Genotypic diversity and antifungal susceptibility of environmental isolates of Cryptococcus neoformans from the Yangtze River Delta region of East China

Although cryptococcosis is widely recognized as infection by Cryptococcus neoformans sensu lato from environmental sources, information concerning the characteristics of environmental isolates of C. neoformans s. l. and how they are related to clinical isolates is very limited, especially in East China. In this study, 61 environmental isolates of C. neoformans were recovered from pigeon (Columba livia) droppings from the Yangtze River Delta region of East China. These isolates were genotyped using the ISHAM-MLST consensus scheme and their antifungal drug susceptibilities were determined following the CLSI M27-A3 guidelines. The 61 isolates were found belonging to 13 sequence types (STs), including several novel STs such as ST254 and ST194. The dominant ST in this environmental sample was ST31, different from that of clinical strains (ST5) in this region. Azole-resistance, such as fluconazole (FLU)-resistance, was observed among our environmental C. neoformans isolates. The findings of this study expand our understanding of ecological niches, population genetic diversity, and azole-resistance characteristics of the yeast in East China. Our research lays the foundation for further comparative analysis the potential mechanisms for the observed differences between environmental and clinical populations of C. neoformans in China.

Lay summary: Cryptococcosis is widely recognized as infection by Cryptococcus neoformans sensu lato from environmental sources. However, there is currently limited information about the genetic diversity and antifungal susceptibility of environmental C. neoformans s. l. isolates, including how they may differ from clinical samples. In this study, we collected 61 environmental C. neoformans isolates from domestic pigeon droppings from the Yangtze River Delta region of East China. These isolates were genotyped using multi-locus sequencing. We found a high genotypic diversity in this population of C. neoformans, with several novel genotypes and a distribution of genotypes different from that of clinical strains in this region. Azole-resistance, such as fluconazole (FLU)-resistance, was observed among our environmental C. neoformans isolates. The findings of this study expand our understanding of ecological niches, genetic diversity, and azole-resistance characteristics of the yeast in East China. Our research lays the foundation for phylogenomic analysis investigating why and how disparate population structures of C. neoformans isolates formed between environmental and clinical sources in the region.