Faster Cryptococcus Melanization Increases Virulence in Experimental and Human Cryptococcosis

Abstract

<i>Cryptococcus</i> spp. are human pathogens that cause 181,000 deaths per year. In this work, we systematically investigated the virulence attributes of <i>Cryptococcus</i> spp. clinical isolates and correlated them with patient data to better understand cryptococcosis. We collected 66 <i>C. neoformans</i> and 19 <i>C. gattii</i> clinical isolates and analyzed multiple virulence phenotypes and host-pathogen interaction outcomes. <i>C. neoformans</i> isolates tended to melanize faster and more intensely and produce thinner capsules in comparison with <i>C. gattii</i>. We also observed correlations that match previous studies, such as that between secreted laccase and disease outcome in patients. We measured <i>Cryptococcus</i> colony melanization kinetics, which followed a sigmoidal curve for most isolates, and showed that faster melanization correlated positively with LC3-associated phagocytosis evasion, virulence in <i>Galleria mellonella</i> and worse prognosis in humans. These results suggest that the speed of melanization, more than the total amount of melanin <i>Cryptococcus</i> spp. produces, is crucial for virulence.