Saksenaea vasiformis complex - Zygomycete
Note: I had been debating with myself whether
to post this organism at all as I have so few photos to share. The photos I am posting show only the most
basic characteristic features that would clue you in that this is a Zygomycete. Still, it may be of interest to some….and,
what else am I going to do with the photos?
Until recently, Saksenaea
vasiformis was recognized as the sole species within this genus. Currently, three species are recognized[i]
and can be differentiated by genetic, morphological and physiological
characteristics. Now recognized are; S. vasiformis which produces mainly
cylindrical sporagniospores with rounded ends, S. erythrospora which has large sporangiophores and sporangia,
which produce biconcave ellipsoidal sporangiospores, and S. oblongiaspora, characterized by oblong sporangiospores and its
failure to grow at 42ᵒC.
Ecology: Saksenaea
species can be found worldwide, having been isolated from soils in India,
Brazil, Panama, Honduras, as well as the United States.
Pathology: Though found worldwide, Infections
occur most commonly in tropical and sub-tropical climates. Saksenaea
species have been implicated in both human and animal disease. Unlike many of the emerging fungal diseases, it
appears that Saksenaea infects
immunocompetent hosts more readily than those with underlying, and usually predisposing
conditions. The most common mode of
infection is through some traumatic implantation of material containing the
sporangiospores though the respiratory tract may be the route of infection with
disseminated infections. Clinical
symptoms and presentation can be quite varied –from a slow, localized invasion
to rapidly spreading disseminated infection.
The spectrum of infections described in the literature range from skin
and soft tissue infection to bone (osteomyelitis) and rhino-orbito-cerebral
involvement. Skin and soft tissue
infections may present with necrotizing fasciitis or cellulitis. While infections remain localized, they may respond
to a combination of necrotic tissue debridement and aggressive antifungal
therapy, otherwise amputation may be the only recourse. Overall the mortality rate as a result of
infection is about 40%[ii]. Disseminated infections have a significantly
higher associated mortality rate of about 75%, while rhino-orbito-cerebral
infections have an estimated mortality rate of 83% based on published reports. Thankfully, infections with Saksenaea species remain relatively
uncommon.
Saksenaea species characteristics (in general) follow
Macroscopic Morphology:
A rapidly expanding fluffy, spider-like colony on
Sabouraud Dextrose Agar incubated at 30ᵒC.
The growth may fill the Petrie dish within 48 hours. It may be a “lid-lifter” and growth attempt
to escape through poorly sealed plates after 72 plus hours. The colony appears off-white to greyish in
colour.
Saksenaea species - 48 hours growth on SAB (or SDA) at 30ᵒC (Nikon)
Saksenaea species -as above, but an oblique view (Nikon)
Saksenaea species - 4 days growth on SAB (or SDA) at 30ᵒC (Nikon)
Microscopic Morphology:
Saksenaea produces broad hyaline, mostly aseptate,
hyphae. Simple and unbranched sporangiophores
(24 – 64 µm in length), develop a flask-shaped sporangium (50 – 150 µm in
length). The base of the sporangium
above the hemispherical collumella is rather broad or swollen in appearance but
narrows down into a long neck towards the apex.
Smooth walled sporangiospores (1.5 – 2.0 X 3 – 4 µm) vary in shape
depending on the species as described above in ‘Notes’. When mature, the sporangiospores are released
through the top of the sporangiophore.
Dichotomously branching rhizoids develop at the base of the
sporangiophore. If this Zygomycete has
produced its typical fruiting structure (sporangium), the overall structure of Saksenaea is unique and easy to
identify. But there lies the problem…
Problems:
It is rather difficult to induce Saksenaea to induce
produce fruiting structures and subsequent sporulation. Let’s back up a bit…
If you get a rapidly growing, fluffy colony which
produces broad (wide) hyphae, there is a good chance you have a
Zygomycete. If you place the mould on
relatively rich mycological media, such as Sabouraud Dextrose Agar or Potato
Dextrose Agar, and don’t get fruiting structures produced, you may have either
a Saksenaea species or Apophysomyces species. Both are notoriously suborn when it comes to inducing
sporulation on richer mycological media.
Media such as Czapek agar may produce better results. If this fails and you have lots of patience,
you can try the agar block – sterile water technique as outlined by Padhye
& Ajello[iii]. While the experienced mycologist may be able
to tell Apophysomyces from Saksenaea without inducing sporulation,
it is valuable in further speciation when not resorting to other means of
identification such as molecular.
Although I attempted the agar –sterile water technique
described by Padhye & Ajello, I was not successful in inducing sporulation
and therefore the distinctive flask-like sporangium was not produced, nor the
spores within. Features not produced
cannot be photographed and I regret that I am unable to share them with you. As I work in a clinical laboratory, we carry
only basic media and time is limited –I regret that I could not continue to
pursue this challenge.
Because the organism could not be induced to produce its
fruiting structures and sporangiospores, it was impossible to use these
morphological structures to determine the specific identification of this
Saksenaea species.
Saksenaea species - so here is about all I could get. The photo above shows the sporangiophore with the hemispherical shaped collumella at the apex (top). From the inset photo you can see what the fungus would look like had it produced (or retained) the flask-like sporangium.
(400+10X, LPCB, DMD-108)
Important: For the first time ever, I have posted a photo on this blog site which I have not personally taken. I felt that I could not post the photos I had without showing what the mature and fully intact Saksenaea looked like. The inset photo is shown here by the kind permission of Dr. David Ellis of the University of Adelaide's Mycology Website. My photos are free to share, however I request that this photo not be shared as the inset photo is the property of Dr. Ellis.
Saksenaea species - again we see the hemispherically shaped collumella at the apex of the sporangiophore (arrows). Sporangium and sporangiospores are absent.
(400X, LPCB, DMD-108)
Saksenaea species - as above
(400X, LPCB, DMD-108)
Saksenaea species - ditto
(400+10X, LPCB, DMD-108)
Saksenaea species - a clue that this is a zygomycete is the broad, almost aseptate hyphae that the mould produces. The measurement seen within the large hyphae running through the photo reads 24.22 µm -that is wide!
(400X, LPCB, DMD-108)
(400X, LPCB, DMD-108)
Saksenaea species - a close look at the hyphae in the previous photo. Note that there is the septation at the center of the photo. (1000+10X, LPCB, DMD-108)
Saksenaea species - for the most part, the growth that I obtained, whether by slide culture or adhesive tape technique, appeared as above - just a tangled myceleum with no reproductive fruiting structures. (400X, LPCB, DMD-108)
So there you have it - the best I could do with the time and resources I had at hand.
[i]Molecular
phylogeny and proposal of two new species of the emerging pathogenic fungus Saksenaea
Alvarez, E, Garcia-Hermoso, D, Sutton, DA, Cano, JF,
Stchigel, AM. Hoinard, D, Fothergill, AW, Rinaldi, MG, Dromer, F, Guarro,
J. Microbiol 2010;48 (12):4410-16
[ii]
Mucormycosis caused by unusual mucormycetes, non-Rhizopus, -Mucor, and Lichtheimia species
Gomes, MX, Lewis, RE, Kontoyiannis, DP, Clin Microbiol
Rev. 2011; 24(2):411-445
[iii] Simple
Method of Inducing Sporulation in Apophysomyces
elegans and Saksenaea vasiformis
Arvind A. Padhye and Libero Ajello; Journ Clin Micro,
Sept 1988; 1861 - 63
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