Penicillium citrinum

Penicillium citrinum

Ecology:  Penicillium citrinum is a commonly occurring filamentous fungus with worldwide distribution.  It has been isolated from a variety of sources including soils, decaying vegetation, foodstuffs (beans, coffee, cereals & spices) as well as a variety of indoor environments.

Pathology:  While Penicillium species are generally regarded as laboratory contaminants, or at best, opportunists, a number of species have been implicated as being involved in the disease process.  While Penicillium species may be isolated from clinical specimens, it is commonly believed that a true infection can only be established by histological demonstration of tissue invasion.  With that in mind, Penicillium citrinum has been reported in mycotic keratitis (eye), lung infections (pneumonia), a single case of a urinary tract infection (UTI) and one of pericarditis.  Their contribution to the disease process may be secondary an additional underlying illness.  As with all fungi, immunocompromised individuals may be at greater risk of infection including those rarely considered as pathogenic.

Macroscopic Morphology:  Penicillium citrinum exhibits moderately slow growth on Sabouraud-Dextrose agar (SAB) at 30ᵒC.  Surface texture is velutinous (soft, velvety surface) to floccose (woolly tufts of soft “hairs”).  The colonial growth appears radially sulcate (narrow, deep furrows or radial grooves –like spokes on a wheel).  The mature colony has a central greyish-turquoise to greyish-orange colour with a white periphery (outer edge).  Exudates (extrolites) are frequently produced which appear as drops of liquid upon the surface of the colony.  These may appear clear, to pale yellow, to a reddish-brown in colour.  Some strains may also produce a soluble pigment which can diffuse into the surrounding medium.  The reverse is a pale yellow to a light yellow-brown. Colours and growth characteristics are, of course, media and strain dependent.

 

Penicillium citrinum-SAB, 14 days incubation at 30ᵒC (Nikon)

Note the drops of exudate (extrolites) which have formed on the surface.

Colour variation due to maturing of colony but also a difference in my lighting for photography.

 Exudates (or Extrolites): Some fungi can produce exudates as a by-product of their growth, many of which can be collected for commercial use.  Mycotoxins are by-products (secondary metabolites) which are potent poisons.  Penicillium citrinum produces Citrinin, a nephrotoxic mycotoxin which derives its name from the fungus.  It may also produce other extrolites such as tanzowaic acid A, quinolactacins, quinocitrinines, asteric acid and compactin.

Microscopic Morphology:  Penicillium citrinum produces septate, hyaline (clear, not pigmented) hyphae.  Smooth-walled conidiophores stipes are rather long (100 – 300 µm) and is biverticillate (see diagram at end of post).  Metulae are 12 – 15 µm in length which are found in whorls of 3 – 5 divergent structures.  Phialides are ampuliform (flask-shaped) and about 7 – 12 µm in length.  Conidia (2.2 – 3.0 µm dia.) are globose to sub-globose (round to off-round) and are smooth or have a finely roughened surface.  Conidia resist disruption and form rather long chains.  These characteristics: the metulae longer than the phialides and the conidia being both spherical and produced in well-defined chains, are distinguishing features of Penicillium citrinum.

 Penicillium citrinum-  distinguishing features of Penicillium 'species' can already be made out at low magnification. (250X, LPCB, DMD-108)

 Penicillium citrinum-  distinguishing features of Penicillium 'species' much more evident at 400X.

Typical "fingers" made up of the metulae and phialide structures from which chains of conidia extend. (400X, LPCB, DMD-108)

Penicillium citrinum- a mass of overlapping fruiting structures with copious amounts of conidia.

(1000X, LPCB, DMD-108)

Penicillium citrinum- a little less congested in this photo.  Conidiophores (stipes) seen from which extend the metulae and conidia producing phialides.  Conidia are globose (round) to sub-globose (somewhat off-round) in shape,  (1000X, LPCB, DMD-108)

Penicillium citrinum- long metulae and the somewhat shorter phialides are clearly distinguishable in this photograph.  The conidia are generally smooth or can have a finely roughened surface.

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

 Penicillium citrinum- another view.

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

 Penicillium citrinum- exhibits biverticillate branching meaning that the conidiophore can branch and the metulae & phialides extend from these branches.  Triverticillate would have the conidia branching and then the branches also branching to finally produce the metulae & phialide fruiting structures.

