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Mucor spp.
(described by Micheli ex Saint-Amans in 1821)

Say Me

Taxonomic classification

Kingdom: Fungi
Phylum: Zygomycota
Order: Mucorales
Family: Mucoraceae
Genus: Mucor

Description and Natural 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. [531, 1295, 2165, 2202].

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.

Synonyms

See the summary of synonyms for Mucor spp.

Pathogenicity and Clinical Significance

Mucor spp. are among the fungi causing the group of infections referred to as zygomycosis. Although the term mucormycosis has often been used for this syndrome, zygomycosis is now the preferred term for this angio-invasive disease. Zygomycosis includes mucocutaneous and rhinocerebral infections, as well as septic arthritis, dialysis-associated peritonitis, renal infections, gastritis and pulmonary infections. Diabetic ketoacidosis and immunosuppression are the most frequent predisposing factors. Desferoxamine treatment, renal failure, extensive burns, and intravenous drug use may also predispose to development of zygomycosis. Vascular invasion that causes necrosis of the infected tissue, and perineural invasion are the most frustrating features of these infections. Of note, due to its relatively limited activity, itraconazole prophylaxis in immunosuppressed patients may select the fungi in phylum Zygomycota as the cause of infections [3, 8, 12, 19, 217, 234, 243, 277, 278, 279, 375, 763, 911, 1581, 1703, 1792, 1918, 2023, 2149, 2182].

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 [531, 1295, 2202].

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 [531, 1295, 2202, 2341].

Histopathologic Features

See our histopathology page.

Compare to

Mucor spp. must be differentiated from the other genera included in the phylum Zygomycota:
Absidia
Apophysomyces
Rhizomucor
Rhizopus
Mortierella

The features that help in differentiation of these genera are summarized in the table below [531, 1295, 2144, 2202].

Genus Best growth Sporangi-
ophore
Apophysis Columella Sporan-
gium
Rhizoid Stylo-
spore
Absidia 45°C Branched, hyaline Conical, not prominent Dome-shaped Pear-shaped +, but usually indistinct -
Apophysomyces >42°C Usually unbranched, grayish-brown Bell-shaped, not prominent Usually dome-shaped, rarely elongated Pear-shaped + -
Mortierella 40°C Branched, hyaline - - Spherical + +/-
Mucor <37°C Branched or unbranched, hyaline - +, in varying shapes Spherical - -
Rhizomucor 54°C Branched, brown - Spherical Spherical + -
Rhizopus 45°C Unbranched and brown mostly Not prominent Spherical or elongated Spherical + -


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 [2432].

For MICs of various antifungal drugs for Mucor, see our susceptibility database.

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 [815, 1683]. 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 [292, 723, 763, 805, 887, 911, 1004, 1233, 1366, 1470, 1588, 1656, 1751, 1755, 1794, 2033, 2185, 2486].



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References

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763. Frater, J. L., G. S. Hall, and G. W. Procop. 2001. Histologic features of zygomycosis - Emphasis on perineural invasion and fungal morphology. Arch Pathol Lab Med. 125:375-378.

805. Garcia-Diaz, J. B., L. Palau, and G. A. Pankey. 2001. Resolution of rhinocerebral zygomycosis associated with adjuvant administration of granulocyte-macrophage colony-stimulating factor. Clin Infect Dis. 32:E166-E170.

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887. Grauer, M. E., C. Bokemeyer, T. Welte, M. Freund, and H. Link. 1993. Successful treatment of Mucor pneumonia in a patient with relapsed lymphoblastic leukemia after bone marrow transplantation. Bone Marrow Transplant. 12:421-424.

911. Guardia, J. A., J. Bourgoignie, and J. Diego. 2000. Renal mucormycosis in the HIV patient. Amer J Kidney Dis. 35:E241-E245.

1004. Hay, R. J. 1994. Liposomal amphotericin B, AmBisome. J. Infect. 28:35-43.

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1295. Larone, D. H. 1995. Medically Important Fungi - A Guide to Identification, 3rd ed. ASM Press, Washington, D.C.

1366. Lopez-Berestein, G., V. Fainstein, R. Hopfer, K. Mehta, M. P. Sullivan, M. Keating, M. G. Rosenblum, R. Mehta, M. Luna, E. M. Hersh, and et al. 1985. Liposomal amphotericin B for the treatment of systemic fungal infections in patients with cancer: a preliminary study. J Infect Dis. 151:704-10.

1470. Maury, S., T. Leblanc, M. Feuihade, J.-M. Molina, and G. Schaison. 1998. Successful treatement of disseminated mucormycosis with liposomal amphotericin B and surgery in a child with leukemia. Clin. Infect. Dis. 26:200-202.

