Mechanisms of azole antifungal resistance in clinical isolates of Candida tropicalis

Abstract

This study was designed to understand the molecular mechanisms of azole resistance in Candida tropicalis using genetic and bioinformatics approaches. Thirty-two azole-resistant and 10 azole-susceptible (S) clinical isolates of C. tropicalis were subjected to mutation analysis of the azole target genes including ERG11. Inducible expression analysis of 17 other genes potentially associated with azole resistance was also evaluated. Homology modeling and molecular docking analysis were performed to study the effect of amino acid alterations in mediating azole resistance. Of the 32 resistant isolates, 12 (37.5%) showed A395T and C461T mutations in the ERG11 gene. The mean overexpression of CDR1, CDR3, TAC1, ERG1, ERG2, ERG3, ERG11, UPC2, and MKC1 in resistant isolates without mutation (R-WTM) was significantly higher (p<0.05) than those with mutation (R-WM) and the sensitive isolates (3.2–11 vs. 0.2–2.5 and 0.3–2.2 folds, respectively). Although the R-WTM and R-WM had higher (p<0.05) CDR2 and MRR1 expression compared to S isolates, noticeable variation was not seen among the other genes. Protein homology modelling and molecular docking revealed that the mutations in the ERG11 gene were responsible for structural alteration and low binding efficiency between ERG11p and ligands. Isolates with ERG11 mutations also presented A220C in ERG1 and together T503C, G751A mutations in UPC2. Nonsynonymous mutations in the ERG11 gene and coordinated overexpression of various genes including different transporters, ergosterol biosynthesis pathway, transcription factors, and stress-responsive genes are associated with azole resistance in clinical isolates of C. tropicalis.

The Risk Factors and Mechanisms of Azole Resistance of Candida tropicalis Blood Isolates in Thailand: A Retrospective Cohort Study

“…However, we found a higher level of expression of the CDR1 gene in the R-WOM isolates. A recent study also revealed the role of the Tac1, which regulates the overexpression of the CDR1 gene [ 38 ]. However, further investigations are needed to study the precise function of the other efflux pump genes such as CDR2 and CDR3 genes in azole-resistant C. tropicalis from our institute [ 37 , 38 ].…”

Characterization of Virulence Factors in Candida Species Causing Candidemia in a Tertiary Care Hospital in Bangkok, Thailand

“…The Y132F mutation is responsible for the loss of the normal hydrogen bonding between tyrosine and heme. This alteration affects drug binding because heme is a binding cofactor of azole for ERG11 [ 35 , 36 , 37 ]. Substitutions of both Y132F and S154F prevented the development of Pi-Pi and Pi-cation interactions between the cofactor and the ligand molecules, which lowers the overall binding energy of the altered docked complex [ 35 ].…”

Water Quality, Heavy Metals, and Antifungal Susceptibility to Fluconazole of Yeasts from Water Systems

“…Similarly, antifungal resistance to FCZ has been reported in Candida species from tropical freshwater environments in Brazil and China [ 9 , 53 , 54 , 55 ]. The presence of environmental yeasts with high resistance to FCZ is probably due to the fact that this azole is the most widely used antifungal in humans and animals, and it is among the most reported drugs in hospital and home wastewater [ 56 , 57 ]. In addition, there are fungicides routinely used in agriculture that share the action mechanism of azoles, which can generate cross-resistance in yeasts found in these aquatic environments [ 56 , 57 , 58 ].…”

“…The presence of environmental yeasts with high resistance to FCZ is probably due to the fact that this azole is the most widely used antifungal in humans and animals, and it is among the most reported drugs in hospital and home wastewater [ 56 , 57 ]. In addition, there are fungicides routinely used in agriculture that share the action mechanism of azoles, which can generate cross-resistance in yeasts found in these aquatic environments [ 56 , 57 , 58 ]. In Asia, some studies reported a significant increase in resistant C. tropicalis isolated from poultry, and this has been associated with the extensive use of azoles in agriculture [ 56 , 59 , 60 ].…”

“…Brilhante et al suggested that azole resistance in the Candida strains recovered from aquatic environments would be influenced by the activity of efflux pumps [ 53 ]. Several chemical compounds present in the environment, when interacting with microorganisms, would trigger the expression of genes that lead to these efflux pumps or other proteins involved in resistance to antifungals [ 56 , 57 , 58 ].…”