Cryptococcus: Mycology and Virulence Professor Malcolm D. Richardson Mycology Reference Centre, Manchester Manchester University NHS Foundation Trust

Intended learning outcomes To be aware of the common species and habitats of Cryptococcus To understand the structure of Cryptococcus yeasts To be aware of the different serotypes of Cryptococcus spp. To be aware of the virulence factors of Cryptococcus spp.

Cryptococcus Ubiquitous encapsulated yeasts belonging to the division Basidiomycota. Over 70 species of Cryptococcus are known, however, Cryptococcus neoformans and C. gattii are the two main species implicated in nearly all cases of human cryptococcosis. C. neoformans has 2 distinct varieties: C. neoformans var. neoformans C. neoformans var. grubii Other species of less clinical significance includes: C. laurentii, C. adeliensis, C. albidus, etc.

Structure Yeast: round or oval Surrounded by polysaccharide capsules 4-6mm in diameter Surrounded by polysaccharide capsules 20-30mm thick “Titan” cells ~90-100 mm Melanised Negatively stains with India Ink and nigrosin Stains with PAS and mucicarmine

Habitat C. neoformans C. gattii Frequently isolated from soil contaminated with pigeon or other bird droppings and NOT in fresh wet droppings. The precise link between C. neoformans and birds to date remains unclear. Birds do not get infected. C. gattii Isolated from decaying wood in the red gum group of eucalyptus trees, cedar, oak and other native trees. C. gattii has not been isolated from bird droppings.

Serotypes of Cryptococcus spp. PATHOGEN SEROTYPE GEOGRAPHICAL DISTRIBUTION ENVIRONMENTAL ASSOCIATION AFFECTED PATIENT GROUPS C. neoformans var grubii A Worldwide Birds, particularly pigeon excreta HIV patients (98% of all isolates ) Immunocompromised patients Rarely immunocompetent C. gattii B,C Tropics and subtropics Eucalyptus trees Immunocompetent patients var neoformans D European countries var grubii/var neoformans hybrid AD Not known Rare clinical isolate Immunocompromised JN Day :Practical Neurology, 2004, 4, 274–285

Virulence factors Major virulence Other virulence Polysaccharide capsule formation Melanin pigment production Ability to grow well at 370C Phenotypic switching Other virulence Secreted phospholipase B Urease production Enzymes associated with protection against oxidative stresses

Virulence factors Polysaccharide capsule formation Key roles Comprised of glucuronoxylomannan (GXM) and galactoxylomannan (GalXM) Key roles Anti-phagocytic Antibody unresponsiveness Inhibition of leucocyte migration Deregulation of cytokine secretion Interference with antigen presentation L-selectin & tumor necrosis factor loss

Virulence factors Melanin pigment production Key Roles Antioxidant Catalyzed by the enzyme Phenol oxidase Key Roles Antioxidant Cell wall support and integrity Interference with T-cell response Reduction of susceptibility to antifungal agents Abrogation of antibody mediated phagocytosis Protection from extreme temperature

Virulence factors Phenotypic switching Occurs during chronic infection Common in serotype A and D strains of C. neoformans Associated with differential gene expression and capsule changes in virulence “Titan” cell formation Titan cells Normal sized cell Titan cell

Summary Cryptococcus are ubiquitous encapsulated yeasts. C. neoformans and C. gatti are the two main species implicated in clinical disease. Cryptococcus spp. have a number of virulence factors. C. neoformans var. grubii (serotype A) is the most common cause of disseminated disease in HIV/AIDs patients.

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