infections.

Invasive candidiasis is primarily diagnosed with blood culture. Candida spp. are the most common yeast cultured from clinical specimens. Candida albicans is characterized macroscopically by growth of smooth, white colonies with surrounding “feet” which represent projections of pseudohyphae. The pseudohyphae are distinguished microscopically from true hyphae by constriction of the cells where they meet (with true hyphae, the cell walls will remain parallel). When incubated at 37 C for 2 hours C. albicans will produce germ tubes (extensions from the yeast cell representing an attempt at forming true hyphae).

References

Pappas, P., Lionakis, M., Arendrup, M. et al. Invasive candidiasis. Nat Rev Dis Primers 4, 18026 (2018). https://doi.org/10.1038/nrdp.2018.26.

Bays DJ, et al. Epidemiology of Invasive Candidiasis. Clin Epidemiol. 2024 Aug 28;16:549-566. doi: 10.2147/CLEP.S459600.