Resistance of Asian Cryptococcus neoformans serotype A is confined to few microsatellite genotypes

Abstract

Background: Cryptococcus neoformans is a pathogenic yeast that causes cryptococcosis, a life threatening disease. The prevalence of cryptococcosis in Asia has been rising after the onset of the AIDS epidemic and estimates indicate more than 120 cases per 1,000 HIV-infected individuals per year. Almost all cryptococcal disease cases in both immunocompromised and immunocompetent patients in Asia are caused by C. neoformans var. grubii. Epidemiological studies on C. neoformans in pan-Asia have not been reported. The present work studies the genetic diversity of the fungus by microsatellite typing and susceptibility analysis of approximately 500 isolates from seven Asian countries.

Methodology/principal findings: Genetic diversity of Asian isolates of C. neoformans was determined using microsatellite analysis with nine microsatellite markers. The analysis revealed eight microsatellite complexes (MCs) which showed different distributions among geographically defined populations. A correlation between MCs and HIV-status was observed. Microsatellite complex 2 was mainly associated with isolates from HIV-negative patients, whereas MC8 was associated with those from HIV-positive patients. Most isolates were susceptible to amphotericin B, itraconazole, voriconazole, posaconazole, and isavuconazole, but 17 (3.4%) and 10 (2%) were found to be resistant to 5-flucytosine and fluconazole, respectively. Importantly, five Indonesian isolates (approximately 12.5% from all Indonesian isolates investigated and 1% from the total studied isolates) were resistant to both antifungals. The majority of 5-flucytosine resistant isolates belonged to MC17.

Conclusions: The findings showed a different distribution of genotypes of C. neoformans var. grubii isolates from various countries in Asia, as well as a correlation of the microsatellite genotypes with the original source of the strains and resistance to 5-flucytosine.

Figure 1. Genotypic variation of C. neoformans isolates from different Asian countries by microsatellite typing.

(A) Minimum spanning tree based on a multistate categorical analysis representing 429 C. neoformans var. grubii isolates from different countries. Each circle represents a unique genotype. The size of the circle corresponds to the number of isolates within that genotype. Numbers and connecting lines correspond to the number of different markers between genotypes. Genotypes with identical colors are part of a microsatellite complex (MC). Circles without color are unique genotypes that are not part of a MC.; (B) Same as A, but now showing the genotypes from different geographic locations. Different colors correspond to different countries.; (C) Same as A and B, but now showing the genotypes from clinical and environmental sources.; (D) Same as A, B and C, but now showing the genotypes of Thai and Japanese population from clinical and environmental sources.