Whole genome sequencing of a clinical drug resistant Candida albicans isolate reveals known and novel mutations in genes involved in resistance acquisition mechanisms.

Roy A Khalaf,Jaroslav Hrabak,Nour Fattouh,Matej Medvecky

doi:10.1099/jmm.0.001351

Roy A Khalaf, Jaroslav Hrabak + Show 2 more

Open Access

https://doi.org/10.1099/jmm.0.001351

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Abstract

Candida albicans is an opportunistic pathogen accounting for the majority of cases of Candida infections. Currently, C. albicans are developing resistance towards different classes of antifungal drugs and this has become a global health burden that does not spare Lebanon. This study aims at determining point mutations in genes known to be involved in resistance acquisition and correlating resistance to virulence and ergosterol content in the azole resistant C. albicans isolate CA77 from Lebanon. This pilot study is the first of its kind to be implemented in Lebanon. We carried out whole genome sequencing of the azole resistant C. albicans isolate CA77 and examined 18 genes involved in antifungal resistance. To correlate genotype to phenotype, we evaluated the virulence potential of this isolate by injecting it into BALB/c mice and we quantified membrane ergosterol. Whole genome sequencing revealed that eight out of 18 genes involved in antifungal resistance were mutated in previously reported and novel residues. These genotypic changes were associated with an increase in ergosterol content but no discrepancy in virulence potential was observed between our isolate and the susceptible C. albicans control strain SC5314. This suggests that antifungal resistance and virulence potential in this antifungal resistant isolate are not correlated and that resistance is a result of an increase in membrane ergosterol content and the occurrence of point mutations in genes involved in the ergosterol biosynthesis pathway.

Highlights

Candida is a genus of fungi that is part of the normal human microbiota, colonizing many bodily parts such as the gut and skin [1]
This study aims at determining point mutations in genes known to be involved in resistance acquisition and correlating resistance to virulence and ergosterol content in the azole resistant C. albicans isolate CA77 from Lebanon
This suggests that antifungal resistance and virulence potential in this antifungal resistant isolate are not correlated and that resistance is a result of an increase in membrane ergosterol content and the occurrence of point mutations in genes involved in the ergosterol biosynthesis pathway

Summary

Introduction

Candida is a genus of fungi that is part of the normal human microbiota, colonizing many bodily parts such as the gut and skin [1]. Allylamines, azoles, and morpholines interfere with genes that code for enzymes having crucial roles within the ergosterol biosynthesis pathway. This yeast metabolic pathway allows the conversion of acetyl coenzyme A into the lipid ergosterol which is the main component of the C. albicans cell membrane. Within the ergosterol biosynthesis pathway, allylamines and azoles mainly target the ERG1 and ERG11 genes, respectively while morpholines mainly target the ERG24 and ERG2 genes [5, 6] Regarding polyenes, they act by directly binding to ergosterol at the level of the C. albicans cell wall rendering it more permeable. Echinocandins, on the other hand, interfere with the cell wall component glucan since they

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