Mucor racemosus

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Code: m4
Latin name: Mucor racemosus
Source material: Spores and mycelium
Family: Mucoraceae

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A mould, which may result in allergy symptoms in sensitised individuals.

Allergen Exposure

The Mucor genus consists of at least 39 species. (1) Mucor racemosus was one of the first soil fungi ever to be discovered and was isolated as early as 1886. M. racemosus is a dimorphic, facultative anaerobic zygomycete, capable of vegetative growth in either a filamentous phase or as spherical yeasts. (2) It is a rapid-growing fungus, usually dark grey or light olive-grey when grown on typical laboratory media. It is easily recognisable microscopically by its tall (up to 2 cm) needle-like sporangiophores and large sporangium.

M. racemosus has a worldwide distribution and is reported frequently all over Europe, and in the Americas from Alaska to Brazil. The species is primarily a soil fungus but has been found elsewhere, such as in horse manure, plant remains, grains, vegetables and nuts. In the tropics it is found at the higher altitudes. It is often seen on soft fruit, fruit juice and marmalade. M. racemosus has also been isolated from other sources, such as soft camembert cheese. (3)

Similarly, in a Turkish study of 91 mould isolates obtained from 69 traditional cheese samples (18 kasar cheese, 22 civil cheese, 23 lor (whey curd), 6 tulum cheese), the mould isolates were 69.3% Penicillium, 14.3% Geotrichum, 7.7% Chrysosporium, 5.5% Mucor, 3.3% Rhizopus spp. (4) 

M. racemosus may be utilised in the manufacture of sufu, a fermented cheese-like soybean product common in China and Vietnam. It is obtained by fungal fermentation of soybean curd (tofu), which results in moulded tofu or 'pehtze'. The final product (sufu) is obtained by maturing pehtze in a brine containing alcohol and salt for several months. (5) 

Mucor is also the most common mould found in floor dust in houses, and is considered an indoor mould. (6) 

It has also been isolated from dry pet foods, and there is a risk not only to pets that are exposed to the toxins that may be produced by this mould, but also to humans exposed to these products. (7)

The species of genus Mucor are a group of fungal microbes with important biotechnological potential, and are responsible for the production of some industrial enzymes. (8)

Allergen Description

No allergens have been characterised.

Potential Cross-Reactivity

No studies have evaluated the cross-reactive potential of M. racemosus.

Clinical Experience

IgE-mediated reactions

Anecdotal evidence suggests that M. racemosus is a common and important mould allergen that induces sensitisation and symptoms of asthma and allergic rhinitis in sensitised individuals, with patients showing hypersensitivity in both skin-prick and provocation tests. (9, 10, 11) However, few studies have been reported to date; it is possible that the allergy occurs more frequently than has been reported. M. racemosus has also been associated with causation of extrinsic allergic alveolitis. (12) The symptoms, which may occur 6 to 8 hours after exposure, include: elevated temperature, flu-like symptoms, general malaise, and difficulty in breathing followed by asthma later.

Mucor is also an uncommon opportunistic pathogen, affecting individuals with significantly compromised immune systems.

In a study evaluating serum-specific analysis, serum-specific IgE antibodies were detected in 77.8% of the patients tested, compared to 33.3% in skin-prick tests. (13)

Mould hypersensitivity may play a role in chronic sinusitis. Although Mucor has been identified in allergic fungal sinusitis, a case of Mucor-associated mycetoma in association with immediate hypersensitivity to Mucor was described in a 39-year-old Chinese male who presented with a 10-year history of nasal congestion, with the left side of the nose being more affected. The patient also complained of a foul smell in his nose and occasional yellowish discharge from the left side of his nose. Fungal cultures of the mucoid material obtained by surgical intervention revealed no growth. The total IgE was 83 IU/mL. Because of the fungal elements noted on histopathology, extensive fungal aeroallergen detection was attempted. No specific IgE was found for any of the major, well-known allergens; however, the specific IgE to M. racemosus was raised to 2.14 kIU/ml. (14)

A 22-year-old woman was reported who had developed recurrent episodes of fever, cough and dyspnoea after repeated exposure to a misting fountain at home. A diagnosis of extrinsic allergic alveolitis (EAA) was made following detection of serum antibodies against the fountain water and the cultures of Bacillus subtilis, M. racemosus, M. mucedo, and Saccharomyces cerevisiae from the water, as well as the detection of specific IgG antibodies against Bacillus subtilis and both Mucor species. An inhalation challenge using the misting fountain resulted in a positive reaction. The authors point out that as the use of these humidifier systems has become widespread in homes, clinicians should be aware of this specific type of EAA, which they suggest may be termed ‘misting fountain alveolitis’. (12)

In a study of the role of imperfect fungi in the aetiology of perennial rhinitis, out of 26 patients hypersensitivity to imperfect fungi was confirmed in 30.8%: to Candida albicans in 3.8%, Aspergillus fumigatus in 11.5%, Alternaria alternata in 3.8%, M. racemosus in 7.6% and to Cladosporum herbarum in 3.8%. (15)

A number of studies have evaluated sensitisation to M. racemosus in a local population.

