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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Aspergillus flavus

Aspergillus flavus (fungus)

Ecology & Pathogenicity;

Found worldwide. Ubiquitous in nature and is the second most common cause of invasive aspergillosis next to Aspergillus fumigatus. Has been implicated in pulmonary, systemic, sinus, ear and other infections. Most widely reported food-borne fungus and can be found colonizing decaying vegetation, crops and seeds. Has also been implicated as both an insect and animal pathogen. (For a slightly more expanded description of pathogenicity, see the intro to the Aspergillus fumigatus post.)

Macroscopic Colony Morphology;

Very rapid rate of growth, maturing in about three days. Surface is greenish-yellow to olive and may have a white border. Texture is often floccose, especially near the center and overall can be velvety to woolly. Unremarkable cream to tan to yellowish reverse on Sabouraud Dextrose media.

Aspergillus flavus on SAB media at 72 hour at 30^oC

(note greenish-yellow colour with white edge)

(click on any photo to enlarge for better viewing)

Microscopic Morphology;

Septate hyphae with rather long conidiophores (~400-800 X 8-17 µm) which have a rather rough texture or even spiny, especially just below the vesicle. Vesicles are spherical to elongate and about 20 – 45 µm wide. Aspergillus flavus can be variable in seriation with most strains being about 20% biseriate however some strains can be almost entirely uniseriate. Metulae (8-10 X 5-7 µm) cover three quarters to the entire surface of the vesicle from which the phialides (7-12 X 3-4 µm) form. The metulae support the phialides and together form the biseriate structure. Conidia are globose to ellipsoidal (3-6 µm) with smooth to finely roughened walls.

(Photos below are of a ~30hr old slide culture preparation taken with the DMD-108 digital microscope - except where noted)

Aspergillus flavus mycelium &, conidiophores (LPCB) (X250)

Tangled web of the Aspergillus flavus mycelium as above (X250)

Aspergillus flavus conidiophore bearing vesicle (X1000)

look for the biseriate structure (metulae & phailide) on this and the following photos

Aspergillus flavus vesicle bearing metulae & phialides from which forms the conidia

Aspergillus flavus (LPCB X1000)

Look for the Biseriate structure - Rough surface of conidiophore at its apex (where it meets the vesicle ) is evident in this photo. This roughness is a diagnostic feature of Aspergillus flavus.

Aspergillus flavus (LPCB X1000) Biseriate structure may be easier seen in this photo.

Aspergillus flavus (LPCB X1000)

(Too many photos, but I just like them!)

Aspergillus flavus (LPCB X1000 + 10X digital magnification from DMD-108 Scope)

Though difficult to see, the slighly rough wall can be visualized on several of the conidia, particularly in the lower left of the photo. The conidiophore also has this rough or gently spiked texture particularly at the apex (where it meets the vesicle)

Also note that phialides radiate from vesicle in all directions as opposed to A.fumigatus where they tend found on the upper 2/3rds of the vesicle and extend parallel to the conidiophore.

Aspergillus flavus (LPCB X1000)

(again, enlarge photo and look for the rough texture of the conidia's surface)

Aspergillus flavus - more typical appearance with phialides radiating from vesicle in all directions. This photo taken from adhesive tape preparation of 72 hr fully mature culture. This technique was quite disruptive, dispersing conidia throughout the preparation.

(LPCB X400 -Nikon)

Mycotoxins;

Many Aspergillus flavus isolates are capable of producing aflatoxins, very potent carcinogens. (Aflatoxin B₁, cyclopiazonic acid, 3-nitroproprionic acid.)

Intended as Aspergillus flavus computer screen 'Wallpaper' (1024X768 when posted)

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Aspergillus niger

(Fillamentous fungi)
Subgenus: Circumdati, Section: Nigri

This fungus was a bit of a challenge to photograph as it matured so quickly that conidia were often well dispersed when I was prepared to photograph the culture. It was difficult to find really good examples of the vesicles bearing metulae, phialides bearing intact conidial spores. Both adhesive tape preparations and slide cultures were studied.

Ecology; Ubiquitous, worldwide distribution, commonly found in mesophilic environments. One of the most common of the fungi in soil, rotting fruit & plant matter as well as many indoor environments. A.niger may be found as a common laboratory contaminant.

Macroscopic; Rapidly growing on Saboraud-Dextrose Agar starting with a white to yellowish felt-like mat of mycelia, quickly turning black as conida develop the pigment aspergillin during maturation. Reverse remains white to pale in colour.

Aspergillus niger on Sabouraud-Dextrose Agar 72 hrs at 30C
Black pigment from conidia maturing from center of colony
(click on photo to enlarge for better viewing)

Microscopic; Septate, hyaline (clear) hyphae. Conidiophores (Stipes) are long (400-3000 µm) with spherical vesicles at the apex measuring 30-75 µm. Aspergillus niger is biserate - metulae just about cover the entire surface from which the phialides extend. Conidia are globose, brown to black in colour, measure 3.5-4.5 µm in diameter and have a rough surface.

Large vesicle at end of broken conidiphore bearing metulae & phialides with black pigmented conidia already dispersed. Adhesive tape preparation was too disruptive in capturing structures intact. (LPCB X400)

Ditto (LPCB X400)
(Click on photos to enlarge for better viewing)

Aspergillus niger (LPCB X400)

Pathogenicity; not tremendously pathogenic however has been implicated in aspergillosis particularly in immunocompromised patients. Has also been isolated from ear infections (otomycosis), often as a secondary invader, establishing itself after/on top of a bacterial infection.

Industry; A.niger produces a number of useful enzymes which have been utilized by industry in the production of a variety of products such as citric acid. The possibility of A.niger being capable of producing mycotoxins remains controversial.

Treatment; Studies on the susceptibility of A.niger to antifungal agents remain inadequate. Isolates should be tested individually if therapy is warranted. Voriconizole as been shown to be effective in documented cases as well as Itraconazole and Amphoterecin B.

Intended as Aspergillus niger computer wallpaper (1024 X 768) when posted.
(click on photo to enlarge for better viewing)

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