1824. Phenotypic differences of Cryptococcus gattii genotypes:  implications for virulence in a Drosophila model of infection
Session: Oral Abstract Session: Fungal Infections
Saturday, October 5, 2013: 3:15 PM
Room: The Moscone Center: 300
Background: Cryptococcosis is caused by one of two species of encapsulated yeast; Cryptococcus neoformans and C. gattiiC. gattii, although traditionally associated with tropical and subtropical regions, has become an emerging pathogen with new ecological niches.  Compared to the more common pathogen, C. neoformans, little is known about C. gattii virulence, especially as it relates to different genotypes.  We performed a quantitative analysis of virulence factor production between C. gattii genotypes and attempted to correlate with death in a Drosophila melanogaster model of infection.

Methods: 50 Cryptococcus isolates (5 VNI, 10 VGI, 10 VGIIa, 6 VGIIb, 4 VGIIc, 10 VGIII, 5 VGIV) obtained from clinical and veterinary sources were evaluated.  Isolates were genotyped using a consensus multi-locus typing scheme.  Between genotypes we compared: a) growth at 30 and 37oC (YPD media); b) melanin production on both dopamine and epinephrine containing media at 30 and 37oC; c) capsule size under optimal capsule-inducing conditions; d) resistance to killing by H2O2; and e) susceptibility testing (M27-A3 method). Finally, we compared fly survival after each isolate was inoculated into 60 wild-type [WT] flies (3 independent experiments) at a concentration of 2 x 109 cells/mL. 

Results: VGIII isolates grew best at 30oC, with significant increases in growth compared to all other genotypes (p=<0.0001).  At 37oC, VNI isolates grew best, with significant differences seen compared to genotypes VGI, VGIIa, and VGIII (p<0.04).  VGI and VGIII isolates produced larger capsules than other genotypes (p<0.02).  Melanin production was comparable across temperature and media conditions. Resistance to killing by H2O2 was most prominent in VNI isolates while VGIII were most susceptible (p=<0.05). VGIIc isolates exhibited higher MICs to fluconazole than other genotypes. VGIII was the most virulent genotype observed in our Drosophila model.

Conclusion: We found genotype-specific differences in C. gattii by in vitro characterization of virulence factor production. However, except growth at 30oC, these differences correlated poorly with virulence in our Drosophila model.  Comparative virulence studies using animal models at 37oC will be helpful in elucidating the temperature-dependence of established virulence factors in C. gattii.   

George R. Thompson III, MD, Medical Microbiology and Immunology, University of California-Davis, Davis, CA, Nathaniel Albert, BS, MD Anderson Cancer Center, Houston, TX, Greg Hodge, PhD, Medical Microbiology and Immunology, UC Davis, Davis, CA, Jane Sykes, DVM, Veterinary Medicine, UC Davis, Davis, CA, Derek Bays, University of California - Davis, Davis, CA, Carolina Firacative, Sydney Medical School - Westmead, Sydney, Australia, Sydney, Australia, Wieland Meyer, The University of Sydney, Sydney, Australia and Dimitrios Kontoyiannis, MD, ScD, FIDSA, The University of Texas M.D. Anderson Cancer Center, Houston, TX


G. R. Thompson III, None

N. Albert, None

G. Hodge, None

J. Sykes, None

D. Bays, None

C. Firacative, None

W. Meyer, None

D. Kontoyiannis, Merck: Investigator, Scientific Advisor and Speaker's Bureau, Consulting fee, Research grant and Speaker honorarium
Gilead: Speaker's Bureau, Speaker honorarium
Astellas: Investigator, Research grant
T2 biosystems: Investigator, Research grant

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