ERG11 mutations and upregulation in clinical itraconazole-resistant isolates of Candida krusei.

To better understand the association between the ERG11 gene and drug resistance in Candida krusei, C. krusei strains were isolated from patients from January 2010 to May 2013. Susceptibility to 5-fluorocytosine (5-FC), amphotericin B (AMB), voriconazole (VRC), fluconazole (FLC), and itraconazole (ITR) were tested by broth microdilution method. Mutations were detected using PCR amplification and gene sequencing. Expression levels of ERG11 were measured by real-time PCR and compared by a 2-tailed Student's t test between ITR-susceptible strains and ITR-resistant strains. In total, 15 C. krusei strains were obtained, of which 20.00%, 53.33%, and 40.00% were resistant to 5-FC, FLC, and ITR, respectively, whereas all isolates were susceptible to AMB and VRC. Three synonymous codon substitutions were found in ERG11, including T939C, T642C, and A756T. However, T939C was found in both resistant and susceptible C. krusei strains. The expression level of ERG11 was significantly higher in resistant C. krusei strains (1.34 ± 0.08) than in susceptible C. krusei strains (0.94 ± 0.14) (t = 3.74, p < 0.05). Our study demonstrates that point mutations (T642C and A756T) accompanied with the overexpression of ERG11 might be involved in the molecular mechanisms of drug resistance in C. krusei.