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Allergen Encyclopedia
Table of Contents

Whole Allergen

m11 Rhizopus nigricans

m11 Rhizopus nigricans Scientific Information

Type:

Whole Allergen

Display Name:

Rhizopus nigricans

Route of Exposure:

Inhalation, occupational health

Family:

Mucoraceae

Species:

nigricans

Latin Name:

Rhizopus nigricans

Summary

Rhizopus nigricans (also known as R. stolonifer) is a mold of the Order Mucorales commonly found in humid environments, both indoors and outdoors. R. nigricans can contaminate most human environments, including crops and foodstuffs. The spores are the particles that induce sensitization.

People affected by mold sensitization are often already sensitized to other allergens, confounding the clinical picture. Allergic rhinitis and asthma appear to be the clinical presentations most commonly associated with mold allergy and sensitivity to R. nigricans; patients may also experience allergic dermatitis. Cross-reactivity with other molds and commons foods such as spinach and mushroom may occur.

Allergen

Nature

Rhizopus nigricans (also known as R. stolonifer, agent of soft rot in crops) is characterized by complex rhizoids, sporangiophores, sporangium and sporangia. The main mycelium is conical/cylindrical in shape, up to 140 μm, with many branches conferring a tangled appearance. The mycelium produces erect hyphae, initially whitish and later forming black sporangiophores of 1-3 mm in length by 20-25 μm in diameter. Each sporangiophore produces a single spherical sporangium, containing sporangiospores. The spores vary in size, with the globose (spherical) type the most common shape (1).

The warmer months of spring and summer represent the peak of spores being present in the environment, although certain fungi are able to produce spores all year round. There is considerable overlap between peak spore season and other allergens such as grass and weed pollens, often masking the pathology caused by fungal spores in multi-sensitized people (2). R. nigricans showed no definite seasonal pattern (3).

R. nigricans is a common agent of crop and food spoilage (1). Alongside other members of the Order Mucorales, it is a permanent inhabitant of the human environment (4). Rhizopus spp. have been identified in spoiled pears (5), cereals (maize, wheat and barley; (6)) and sweet potatoes (7). It is also commonly found on bread surface (8). A Portuguese study found evidence of R. stolonifer in approximately 3% of tap water samples analyzed (9).

Spoiled crops and foods affected by R. stolonifer present moist/wet areas that become quickly covered by a gray, hairy mycelium presenting black-tipped sporangia. The initial infection of the crop occurs during harvest, handling and storage (6, 7, 10).

Taxonomy

Rhizopus nigricans (R. stolonifera) belongs to the Family Mucoraceae, Order Mucorales, Class Zygomycetes (1, 11).

Tissue

Spores and mycelium represent the tissues able to sensitize patients and cause allergic reactions (2).

Epidemiology

Worldwide distribution 

Molds of the Genus Rhizopus are accountable for most cases of rhino-, orbital- and cerebral infections worldwide (4).

In a German study, R. nigricans was found to be one of the five most common fungal agents of sensitization (12).

Risk factors 

Relative humidity appeared to be a significant predictor for the airborne presence of a variety of fungal components (13), including R. stolonifer (8).

The risk of sensitization to molds was significantly increased by pre-existing atopy (14).

Certain workplaces may present an occupational health hazard in regards to fungal allergies; R. nigricans particles were commonly found in air samples from sawmills, especially those processing conifers (15). Museums, archives and libraries with old records may also pose a higher workplace risk (16). Exposure to damp and moldy workplaces (including healthcare settings, schools, offices, laboratories, children nurseries and production plants) is a risk factor for new-onset adult asthma (14).

Environmental Characteristics

Worldwide distribution 

Fungal allergies are a worldwide health issue (2). R. nigricans is most prevalent in temperate and subtropical regions, though also commonly found in the warmer tropics (7). Allergic disorders caused by molds are frequent across India, with allergy-related hospitalization a common occurrence (13).

Rhizopus may contribute only a small fraction of the total aerial catch, but was accountable for 15% of skin positive reactions in the patients studied (3).

Route of Exposure

Main 

Inhalation of spores and other parts of the mold (2).

Secondary 

Ingestion and skin contact (2).

Detection

Main methods 

An Andersen air sampler can be used to detect R. stolonifer in the air (8).

Measures

The concentration of airborne R. stolonifer can range between 4-47 CFU/m3 (8)

Clinical Relevance

Molds cause new-onset adult asthma (14). Allergic rhinitis and asthma are the main conditions that can develop (and worsen in patients already affected) following exposure and sensitization to mold allergens. In particular, R. nigricans was responsible for 16.7% of positive skin tests and increased specific IgE in patients with allergic rhinitis (17).

In children, fever, dyspnea, wheezing and reduced lung capacity was observed in two siblings later diagnosed with allergic bronchopulmonary mycosis caused by R. nigricans (18).

A multi-mold extract containing R. nigricans antigens was used for skin-prick tests (SPTs) in children with allergic dermatitis; in this study, between 6-8% of children had a positive skin reaction to the mold extract (19).

Diagnostics Sensitization

Tests aimed at diagnosing fungal allergies are often in disagreement, as the antigenicity and therefore allergenicity of each extract can vary depending on strain variabilities, spontaneous mutations, different provenance of the raw materials, degrading enzymes (2). Usually, allergy to R. nigricans can be diagnosed with bioassays such as Skin Prick Test (SPT), or immunoassays in vitro (ELISA). SPT reactions to R. nigricans allergens in patients with respiratory allergies varied in positivity, with 41% of patients showing mild to moderately positive reactions, 15% showing moderately positive reactions and 9% showing highly positive skin reactions (3). In the same study, the serum of SPT+ (positive) patients was tested by ELISA for the presence of IgE specific for the fungal antigens that caused the positive skin reactions. This showed 66% concordance for R. nigricans antigens between the positives to the bioassay SPT and the in vitro immunoassay (3).

