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MUCOR
Mould
The U.S Government’s
Occupational Safety and Health Administration [OSHA] lists the following as the
health effects of Mucor mould: Allergen, Irritant,
Hypersensitivity pneumonitis, Dermatitis.
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Taxonomic Classifications
Kingdom: Fungi
Phylum: Zygomycota
Order: Mucorales
Family: Mucoraceae
Genus: Mucor
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Toxic Mould Species:
Mould Pictures Absidia Mould Alternaria Mould Aspergillus Mould Aureobasidium Mould Blastomyces Mould Candida Mould Coccidioides Cryptococcus Mould Curvularia Mould Histoplasma Mould Mucor Mould Penicillium Mould Pseudallescheria Sporothrix Mould Stachybotrys Mould Verticillium Mould Yeast |
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Colonies fast-growing, whitish to greyish, usually thick
owing to the abundant upright sporangiophores. Spores (sporangiospores)
produced inside spherical sporangia at the tips of the sporangiophores,
brownish. Always with a large columella that remains after the
sporangial wall is broken (a). Large dark
zygospores may be produced. Common almost everywhere fungi occur.
Ref: Schipper 1978 |
Zygospores of Mucorales
These structures represent the sexually reproductive spores of
several genera of Mucorales. They are usually dark, roughened, 1-celled,
and connected to the filaments by short cells called suspensors. They
rarely occur apart from asexual fruiting structures and are not normally
used exclusively for identification purposes.
Ref: Schipper, Samson, and
Stalpers 1975; Zycha and Siepmann 1970
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(Courtesy of
http://www.botany.utoronto.ca) |
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Sporangia, columella and sporangiospores of Mucor sp.
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Colonies are very fast growing, cottony to fluffy, white to yellow,
becoming dark grey with the development of sporangia. Sporangiophores
are erect, simple or branched, forming large (60-300 um in diameter)
terminal, globose to spherical, multi-spored sporangia, without
apophyses and with well developed subtending columellae. A conspicuous
collarette (remnants of the sporangial wall) is usually visible at the
base of the columella following sporangiospore dispersal.
Sporangiospores are hyaline, grey or brownish, globose to ellipsoidal
and smooth-walled or finely ornamented. Stolons and rhizoids are absent,
however, chlamydoconidia and zygospores may be present.
(Courtesy of
Mycology Online) |
Description and Habitats
Mucor mould is a
filamentous fungus found in soil, plants, decaying fruits and vegetables. As
well as being ubiquitous in nature and a common laboratory contaminant,
Mucor spp. may cause infections in man, frogs, amphibians, cattle, and
swine. Most of the Mucor spp. are unable to grow at 37°C and the
strains isolated from human infections are usually one of the few
thermotolerant Mucor mould.
Species
The genus Mucor contains
several species. The most common ones are Mucor amphibiorum, Mucor
circinelloides, Mucor hiemalis, Mucor indicus, Mucor
racemosus, and Mucor ramosissimus. This genus can be
differentiated from Absidia, Rhizomucor, and Rhizopus by the
absence of stolons and rhizoids. The genus contains 49 recognized taxa, many
of which have a widespread occurrence and are of considerable economic
importance. However, few species have been recovered from well-documented
cases of zygomycosis, and infections due to members of this genus are rare.
Mucor indicus, Mucor ramosissimus and Mucor circinelloides
have all been implicated in human infections.
Health Effects
Mucor
is a dangerous mould that can adversely affect one's respiratory system. It
is a possible cause of the dangerous mould disease zygomycosis. For
those of you who watched the very disturbing feature on the Ripley's
Believe It or Not cable TV show about a man's face [eyes, nose,
cheeks, and everything else between his mouth and his forehead] having
been eaten away by a mould that began to grow in the man's sinus cavities,
the flesh-eating mould that ate his face was actually the very unhealthy
mould Mucor!!!
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Mucor mould under the microscope!
Identifying Filamentous Fungi by Guy St.-Germain and Richard
Summerbell. |
Macroscopic Features
Colonies
of Mucor grow rapidly at 25-30°C and quickly cover the surface of
the agar. Its fluffy appearance with a height of several cm resembles cotton
candy. From the front, the color is white initially and becomes grayish
brown in time. From the reverse, it is white. Mucor indicus is an
aromatic species and may grow at temperatures as high as 40°C. Mucor
racemosus and Mucor ramosissimus, on the other hand, grow poorly
or do not grow at all at 37°C.
Microscopic
Features
Nonseptate
or sparsely septate, broad (6-15 µm) hyphae, sporangiophores, sporangia,
and spores are visualized. Intercalary or terminal arthrospores (oidia)
located through or at the end of the hyphae and few chlamydospores may also
be produced by some species. Apophysis, rhizoid and stolon are absent.
Sporangiophores are short, erect, taper towards their apices and may form
short sympodial branches. Columella are hyaline or dematiaceous and are
hardly visible if the sporangium has not been ruptured. Smaller sporangia
may lack columella. Sporangia are round, 50-300 µm in diameter, gray to
black in color, and are filled with sporangiospores. Following the rupture
of the sporangia, sporangiospores are freely spread. A collarette may
sometimes be left at the base of the sporangium following its rupture. The
sporangiospores are round (4-8 µm in diameter) or slightly elongated.
Zygospores, if present, arise from the mycelium.
The
branching of sporangiophores (branched or unbranched), the shape of the
sporangiospores (round or elongated), maximum temperature of growth,
presence of chlamydospores, assimilation of ethanol, and molecular analysis
aid in differentiation of Mucor mould species from each other.
Laboratory Precautions
No
special precautions other than general laboratory precautions are required.
Susceptibility
Few data are available on
the in vitro susceptibility profile of Mucor spp. In an in vitro
study comparing the in vitro activity of amphotericin
B, ketoconazole,
itraconazole,
and voriconazole,
amphotericin B yielded the lowest MICs against Mucor spp. Among the
azoles, while the MICs of ketoconazole and itraconazole were comparable,
voriconazole yielded considerably high MICs.
Similar to the other genera belonging
to the phylum Zygomycota, treatment of Mucor infections remains
difficult. Due to its property to invade vascular tissues, infarction of the
infected tissue is commmon and mortality rates are very high. Early
diagnosis is crucial and surgical debridement or surgical resection, as well
as antifungal therapy, are usually required. Amphotericin B is the most
commonly used antifungal agent. Liposomal
amphotericin B and other lipid-based amphotericin B formulations, such
as amphotericin
B colloidal dispersion have also been used in some cases with
zygomycosis.
Response rates are unfortunately
unsatisfactory. Reversal of immunosuppression is one of the most significant
factors influencing the clinical outcome. Adjuvant therapy with cytokines,
particularly the colony stimulating factors, has anecdotally been associated
with better clinical response. There are also a few data on successful use
of fluconazole
and terbinafine
in treatment of zygomycosis, which require validation. Interestingly,
fluconazole in combination with trovafloxacin or ciprofloxacin proved to be
effective in a murine model of pulmonary zygomycosis. |
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