DESCRIPTIONS OF MEDICAL FUNGI

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Descriptions of Medical Fungi
Candida Berkhout
Dalmau Plate Culture: To set up a yeast morphology plate, dip a flamed sterilised
straight wire into a culture and then lightly scratch the wire onto the surface of a
cornmeal/tween 80, rice/tween 80 or yeast morphology agar plate, then place a flamed
coverslip onto the agar surface covering the scratches. Dalmau morphology plates
are examined in-situ directly under the low power of a microscope for the presence
of pseudohyphae which may take up to 4-5 days at 26 O C to develop. C. albicans
also produces characteristic large, round, terminal, thick-walled vesicles (often called
chlamydospores). For best results a light inoculum should be scratched into the agar
surface using a wire.
10 μm
a
5 mm
b
Dalmau plate culture of Candida albicans showing (a) colonies growing out from
scratches on the surface of a cornmeal/tween 80 agar plate, and (b) the production of
large round, thick-walled chlamydospores. Note: A coverslip has been placed onto the
agar surface covering the scratches.
Physiological and Biochemical Tests: including fermentation and assimilation studies
should be performed based on those used at the Centraalbureau voor Schimmelcultures
(CBS), Delft, The Netherlands (Kurtzman et al. 2011). Reliable commercially available
yeast identification systems are the API 20C AUX, API ID 32C, Biolog YT Station and
Vitek 2 YST ID systems. However, they can only be used to identify those species in
their respective databases, and may misidentify yeasts that are not represented.
Other Supplementary Tests include growth at 37 O C, cycloheximide resistance and
hydrolysis of urea.
MALDI-TOF MS: The Bruker MALDI-TOF database is useful for identification of most
clinical yeasts. The MALDI-TOF Vitek MS has been reported to misidentify some
yeasts, notably Candida metapsilosis as Candida parapsilosis (Nobrega et al. 2014).
Molecular Identification: ITS sequencing is useful for the identification of most clinical
yeasts.
References: Barnett et al. (1983), Kurtzman and Fell (1998, 2011), de Hoog et al.
(2000, 2015).