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

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.
Clinical Microbiology and Infection (Impact Factor: 5.77). 03/2010; 17(2):251-8. DOI: 10.1111/j.1469-0691.2010.03222.x
Source: PubMed


Clin Microbiol Infect 2011; 17: 251–258
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.

Download full-text


Available from: Richard Malik, Oct 13, 2014
  • Source
    • "Previous studies indicated that C. gattii AFLP6A/VGIIa, the so-called major Vancouver Island outbreak genotype, and strains with genotype AFLP6C/VGIIc from the Pacific Northwest outbreak are highly virulent in different host models, while strains that belong to the minor Vancouver Island outbreak genotype AFLP6B/VGIIb were less virulent or non-virulent [3], [6], [18], [19]. To further elucidate the virulence potential among strains within the basal lineages of the coalescence tree, we investigated the virulence of 22 C. gattii strains using mice and macrophage pathogenicity assays ([3], [19]; Figs. 1, 4 and 5; Table S3). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Over the past two decades, several fungal outbreaks have occurred, including the high-profile 'Vancouver Island' and 'Pacific Northwest' outbreaks, caused by Cryptococcus gattii, which has affected hundreds of otherwise healthy humans and animals. Over the same time period, C. gattii was the cause of several additional case clusters at localities outside of the tropical and subtropical climate zones where the species normally occurs. In every case, the causative agent belongs to a previously rare genotype of C. gattii called AFLP6/VGII, but the origin of the outbreak clades remains enigmatic. Here we used phylogenetic and recombination analyses, based on AFLP and multiple MLST datasets, and coalescence gene genealogy to demonstrate that these outbreaks have arisen from a highly-recombining C. gattii population in the native rainforest of Northern Brazil. Thus the modern virulent C. gattii AFLP6/VGII outbreak lineages derived from mating events in South America and then dispersed to temperate regions where they cause serious infections in humans and animals.
    Full-text · Article · Aug 2013 · PLoS ONE
  • Source
    • "Geographic distribution of the molecular types identified in Central and South America (c). Molecular typing data have been combined from the following references: Guatemala [64], Honduras [11], Cuba [89–91], Puerto Rico [92], Aruba [11, 17], Venezuela [64], Colombia [29, 64, 93–96], Perù [64], Uruguay [11, 17], Brazil [11, 17, 29, 38, 46, 64, 97–118], Argentina [15, 64, 119], and Chile [64]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Cryptococcosis is a fungal disease affecting more than one million people per year worldwide. The main etiological agents of cryptococcosis are the two sibling species Cryptococcus neoformans and Cryptococcus gattii that present numerous differences in geographical distribution, ecological niches, epidemiology, pathobiology, clinical presentation and molecular characters. Genotyping of the two Cryptococcus species at subspecies level supplies relevant information to understand how this fungus has spread worldwide, the nature of its population structure, and how it evolved to be a deadly pathogen. At present, nine major molecular types have been recognized: VNI, VNII, VNB, VNIII, and VNIV among C. neoformans isolates, and VGI, VGII, VGIII, and VGIV among C. gattii isolates. In this paper all the information available in the literature concerning the isolation of the two Cryptococcus species has been collected and analyzed on the basis of their geographical origin, source of isolation, level of identification, species, and molecular type. A detailed analysis of the geographical distribution of the major molecular types in each continent has been described and represented on thematic maps. This study represents a useful tool to start new epidemiological surveys on the basis of the present knowledge.
    Full-text · Article · Jan 2013
  • Source
    • "However, after the cryptococcosis outbreak caused by C. gattii on Vancouver Island Canada in 1999 [15], C. gattii has gained prominence as a primary pathogen. Genetic characterizations of C. gattii have been conducted mostly to decipher the virulence traits of the species [41], [42], [43], [44], [45] and not its ability to utilize nitrogen or carbon. Since these biochemical features are crucial for understanding the differences in pathobiology between the two species, we compared the GAT1 regulation of the amino acid utilization and its effect on virulence. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Two members of the Cryptococcus neoformans-gattii species complex, the etiologic agents of cryptococcosis, can be differentiated by biological, biochemical, serological and molecular typing techniques. Based on their differences in carbon and nitrogen utilization patterns, cost effective and very specific diagnostic tests using D-proline and canvanine-glycine-bromthymol blue (CGB) media have been formulated and are widely used for identification of the two species. However, these methods have yet to be tested for strains with confirmed molecular types to assess the degree of specificity for each molecular type in the two species. We collected global isolates of every major molecular type available and tested their patterns of nitrogen utilization. We confirmed specificity of the CGB test to be 100% regardless of molecular type while the D-proline test yielded 8-38% false negative results in three of the four C. gattii molecular types, VGI-VGIII. The utilization pattern of a new set of amino acids: D-alanine, L-tryptophan and L-phenylalanine, showed species specificity comparable to that of D-proline. We discovered that the transcription factor Gat1 (Are1) regulates the utilization of nitrogen differently between C. neoformans and C. gattii strains. Unlike in C. neoformans, expression of the genes encoding glycine decarboxylase complex in C. gatti was only partially suppressed by nitrogen catabolite repression in the presence of ammonium. GAT1 in C. neoformans controlled the induction of three of the four genes encoding the glycine decarboxylase complex when glycine was used as the sole nitrogen source while in C. gattii its regulation of these genes was less stringent. Moreover, while virulence of C. neoformans strains in mice was not affected by Gat1, the transcription factor positively influenced the virulence of C. gattii strain.
    Full-text · Article · Mar 2012 · PLoS ONE
Show more