Urease as a virulence factor in experimental cryptococcosis

Urease catalyzes the hydrolysis of urea to ammonia and carbamate and has be en found to be an important pathogenic factor for certain bacteria. Cryptoc occus neoformans is a significant human pathogenic fungus that produces lar ge amounts of urease; thus we wanted to investigate the importance of ureas e in the pathogenesis of cryptococcosis. We cloned and sequenced the genomi c locus containing the single-copy C. neoformans urease gene (URE1) and use d this to disrupt the native URE1 in the serotype A strain H99, The ure1 mu tant strains were found to have in vitro growth characteristics, phenoloxid ase activity, and capsule size similar to those of the wild type. Compariso n of a ure1 mutant with H99 after intracisternal inoculation into corticost eroid-treated rabbits revealed no significant differences in colony counts recovered from the cerebrospinal fluid. However, when these two strains wer e compared in both the murine intravenous and inhalational infection models , there were significant differences in survival. Mice infected with a ure1 strain Lived longer than mice infected with H99 in both models. The ure1 s train was restored to urease positivity by complementation with URE1, and t wo resulting transformants were significantly more pathogenic than the ure1 strain. Our results suggest that urease activity is involved in the pathog enesis of cryptococcosis but that the importance may be species and/or infe ction site specific.