Cryptococcus laurentii

Cryptococcus laurentii is an extremely rare human pathogen. This fungus was previously considered saprophytic and nonpathogenic to humans, but it has been isolated as the etiologic agent of skin infection, keratitis, endophthalmitis, lung abscess, peritonitis,meningitis and fungaemia.

Ecology

C. laurentii is the most frequently encountered yeast in tundra, Antarctic and prairie soils as well as the phyllosphere of numerous ecosystems. The faecal matter of healthy birds has been identified as an important repository for cryptococcal fungi. Although the related species C. neoformans has been identified as an important human pathogen, infections with C. laurentii occur almost exclusively in immuno-compromised individuals and rarely result in clinically significant outcomes. C. laurentii is psychrophillic and grows poorly above 30°C temperatures. While optimal growth temperatures of 15°C have been reported for this species, it is cryotolerant and can be successfully cultured at near freezing conditions. C. laurentii has been described as a facultative alkaliphile.

On Sabouraud's dextrose agar colonies are cream colored, often becoming a deeper orange-yellow with age, with a smooth mucoid texture. Microscopic morphology : Spherical and elongated budding yeast-like cells or blastoconidia, 2.0-5.5 x 3.0-7.0 μm in size. No pseudohyphae present.

India Ink Preparation:

Positive - narrow but distinct capsules surrounding the yeast cells are present.

Dalmau Plate Culture on Cornmeal and Tween 80 Agar:

Budding yeast cells only. No pseudohyphae present.

Physiological Tests:

Germ Tube test is Negative
Hydrolysis of Urea is Positive
Growth on Cycloheximide medium is Variable
Growth at 37C is Negative (weak growth in some strains)

Fermentation Reactions:

Where fermentation means the production of gas and is independent of pH changes.

Negative: Glucose; Sucrose; Lactose; Galactose; Maltose; Trehalose.

Appearance:

Susceptibility:

  • Can be fluconazole resistant
  • Usually treated with amphotericin

AMH.