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Also read: Cryptococcus attacks Vancouver, Canada

Taxonomic classification

Kingdom: Fungi
Phylum: Basidimycota
Subphylum: Basidimycotina
Order: Sporidiales
Family: Sporidiobolaceae
Genus: Filobasidiella (Cryptococcus)

Cryptococcus neoformans

Laboratory Culture @ 25C or 37C

Tissue/Exudate Form

Source: Veterinary Pathology

Cryptococcus laurentii



Cryptococcus laurentii on Dalmau plate. Note the absence of hyphae.

  • Colonies are white or greenish on birdseed agar; cream to yellow, pink, orange, or tan on routine growth media
  • Like C. neoformans, may grow at 37 C on Sabouraud. dextrose agar
  • Like other Cryptococcus species, urease positive
  • Used within the laboratory as a control organism to test purity of sugars within certain media
  • Yeast ovoid to elongate, as single cells or in pairs or occasionally in chains of 3 or more cells

Source of Cryptococcus laurentii information: UCSF Medical Center website

Description and Habitats

Cryptococcus is an encapsulated yeast. Following its first identification in nature from peach juice samples, the major environmental sources of Cryptococcus neoformans have been shown to be either soil contaminated with pigeon droppings (Cryptococcus neoformans var. neoformans) or eucalyptus trees and decaying wood forming hollows in living trees (Cryptococcus neoformans var. gattii). Cryptococcus neoformans var. gattii was also isolated from goats with pulmonary disease.


The genus Cryptococcus includes around 37 species. Cryptococcus neoformans is the only species that is pathogenic based on the mycological information found on Among the other Cryptococcus  are Cryptococcus albidus, Cryptococcus laurentii, Cryptococcus terreus, Cryptococcus uniguttulatus, Cryptococcus luteolus and Cryptococcus gastricus.

Health Effects


Cryptococcosis manifests itself most commonly as meningitis but in recent years many cases of pulmonary disease have been recognized. C. neoformans is a very distinctive yeast. The cells which are spherical and 3-7 microns in diameter, produce buds which characteristically are narrow-based and the organism is surrounded by a polysaccharide capsule. There is evidence that the capsule may suppress T-cell function and can be considered a virulence factor. C. neoformans also produces an enzyme called phenoloxidase which appears to be another virulence factor.

The ecological niche of C. neoformans is pigeon and chicken droppings. However, although this organism can be easily recovered from pigeon droppings, a direct epidemiological link has yet to be established between exposure to pigeon droppings and a specific human infection. Infection and disease production is probably a property of the host--not the organism. 

The source of human infection is not clear. This organism is ubiquitous, especially in areas like abandoned buildings contaminated with pigeon droppings. The portal of entry is the respiratory system. Evidence is developing which indicates that the initial exposure may be many years prior to the manifestation of disease. The organism can be sequestered for this time.

Infection may be subacute or chronic. The highly fatal meningoencephalitis caused by C. neoformans has a prolonged evolution of several months. The patients symptoms may begin with vision problems and headache, which then progress to delirium, nuchal rigidity leading to coma and death unless the physician is thinking about cryptococcus and does a spinal tap for diagnosis and institutes aggressive therapy. The CSF is examined for its characteristic chemistry (elevated protein and decreased glucose), cells (usually monocytes), and evidence of the organism. The latter is measured by the visual demonstration of the organism (India Ink preparation) or by a serologic assay for the antigen of C. neoformans. The India Ink test, which demonstrates the capsule of this yeast, is supplemented by the latex agglutination test for antigen which is more sensitive and more specific. The Latex Agglutination test measures antigen, NOT antibody. A decreasing titer indicates a good prognosis, while an increasing titer has a poor prognosis. 

When you consider Cryptococcosis, think of Capsules and CNS disease. In addition to causing meningitis, C. neoformans may also infect lungs and skin. The disease in the lungs and skin is characterized by the formation of a granulomatous reaction with giant cells. As with other fungal diseases, there has been an increase in the recognition of pulmonary infection. The yeast may also form a mass in the mediastinum called a cryptococcoma. 

The geographical distribution of this organism is world-wide. The clinical material sent to the lab is CSF, biopsy material, and urine (for some unexplained reason the organism can be isolated from the urine in both the CNS and systemic infections). This organism will grow overnight on bacterial or fungal media at 37 C. but growth is a little slower at room temperature. In culture the organism grows as creamy, white, mucoid (because of the capsule) colonies. Growth in culture is usually visible in 24 to 48 hours. As the culture ages, it turns brown due to a melanin produced by the phenoloxidase. The organism is a round, single cell, yeast surrounded by a capsule. Identification is based on physiological reactions. Pathologists use a mucicarmine stain, which stains the capsule, to identify the organism in tissue sections. There is usually little or no inflammatory response. The Direct Fluorescent Antibody test identifies the organism in culture or tissue section specifically, by causing the yeast cell wall to stain green.  To test the patient's serum there are 3 serologic tests: The Indirect Fluorescent Antibody test, the Tube Agglutination test for antibody, and the Latex Agglutination test for antigen. The latex agglutination test can be used as a prognostic test. As the patient improves, the serum antigen titer will also decrease. 