A study undertaken in North-East Netherlands, to see whether the principal airborne fungi were also found to be the most reactive in skin testing, compared atmospheric samples taken with (at the same time) skin tests of 833 patients with symptoms of recurrent bronchial obstructive and suspected to be due to an underlying allergy. Almost three-quarters of the airborne fungal ‘flora’ was made up of seven genera, namely (in decreasing order of proportion): Cladosporium (42.6%), Botrytis (8.6%), Yeasts (7%), Penicillium (5.8%), Basidiomycetes (5.7%), Aspergillus (3.7%), and Alternaria (0.9%). In skin-testing, however, a different order emerged, namely: Beauveria (6.8%), Botrytis (6.1%), Aspergillus (4.7%), Mucor (3.8%), Epicoccum (3%), Cladosporium (2.3%), and Alternaria (1.1%). It was concluded that the most prevalent airborne moulds were not necessarily the most potent allergens, at least in skin testing. (16)

In a Turkish study of 614 respiratory allergic patients (72.6% with extrinsic asthma and 27.4% with allergic rhinitis) tested for 19 moulds, Aspergillus fumigatus was the most important fungus, resulting in positive skin tests in 26%. Other important moulds, in decreasing frequency of positive skin tests, were Trichophyton rubrum, Mucor, Penicillium notatum, Aspergillus niger and Alternaria tenius. (17)

In a study in Sao Paulo, Brazil, evaluating sensitisation in 201 patients with asthma and/or allergic rhinitis to 42 airborne fungi using skin-specific IgE tests, 15 were shown to be sensitised to Alternaria, 15 to Aspergillus, 23 to Aureobasidium, 37 to Candida, 15 to Chaetomium, 19 to Epicoccum, and 17 to Mucor. (18)

In Central and Southern Europe it is common practice to add flavour-enhancing moulds to traditional foods such as dry sausage, salami, Spanish ham, and French cheese. A 24-year-old man diagnosed with rhinoconjunctivitis and asthma due to allergy to pollen, mites, and mould had in the previous year experienced 2 episodes of facial angioedema immediately after eating a few slices of dry sausage, which he had tolerated previously on many occasions. Skin-prick tests were positive for grass pollen, house dust mites, and moulds (Alternaria alternata, Penicillium notatum, Mucor racemosus, and Pullularia, Stemphylium, Helminthosporum, and Fusarium spp.), and negative for all the food allergens tested. Total serum IgE was 1513 kU/L. Specific IgE was positive for Alternaria alternata (58 kU/L), Mucor racemosus (2.67 kU/L), and Penicillium notatum (3.03 kU/L). The microbiologists isolated Penicillium and Mucor spp. in the sausage skin. The labial challenge test yielded a positive result, with the onset of angioedema of the lips, tongue, and uvula within 5 minutes. The diagnosis was facial angioedema after dry sausage ingestion due to IgE-mediated allergy to Penicillium and Mucor spp. The patient was advised to avoid all products commonly contaminated with moulds, such as dry, fermented sausages, Spanish ham, foie gras, and French cheeses such as Roquefort and Camembert. (19)

Other reactions

Nil reported. 

Compiled by Dr Harris Steinman.


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  2. Borgia PT, Gokul NK, Phillips GJ. Respiratory-competent conditional developmental mutant of Mucor racemosus. J Bacteriol. 1985;164(3):1049-56.
  3. Bekada AMA, Benakriche B, Hamadi K, Bensoltane A. Modelling of effects of water activity, pH and temperature on the growth rate of Mucor racemosus isolated from soft Camembert cheese. World J Agricultural Sciences. 2008;4(6):790-4.
  4. Erdogan A, Gurses M, Turkoglu H, Sert S. The determination of mould flora of some Turkish cheese types (Kasar, Civil, Lor, Tulum). Pakistan J Biol Sci 2001;4(7):886-7.
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  9. Foucard T, Dreborg S, Eds. Mould Allergy Workshop. Pharmacia Diagnostics AB, Uppsala, Sweden. 1984.
  10. Soeria-Atmadja D, Onell A, Kober A, Matsson P, Gustafsson MG, Hammerling U. Multivariate statistical analysis of large-scale IgE antibody measurements reveals allergen extract relationships in sensitized individuals. J Allergy Clin Immunol 2007;120(6):1433-40.
  11. Dezfoulian B, De la Brassinne M. Comparison of IgE-dependant sensitization rate to moulds, dermatophytes and yeasts in patients with typical allergic diseases compared to those with inflammatory dermatitis. Rev Fr Allergol Immunol Clin 2006; 46(1):2-8.
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  14. Lin RY, Aziz MS, Yoo-Bowne H. Maxillary sinus mycetoma associated with hypersensitivity to Mucor racemosus. Internet J Asthma Allergy Immunol 2006;5(1).
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  16. Beaumont F, Kauffman HF, De Monchy JG, Sluiter HJ, De Vries K. Volumetric aerobiological survey of conidial fungi in the north-east Netherlands. II. Comparison of aerobiological data and skin tests with mold extracts in an asthmatic population. Allergy 1985;40(3):181-6.
  17. Guneser S, Atici A, Koksal F, Yaman A. Mold allergy in Adana, Turkey. Allergol Immunopathol (Madr) 1994;22(2):52-4.
  18. Mohovic J, Gambale W, Croce J. Cutaneous positivity in patients with respiratory allergies to 42 allergenic extracts of airborne fungi isolated in Sao Paulo, Brazil. Allergol Immunopathol (Madr) 1988;16(6):397-402.
  19. Bobolea I, Barranco P, Jurado-Palomo J, Pedrosa M, Quirce S. Allergy to dry fermented sausage. J Investig Allergol Clin Immunol 2009;19(4):324-5.



As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.