Prevention and Therapy

Allergen immunotherapy

Immunotherapy is currently not recommended for patients allergic to molds, due to complexities of the allergens and patient co-allergies (2).

Prevention strategies 

Avoidance is difficult in the case of aeroallergens encountered outdoors. Indoors, avoidance may be possible in certain circumstances, for example if visible mold is found (2).

Molecular Aspects

Allergenic molecules

At least 31 different R. nigricans antigens were identified and characterized by crossed immunoelectrophoresis (CIE) and other assays (20).

Cross-reactivity

Cross-reactivity can occur when epitopes of protein and carbohydrate structures are shared between antigens from different fungi; these can be taxonomically related species, but also quite distantly related, or not at all related (2). A Spanish study demonstrated the existence of an allergen showing cross-reactivity between molds and common foods, such as spinach and mushroom (21).

Compiled By

Author: RubyDuke Communications

Reviewer: Dr. Christian  Fischer

 

Last reviewed: January  2022

References
  1. Bautista-Baños S, Bosquez-Molina E, Barrera-Necha LL. Rhizopus stolonifer (Soft Rot).  Postharvest Decay: Control Strategies2014.
  2. Twaroch TE, Curin M, Valenta R, Swoboda I. Mold allergens in respiratory allergy: from structure to therapy. Allergy Asthma Immunol Res. 2015;7(3):205-20.
  3. Kochar S, Ahlawat M, Dahiya P, Chaudhary D. Assessment of allergenicity to fungal allergens of Rohtak city, Haryana, India. Allergy Rhinol (Providence). 2014;5(2):56-65.
  4. Walther G, Wagner L, Kurzai O. Updates on the Taxonomy of Mucorales with an Emphasis on Clinically Important Taxa. J Fungi (Basel). 2019;5(4).
  5. Kwon JH, Lee CJ. Rhizopus Soft Rot on Pear (Pyrus serotina) Caused by Rhizopus stolonifer in Korea. Mycobiology. 2006;34(3):151-3.
  6. Tabuc C, Marin D, Guerre P, Sesan T, Bailly JD. Molds and mycotoxin content of cereals in southeastern Romania. J Food Prot. 2009;72(3):662-5.
  7. Nelson S. Rhizopus Soft Rot of Sweetpotato. 2009.
  8. Sircar G, Bhattacharya SG. 221 Allergenic Significance of Airborne Rhizopus Stolonifer (ehrenb.) Vuill, a Common Bread Mold. The World Allergy Organization Journal. 2012;5(Suppl 2):S90-S.
  9. Gonçalves AB, Paterson RR, Lima N. Survey and significance of filamentous fungi from tap water. Int J Hyg Environ Health. 2006;209(3):257-64.
  10. Bautista-Baños S, Bosquez-Molina E, Barrera-Necha LL. Chapter 1 - Rhizopus stolonifer (Soft Rot). In: Bautista-Baños S, editor. Postharvest Decay. San Diego: Academic Press; 2014. p. 1-44.
  11. Uniprot.org. Taxonomy - Rhizopus stolonifer (Rhizopus nigricans) 2021 [cited 2021 16.11.21]. Available from: https://www.uniprot.org/taxonomy/4846.
  12. Koschel D, Mailänder C, Schwab Sauerbeck I, Schreiber J. Non-allergic severe asthma: is it really always non-allergic? The IDENTIFY project. Allergy, Asthma & Clinical Immunology. 2020;16(1):92.
  13. Bhattacharya K, Sircar G, Dasgupta A, Gupta Bhattacharya S. Spectrum of Allergens and Allergen Biology in India. Int Arch Allergy Immunol. 2018;177(3):219-37.
  14. Karvala K, Toskala E, Luukkonen R, Lappalainen S, Uitti J, Nordman H. New-onset adult asthma in relation to damp and moldy workplaces. Int Arch Occup Environ Health. 2010;83(8):855-65.
  15. Klarić M, Varnai VM, Calušić AL, Macan J. Occupational exposure to airborne fungi in two Croatian sawmills and atopy in exposed workers. Ann Agric Environ Med. 2012;19(2):213-9.
  16. Zielinska-Jankiewicz K, Kozajda A, Piotrowska M, Szadkowska-Stanczyk I. Microbiological contamination with moulds in work environment in libraries and archive storage facilities. Ann Agric Environ Med. 2008;15(1):71-8.
  17. Kołodziejczyk K, Bozek A. Clinical Distinctness of Allergic Rhinitis in Patients with Allergy to Molds. Biomed Res Int. 2016;2016:3171594.
  18. Benzrath S, Schlegtendal A, Brinkmann F, Koerner-Rettberg C. Allergic bronchopulmonary mycosis due to rhizopus nigricans in two siblings with and without CF? European Respiratory Journal. 2016;48(suppl 60):PA1247.
  19. Sybilski AJ, Zalewska M, Furmańczyk K, Lipiec A, Krzych-Fałta E, Samoliński B. The prevalence of sensitization to inhalant allergens in children with atopic dermatitis. Allergy Asthma Proc. 2015;36(5):e81-5.
  20. Sridhara S, Gangal SV, Joshi AP. Immunocheraical investigation of allergens from Rhizopus nigricans. Allergy. 1990;45.
  21. Herrera-Mozo I, Ferrer B, Luís Rodriguez-Sanchez J, Juarez C. Description of a novel panallergen of cross-reactivity between moulds and foods. Immunol Invest. 2006;35(2):181-97.