1581. Morrison, V. A., R. J. Haake, and D. J. Weisdorf. 1993. The spectrum of non-Candida fungal infections following bone marrow transplantation. Medicine (Baltimore). 72:78-89.

1588. Moses, A. E., G. Rahav, Y. Barenholz, J. Elidan, B. Azaz, S. Gillis, M. Brickman, I. Polacheck, and M. Shapiro. 1998. Rhinocerebral mucormycosis treated with amphotericin B colloidal dispersion in three patients. Clin Infect Dis. 26:1430-1433.

1656. Nosari, A., P. Oreste, M. Montillo, G. Carrafiello, M. Draisci, G. Muti, A. Molteni, and E. Morra. 2000. Mucormycosis in hematologic malignancies: an emerging fungal infection. Haematologica. 85:1068-1071.

1683. Okhuysen, P. C., J. H. Rex, M. Kapusta, and C. Fife. 1994. Successful treatment of extensive posttraumatic soft-tissue and renal infections due to Apophysomyces elegans. Clin. Infect. Dis. 19:329-331.

1703. Pagani, J. J., and H. I. Libshitz. 1981. Opportunistic fungal pneumonias in cancer patients. Am. J. Roentgenol. 137.

1751. Penk, A., and L. Pittrow. 1999. Therapeutic experience with fluconazole in the treatment of fungal infections in diabetic patients. Mycoses. 42:97-100.

1755. Perez, A. 1999. Terbinafine: broad new spectrum of indications in several subcutaneous and systemic and parasitic diseases. Mycoses. 42:111-114.

1792. Pickles, R., G. Long, and R. Murugasu. 1994. Isolate renal mucormycosis. Med. J. Aust. 160:514-516.

1794. Pidhorecky, I., J. Urschel, and T. Anderson. 2000. Resection of invasive pulmonary aspergillosis in immunocompromised patients. Annals Surg Oncology. 7:312-317.

1918. Ribes, J. A., C. L. Vanover-Sams, and D. J. Baker. 2000. Zygomycetes in human disease. Clin Microbiol Rev. 13:236-301.

2023. Sane, A., S. Manzi, J. Perfect, A. J. Herzberg, and J. O. Moore. 1989. Deferoxamine treatment as a risk factor for zygomycete infection. 159:151-152.

2033. Sastre, J. L., J. Perez-Oteyza, J. Lopez, C. Cervero, A. Sanchez-Sousa, J. Garcia-Larana, J. A. Cancelas, J. Odriozola, and J. L. Navarro. 1994. [Pulmonary mucormycosis in leukemic patients. Apropos of 2 cases]. Sangre. 39:53-5.

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2149. Stave, G. M., T. Heimberger, and T. M. Kerkering. 1989. Zygomycosis of the basal ganglia in intravenous drug users. Am. J. Med. 85:115-116.

2165. Stewart, N. J., B. L. Munday, and T. Hawkesford. 1999. Isolation of Mucor circinelloides from a case of ulcerative mycosis of platypus (Ornithorhynchus anatinus), and a comparison of the response of Mucor circinelloides and Mucor amphibiorum to different culture temperatures. Med Mycol. 37:201-206.

2182. Stringer, S. P., and M. W. Ryan. 2000. Chronic invasive fungal rhinosinusitis. Otolaryngol Clin N Amer. 33:375-387,X.

2185. Sugar, A. M., and X. P. Liu. 2000. Combination antifungal therapy in treatment of murine pulmonary mucormycosis: Roles of quinolones and azoles. Antimicrob. Agents Chemother. 44:2004-2006.

2202. Sutton, D. A., A. W. Fothergill, and M. G. Rinaldi (ed.). 1998. Guide to Clinically Significant Fungi, 1st ed. Williams & Wilkins, Baltimore.

2341. Voigt, K., E. Cigelnik, and K. O'Donnell. 1999. Phylogeny and PCR identification of clinically important zygomycetes based on nuclear ribosomal-DNA sequence data. J Clin Microbiol. 37:3957-3964.

2432. Wildfeuer, A., H. P. Seidl, I. Paule, and A. Haberreiter. 1998. In vitro evaluation of voriconazole against clinical isolates of yeasts, moulds and dermatophytes in comparison with itraconazole, ketoconazole, amphotericin B and griseofulvin. Mycoses. 41:309-319.

2486. Zander, D. S., M. J. Cicale, and P. Mergo. 2000. Durable cure of mucormycosis involving allograft and native lungs. J Heart Lung Transplant. 19:615-618.



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