MDR1 overexpression combined with ERG11 mutations induce high-level fluconazole resistance in Candida tropicalis clinical isolates

Abstract

BackgroundMarked increases in fluconazole resistance in Candida tropicalis have been recently reported. In this study, the molecular mechanisms behind fluconazole resistance were investigated.MethodsTwenty-two C. tropicalis clinical isolates, including 12 fluconazole-resistant isolates and 10 fluconazole-susceptible isolates, were collected from a tertiary care teaching hospital in Beijing between 2013 and 2017. Antifungal susceptibility testing, multilocus sequence typing, ERG11 amplification and sequencing, quantitative real-time reverse transcription-polymerase chain reaction (ERG11, UPC2, MDR1, and CDR1), and clinical data collection were performed for all C. tropicalis isolates.ResultsMultilocus sequence typing revealed that the 10 fluconazole-susceptible isolates and 12 fluconazole-resistant isolates were divided into nine and seven diploid sequence types, respectively. Of the 12 patients with fluconazole-resistant isolates, six had been previously exposed to azole and four had a fatal outcome. Y132F and S154F amino acid substitutions in Erg11p were found in all fluconazole-resistant isolates except one. MDR1 gene overexpression was identified in fluconazole-resistant isolates. In particular, seven high-level fluconazole resistant isolates (minimum inhibitory concentration ≥ 128 mg/L) and three pan-azole resistant isolates were identified. CDR1, ERG11, and UPC2 gene expression levels in fluconazole-resistant isolates were not significantly different from the control isolates (P = 0.262, P = 0.598, P = 0.114, respectively).ConclusionsThis study provides evidence that the combination of MDR1 gene overexpression and ERG11 missense mutations is responsible for high-level fluconazole resistance and pan-azole resistance in C. tropicalis clinical isolates. To the best of our knowledge, this is the first study investigating the relationship between MDR1 gene overexpression and increased fluconazole resistance.

Candida tropicalis distribution and drug resistance is correlated with ERG11 and UPC2 expression

“…The increased resistance rate of C. tropicalis to azole antifungal drugs might be related to the easy application of such drugs and the relatively mild adverse reactions [18]. In the clinic, a large number of patients with severe fungal infections and long-term application of these drugs were subjected to prophylactic treatments, which would lead to drug resistance [19]. Moreover, in this study, the ERG11 and UPC2 genes of 50 strains of C. tropicalis were assessed, and our results showed that the relative expression level of the ERG11 gene in the drug-resistant group was higher than it was in the sensitive group, which is in line with the ndings from Jiang et al [20] regarding the high expression of ERG11 in uconazole-resistant C. tropicalis.…”

The Quiet and Underappreciated Rise of Drug-Resistant Invasive Fungal Pathogens

“…As for other NAC species, MDR was reported in some studies and, strikingly, almost 1% of the Indian C. tropicalis blood isolates are resistant to the three major classes of antifungals [138]. Unlike C. parapsilosis, it appears that ERG11 overexpression is a more prominent FLZR mechanism than efflux pump activity in C. tropicalis [151][152][153][154], and MDR1 overexpression [152,155,156] is more prevalent than CDR1 overexpression [152,156]. Surprisingly, FLZR C. tropicalis isolates lacking any accountable mutation in ERG11 and not overexpressing efflux pumps were also identified, suggesting the involvement of other, unknown, mechanisms [156].…”

Candida tropicalis distribution and drug resistance correlated to ERG11 and UPC2 expression

“…The increased resistance rate of Candida tropicalis to azoles might be related to the easy application of such drugs and the relatively mild adverse reactions [17]. In clinic, a large number of patients with severe fungal infections and long-term application of these drugs were subjected to the prophylactic treatments, which would lead to the drug resistance [18]. Moreover, in this study, the ERG11 and UPC2 genes of 50 strains of Candida tropicalis were detected, and our results showed that the relative expression level of ERG11 gene in the drug-resistant group was significantly higher than the sensitive group, in line with the findings from Jiang et al [19] concerning the high expression of ERG11 in fluconazole-resistant fungi.…”