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Published on: December 28, 2017
Changes in susceptibility to posaconazole in clinical isolates of Candida albicans
Xin Li1, Nathaniel Brown, Andrew S Chau
1Schering-Plough Research Institute, 2015 Galloping Hill Road, 4700 Kenilworth, NJ 07033, USA.
Objectives:
To characterize the molecular mechanisms responsible for reduced susceptibility to azoles in Candida albicans clinical isolates.
Materials And Methods:
Seven sequential C. albicans isolates were cultured from an AIDS patient treated with posaconazole for refractory oropharyngeal candidiasis. Expression levels of the CDR1, CDR2 and MDR1 genes, encoding efflux pumps previously implicated in azole resistance, and ERG11, encoding the azole target site, were monitored using northern blot and real-time PCR. The ERG11 genes from all seven isolates were sequenced.
Results:
The seven closely related isolates exhibited significant decreases in susceptibility to fluconazole (MIC >or= 32 mg/L) and voriconazole (MIC >or= 2 mg/L) and progressive decreases in susceptibility to both posaconazole (isolates 1-4 MIC 0.25 mg/L, isolates 5-7 MIC 2 mg/L) and itraconazole (isolates 1-4 MIC 1 mg/L, isolates 5-7 MIC > 8 mg/L). None of the isolates exhibited any significant changes in the expression levels of ERG11 or the efflux pump genes. All seven isolates had multiple mutations in ERG11; isolates one through four each had five missense mutations; four of the resultant amino acid changes were previously associated with azole resistance. The fifth isolate had an additional novel mutation in one copy of ERG11, resulting in a Pro-230 to Leu substitution. This mutation was present in both ERG11 genes in the last two isolates. Select ERG11 genes were expressed in Saccharomyces cerevisiae, the ERG11 allele with all six mutations conferred the highest level of posaconazole resistance.
Conclusions:
Multiple mutations in ERG11 are required to confer decreased susceptibility to posaconazole.
Insights
Multiple mutations in the ERG11 gene are key to reduced susceptibility to posaconazole in Candida albicans. These genetic changes, not altered gene expression, drive antifungal resistance in clinical isolates.
Area of Science:
- Medical Mycology
- Molecular Biology
- Antimicrobial Resistance
Background:
- Azole antifungals are crucial for treating Candida albicans infections.
- Reduced susceptibility to azoles poses a significant clinical challenge, particularly in immunocompromised patients.
- Understanding the genetic basis of azole resistance is vital for developing effective treatment strategies.
Purpose of the Study:
- To investigate the molecular mechanisms behind decreased azole susceptibility in *Candida albicans* clinical isolates.
- To identify specific genetic alterations in *C. albicans* associated with resistance to fluconazole, voriconazole, posaconazole, and itraconazole.
Main Methods:
- Cultured seven sequential *C. albicans* isolates from an AIDS patient undergoing posaconazole treatment.
- Monitored expression of efflux pump genes (CDR1, CDR2, MDR1) and the azole target gene (ERG11) using northern blot and real-time PCR.
- Sequenced the ERG11 genes from all seven isolates to identify mutations.
Main Results:
- All seven isolates showed decreased susceptibility to fluconazole, voriconazole, posaconazole, and itraconazole.
- No significant changes in the expression levels of ERG11 or efflux pump genes were observed.
- Multiple mutations in ERG11 were identified in all isolates, with novel mutations correlating with increased posaconazole resistance.
Conclusions:
- Decreased susceptibility to posaconazole in *C. albicans* is primarily driven by multiple mutations within the ERG11 gene.
- Genetic alterations in ERG11, rather than changes in gene expression, are the main mechanism conferring azole resistance.
- These findings highlight the importance of ERG11 mutations in the development of antifungal resistance.
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