Saturday 28 November 2015

Saksenaea vasiformis complex

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…

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 - line drawing of structures discussed

 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)

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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