Pithomyces species

Pithomyces species  -Hyphomycete

Ecology:

The genus Pithomyces has approximately 50 recognized species to date.   Speciation is most accurately achieved by molecular means; however, careful observation of morphological features can identify this mould to the genus level.

Pithomyces species are dematiaceous saprobes (darkly pigmented moulds which commonly grow on dead organic matter) and may be found on the leaves and stems of a variety of plants. They have also been isolated from decaying wood, tree bark (Acacia) and from soil.

Pathogenicity:

Pithomyces species have been implicated in human disease however their role has not been sufficiently substantiated.  Pithomyces has reportedly been isolated from finger and toe nails, a hand lesion (skin scrapings), peritoneal fluid, bronchial washings, and from a chronic nasal polyposis. The mould may also contribute to general allergic reactions.  In the United States, the most commonly isolated Pithomyces species appear to be P. chartarum, P. sacchari, and P. maydicus.

Pithomyces species have been implicated in pithomycotoxicosis (facial eczema) of ruminants such as sheep, cattle and goats.  P.chartarum, in particular is considered the cause of facial eczema in sheep.

Pithomyces species are commonly considered to be laboratory contaminants, however, they should not be ruled out without careful consideration, particularly in immunocompromised patients.

Macroscopic Morphology:

Pithomyces exhibits fairly rapid growth, maturing in about five days to a week.  Colonies on SAB at 30ᵒC are olivaceous, light to dark brown to brownish-black.  Colour is species and media dependant.  Dark brown to black areas, may be seen macroscopically on some species (P. atro-olivaceus), revealing sporodochia (pleural of sporodochium), which are areas of greater conidial production.  The overall colonial texture is downy to cottony, with a short feathery nap (effuse).  The reverse is brown to brownish-black in colour.

The isolate presented in this blog (SAB 30ᵒC) post had a lighter cream coloured fringe or edge to the colony.

 Pithomyces species - Sabouraud-Dextrose Agar (SAB), 1 Week, 30ᵒC (Nikon)

Microscopic Morphology:

Pithomyces species produce septate, sub-hyaline (pale to light brown) hyphae.  Conidiophores are generally short (peg-like, ~10 µm length), and rather poorly differentiated from the vegetative hyphae from which they extend.  Conidia (10 – 17 µm X 18 – 30 µm) are produced singly at the apex of the conidiophore where they are attached by a short denticle.  After conidial dehiscence (release of conidia), a visible annular frill may remain at the conidial base where once attached to the conidiophore.  Conidia are muriform (have both longitudinal and transverse septations) and are broadly ellipsoidal to ovate (egg shaped) or pyriform (pear shaped) in shape.  P.chartarum usually exhibits 2 – 5 transverse septa with 0 – 3 longitudinal septa. The muriform or septation pattern may be species dependant; P. atro-olivaceus may only produce horizontal septa.  Conidia are dark brown in colour when mature and usually have an echinulate (spiny or prickly) or verruculose/verrucose (warty) texture. 

Caution: Micron scale (µm) may change between 50 or 100 µm at higher magnifications.

 Pithomyces species - Initial view -growth from the edge of a slide culture.

(250X, LPCB, DMD-108)

Pithomyces species - darkly pigmented conidia with internal septations are seen.

(400X, LPCB, DMD-108)

Pithomyces species - Numerous, pigmented conidia seen.  Insert shows the muriform (both longitudinal and transverse septa) septations.

(400X, LPCB, DMD-108)

Pithomyces species - after conidial dehiscence (release of conidia), a visible annular frill may remain at the conidial base where once attached to the conidiophore.  (400X, LPCB, DMD-108)

Pithomyces species - conidia are broadly ellipsoidal to ovate (egg shaped) or pyriform (pear shaped) in shape. (400X, LPCB, 400X)

Pithomyces species - Conidia are borne on short stalks. Brownish pigment has exuded from the hyphae and can be seen as the brown haze alongside the hypha. (400X, LPCB, DMD-108)

Pithomyces species - conidiophores are generally short (peg-like, ~10 µm length), and rather poorly differentiated from the vegetative hyphae from which they extend.  (400X, LPCB, DMD-108)

Pithomyces species - as above.  (400+10X, LPCB, DMD-108)

Pithomyces species - conidia (10 – 17 µm X 18 – 30 µm) are produced singly at the apex of the conidiophore where they are attached by a short denticle.  (400+10X, LPCB, DMD-108)

Pithomyces species - septate hypha with pigment seen along the outer walls of several. Conidium on short stalk is seen at center right. (400+10X, LPCB, DMD-108)

Pithomyces species - single, elongated conidium seen at the apex of a withering hyphal element or conidiophore. (400+10X, LPCB, DMD-108)

Pithomyces species - some chains appeared to be formed by this particulate isolate. Only one source I consulted (Davone -see sidebar) stated that Pithomyces species do not chain. I isolate presented here conforms to the characteristics described for Pithomyces with the exception of chain formation by the conidia. This should not be confused with the chain-like formation of conidia as seen in Alternaria species. (400+10X, LPCB, DMD-108)

Pithomyces species - ditto.

