Nutritional Requirements and Their Importance for Virulence of Pathogenic Cryptococcus Species

Watkins, Rhys A; King, Jason; Johnston, Simon A.

doi:10.3390/microorganisms5040065

Cited by 30 publications

(25 citation statements)

References 192 publications

(263 reference statements)

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“…Cryptococci are free-living fungi with a life cycle that is not dependent on infecting an animal host. It has therefore been proposed that the mechanisms that allow C. neoformans to survive and grow in macrophages have primarily evolved to avoid predation by phagocytes in its natural environment, such as amoebae (Steenbergen et al, 2001 ; Casadevall, 2012 ; Watkins et al, 2017 ).…”

Section: Introductionmentioning

confidence: 99%

Cryptococcus neoformans Escape From Dictyostelium Amoeba by Both WASH-Mediated Constitutive Exocytosis and Vomocytosis

Watkins

Andrews

Wynn

et al. 2018

Front. Cell. Infect. Microbiol.

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Cryptococcus neoformans is an environmental yeast that can cause opportunistic infections in humans. As infecting animals does not form part of its normal life-cycle, it has been proposed that the virulence traits that allow cryptococci to resist immune cells were selected through interactions with environmental phagocytes such as amoebae. Here, we investigate the interactions between C. neoformans and the social amoeba Dictyostelium discoideum. We show that like macrophages, D. discoideum is unable to kill C. neoformans upon phagocytosis. Despite this, we find that the yeast pass through the amoebae with an apparently normal phagocytic transit and are released alive by constitutive exocytosis after ~80 min. This is the canonical pathway in amoebae, used to dispose of indigestible material after nutrient extraction. Surprisingly however, we show that upon either genetic or pharmacological blockage of constitutive exocytosis, C. neoformans still escape from D. discoideum by a secondary mechanism. We demonstrate that constitutive exocytosis-independent egress is stochastic and actin-independent. This strongly resembles the non-lytic release of cryptococci by vomocytosis from macrophages, which do not perform constitutive exocytosis and normally retain phagocytosed material. Our data indicate that vomocytosis is functionally redundant for escape from amoebae, which thus may not be the primary driver for its evolutionary selection. Nonetheless, we show that vomocytosis of C. neoformans is mechanistically conserved in hosts ranging from amoebae to man, providing new avenues to understand this poorly-understood but important virulence mechanism.

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Section: Introductionmentioning

confidence: 99%

Cryptococcus neoformans Escape From Dictyostelium Amoeba by Both WASH-Mediated Constitutive Exocytosis and Vomocytosis

Watkins

Andrews

Wynn

et al. 2018

Front. Cell. Infect. Microbiol.

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“…One explanation is that nutrient starvation is hypothesised to be one mechanism by which macrophages kill phagocytosed pathogens. In our PCLS methodology, we may have inadvertently affected this process as we use a relatively glucose rich media to maintain viable slices (6).…”

Section: Discussionmentioning

confidence: 99%

“…Cryptococcal infection is one of the leading causes of mortality in HIV/AIDS patients (15%), estimated to cause over 200,000 infections globally a year and more than 180,000 deaths (4). C. neoformans has evolved multiple virulence mechanisms related to an ecological niche in the soil and tree saprophyte in response to natural predators such as amoebae that have allowed this fungus to cause disease (5,6). These include a polysaccharide capsule, production of oxygen scavenging melanin and the ability to modulate host immunity (7)(8)(9)(10).…”

Section: Introductionmentioning

confidence: 99%

The mouse lung early cellular innate immune response is not sufficient to control fungal infection with Cryptococcus neoformans

Rudman

Marriott

Carlin

et al. 2019

Preprint

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Cryptococcus neoformans causes life-threatening infection in the immunocompromised. This and other opportunistic pathogens are an increasing threat as immunosuppression increases globally. To counter antibiotic resistance, there is precedent for developing immune enhancing therapy. However, our understanding of how immunocompetent patients resolve these infections is poor as opportunistic infections typically resolve subclinically. Because this has led to a lack of clinical data, we rely on animal models. Current in vivo infection models either lack mammalian immunity or are not compatible with long term high content imaging required to model the complexities of human host-pathogen interactions. Therefore, we have developed an ex vivo murine precision cut lung slice (PCLS) model to understand innate immunity in cryptococcosis. C57BL/6 mice were sacrificed 0 or 24 hours post infection with KN99α cryptococci. Lungs were inflated with 37 o C agarose, 300μm thick PCLS were prepared on a vibratome and imaged by confocal or wide-field fluorescence microscopy.Using PCLS and immunofluorescence, we demonstrate cryptococcal replication and clearance rates are balanced over the first 24 hours of infection. Cell-mediated immunity is alveolar macrophage centric, although alveolar macrophages demonstrate limited phagocytosis of cryptococci and enable intracellular cryptococcal replication. Cryptococcus neoformans responded to the lung environment by forming enlarged cells, although these were not large enough to be titan cells. To further understand cryptococcal proliferation in vivo, we also infected animals with plb1 mutant Cryptococcus neoformans that has been shown to exhibit proliferation defects in vivo. We found no difference in fungal burden with plb1 infected animals 24 hours post infection, but observed significantly larger fungal cells and no incidences of phagocytosis. Thus, the PCLS model can be used to assess the lung immune response early in cryptococcal infection, demonstrating that resident lung macrophages cannot control cryptococcal infection and offer an intracellular niche for Cryptococcus neoformans growth.

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“…Cryptococcal cells are mesophilic, and thus well adapted to survive at lower environmental temperatures than in mammalian bodies. Hence cryptococcal cells have been isolated from environmental hosts such as amoeba [71]. Given the vast difference in the internal temperature of a host such as an amoeba compared to a mammalian host, it is clear the argument of Guijarro and co-workers is true that the regulation of virulence genes in response to temperature shift is modulated in different ways depending on the hosts [72].…”

Section: Thermotolerancementioning

confidence: 99%

Environmental Factors That Contribute to the Maintenance of Cryptococcus neoformans Pathogenesis

et al. 2020

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The ability of microorganisms to colonise and display an intracellular lifestyle within a host body increases their fitness to survive and avoid extinction. This host–pathogen association drives microbial evolution, as such organisms are under selective pressure and can become more pathogenic. Some of these microorganisms can quickly spread through the environment via transmission. The non-transmittable fungal pathogens, such as Cryptococcus, probably return into the environment upon decomposition of the infected host. This review analyses whether re-entry of the pathogen into the environment causes restoration of its non-pathogenic state or whether environmental factors and parameters assist them in maintaining pathogenesis. Cryptococcus (C.) neoformans is therefore used as a model organism to evaluate the impact of environmental stress factors that aid the survival and pathogenesis of C. neoformans intracellularly and extracellularly.

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Nutritional Requirements and Their Importance for Virulence of Pathogenic Cryptococcus Species

Cited by 30 publications

References 192 publications

Cryptococcus neoformans Escape From Dictyostelium Amoeba by Both WASH-Mediated Constitutive Exocytosis and Vomocytosis

Cryptococcus neoformans Escape From Dictyostelium Amoeba by Both WASH-Mediated Constitutive Exocytosis and Vomocytosis

The mouse lung early cellular innate immune response is not sufficient to control fungal infection with Cryptococcus neoformans

Environmental Factors That Contribute to the Maintenance of Cryptococcus neoformans Pathogenesis

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