Molecular identification, antifungal resistance and virulence of Cryptococcus neoformans and Cryptococcus deneoformans isolated in Seville, Spain

Abstract

Cryptococcal meningitis is one of the leading causes of death in HIV/AIDS patients. Our aim was to in order to characterise the epidemiology, antifungal susceptibility pattern and virulence of 28 Cyptococcus sp. strains recovered from 12 AIDS patients during two years in a Spanish single institution. Antifungal susceptibility testing was performed according to the CLSI protocols. Clinical strains were molecularly characterised by serotyping, mating type, PCR fingerprinting (M13 and GACA₄ microsatellites) and analysis of two rDNA regions (IGS1 and ITS). Sequencing of the ERG11 gene was used to explore mechanisms of fluconazole resistance. Differences in virulence between species were studied in a Galleria mellonella infection model. Cryptococcus deneoformans and C. deneoformans x Cryptococcus neoformans hybrids were the most frequent variety (65%) followed by C. neoformans (35%). Strains were categorised according to 13 microsatellite genotypes and mixed infections could be detected in three patients. Twenty-nine per cent of the strains were fluconazole resistant. In one of the patients, the fluconazole resistance phenotype was associated with a point mutation in the ERG11 gene responsible for the amino acid substitution G470R. C. neoformans strains were able to kill G. mellonella larvae more efficiently than C. deneoformans and hybrids between both species. Precisely molecular characterisation of C. neoformans species is important for an accurate patient's management.

Keywords: Cryptococcus species; azole resistance evolution; mixed infection.