(400+10X, LPCB, DMD-108)

Pithomyces species - yet another photo at higher magnification...
(1000X, LPCB, DMD-108)

Pithomyces species - oval conidium at apex of a short stock which shows little differentiation from the vegetative hyphae. (1000X, LPCB, DMD-108)

Pithomyces species - pigment escaping from the hyphae into the surrounding medium.
Vegetative mycelium composed of thin-walled hyaline, septate, smooth or verrucose, septate hyphae, 4–7 µm diameter, which may give rise to chains of verrucose, one-celled, dark brown, intercalary chlamydospores 10 -20 µm X 8 - 18 µm[i].

(1000X, LPCB, DMD-108)

Pithomyces species - pigment escaping from the septate hyphae into the surrounding medium.  Annular frill can be seen attached to the anterior end of the conidium.
(1000X, LPCB, DMD-108)

 

Pithomyces species - more intercalary chlamydospores seen as described two photos above.
(1000X, LPCB, DMD-108)

 

Pithomyces species - Conidia are dark brown in colour when mature and usually have an echinulate (spiny or prickly) or verruculose/verrucose (warty) texture.  The conidium at center-right clearly shows a spiny or prickly surface.  Intense uptake of the Lactophenol Cotton Blue (LPCB) dye somewhat obscures the muriform septations within the conidium.

Pithomyces species - appears to be attached at both ends which would make it an intercalary chlamydospore (?)
 (1000+10X, LPCB, DMD-108)

Pithomyces species - short, peg-like, conidiophores arising from the vegetative hyphae at right-angles with single pigmented, muriform conidium at each apex.
(1000X, LPCB, DMD-108)

Pithomyces species -here you get it all as described in previous photos.  Pigmented septate hyphae with pigment escaping into the surrounding medium.  Prickly surfaced muriform conidia borne singly on short peg-like conidiophores.  The free conidium closest to the top shows the annular frill which remains from where it was attached to the conidiophore.
(1000X, LPCB, DMD-108)

Pithomyces species -two, rather smooth walled, conidia attached to the hypha by short conidiophores.
(1000+10X, LPCB, DMD-108)

Pithomyces species - some chaining (?) evident.
(1000X, LPCB, DMD-108)

Pithomyces species - single muriform conidium at the end of a short conidiophore.
(1000+10X, LPCB, DMD-108)

Pithomyces species - single muriform conidium at the end of a short, rather twisted,  conidiophore.(1000+10X, LPCB, DMD-108)

Pithomyces species - conidia are borne singly at the ends of the conidiophores.
(1000+10X, LPCB, DMD-108)

Pithomyces species - I'm trying to figure this one out.  Are those two conidia arising from two, obscured, conidiophores, or is one an intercallary chlamydospore with a conidiophore & conidium arising from the same area of the hypha?.

Pithomyces species - Sources state that Pithomyces conidiophores produce single conidia.  Does this photo show a single conidium at the end of a short, pale pigmented conidiophore or is conidiphore the LPCB stained structure arising from the hyphae below with the apex of the conidiophore branched, and one conidium missing?  You decide...

(1000+10X, LPCB, DMD-108)

Pithomyces species -muriform conidia at the end of short peg-like conidiophores.
(1000+10X, LPCB, DMD-108)

Pithomyces species -conidia texture described as echinulate (spiny or prickly) or verruculose/verrucose (warty) texture.
 (1000+10X, LPCB, DMD-108)

 

Pithomyces species - conidia which aren't over-saturated with the LPCB stain and more clearly show the muriform septation within.

