Antifungal susceptibility of cryptococcus neoformans clinical isolates from different cities of Argentina

Abstract

Background: Long-term fluconazole maintenance therapy in AIDS patients has generated concern that resistance strains might emerge. The clinical breakpoints for Cryptococcus spp. are not yet available. It is well known that the susceptibility vary according to genotyping and geographic regions. Therefore it is mandatory to study the susceptibility of Argentinian isolates to follow therapeutic criteria based on Epidemiological Cutoff Values (ECVs). The aim of the present study was to evaluate the activity of six antifungal drugs against a collection of Cryptococcus neoformans isolated in Argentina. Methods & Materials: C. neoformans clinical isolates (n: 88) were obtained in four cities of the Argentina (Buenos Aires, Rosario, Santa Fe and Paraná). Fluconazole, itraconazole, voriconazole, posaconazole, amphotericin B and flucytosine MICs were determined by the CLSI broth microdilution method document M27-A3/S4. Candida parapsilosis ATCC 22019 and Candida krusei ATCC 6258 were used as quality control. Results: Voriconazole MICs geometric mean was 0.06 μg/ml (range 0.03-0.12), Itraconazole 0.07 μg/ml (0.03-0.25), Posaconazole 0.99 μg/ml (0.03 - 0.25), Amphotericin-B 0.15 μg/ml (0.03-0.5), Flucytosine 3.52 μg/ml (2-8) and Fluconazole 4.13 μg/ml (1-16). Fluconazole and Flucytosine showed the highest number of non-wild type strains. For the azole, 31.8% of the isolates showed MIC values above the ECV while for the pyrimidine analog 10.0% of the strains were included in this category. Cross-resistance was observed in four isolates that were classified as non-Wild Type to Fluconazole and Itraconazole, to Fluconazole and Posaconazole, Flucytosine and Fluconazole and to Amphotericin B and Fluconazole. Only one strain was considered as Non Wild Type for three drugs (Fluconazole, Posaconazole and Flucytosine). Conclusion: The most active azole drug against C .neoformans was Voriconazole followed by Itraconazole, Posaconazole and Fluconazole. Considering that VNI is the most prevalent genotype in Argentina almost one third of the strains should be considered as non-wild type. Therefore it is necessary to investigate the molecular mechanisms involved in azole resistance phenotype in order to have the theoretical basis to design molecular diagnostic tools able to quickly uncover resistant isolates.