Monday 17 January 2011

Pseudallescheria boydii/Scedosporium apiospermum

Pseudallescheria boydii/Scedosporium apiospermum
Pseudallescheria boydii (sexual state) -Teliomorph
Scedosporium apiospermum (asexual state)

The names above refer to the same fungus exhibiting different reproductive states. The sexual state name (Pseudallescheria boydii) takes priority over the asexual state name (Scedosporium apiospermum). However, the sexual state often is not present in clinical specimens and unless it is observed, the fungus must be referred to by the asexual name of Scedosporium apiospermum.

The fungus is cosmopolitan and can be isolated from rural soils, polluted water, composts and manure.

Macroscopic (Colony);
  • Moderately rapid growing colony at 25C which matures in about a week.
  • Texture is woolly to cottony.
  • Colony is white becoming greyish or smokey-brown on the surface; reverse is pale with brownish-black zones.
  • Sexual state P. boydii is inhibited by cycloheximide (fungal selection agars) while the asexual state S.apiospermum is not inhibited.

  • Hyphae are hyaline, septate (2 - 4 µm dia.)
  • Conidiophores bearing annellides are of varying length and exhibit little differentiation from the vegetative hyphae.
  • Conidia (annelloconidia) are unicellular, pale brown, ovoid with truncate bases formed singly or in small clusters at the ends of the conidiophores or from short annellidic necks arising directly from the hyphae.
  • Fascicles of conidiophores bound together in synemata are sometimes present and is a variation of the asexual state referred to as the Graphium synanamorph (one anamorph somewhat resembles a wheat sheaf, the other anamorph a bulb on a stalk[ not flattend as in LPCB prep.]).
  • Large (50 to 250 µm) brown cleistiothecia (of the sexual P.boydii) may develop after 2 to 3 weeks of incubation. More likely to be found at center of colony.
  • Ascospores are yellow-brown and ellipsoidal in shape.
Scedosporium apiospermum hyphae & (annello)conidia
(LPCB sticky tape preparation at 250X)
-click to enlarge-

Scedosporium apiospermum septate hyphae, conidiophores & conidia
(LPCB sticky tape preparation at 400X)
-click to enlarge-

Annelloconidia showing truncate base/scar -wider at apex
-click to enlarge-

Scedosporium apiospermum asexual Graphium synanamporph
(Fascicles of conidiophores bound together in synemata -wheat sheaf appearance)
-click to enlarge-

Graphium synanamorph
(Slide culture on Corn Meal Agar-edge of agar at photo bottom 250X)
-click to enlarge-

As Above Description
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Immature Cleistothecium at 10 days Corn Meal slide culture LPCB
(Hyphae & Conidia can be seen in surrounding background)
-click to enlarge-

Immature Cleistiothecium of Pseudallescheria boydii
(Corn meal agar slide culture-unstained X400 ~10 days)
-click to enlarge for better viewing-

**New: Feb 17th, 2011

Split Mature P.boydi clestiothecium
(taken with the DMD-108 microscope)
(click on image to enlarge)

Mature P.boydi clestiothecium split and releasing ascospores
(ascospore inset)
(Click on photo to enlarge for better viewing)

P.boydi clestiothecium split open revealing lemon shaped ascospores within.
(click on photo to enlarge for better viewing)

***Note: The sexual stage of P.boydi was induced using corn meal agar both as a slide culture and extended incubation of the plate media. The last two photos (Feb 17th) from corn meal agar media after about 8 weeks of incubation. A small segment of agar was cut out of the plate and placed on a glass microscope slide. A second slide was placed on top of the agar and the agar was crushed between the two (The clestiothecia of P.boydi were much more difficult to split open than those of Aspergillus nidulans.) The the two slides were then separated, leaving material on both. A drop of KOH was added to help clear and define the organism.

An occasional agent of infections including mycetoma, cutaneous or subcutaneous invasion, most often of the feet and hands. Has been implicated in otitis, sinusitis, keratitis, endophthamitis, pneumonia, endocarditic, meningitis, osteomyelitis and cerebral abscesses. Disseminated disease more likely to occur in debilitated patients or those immunocompromised. Is also now recognized as an agent of phaeaohyphomycosis


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