DESCRIPTIONS OF MEDICAL FUNGI

12
Descriptions of Medical Fungi
Aspergillus Micheli ex Link
Aspergillus is a very large genus containing about 250 species, which are currently
classified into seven subgenera that are in turn subdivided into several sections
comprised of related species (Raper and Fennell 1965, Gams et al. 1985, Geiser
et al. 2007). Traditionally, clinical microbiology laboratories have relied heavily
on morphology-based identification methods to differentiate Aspergillus species.
However many species, especially members of the section Fumigati have overlapping
morphological characteristics, which has allowed several genetically distinct species
to be misidentified (Balajee et al. 2005, 2007). This has led to the clustering of species
with overlapping morphologies into “species complexes”, so that laboratories may
report more accurately morphology-based identifications.
Identification of clinical isolates of Aspergillus to species level may be important given
that different species have variable susceptibilities to multiple antifungal drugs. For
example, in vitro and in vivo studies have demonstrated that A. terreus isolates are
largely resistant to the antifungal drug amphotericin B, A. ustus isolates appear to
be refractory to azoles, and A. lentulus and Petromyces alliaceus have low in vitro
susceptibilities to a wide range of antifungals including amphotericin B, azoles, and
echinocandins (Balajee et al. 2005, 2007).
Molecular Identification: Recommended barcoding gene: β-tubulin. General criteria
for identification were outlined by Balajee et al. (2007). Phylogenetic relationships of
the entire genus were presented by Wang et al. (1999) and Peterson (2000, 2008).
MALDI-TOF MS: A comprehensive ‘in-house’ database of reference spectra allows
accurate identification of species of Aspergillus even within complexes e.g. A. fumigatus
sensu stricto and A. lentulus (Lau et al. 2013, Sleiman et al. 2015).
a
b
c
d
Four species in the Aspergillus fumigatus complex showing overlapping morphological
characteristics; (a) Aspergillus fumigatus, (b) Aspergillus lentulus, (c) Neosartorya
fischeri and (d) Aspergillus felis.