UC Davis

Compared to Cryptococcus neoformans, little is known about the virulence of the molecular types in Cryptococcus gattii. We compared in vitro virulence factor production and survival data using a Drosophila model of infection to further characterize the phenotypic features of different cryptococcal molecular types. Forty-nine different isolates were inoculated into wild-type flies and followed for survival. In vitro, isolates were assessed for growth at 30 and 37°C, melanin production, capsule size, resistance to H(2)O(2), and antifungal susceptibility. A mediator model was used to assess molecular type and virulence characteristics as predictors of survival in the fly model. VGIII was the most virulent molecular type in flies (P < 0.001). At 30°C, VGIII isolates grew most rapidly; at 37°C, VNI isolates grew best. C. gattii capsules were larger than those of C. neoformans (P < 0.001). Mediator model analysis found a strong correlation of Drosophila survival with molecular type and with growth at 30°C. We found molecular-type-specific differences in C. gattii in growth at different temperatures, melanin production, capsule size, ability to resist hydrogen peroxide, and antifungal susceptibility, while growth at 30°C and the VGIII molecular type were strongly associated with virulence in a Drosophila model of infection.