DESCRIPTIONS OF MEDICAL FUNGI

190
Descriptions of Medical Fungi
Talaromyces marneffei (Segretain et al.) Samson et al.
Synonymy: Penicillium marneffei Segretain et al.
WARNING: RG-3 organism. Cultures of Talaromyces marneffei may represent a
biohazard to laboratory personnel and should be handled with caution in a class II
Biological Safety Cabinet (BSCII). T. marneffei exhibits thermal dimorphism and is
endemic in Southeast Asia and the southern region of China.
Samson et al. (2011b) redefined Talaromyces by combining Penicillium subgenus
Biverticillium into Talaromyces based upon phylogenetic analysis of the ITS and RPB1
loci. The genus contains 88 species that were placed into seven sections based on a
multigene phylogeny of the ITS, β-tubulin and RPB2 regions (Yilmaz et al. 2014). T.
marneffei is the only known dimorphic species in the genus, producing filamentous
growth at 25 O C and a yeast phase at 37 O C (Andrianopoulos 2002).
Molecular Identification: ITS sequencing is recommended, as well as β-tubulin as a
secondary molecular marker for identification (Yilmaz et al. 2014).
Morphological Description: Colonies at 25 O C are fast growing, suede-like to downy,
white with yellowish-green conidial heads. Colonies become greyish-pink to brown
with age and produce a diffusible brownish-red to wine-red pigment. Conidiophores
generally biverticillate and sometimes monoverticillate; hyaline, smooth-walled and
bear terminal verticils of three to five metulae, each bearing three to seven phialides.
Phialides are acerose to flask-shaped. Conidia are globose to subglobose, 2-3 µm in
diameter, smooth-walled and are produced in basipetal succession from the phialides.
On brain heart infusion (BHI) agar containing blood incubated at 37 O C, colonies are
rough, glabrous, tan-coloured and yeast-like. Microscopically, yeast cells are spherical
to ellipsoidal, 2-6 µm in diameter, and divide by fission rather than budding. Numerous
short hyphal elements are also present.
Histopathology: Tissue sections show small, oval to ellipsoidal yeast-like cells, 3 µm in
diameter, either packed within histiocytes or scattered through the tissue. Occasional,
large, elongated sausage-shaped cells, up to 8 µm long, with distinctive septa may be
present.
Key Features: Talaromyces marneffei is the only dimorphic species of Talaromyces,
which grows as a yeast at 37 O C. It produces a red soluble pigment on general media
and conidiophores have flask-shaped to acerose phialides.
References: Pitt (1979), Ramirez (1982), de Hoog et al. (2000, 2015), Andrianopoulos
(2002), Lyratzopoulos et al. (2002), Samson et al. (2011b), Visagie et al. (2014), Yilmaz
et al. (2014).