Sunday 29 November 2015

Stachybotrys species



Stachybotrys species

Ecology:
Stachybotrys is a common cosmopolitan saprobe (lives on decaying vegetative material) which can be found in soil.  It is frequently found in the indoor environment, particularly in damp areas.  Anyone who has removed water damaged wallpaper or lifted soggy cardboard boxes and found black discolouration on the material, may very well have encountered Stachybotrys mould.  It seems to particularly like to feast on the glues used in wallpaper and paper tape adhesives.  That powdery black residue on water damaged books may also yield Stachybotrys.  Stachybotrys may contain up to fifty species though I suspect this is under review using molecular methods.

Pathogenicity:
Stachybotrys has long been considered as non-pathogenic to humans or animals.  More recently, evidence has been gathering that, although not a source of topical or systematic infection, the mould may be responsible for toxicosis following inhalation of the spores.  It has been suspected as a cause of acute idiopathic pulmonary haemorrhage in infants, but its complete relation to human diseases is not yet fully understood.

The fungus has also been implicated in what has been termed ‘sick building syndrome’.  Buildings which have an overall moisture problem, or those that have had been damaged by flood waters may be prone to extensive Stachybotrys (and other) fungal invasion.  Wall coverings, ceiling tiles, and gypsum (sheet rock) wall boards and jute floorcoverings may all be contaminated.  Unless extensive renovations are undertaken, occupants may develop fatigue, headaches, chest tightness, mucous membrane irritation and pulmonary disease as a result of the fungal infestation.

Animals and horses in particular, may develop, what has been termed stachybotryotoxicosis after ingestion of feed (hay, etc.) heavily contaminated with Stachybotrys chartarum.  It is characterized as an irritation of the mouth, throat, and nose which may lead to dermal necrosis and possible shock.  Stachybotrys chartarum is known to produce a variety of toxins; macrocytic trichothecenes and related trichoverroids: roridin E and L-2; satratoxins F, G, and H; isosatratoxins F, G, and H; verrucarins B and J; and the trichoverroids, trichoverrols A and B and trichoverrins A and B.

According to the Center for Disease Control and Prevention, "The term 'toxic mould' is not accurate. While certain moulds are toxigenic, meaning they can produce toxins (specifically mycotoxins), the moulds themselves are not toxic, or poisonous.

Macroscopic Morphology:

Note:  Sadly I have no photos of Stachybotrys colonies to share with the reader.  A colleague provided swabs from blackened areas on damp washroom wallboard during a renovation.  Days later, a quick adhesive tape mount of preliminary growth revealed the Stachybotrys posted below.  Unfortunately it was quickly overgrown by other moulds present in the same sample and at a particularly busy time in the lab, I could not devote more time to its isolation.  My hope was to obtain the mould from some other source at a more convenient time, which sadly, never came.   'Google Images' brings up a number of images of both the colonies on mycological media as well as 'in-situ' -on walls etc.  Permissions could not be obtained to link to the photo which I felt best represented this mould's growth.

Stachybotrys exhibits rapid growth, maturing in three to four days.  It has a powdery to cottony texture.

The surface colouration is initially white but quickly becomes  black but may also exhibit pink or orange on the surface depending on the growth medium and species.

The reverse is also dark brown or black


Microscopic Morphology:

Stachybotrys has hyphae which are septate and hyaline when young but may darken with maturity.


Conidiophores may also be hyaline or may develop an olivaceous or dark pigmentation.  The conidiophores may be septate, simple or branched.  Conidiophores may show a rough-wall texture, particularly at the upper part, near the phialides.



Phialides (9-14 µm in length) may be hyaline, olivaceous to black in colour. They are ellipsoidal in shape and form in groups of 3 to 10 at the apex of the conidiophore
Phialides produce conidia singly and successively into a slime droplet that covers the phialides.


The conidia are 7 to 12 by 4 to 6 µm, black, unicellular, ellipsoidal in shape and smooth to rough-walled.  Conidia are borne in slimy masses at the apices of the phialides.

Stachybotrys species -phialides are 9-14 µm in length and are borne in slimy masses at the apices of the phialides.
  (1000X, LPCB, DMD-108)

Stachybotrys species -phialides are ellipsoidal in shape and form in groups of 3 to 10 at the apex of the conidiophore.  The phialides are 9-14 µm in length.
 (1000X, LPCB, DMD-108)
 
 
 Stachybotrys species -conidiophores may show a rough-wall texture, particularly at the upper part, near the phialides.
 (1000X, LPCB, DMD-108)


Stachybotrys species - conidiophores may be septate, simple or branched.  Here both septation and branching are clearly visible.
(1000X, LPCB, DMD-108)


 Stachybotrys species -conidia are 7 to 12 by 4 to 6 µm, black, unicellular, ellipsoidal in shape and smooth to rough-walled.  In this photo the slimy mass of conidia have been disrupted.
(1000X, LPCB, DMD-108)

 Stachybotrys species -This photo again shows a disrupted mass of ellipsoidal conidia.  The dark pigmentation obliterated fine detail.  Rough texture on the upper portion of the phialide is evident.
(1000X, LPCB, DMD-108)

Stachybotrys species -conidiophores may also be hyaline or may develop an olivaceous or dark pigmentation.  (1000X, LPCB, DMD-108)

 
 Stachybotrys species -hyphae are septate and hyaline when young but may darken with maturity.
 (1000X, LPCB, DMD-108)

Notes:
Stachybotrys is highly cellulolytic which is why it enjoys growing on the various substrates already mentioned.  It grows quite readily in materials low in nitrogen.
Stachybotrys differs from Memnoniella by not producing conidia in chains
While both the above genera are environmental contaminants, they are seldom isolated in the clinical laboratory.
Stachybotrys grows well at 37ᵒC

One method of isolating or recovering Stachybotrys is to streak suspected conidia from the source onto dampened filter paper (eg. Whatman).  Incubate the paper at 25 to 30ᵒC for about a week and look for dark patches.  Transfer any growth to Sabouraud Dextrose Agar or Corn Meal Agar.  Some sources claim that the fungus grows better on less nutritious media and this feature may assist in isolating it from more fastidious, yet fast growing fungi.


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