Global VGIIa isolates are of comparable virulence to the major fatal Cryptococcus gattii Vancouver Island outbreak genotype

Authors

  • P. Ngamskulrungroj,

    1.  Molecular Mycology Research Laboratory, Centre for Infectious Disease and Microbiology, Westmead Millennium Institute, Westmead Hospital, Sydney Medical School – Westmead, The University of Sydney, Westmead, NSW, Australia
    2.  Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
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  • C. Serena,

    1.  Molecular Mycology Research Laboratory, Centre for Infectious Disease and Microbiology, Westmead Millennium Institute, Westmead Hospital, Sydney Medical School – Westmead, The University of Sydney, Westmead, NSW, Australia
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  • F. Gilgado,

    1.  Molecular Mycology Research Laboratory, Centre for Infectious Disease and Microbiology, Westmead Millennium Institute, Westmead Hospital, Sydney Medical School – Westmead, The University of Sydney, Westmead, NSW, Australia
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  • R. Malik,

    1.  Centre for Veterinary Education, The University of Sydney, Sydney, NSW, Australia
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  • W. Meyer

    1.  Molecular Mycology Research Laboratory, Centre for Infectious Disease and Microbiology, Westmead Millennium Institute, Westmead Hospital, Sydney Medical School – Westmead, The University of Sydney, Westmead, NSW, Australia
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Corresponding author and reprint requests: W. Meyer, Molecular Mycology Research Laboratory, CIDM, ICPMR, Westmead Hospital, Level 3, Room 3114A, Darcy Road, Westmead, NSW 2145, Australia
E-mail:w.meyer@usyd.edu.au

Abstract

Clin Microbiol Infect 2011; 17: 251–258

Abstract

The ongoing cryptococcosis outbreak on Vancouver Island, BC, Canada, is caused by two VGII sub-genotypes of the primary pathogen, Cryptococcus gattii: VGIIa isolates predominate, whereas VGIIb isolates are rare. Although higher virulence of the VGIIa genotype has been proposed, an unresolved key question is whether VGIIa isolates from other regions are also more virulent than VGIIb isolates. We report the relationship between genotype and virulence for a global collection of C. gattii VGIIa and VGIIb isolates (from Australia, Argentina, Brazil, Canada, Thailand and the USA). In vitro and in vivo virulence studies were conducted. At 37°C, growth [at 18 h: 0.2 optical density (OD) difference, p 0.026; at 36 h: 0.6 OD difference, p 0.036) and mean melanin production (OD = 0.25 vs. OD = 0.15, p 0.059] of VGIIa isolates was greater than that of VGIIb isolates. The inhibitory effect of high temperature on melanin production of VGIIa isolates was less than that of VGIIb isolates (OD = 0.36 vs. OD = 0.69; p 0.001). Capsule production at 37°C of VGIIa isolates was less than that of VGIIb isolates. All VGIIa isolates were fertile, whereas only 17% of VGIIb isolates were fertile (p <0.001). In vivo virulence studies using the BALB/c mice nasal inhalation model revealed that VGIIa isolates were more virulent than VGIIb isolates (p <0.001) independent of their clinical (p 0.003) or environmental origin (p <0.001). This study established a clear association between genotype and virulence of the primary fungal pathogen, C. gattii.

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