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Infection and Immunity, October 2009, p. 4345-4355, Vol. 77, No. 10
0019-9567/09/$08.00+0 doi:10.1128/IAI.00542-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Spores as Infectious Propagules of Cryptococcus neoformans
,
Rajesh Velagapudi,1
Yen-Ping Hsueh,1
Scarlett Geunes-Boyer,2
Jo Rae Wright,2 and
Joseph Heitman1,3,4*
Department of Molecular Genetics and Microbiology,1 Department of Cell Biology,2 Department of Medicine,3 Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 277104
Received 18 May 2009/ Returned for modification 14 June 2009/ Accepted 15 July 2009
Cryptococcus neoformans and Cryptococcus gattii are closely related pathogenic fungi that cause pneumonia and meningitis in both immunocompromised and immunocompetent hosts and are a significant global infectious disease risk. Both species are found in the environment and are acquired via inhalation, leading to an initial pulmonary infection. The infectious propagule is unknown but is hypothesized to be small desiccated yeast cells or spores produced by sexual reproduction (opposite- or same-sex mating). Here we characterize the morphology, germination properties, and virulence of spores. A comparative morphological analysis of hyphae and spores produced by opposite-sex mating, same-sex mating, and self-fertile diploid strains was conducted by scanning electron microscopy, yielding insight into hyphal/basidial morphology and spore size, structure, and surface properties. Spores isolated by microdissection were found to readily germinate even on water agarose medium. Thus, nutritional signals do not appear to be required to stimulate spore germination, and as-yet-unknown environmental factors may normally constrain germination in nature. As few as 500 CFU of a spore-enriched infectious inoculum (
95% spores) of serotype A C. neoformans var. grubii were fully virulent (100% lethal infection) in both a murine inhalation virulence model and the invertebrate model host Galleria mellonella. In contrast to a previous report on C. neoformans var. neoformans, spores of C. neoformans var. grubii were not more infectious than yeast cells. Molecular analysis of isolates recovered from tissues of infected mice (lung, spleen, and brain) provides evidence for infection and dissemination by recombinant spore products. These studies provide a detailed morphological and physiological analysis of the spore and document that spores can serve as infectious propagules.
* Corresponding author. Mailing address: Duke University Medical Center, 322 CARL Building, Box 3546, Durham, NC 27710. Phone: (919) 684-2824. Fax: (919) 684-5458. E-mail: heitm001{at}duke.edu
Published ahead of print on 20 July 2009.
Supplemental material for this article may be found at http://iai.asm.org/.
Infection and Immunity, October 2009, p. 4345-4355, Vol. 77, No. 10
0019-9567/09/$08.00+0 doi:10.1128/IAI.00542-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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