Molecular epidemiology of Cryptococcus neoformans in Brazil and the United States: evidence for both local genetic differences and a global clonal population structure

Abstract

Little is known about the global molecular epidemiology of the human pathogenic fungus Cryptococcus neoformans. We studied 51 clinical and environmental (pigeon excreta) isolates from two cities in Brazil (Belo Horizonte and Rio de Janeiro) by analyzing their carbon assimilation patterns, electrophoretic karyotypes, restriction fragment length polymorphisms (RFLPs) with the C. neoformans repetitive element-1 (CNRE-1), and URA5 sequences. Results were compared to those previously obtained for isolates from New York City by the same DNA typing methods. Computer-assisted analysis of RFLPs and contour-clamped homogeneous electrophoresis (CHEF) patterns and URA5 sequences was performed to generate dendrograms. Some environmental and clinical isolates were found to be indistinguishable by CHEF, CNRE-1 RFLP, and URA5 sequence analyses. Similarly, some isolates from Rio de Janeiro and Belo Horizonte were indistinguishable by the three DNA typing techniques. Overall, Brazilian isolates appeared to be less heterogeneous by DNA analysis than isolates from other regions. Several Brazilian isolates were highly related to New York City isolates. Phylogenetic analysis of the sequences obtained for the Brazilian isolates and those obtained for New York City isolates was congruent with the dendrogram generated from the CNRE-1 RFLP data. In summary our results indicate (i) that the discriminatory power of the DNA typing method differs for Brazilian and New York City strains, with the order being CNRE-1 RFLP analysis > URA5 sequence analysis > CHEF analysis and CHEF analysis > URA5 sequence analysis > CNRE-1 RFLP analysis, respectively; (ii) that there are differences in local genetic diversity for Brazilian and New York City isolates; (iii) that there is additional evidence linking clinical isolates to those in pigeon excreta; and (iv) that some isolates from Brazil and New York City are closely related, consistent with the global dispersal of certain pathogenic strains.