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

Longyang Jin,Hui Wang,Xiaojuan Wang,Qi Wang,Hongbin Chen,Zhuorui Cao,Yichen Wang

doi:10.1186/s12879-018-3082-0

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.

Highlights

Marked increases in fluconazole resistance in Candida tropicalis have been recently reported
Our findings suggest that ERG11 missense mutations and increased MDR1 gene expression are highly correlated with fluconazole resistance in C. tropicalis clinical isolates
ERG11 gene mutations Sequence analysis of the ERG11 gene revealed no missense mutations in any control isolate

Summary

Introduction

Marked increases in fluconazole resistance in Candida tropicalis have been recently reported. Azole antifungal agents are widely used in the battle against clinical Candida infections [5]. C. tropicalis was susceptible to azole and other antifungal agents. Azole resistance in C. tropicalis has been recently observed, possibly owing to the extensive use of antifungals in medical institutions [7]. Jin et al BMC Infectious Diseases (2018) 18:162 the widespread use of azoles has been deemed to be an independent risk factor for fluconazole resistance in Candida species [11]. C. tropicalis appears to develop fluconazole resistance much more rapidly than other Candida species under in vitro selection [12]

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