Atypical Cryptococcus neoformans isolate from an HIV-infected patient in Brazil.

Abstract

Cryptococcus neoformans is an important fungal pathogen in immunocompromised hosts. Capsulation, urease and melanin synthesis activity of the fungus are well known virulence factors. Although artificial melanin-deficient mutants of Cr. neoformans have been investigated, the clinical mutant is rare. We found a Cr. neoformans isolate in the cerebrospinal fluid of an AIDS patient which produced a light tan colony on a caffeic acid cornmeal agar (CACA) plate. The mycological feature of the isolate was as follows; normal capsulation, defective inositol assimilation ability, serotype A; urease-positive; mating type alfa; haploid; extremely slow growth in RPMI 1640 medium, Sabouraud dextrose broth, brain heart infusion broth and yeast nitrogen base; lower production of melanin with L-DOPA substrate; and low virulence to ddY mice. We also investigated the partial DNA sequence of CNLAC1 gene between the 3085th to 3623rd base. There were many substitutions, 3 insertions and 3 deletions in the isolate compared with GenBank accession number L22866. The result indicated some functional disorder in the gene. Although the CACA plate is an excellent selective medium for Cr. neoformans, other identification methods should also be used.