(1000X, LPCB, DMD-108)

 Penicillium citrinum- Phialides are ampuliform (flask-shaped) and about 7 – 12 µm in length.  Again, conidia (2.2 – 3.0 µm dia.) are globose to sub-globose (round to off-round) and are smooth or have a finely roughened surface. (1000+10X, LPCB, DMD-108)

 Penicillium citrinum- Here we see the proportions of the metulae (M) and the 'flask-shaped' phialides (P) with the metulae being substantially longer than the phialides,  The biverticillate structure is evident in this photo. (ie. each branch extending from the conidiophore (stipe), branches only once and then bears a fruiting structure consisting of the metulae and phialides.

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

Penicillium citrinum- another example.

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

Penicillium citrinum- a few more photos to finish up.

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

Penicillium citrinum- suitable for framing!

(1000X, LPCB, DMD-108)

Penicillium citrinum

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

Penicillium citrinum

(400X, LPCB, DMD-108)

Penicillium citrinum- another colony showing the exudate (extrolites) which accumulate on the colony surface after extended incubation.  These metabolites may be potent poisonous mycotoxins or might have beneficial uses in industrial or pharmaceutical applications. (Nikon)

Physiology:  The spores of Penicillium citrinum fail to germinate at 5ᵒC and may show restricted growth at 37ᵒC.

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Ochroconis species

Ochroconis species (Hyphomycete)  Fungus

Ecology:

Ochroconis species are primarily soil saprobes (live on decaying vegetative matter), found in the soil worldwide.   As of 2014, there are thirteen recognized species of Ochroconis.

Pathology:

Ochroconis species have been recovered from central nervous system (CNS) infections as well as pulmonary (lung) infections, from both immunocompromised and immuocompetent hosts.  In particular, Ochroconis gallopava is considered to be a neurotropic opportunist and proposals have been made to place this fungus into a new genus, Verruconis. 

Ochroconis species are considered to be mesophilic (preferring moderate temperatures) however they can cause disease in several species of cold-blooded animals, particularly fish such as coho salmon and rainbow trout.  Ochroconis species are known to cause encephalitis in chickens, turkeys and other fowl.

Macroscopic Morphology:

The rate of growth is rather slow growing as measured by the expanding colony but will mature to produce conidia usually within 5 days.

The texture is described as velvety to felt-like or floccose.

The colony colour is usually a reddish-brown to chocolate brown to a dark olive-grey.  The reverse is a dark brown to black.

A red to brown pigment may diffuse into the medium.

 Ochroconis on Sabouraud Dextrose Agar (SAB) incubated at 30˚C for 3 weeks. (Nikon)

Ochroconis- same organism as above but with different background and lighting to show variations in texture and pigment.  SAB, 30˚C, 3 weeks. (Nikon)

 

Ochroconis on SAB - colony center rises off and above the agar surface resembling and inverted shallow bowl.  Looked like a small hollow mountain! 

Below, right - shows the Reverse of the Ochroconis presented here.  The lighter section which appears in the center of the larger colony is the area that has "cupped" and lifted off of the surface of the agar.  (Nikon) 

Microscopic Morphology:

Ochroconis produces septate hyphae which are hyaline (clear) to pale brown in colour.

Conidiophores are also hyaline to pale brown. They arise erect and unbranched from the hyphae and usually have a knobby or bent appearance.  The conidiophores have apical denticles in a sympodial arrangement from which the conidia have formed.  Conidia (2.5 – 4.5 µm X 11 – 18 µm) are usually 2 to 4 celled, depending on the species.  Conidia are cylindrical to club shaped and after detachment from the conidiophore (denticle), an inconspicuous frill may remain on both the denticle and the conidium base.

Ochroconis species - edge of growth of slide culture as initially viewed at low magnification.  Hyphae radiating out from point of inoculation after 1 week of incubation.

