Candida krusei

C. krusei is a diploid, dimorphic ascomycetous yeast that colonizes the mucosa of healthy individuals. However, this yeast can cause life-threatening infections in immunocompromised patients, with patients with hematologic malignancies and patients receiving prolonged azole prophylaxis being at higher risk.

Although Candida albicans remains the main cause of candidiasis, in recent years a significant number of infections have been attributed to "non-albicans Candida species" (NAC), including Candida krusei. This epidemiological change can be partly explained by the increasing resistance of NAC species to antifungal drugs (Pfaller MA et al. 2008).

Candida krusei is defined as a potentially multidrug-resistant (MDR) fungal pathogen due to its intrinsic resistance to fluconazole in combination with a reduced sensitivity to flucytosine and amphotericin B.

C. krusei was most frequently isolated in Europe (≥5 % of all Candida sp. isolates) in the Eastern European countries Czech Republic (7.6 %), Poland (6.0 %) and Slovakia (5.1 %). C. krusei was extremely rare (<1 %) in the Netherlands (0.5 %). C. krusei was also rather rare in the Asia-Pacific region (1.3 %) and in Latin America (1.7 %).

Fungal infections are usually treated with five main classes of antifungal agents, which include azoles, echinocandins, polyenes, allylamines and nucleoside analogs. C. krusei has intrinsic resistance to fluconazole and rapidly develops acquired resistance to other antifungals. Among the systemically active antifungals, the echinocandins appear to be the most effective against this important pathogen (Jamiu AT et al. 2021).

Significant differences were observed in the susceptibility of C. krusei to voriconazole. Isolates from North America were the most susceptible, while the lowest overall susceptibility was observed in isolates from Latin America. The lowest susceptibility to voriconazole (<70 %) was observed in the Latin American countries Brazil, Colombia (61.8 %) and Mexico (63.6 %). The highest were found in Australia (100 %), Taiwan (94.7 %), Thailand (100 %), the Netherlands (100 %), Belgium (97.3 %) and Germany (90.9 %). These extreme differences in the susceptibility of C. krusei to voriconazole emphasize the importance of antifungal susceptibility testing in this species when considering voriconazole as a therapeutic option (Jamiu AT et al. 2021).

Several authors have reported complicated infections caused by C. krusei in patients receiving fluconazole or amphotericin B. In addition, amphotericin B has significantly delayed efficacy kinetics against C. krusei compared to Candida albicans. In the past, C. krusei was mainly isolated from blood, urine, respiratory tract and skin/soft tissue samples. It has rarely been isolated from genital samples. C. krusei isolates from blood were more susceptible to voriconazole than those from urine (89.0% versus 76.6%). This pattern was similar to that previously reported for another rare Candida species, Candida guilliermondii(Jamiu AT et al. 2021)

1. Domán M et al. (2022) Molecular Phylogenetic Analysis of Candida krusei. Mycopathologia 187:333-343.
2. Jamiu AT et al. (2021) Update on Candida krusei, a potential multidrug-resistant pathogen. Med Mycol 59:14-30.
3. Pfaller MA et al (2008) Global Antifungal Surveillance Group. Candida krusei, a multidrug-resistant opportunistic fungal pathogen: geographic and temporal trends from the ARTEMIS DISK Antifungal Surveillance Program, 2001 to 2005. J Clin Microbiol 46:515-521.