Cryptococcosis is a life-threatening
infection in humans and animals caused by encapsulated yeasts of the genus Cryptococcus. Cryptococcus neoformans and Cryptococcus gattii are the main agents of this mycosis. Until 2002 C. gattii was classified as a variety of C. neoformans but now is accepted as an independent species. The
laccase (phenoloxydase)
enzyme produced by these yeasts is considered one of the main pathogenic factors for its ability to induce
melanin from dihydroxyphenolic compounds. The vast majority of the studies in
laccase and
melanin synthesis have been developed using isolates of C. neoformans. The main objective of this study was to evaluate
laccase activity in strains of C. gattii, serotype B isolated from immunocompetent goats that died of lung and disseminated
cryptococcosis, in several outbreaks occurring in Spain. The
laccase activities of these isolates were compared with those of other strains of C. gattii and C. neoformans. After fungal cell
rupture, the supernatant of each isolate was analyzed for its
laccase activity using as substrate an
L-dopa 20 mM
solution. The degree of enzymatic activity was assessed according to its absorbance at 450 nm and scored using Enzymatic Units (EU). The maximum values were observed in three strains of C. gattii from goats (EU > 12). The smallest values were observed in one environmental isolate of C. gattii serotype C (EU = 0.7). The highest recorded value for C. neoformans was 6.3 EU in a serotype A isolate from one human case of
meningitis. C. gattii serotype B obtained from goats showed different degrees of
laccase activity, being the highest in those isolated from severe outbreaks of
cryptococcosis. This
enzyme appears to represent a major, though nonexclusive, pathogenic factor for Cryptococcus gattii.