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MUCOR Mold SpeciesThe U.S Government’s Occupational Safety and Health Administration [OSHA] lists the following as the health effects of Mucor: Allergen, Irritant, Hypersensitivity pneumonitis, Dermatitis. |
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Taxonomic Classifications
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 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.
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 http://www.mycology.adelaide.edu.au)
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Description and Habitats Mucor 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 spp. 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. Mucor is a dangerous mold that can adversely affect one's respiratory system. It is a possible cause of the dangerous mold 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 mold that began to grow in the man's sinus cavities, the flesh-eating mold that ate his face was actually the very unhealthy mold Mucor!!! |
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Mucor mold under the microscope.
Identifying Filamentous Fungi by Guy St.-Germain and Richard
Summerbell. |
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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 spp. 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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