(1000X, LPCB, DMD-108)

Pithomyces species - thickened and roughened wall of the intercalary chlamydospores.
 (1000+10X, LPCB, DMD-108)

Pithomyces species - chaining of conidia (?) at left.  Two, rather young conidia on short peg-like conidiophores at lower center of photo.
 (1000+10X, LPCB, DMD-108)

Pithomyces species
  (1000+10X, LPCB, DMD-108)

Pithomyces species have to be differentiated from closely related dematiaceous hyphomycetes such as Ulocladium species, Stemphylium species, Alternaria species and Epicoccum species. (See Table Below)
 

Too small to read?  Click on table to get image. Now right click on image and select 'view image'.  In Windows, cursor now has a + sign within it.  Click on image of table to now magnify the table.
Alternatively, just click and download the damn thing...

[i] The Genus Pithomyces in South Africa

W.F.O. Marasas and Ingrid H. Schumann,

Bothalia 10, 4: 509 – 516, 1972

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Sepedonium species

Sepedonium species

Ecology:

Sepedonium species are cosmopolitan saprobes commonly found in temperate soils worldwide.

Pathogenicity:

Sepedonium species are considered to be of low virulence with only three possible cases cited in the literature.  No animal infections are known. When isolated, they are generally considered to be a contaminant.  As with any fungus, they may be opportunistic particularly if the host is immunocompromised.

They are a known parasite of higher basidiomycetes, particularly Bolotales (mushrooms).

Macroscopic Morphology:

Sepedonium exhibits rapid growth at 25-30ᵒC.  Colonies initially appear white or creamy in colour with a rather waxy texture.  As the colony matures it acquires a cottony to woolly texture and develops a golden yellow colour.  A white to cream coloured fringe may remain.  The reverse is frequently described as white or pale, however the isolate presented here has a bright yellow reverse.

 Sepedonium species on Saboraud-Dextrose agar (SAB) incubated at 30ᵒC for 5 days. (Nikon)

 Sepedonium species on Saboraud-Dextrose agar (SAB) incubated at 30ᵒC for 10 days. (Nikon)

Microscopic Morphology:

Hyaline hyphae are septate and may bear simple or branched conidiophores.  They show minimal differentiation from the hyphae from which they arise.  Immediately distinguishing features are the rather large (7 – 17 µm) conidia produced at the apex of the conidiophore.  Conidia are solitary, single-celled, globose to ovoid in shape and have a rather thick, often echinulate or verrucose (roughened) wall.  A phialidic conidial (phialoconidia) state that produces ellipsoidal or cylindrical, smooth walled conidia may sometimes be present, particularly when the colony is young.

Notes on Photography:

Sepedonium offered a few photographic challenges with the techniques and photographic equipment I was using.  

Slide vs Adhesive Tape Technique:  Firstly, I like to take photographs using the slide culture technique as the glass cover slip, if possible, as it offers better transparency than does adhesive tape technique.  The adhesive tape, unless attached to the glass microscope slide smoothly may give an uneven, wavy picture.  The glue surface itself by be visible and deter from the quality of the photo.  The again, on some moulds, the sticky tape surface preserves the delicate arrangement and keeps in place structures which might be dispersed when manipulating the cover slip from a slide culture.  In the case of Sepedonium species, I found that this fungus adhered to the cover slip rather poorly.  The photos below are from both slide and adhesive tape preparations.  I have not stated which as it is the structure which is important.

Choice of camera: I find that both the DMD-108 digital imaging microscope and the Nikon Coolpix camera have advantages and disadvantages when photographing microorganisms.  In the case of moulds, the DMD-108 sometimes tends to over-saturate the blue from the Lacto-phenol Cotton Blue (LPCB) dye and I have not been able to correct for this to my satisfaction at either the instrument itself or with any of several photo-manipulation computer programs.  Structures (conidia below) may appear very dark and blotchy with details obliterated.  The Nikon, paired with the Leica 2000 microscope I routinely use should produce excellent photos, however, even after proper maintenance by a professional service, I often find the quality lacking.  What I find most distracting is the spherical aberration which appears as concentric light and dark lines running through the photograph.  While these rings or ripples running through the image are not seen through the oculars, they are blatantly visible in the digital image, particularly at higher magnifications.  A frosted filter between the light source and condenser minimizes this distracting `bulls-eye`pattern, however it is still present.  It seems to me that the camera lens magnifies any defects in the microscope lens or that somehow they conflict even after Köhler illumination.

Here, as throughout this blog, I use whichever technique (or combination of) most efficiently captures the organisms characteristics.

  Sepedonium species -edge of a slide culture at low magnification.  Hyphae and conidia are visible but too small to show any useful detail for identification.  (250X, LPCB, DMD-108)

Sepedonium species -Large echinulate or verrucose (rough-walled) conida very apparent. 