(LPCB, 250X, DMD-108)

Ochroconis species - Conidia extending from hyphae now become evident at this higher magnification. (LPCB, 250X, Nikon)

Ochroconis species - as we once more increase magnification individual conidia attached to phialides can be seen in more detail.  (LPCB, 400X, Nikon)

Ochroconis species - another view with conidia attached to their phialides. Brown pigmentation seen in lower right of photo.  (LPCB, 400X, Nikon)

Ochroconis species - one more view.  Remember, the fungus grows in three dimensions and even here, within the space between a microscope slide and a cover slip, hyphae and phialides extend forward, into the photo and some backwards, out of the photo.  It is for this reason that the photos often appear to be out of focus as only those features that lie relatively flat along the focal plane appear clearly in the picture. (LPCB, 500X, Nikon)

Ochroconis species - a massive ammount of conidia with the most mature to the right where the brown pigment is most evident. (LPCB, 500X, Nikon)

Ochroconis species - edge of  slide culture (as previous)

(LPCB, 500X, Nikon)

Ochroconis species - a hypha weaves its way from top center to bottom center of this photograph.  Along its length you can see phialides with attached conidia.  (LPCB, 500X, Nikon)

Ochroconis species -a two-celled conidium is seen attached to a phialide that extends from the hypha.  The conidium shows a slight constriction near the center.

(LPCB, 1000X, Nikon)

Ochroconis species -Numerous phialides with attached conidia shown here.  Phialides seen bearing multiple conidia.  Dark pigmentation is also evident as the colony ages.  Most conidia are two-celled, some showing a slight constriction near their center, others (center) showing the furthest end of the conidium being larger than that nearest the phialide from which it originated.  The arrow points to a phialide which has lost it's conidium -a slight scare remains.  

(LPCB, 1000X, DMD-108)

Ochroconis species -a mass of darkly pigmented, septate hyphae as well as a dark blue conidium seen near the left of the photo (LPCB, 1000X, DMD-108)

Ochroconis species -Hyphae with phialides bearing conidia.  Arrows point to phialies with multiple (two) conidia, the one on the left showing the scar remaining after the conidium has detatched.

(LPCB, 1000X, DMD-108)

Ochroconis species -a three-celled conidium appears to be present along with the more numerous two-celled conidia.  (LPCB, 1000+10X, DMD-108)

Ochroconis species -center of photo, conidium attached to a long phialide.

(LPCB, 1000X, DMD-108)

Ochroconis species -Nice photo of a phialide bearing two conidia attached to the parent hypha.

(LPCB, 100X, DMD-108)

Ochroconis species -yet another photo showing much the same.  Phialides bearing multiple conidia with the arrows showing the ragged attachment points which remain after the conida have detatched.

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

Ochroconis species -septation within the hyphae are clearly visible as is the developing brown pigmentation.  Tree Conidia still attached to their brownish pigmented phialides which extend from the hyphae.  Near center, one phialide is seen with a detached conidium nearby.

(LPCB, 1000X, DMD-108)

Ochroconis species -Aging phialides & conidia.  Brown phialide in center of photo has a thinner denticle at it's apex to which the conidium is attatched.

(LPCB, 1000X, DMD-108)

Ochroconis species -again, septations in hyphae are clearly evident.  Conidium near center of photo appears to be supported by a bent denticle.  (LPCB, 1000+10X, DMD-108)

Ochroconis species -conidium at apex attached to phialide by a short denticle.

(LPCB, 1000X, DMD-108)

Ochroconis species - Seen more clearly here, the two-celled conidium is attached to the phialide via a somewhat wavy denticle.  The phialide, in turn is attached to the hypha from which it originated.

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

Ochroconis species -  Here we are looking at the conidium 'head-on' so it appears spherical.  The conidium is attatched to the hypha by this darkly pigment, and apparently degenerating, phialide-denticle structure. (LPCB, 1000+10X, DMD-108)

Ochroconis species - Almost done here.  A phialide bearing two conidia.

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

Ochroconis species

(LPCB, 1000+10X, DMD-108) 

Ochroconis species - Phialide bearing multiple conidia.

(LPCB, 1000+10X, DMD-108) 

Physiology:

Growth is inhibited by cycloheximide.

I'm uncertain as to which specific species I have pictured in this blog as the conidia occasionally show more than 2 cells and can be constricted in the center.  The majority of the conidia from the isolate presented here are two-celled and rather ellipsoidal or cylindrical in shape

Differentiation of the more common species:

Conidia usually 4-celled = Ochroconis tshawytschae

Conidia usually 2-celled = Ochroconis gallopava

Conidia distinctly clavate (club-shaped), with the upper cell wider than the basal cell = Ochroconis humicola

Conidia broadly ellipsoidal and constricted at the septum = Ochroconis constricta

Ochroconis constricta is not known to be pathogenic

 

A new genus Verruconis is proposed for the neurotropic opportunist Ochroconis gallopava.

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