The drugs of choice to treat cryptococcus infection are amphotericin B and 5-Fluorocytosine (5-FC). 5-FC is an oral drug. If it is given as the only treatment, there are relapses so most physicians use both drugs simultaneously. Actually, these two drugs are synergistic, and thus, their association is advantageous.
(Source of Mycosis Information: Mycology Online)

Macroscopic Features

Colonies of Cryptococcus neoformans are fast growing, soft, glistening to dull, smooth, usually mucoid, and cream to slightly pink or yellowish brown in color. The growth rate is somewhat slower than Candida and usually takes 48 to 72 h. It grows well at 25C as well as 37C. Ability to grow at 37C is one of the features that differentiates Cryptococcus neoformans from other Cryptococcus spp. However, temperature-sensitive mutants that fail to grow at 37C in vitro may also be observed. At 39-40C, the growth of Cryptococcus neoformans starts to slow down.

Microscopic Features

On cornmeal tween 80 agar, Cryptococcus neoformans produces round, budding yeast cells. No true hyphae are visible. Pseudohyphae are usually absent or rudimentary. The capsule is best visible in India ink preparations. The thickness of the capsule is both strain-related and varies depending on the environmental conditions. Upon growth in 1% peptone solution, production of capsule is enhanced

Laboratory Precautions

No special precautions other than general laboratory precautions are required.


Usual Susceptibility Patterns for Cryptococcus spp

Susceptibility testing of Cryptococcus neoformans using the NCCLS reference method  is difficult due to the poor growth of the fungus, the related requirement for a relatively long incubation period (72 h), and difficulties in identification of resistant isolates. The only species for which there exists significant amount of data is Cryptococcus neoformans. Broadly stated, isolates of this species generally appear susceptible to amphotericin B, as well as fluconazole and flucytosine. Nevertheless, this depends significantly on the approach to measurement, and isolates which are apparently resistant to all of the current drugs have been identified.

In Vitro Susceptibility

Amphotericin B and other polyenes

Amphotericin B exerts a fungicidal effect on Cryptococcus neoformans. As with Candida spp., the NCCLS method has difficulty distinguishing amphotericin B-resistant isolates from the susceptible ones. However, modifications of this method, such as the use of Antibiotic Medium 3 supplemented to 2% glucose (AM3) instead of the reference RPMI 1640 medium appear useful. Shaking the microplates during incubation also appears helpful.

There are also data indicating that minimum fungicidal concentrations (MFCs) may be better predictors of clinical outcome than MICs. However, these modifications still require validation and standardization. Using E test method instead of NCCLS microdilution methodology may also enhance the detection of amphotericin B-resistant isolates, regardless of the test medium used. The other method under investigation, flow cytometry, in general yields rapid and correlated results with NCCLS reference method and for amphotericin B and fluconazole.

Variety-related differences in susceptibility patterns have also been observed. Cryptococcus neoformans var. gattii appears less susceptible to amphotericin B and flucytosine than var. neoformans. Defects in sterol isomerase and depletion of ergosterol content in fungal cell membrane may result in emergence of resistance to amphotericin B.

The novel lipid nanosphere-encapsulated amphotericin B formulation, NS-718, generates very low MICs. Similar to amphotericin B, liposomal nystatin and the parent compound nystatin also show favorable in vitro activity against most Cryptococcus neoformans isolates.

Promisingly, amphotericin B combined with fluconazole, itraconazole, or posaconazole yielded no antagonism in vitro and appeared synergistic for some isolates. In vitro synergy between amphotericin B and flucytosine or rifampin was observed for Cryptococcus neoformans strains isolated from patients who failed to respond to amphotericin B therapy.


Azoles, particularly fluconazole and itraconazole, have been shown to have fungistatic effects against most Cryptococcus neoformans isolates. Although most Cryptococcus neoformans strains are susceptible to fluconazole, isolates with high MICs have been detected. Alternative susceptibility testing methods may yield results that differ sharply from the NCCLS reference method. Using Etest instead of the reference microdilution method has resulted in misclassification of a number of susceptible Cryptococcus neoformans isolates as being resistant to fluconazole, itraconazole, and flucytosine. Colorimetric methods, on the other hand, might interpret some fluconazole- and flucytosine-resistant isolates as susceptible.

Similarly, most of the Cryptococcus neoformans strains are susceptible to itraconazole in vitro. Among the newer azoles, posaconazole (SCH56592) appears most potent on a weight basis, when compared to voriconazole , fluconazole, itraconazole, and ketoconazole.


Flucytosine has long been used as part of combination therapy of cryptococcal infections. Resistance may develop during monotherapy. Use of yeast nitrogen base as the test medium was reported to be very effective in some investigators' hands in testing flucytosine susceptibility.

Glucan Synthesis Inhibitors (Echinocandins)

These novel agents have essentially no activity against Cryptococcus neoformans. In vitro data suggest that activities of amphotericin B and fluconazole against Cryptococcus neoformans may be enhanced by caspofungin].

In Vivo Efficacy

The most commonly used agents for treatment of cryptococcal infections are amphotericin B, flucytosine, and fluconazole, and particularly amphotericin B and flucytosine in combination. Fluconazole prophylaxis is also in common practice in patients who have recovered from cryptococcal infections. However, clinical failure with fluconazole has been reported. Fluconazole combined with flucytosine and triple therapy with amphotericin B, flucytosine, and fluconazole have been reported as effective. Itraconazole is less effective than fluconazole as maintenance therapy.

The mycological information gathered and organized in this extensive research on the different Pathogenic Molds was  sourced out from the list of websites below: | | | | | | | | | | | | | | | |


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