Morphological structures and types of conidiophore branching in
Penicillium. a. simple; b. one-stage branched; c. two-stage
branched; d. three-stage branched (Samson et al.,
Culture of Penicillium sp.
Colonies are usually fast growing, in shades of green, sometimes white,
mostly consisting of a dense felt of conidiophores. Microscopically,
chains of single-celled conidia (ameroconidia) are produced in basipetal
succession from a specialized conidiogenous cell called a phialide. The
term basocatenate is often used to describe such chains of conidia where
the youngest conidium is at the basal or proximal end of the chain. In
Penicillium, phialides may be produced singly, in groups or from
branched metulae, giving a brush-like appearance known as a penicillus.
The penicillus may contain both branches and metulae (penultimate
branches which bear a whorl of phialides). All cells between the metulae
and the stipes of the conidiophores are referred to as branches. The
branching pattern may be either simple (non-branched or monoverticillate),
one-stage branched (biverticillate-symmetrical), two-stage branched (biverticillate-asymmetrical)
or three- to more-staged branched. Conidiophores are hyaline and may be
smooth- or rough-walled. Phialides are usually flask-shaped, consisting
of a cylindrical basal part and a distinct neck, or lanceolate (with a
narrow basal part tapering to a somewhat pointed apex). Conidia are
globose, ellipsoidal, cylindrical or fusiform, hyaline or greenish,
smooth- or rough- walled. Sclerotia may be produced by some species.
Descriptions and Habitats
Species of Penicillium are recognized by their dense brush-like
spore-bearing structures. The conidiophores are simple or branched and are
terminated by clusters of flask-shaped phialides. The spores (conidia) are
produced in dry chains from the tips of the phialides, with the youngest spore
at the base of the chain, and are nearly always green. Branching is an important
feature for identifying Penicillium species. Some (top figure) are
unbranched and simply bear a cluster of phialides at the top of the stipe.
Others (bottom left) may have a cluster of branches, each bearing a cluster of
phialides. A third type (bottom right) has branches bearing a second order of
branches, bearing in turn a cluster of phialides. These three types of spore
bearing systems (penicilli) are called monoverticillate, biverticillate and
terverticillate respectively. Penicillium is a large and difficult genus
encountered almost everywhere, and usually the most abundant genus of fungi in
The common occurrence of Penicillium species in food is a particular
problem. Some species produce toxins and may render food inedible or even
dangerous. It is a good practice to discard foods showing the development of any
mold. On the other hand some species of Penicillium are beneficial to
humans. Cheeses such as Roquefort, Brie, Camembert, Stilton, etc. are ripened
with species of Penicillium and are quite safe to eat. The drug
penicillin is produced by Penicillium chrysogenum, a commonly occurring
mold in most homes.
Holomorphs: Eupenicillium, Hamigera, Talaromyces,
Trichocoma. Ref: Kulik 1968; Pitt 1980; Raper and Thom 1949; Ramirez,
1982; Samson, Stolk, and Hadlok 1976; Stolk and Samson, 1972, 1983.
The genus Penicillium has several species. The most common
ones include Penicillium chrysogenum, Penicillium citrinum,
Penicillium janthinellum, Penicillium marneffei, and
Penicillium purpurogenum. Identification to species level is based on
colony morphology and microscopic features.
Culture of P. marneffei showing distinctive red diffusable
On Sabouraud's dextrose
agar at 25C, colonies are fast growing, suede-like to downy, white with
yellowish-green conidial heads. Colonies become greyish-pink to brown
with age and produce a diffusible brownish-red to wine red-pigment.
Conidiophores are hyaline, smooth-walled and bear terminal verticils of
3 to 5 metulae, each bearing 3 to 7 phialides. Conidia are globose to
subglobose, 2 to 3 um in diameter, smooth-walled and are produced in
basipetal succession from the phialides.
Phialides and conidia of P. marneffei.
On brain heart infusion
blood agar incubated at 37C, colonies are rough, glabrous, tan-colored
and yeast-like. Microscopically, yeast-cells are spherical to
ellipsoidal, 2 to 6 um in diameter, and divide by fission rather than
budding. Numerous short hyphal elements are also present.