(400X, LPCB, DMD-108)

Sepedonium species - another view, as above.

(400X, LPCB, DMD-108)

Sepedonium species - a phialidic conidial state which produces ellipsoidal or cylindrical, smooth walled conidia (phialoconidia) may sometimes be present, particularly when the colony is young.  These forms are visible at the center of the photo extending to the left with the phialoconidia at the tips.  (400X, LPCB, Nikon)

Sepedonium species - loose phialoconidia are seen throughout the photo as well as two large rough-walled conidia seen near upper center.  (400X, LPCB, DMD-108)

Sepedonium species - single oval or ellipsoidal phialoconidium seen at the end of a conidiophore, with a few loose phialoconidia at upper center.  (1000X, LPCB, DMD-108)

Sepedonium species -and another view of the phialoconidia in the center of the photo and the relationship in size to the rough conidium seen at the center-left of the photo.

(1000X, LPCB, DMD-108)

Sepedonium species -another view, as above.

(1000X, LPCB, DMD-108)

Sepedonium species - large, young, still rather smooth,  conidium at the apex of the conidiophore.  Two free phialoconida seen at upper left.  (1000X, LPCB. DMD-108)

Sepedonium species - two large roughly textured conidia seen with their conidiophores receding out of the focal range of the camera.  The conidia have a rough surface texture which is described by various texts as warty, tuberculate, echinulate or verrucose.  It is this feature which may initially confuse this non-virulent mould with the highly virulent Histoplasma capsulatum.

(1000X, LPCB, DMD-108)

Sepedonium species -large, still rather smooth, conidium seen at the end of its conidiophore.  The thick wall of the conidia can be readily seen in this photo.

  (1000X, LPCB, DMD-108)

Sepedonium species - long conidiophore with a large, rough-walled conidium at the apex.

(400+10X, LPCB, DMD-108)

Sepedonium species - single rough-walled conidium seen in center of photo.

(400+10X, LPCB, DMD-108)

Sepedonium species - conidia attached to conidiophores of varying length.  Insert is just an alternate focus of conidiophore & conidium.  Distinctive, septate hyphae seen.

(400+10X, LPCB, DMD-108)

Sepedonium species - large (7 – 17 µm), rough-walled conidium seen.

(1000X, LPCB, DMD-108)

Sepedonium species - a number of large, rough-walled conidia taken from a mature colony.  This is from an adhesive tape mount.  (1000X, LPCB, DMD-108)

 Sepedonium species - numerous rough-walled conidia.

(400+10X, LPCB, DMD-108)

Sepedonium species - as above.  Conidia are in different planes of focus and therefore the rough texture often appears different on different conidia.

(1000X, LPCB, DMD-108)

Sepedonium species - large conidia still attached to their conidiophores.  Rough, tuberculate surface evident.

  (1000+10X, LPCB, DMD-108)

Sepedonium species - perhaps the most dramatic of the photos showing the rough & thick-walled conidia.

  (1000+10X, LPCB, DMD-108)

Sepedonium species - suitable for framing.

(1000+10X, LPCB, DMD-108)

Sepedonium species - rough & thick-walle conidium attached to what appears to be a short conidiophore.

  (1000+10X, LPCB, DMD-108)

Sepedonium species

(1000X, LPCB, DMD-108)

 Sepedonium species - conidium still attached to a segment of it`s conidiphore.

(Cropped photo, LPCB, Nikon)

Notes:

One source states that Sepedonium may grow poorly if at all at 37ᵒC.  Caution: not a definitive test.

Differentiation from other moulds:

Sepedonium superficially resembles the highly pathogenic mould Histoplasma capsulatum.

·         Growth rate – Sepedonium exhibits rapid growth at 25 - 30ᵒC and may be fully mature after one week while Histoplasma capsulatum grows slowly and may be barely visible after a week’s incubation

·         Sepedonium species are inhibited by cycloheximide and therefore will not grow on Mycosel® or Dermasel® selective media.

·         Sepedonium is not a dimorphic fungus (yeast & mould phase) and will not convert to a yeast phase at 37ᵒC as would Histoplasma.

·         Histoplasma capsulatum –specific GenProbe molecular testing.  Sepedonium negative.

·         Sepedonium species can be distinguished from Chrysosporium species by its conidia’s tuberculate* (echinulate or verrucose) cell wall.

  

  *all terms are descriptions of the rough cell wall.

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