CLINICAL SERVICES

Fungus Testing Laboratory
Mould Direct Line 210-567-2828
Yeast Direct Line 210-567-3106

Fungal Indentification

The Fungus Testing Laboratory is an academic reference laboratory providing fungal identification services for a wide variety of clients. In addition to serving the medical community, we also provide extensive services to Schools of Veterinary Medicine, veterinary reference laboratories, zoos, aquariums, and other research facilities or environmental companies requiring identification of fungal isolates. We welcome discussion during any phase of the identification process, and appreciate receiving clinical information that may facilitate documentation of an organism as the etiologic agent.


Specimen Requirements:
Isolates must be submitted in pure culture on a slant. Any medium that supports the growth of the organism is acceptable.

Mould Identification CPT 87107

  • Human and veterinary clinical isolates are determined to the species level whenever possible for appropriate patient management. To accomplish this, sequence analysis is routinely combined with morphology and phenotypic characteristics by the FTL in order to determine species identity. As we continue to further our understanding of the differences between fungal pathogens and susceptibility to antifungal agents, this level of identification is becoming increasingly important for determining appropriate therapeutic options. Thus, we strive to provide the most extensive identification possible while also providing results in a timely fashion.
  • CPT 87797. Identification of Histoplasma capsulatum var. capsulatum, Blastomyces dermatitidis, and Coccidioides species is confirmed by DNA probe.
  • CPT 87220, 87101, 87107. Specialized testing consisting of KOH, culture, and identification of agents of dermatophytosis or dermatomycosis is offered to the dermatology/podiatry community.
  • Research activities that may be pursued, after discussion with the sender, and at an additional cost include:
    • Identification of isolates by molecular sequencing
    • Molecular sequencing for outbreak strain relatedness
    • Individually-tailored research projects

Yeast Identification CPT 87106

The FTL utilizes a variety of tests to arrive at a final yeast identification. Current methods include one or more of the following:

  • API 20C AUX by bio Merieux
    The API 20C AUX is a ready-to-use micromethod which permits the performance of 19 assimilation for the identification of most clinically significant yeasts and yeast-like organisms in the genera Candida, Cryptococcus, Geotrichum, Hansenula, Hanseniaspora, Torulopsis, Trichosporon, Prototheca, Rhodotroula, Saccharomyces, and Sporobolomyces. Assimilation reactions are complete after 72 hours incubation at 30°C
    The API 20C System consists of a series of cupules containing dehydrated substrates for assimilation reactions. These substrates are reconstituted by the addition of a pure yeast suspension in API basal medium to the cupules. Assimilation is the utilization of a carbon source by a yeast in the presence of oxygen. The assimilation of a sugar results in a turbid well
  • Classic Whickerham assimilation and formation
    Although the API 20C yeast identification strip is the gold standard for identification of yeast fungi to the species level in clinical laboratories, many isolates continue to elude identification via this method. Classic Wickerham fermentation studies may assist in a definitive identification. During fermentation, carbohydrates are fermented to form ethanol and carbon dioxide. Sugars that are fermented (accompanied by gas production) are generally assimilated (accompanied by a color change) as well. The reverse, however, is not necessarily true
  • Cycloheximide susceptibility
    Many yeasts are described in taxonomy references regarding their susceptibility to cycloheximide. This test gives one more characteristic, either susceptible or resistant by which to make a definitive identification.
  • Nitrate assimilation
    Yeasts have the ability to use ammonium sulfate, asparagine, peptone, and urea at reasonable concentrations as the sole source of nitrogen when adequate vitamins are provided. In contrast, aliphatic amines, potassium nitrate, sodium nitrate, and some amino acids are utilized selectively by different yeasts. These latter compounds are very useful in the identification of yeasts.
  • Urea hydrolysis
    A number of yeasts produce the enzyme urease, thereby having the capability to hydrolyze urea. The ability to produce urease is determined with Christensen’s urea agar and provides yet another characteristic by which to make an identification.
  • Macroscopic and microscopic morphology
    Macroscopic descriptions are made from yeast colonies grown on Saboraud Dextrose Agar incubated at 30°. The Dalmau plate (Corn Meal Agar) is useful in determining the microscopic morphology of the yeast. Cultures are evaluated for the production of true hyphae, pseudohyphae, blastoconidia, and Arthroconidia.
  • Temperature Studies
    Temperature studies offer additional information which aid in the identification of yeast isolates. For example, Cryptococcus neoformans can be distinguished from other Cryptococcus sp. by its ability to grow at 37° C.
  • Barnet’s Computer Assisted Key
    Barnet’s Computer Assisted Key is a computerized synoptic key by which results of testing from the above listed methods may be entered. Once the test reactions have been entered, the computer searches the database and reveals fungi that have the same reactions. The probability that a listed organism is the correct organism is also listed.
  • Research activities that may be pursued, after discussion with the sender, and at an additional cost include:
    • Identification of isolates by molecular sequencing
    • Molecular sequencing for outbreak strain relatedness
    • Individually-tailored research projects