Penicillium marneffei exhibits thermal dimorphism by growing in
living tissue or in culture at 37C as a yeast-like fungus or in culture
at temperatures below 30C as a mold. This fungus has been isolated from
bamboo rats and is endemic in Southeast Asia and the southern region of
China. Over 30 cases of hyalohyphomycosis cause by P. marneffei,
especially in AIDS patients have now been reported.
spp. are occasional causes of infection in humans and the
resulting disease is known generically as penicilliosis. Penicilliosis is an infection caused by
Penicillium marneffei, a dimorphic fungus endemic to Southeast Asia and
the southern part of China. Persons affected by
penicilliosis usually have AIDS with low CD4+ cell count of typically <100
cells/cu mm. The average CD4 count at presentation is 63.5 cells/cu mm.
Penicillium marneffei infections have also been reported
in non-AIDS patients with hematological malignancies and those receiving
infection, so called penicilliosis marneffei, is acquired via inhalation and
results in initial pulmonary infection, followed by fungemia and
dissemination of the infection . The lymphatic system, liver, spleen and bones
are usually involved. Acne-like skin papules on face, trunk, and extremities
are observed during the course of the disease. Penicilliosis marneffei
infection is often fatal.
Patients with penicilliosis are occasionally seen outside endemic areas, but most have a
history of travel to an endemic area. The most common presentation is a
disseminated infection manifested by fever, skin lesions, anemia,
generalized lymphadenopathy, and hepatomegaly. Localized infection such as
pneumonia has also been reported.
Penicillium has been isolated from patients with keratitis, endophtalmitis, otomycosis, necrotizing esophagitis, pneumonia, endocarditis,
peritonitis, and urinary tract infections. Most Penicillium
infections are encountered in immunosuppressed hosts. Corneal infections are
usually post-traumatic . In addition to its infectious potential,
Penicillium verrucosum produces a mycotoxin, ochratoxin A, which is
nephrotoxic and carcinogenic. The production of the toxin usually occurs in
cereal grains at cold climates.
Clinical Features of Penicilliosis
Percentage of cases
growing on the floor joists in the basement ceiling of a Massena, New York, that
Certified Mold Inspector Phillip Fry
provided an in depth mold inspection and mold testing in 2002.
colonies of Penicillium other than Penicillium marneffei are rapid
growing, flat, filamentous, and velvety, woolly, or cottony in texture. The
colonies are initially white and become blue green, gray green, olive gray,
yellow or pinkish in time. The plate reverse is usually pale to yellowish.
Penicillium marneffei is thermally
dimorphic and produces filamentous, flat, radially sulcate colonies at 25°C.
These colonies are bluish-gray-green at center and white at the periphery. The
red, rapidly diffusing, soluble pigment observed from the reverse is very
typical. At 37°C, Penicillium marneffei colonies are cream to slightly
pink in color and glabrous to convoluted in texture.
For species other than Penicillium marneffei, septate hyaline hyphae (1.5
to 5 µm in diameter), simple or branched conidiophores, metulae, phialides, and
conidia are observed. Metulae are secondary branches that form on conidiophores.
The metulae carry the flask-shaped phialides. The organization of the phialides
at the tips of the conidiophores is very typical. They form brush-like clusters
which are also referred to as "penicilli". The conidia (2.5-5µm in
diameter) are round, unicellular, and visualized as unbranching chains at the
tips of the phialides.
In its filamentous phase, Penicillium
marneffei is microscopically similar to the other Penicillium
species. In its yeast phase, on the other hand, Penicillium marneffei is
visualized as globose to elongated sausage-shaped cells (3 to 5 µm) that
multiply by fission.
Penicillium marneffei is easily
induced to produce the arthroconidial yeast-like state by subculturing the
organism to an enriched medium like BHI and incubating at 35°C, in which after
a week, yeast-like structures dividing by fission and hyphae with arthroconidia
special precautions other than general laboratory precautions are required.
data are very limited. For Penicillium chrysogenum, MICs of amphotericin
are acceptably low, while the denoted MICs for Penicillium griseofulvum
are higher than those for Penicillium chrysogenum. Notably, Penicillium
marneffei isolates may yield considerably high MICs for amphotericin B, flucytosine,
and relatively low MICs for itraconazole, ketoconazole, voriconazole, and terbinafine.
Further data are required to provide a more precise susceptibility profile for
various Penicillium spp.
Amphotericin B, oral itraconazole, and oral
fluconazole have so far been used in treatment of penicilliosis marneffei. Oral
itraconazole was found to be efficient when used prophylactically against
penicilliosis marneffei in patients with HIV infection.
The mycological information gathered and organized in
this extensive research on the different Pathogenic Molds was sourced
out from the list of websites below:
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