Spectrum and functional properties of <i>ERG11</i> gene mutations in fluconazole-resistant <i>Candida albicans</i> strains isolated from HIV-infected patients

Abstract

Rationale. The low efficacy of azole antimycotics in treatment of Candida infections, especially in HIV-infected patients, is often associated with overexpression of the ERG11 gene in Candida spp., which results in increased production of ergosterol the target of the above antimycotic drugs. Researchers have found ERG11 gene mutations that can modify its overexpression effects by increasing or decreasing it. However, the findings reported by different laboratories and countries are highly contradictory.
 The purpose of the study is to explore the spectrum and functional properties of ERG11 gene mutations in fluconazole-resistant Candida albicans strains isolated from HIV-infected patients.
 Materials and methods. The study was performed using 10 C. albicans strains inherently resistant to fluconazole and voriconazole and isolated from the oropharynx of HIV-infected patients; the strains were provided from the collection of the Gabrichevsky Moscow Research Institute of Epidemiology and Microbiology. The strains were assessed by their sensitivity to antimycotic agents: anidulafungin, micafungin, caspofungin, posaconazole, voriconazole, itraconazole, fluconazole, amphotericin B, 5-flucytosine. Expression levels of the ERG11 gene were measured by quantitative PCR. ERG11 gene mutations were identified by Sanger sequencing.
 Results. Five mutations (E266D, G464S, I471L, D116E, and V488I) were detected in the ERG11 gene in seven C. albicans strains; six strains carried non-associated co-occurring mutations. Increased expression of the ERG11 gene was found in six C. albicans strains. The V488I mutation demonstrated a strong negative association with the increased expression of the ERG11 gene (r = 0.845; p 0.05). The minimum inhibitory concentration (MIC) in strains carrying mutations was a hundred times as low (p 0.05) as MIC in strains without mutations. In mutation carriers, posaconazole and itraconazole MICs were on average 16.5 times as low as MICs of voriconazole and fluconazole (p 0.001). The presence of mutations in the ERG11 gene had almost no effect on MICs of the tested antimycotics of the echinocandin, polyene, and pyrimidine groups.
 Conclusion. Multiple mutations were detected in the ERG11 gene in most of the C. albicans strains isolated from HIV-infected patients and resistant to fluconazole and voriconazole. Except for the V488I mutation, the detected mutations were not associated with the overexpression of the ERG11 gene and decreased the effects of overexpression of the ERG11 gene by up to 100 times, though they did not eliminate the inherent resistance to triazole antimycotics.