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Description and Habitats
According to
de Hoog (1993), species of Sporothrix have been reported as anamorphs
of both ascomycetes and basidiomycetes. However, he believes the name should
be restricted to those with ascomycetous relationships and refers the
basidiomycetous ones to the genus Cerinosterus. Unfortunately,
distinguishing Sporothrix from Cerinosterus with certainty
requires an electron microscope or advanced biochemical techniques.
Isolated from soil,
decaying plant materials, other fungi, insects, and air. Sometimes causing
human disease. Holomorphs: Ophiostoma, Pseudeurotium,
Thecotheus, Stephanoascus, Valsonectria, and others. Ref:
de Hoog 1974, 1993.
Species
The genus
Sporothrix contains three active species. The most common one is
Sporothrix schenckii, followed by Sporothrix cyanescens.
Health Effects
Mycosis:
SPOROTRICHOSIS
Sporotrichosis is usually a chronic infection of the cutaneous or
subcutaneous tissue which tends to suppurate, ulcerate and drain. In recent
years, a pulmonary disease has been seen more frequently. Occasionally,
infection with S. schenckii may result in a mycetoma. Sporotrichosis
is caused by another dimorphic fungus. The infection is also known as "rose
growers disease."
The ecologic niche for this organism is rose thorns,
sphagnum moss, timbers and soil. A study on the occupational distribution of
sporotrichosis showed that forest employees accounted for 17% of the cases,
gardeners and florists, 10%; and other soil-related occupations another 16%.
Sporotrichosis occurs worldwide. Every aspect of this disease (clinical,
pathology, mycology, ecology) was investigated during an epidemic of 3,000
patients in a gold mine in South Africa during the 1940's. Patient history
is very important in this disease also. It is often seen in gardeners and
begins with a thorn prick on the thumb. A pustule develops and ulcerates. It
infects the lymphatic system and then the disease progresses up the arm with
ulceration, abscess formation, break down of the abscess with large amounts
of pus followed by healing. Progression usually stops at the axilla.
Clinical material to be sent to the lab may be pus, biopsy material, or
sputum from pulmonary patients. The yeast form of this fungus in tissue or
in culture, can be round (6-8 um) or fusiform. The fusiform shape is
not the usual form but if a cigar-shaped yeast is observed in tissue, it is
usually diagnostic of sporotrichosis. S. schenckii does not stain
with the usual histopathological stains. If sporotrichosis is suspected, the
pathologist must be informed so he can use special stains. Histologically
asteroid bodies, a tissue reaction (also known as Splendori reaction) may be
seen around the yeast cell. At 25 degrees C, this colony is white-cream and
very membranous, but as it ages for 2-3 weeks it becomes black and leathery.
Microscopically, the mycelium is branching, septate and very delicate, 2-3
um in diameter. The pyriform conidia, 2-4 um form a typical
arrangement in groups at the end of a conidiophore called "daisies."
Serologic tests are not commercially available.
The drug of choice for the
cutaneous form is saturated iodides (e.g., potassium iodide) administered
orally. The patient begins with 2-3 drops, 3-4/days until tolerance to the
drug is built up, then the dose is increased. Potassium iodide may interact
with the host immune system. For the systemic form the drug of choice is
itraconazole or amphotericin B.
Macroscopic
Features
I. Sporothrix schenckii. It is a thermally dimorphic fungus and the
colony morphology varies depending on the temperature of growth. At 25°C,
colonies grow moderately rapidly. They are moist, leathery to velvety, and
have a finely wrinkled surface. From the front and the reverse, the color
is white initially and becomes cream to dark brown in time ("dirty
candle-wax" color). At 37°C, colonies grow moderately rapidly. They
are yeast-like and creamy. The color is cream to beige. The conversion of
the mould form to the yeast form is required for definitive identification
of Sporothrix schenckii.
II. Sporothrix cyanescens. At
25°C, colonies are velvety to powdery and slightly raised in texture.
From the front, the color is initially white and turns to pale purple in
time. From the reverse, an intense lavender-colored diffusing pigment
formation is typical. This pigment is produced on potato dextrose agar
after an incubation of about 3 weeks while it is usually not expressed on
Sabouraud dextrose agar. The production of this lavender-colored pigment
helps in differentiation of Sporothrix cyanescens from Sporothrix
schenckii.
Microscopic
Features
I.
Sporothrix schenckii. Similar to its colony morphology, microscopic
features of Sporothrix schenckii also vary depending on the
temperature of growth. At 25°C, septate hyaline hyphae, conidiophores,
and conidia are observed. Conidiophores are sympodial and appear weakly
differentiated from the vegetative hyphae. They often have an inflated
base and arise at right angles from the hyphae. Conidia have two types.
The first type are unicellular, hyaline to brown, oval, thin-walled, and
are typically arranged in rosette-like clusters at the tips of the
conidiophores. The second type of conidia are brown (dematiaceous),oval or
triangular, thick-walled, cessile, and are attached directly to the sides
of the hyphae. The latter type of conidia are typically present only in
freshly isolated strains. At 37°C, Sporothrix schenckii produces
oval to cigar-shaped (also called "cigar bodies") yeast cells.
Single or multiple buds may be produced by a single yeast cell.
Sporothrix schenckii var. luriei differs from Sporothrix
schenckii by producing large, often septate, budding cells and by not
assimilating creatine and creatinine.
II. Sporothrix cyanescens. Septate hyaline hyphae, conidiogenous
cells, denticles (tooth-like conidium-bearing projections), and primary
and secondary conidia are visualized. The terminal conidiogenous cells
have an inflated appearence. They bear denticles on their surface. The
primary conidia (4-9 x 1.5-3 µm) are hyaline and smooth in appearence.
They are ellipsoidal in shape and bear 1-3 secondary conidia on small
denticles. The secondary conidia (2.5-5 x 0.8-2 µm) are smaller than
primary conidia and pyriform in shape. The conidia rapidly dislodge and
the dislodged conidia look like budding yeast cells. The production of
secondary conidia and the absence of dematiaceous sessile conidia on the
hyphae help in differentiation of Sporothrix cyanescens from Sporothrix
schenckii.
III. Ophiostoma stenoceras. Being the telemorph of Sporothrix
sp., this fungus produces a long-necked perithecia (the round or
pear-shaped structure with an ostiole and containing asci and ascospores
inside) after an incubation of 2-3 weeks.
Laboratory
Precautions
No
special precautions other than general laboratory precautions are
required.
Susceptibility
Available
data suggest that in vitro activity of amphotericin
B and itraconazole
against Sporothrix schenckii is variable and strain-dependent.
(Primary) amphotericin B-resistant isolates have been identified. Terbinafine,
naftifine,
and amorolfine
are active in vitro against Sporothrix schenckii. On the other
hand, fluconazole,
voriconazole
and ravuconazoleyield
high MICs for isolates of Sporothrix schenckii.
Potassium iodide is one of the oldest
therapeutic modalities used for treatment of sporotrichosis. Amphotericin
B, ketoconazole, and itraconazole are now more commonly used in treatment
of Sporothrix schenckii infections. Amphotericin B-resistantand
itraconazole-refractory cases have been reported. Initial treatment with
amphotericin B followed by long term maintenance therapy with itraconazole
may be beneficial in cases with sporotrichosis and AIDS. |
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