Table of Contents

Whole Allergen

m12 Aureobasidium pullulans

m12 Aureobasidium pullulans Scientific Information

Type:

Whole Allergen

Display Name:

Aureobasidium pullulans

Route of Exposure:

Inhalation

Family:

Dothioraceae

Species:

pullulans

Latin Name:

Aureobasidium pullulans

Summary

Aureobasidium pullulans (also known as Pullularia pullulans) is a ubiquitous mold of the Order Dothideales, found in a large variety of environments, indoors and outdoors, including extremes of temperature. It is a widely used organism in the biotechnology and medical industry. The main particles that induce sensitization are the conidia (a type of spore).

Hypersensitivity pneumonitis (HP), allergic rhinitis and worsening of asthma symptoms are the clinical presentations most commonly associated with A. pullulans allergy. This fungus is also an opportunistic pathogen and it is able to cause a wide range of diseases, especially in immunocompromised patients and those with underlying conditions. Cross reactivity with other molds, especially if taxonomically close, may occur.

Allergen

Nature

Aureobasidium pullulans (also known as Pullularia pullulans, black yeast) is a yeast-like ubiquitous saprophyte mold (1, 2). This fungal species is characterized by highly variable phenotype and physiology; three sub varieties have been identified: A. pullulans var. pullulans, A. pullulans var. melanogenum and A. pullulans var. aubasidani (1, 2), some of which were later re-classified as separate species following genomic analyses (3, 4). The hyphae are hyaline (transparent), smooth and single celled, variable in size and shape, form chlamydospores in places and the colony color can turn dark due to melanin production. Budding of conidia (a type of spore) is frequent. A. pullulans is a fast-growing mold, able to withstand extreme osmotic environments (2, 5) and freezing temperatures (6). The variations observed in the types of colony depend on factors such as the type of carbon substrate used in the medium, age of the colony, temperature and light conditions (7).

In a US study, the researchers found that hyaline conidia presence peaked during periods of rainfall and high winds in the fall and winter (8). However, certain fungi are able to produce spores all year round. There is considerable overlap between peak fungal activity season and other allergens such as grass and weed pollens, often masking the pathology caused by fungal spores in people multi-sensitized (9).

A. pullulans can be found as epiphyte on different fruits and crops (apples, grapes, strawberries, citrus fruits, cabbages, wheat, barley, nuts) and other foods (meat, shrimp, flour, frozen foods); it affects the esthetic appearance of food but is not considered a common cause of spoilage (6). Other sources are plant leaves, wood, damp indoor environments (including cement walls, window frames, glass and latex-coated surfaces), animal feed and even rocks (1, 2, 6, 10). Strains that formed part of a genotyping study were also isolated from human sputum and peritoneal dialysis (1).

A. pullulans is important in the field of microbiology and industrial processes because of its ability to produce pullulan (a biodegradable polysaccharide used for coatings and wrappings). Other metabolites and enzymes of Aureobasidium spp. are widely used in the food and medical industry (11).

Taxonomy

Aureobasidium pullulans (Pullularia pullulans) belongs to the Family Dothioraceae, Order Dothideales, Class Dothideomycetes, Phylum Ascomycota (12, 13).

Taxonomic tree of Aureobasidium genus (12, 13)
Domain	Eukaryota
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Dothideomycetes
Order	Dothideales
Family	Dothioraceae
Genus	Aureobasidium

Tissue

Hyaline unicellular conidia (an asexual, colorless microscopic component released in the environment in lieu of sexual reproduction), which can reach high concentrations in the air and represent the main fungal allergen detected (90%; (8)).

Epidemiology

Worldwide distribution

Aureobasidium pullulans causes allergic disease in multiple locations worldwide; including in Poland (14), Mexico (15), Norway (16), North America (8, 17).

Prevalence of hypersensitivity pneumonitis, which may be caused by A. pullulans can vary considerably and if the diagnostic protocols do not agree, it may be underdiagnosed (16).

A study of Skin Prick Tests (SPTs) in asthmatic patients that included A. pullulans in the testing panel resulted in positive reactions in 98% of asthmatic patients and 66% of non-asthmatic controls (14).

Risk factors

Being male was associated with poorer control of asthma symptoms in patients exposed to indoor molds, including A. pullulans (15).

Certain occupations (e.g. farmers) appear to be at higher risk of developing hypersensitivity pneumonitis following exposure to this mold (16).

Night-time, rainy and windy weather were associated with peaks of hyaline conidia concentrations (8).

Immunocompromised patients are more likely to develop opportunistic A. pullulans infections (18).

Environmental Characteristics

Worldwide distribution

A. pullulans is commonly found in cold and temperate climates, but it can also be detected in tropical areas such as Thailand (2, 10). It is thus able to survive and replicate in a large variety of habitats and conditions, without significant changes to its genomic makeup (3).

Route of Exposure

Main

Inhalation of mold components, mostly conidia (8)

Detection

Environmental source

Air

Main methods

Molecular assay using probes that target the 18S ribosomal RNA gene showed satisfactory performance for the early detection of A. pullulans infection (18). Controlled emission chambers have also been used to determine the source of fungal aerosols (8)

Clinical Relevance

Aureobasidium pullulans is a recognized cause of hypersensitivity pneumonitis (HP) in certain professions (farmers;(16)), but also in children (17). The symptoms of HP include fatigue, fever, cough and dyspnea, other flu-like symptoms, headache and weight loss (16). “Humidifier lung” is a type of HP that has been associated with A. pullulans infection (19). In a study of 405 children born to allergic/asthmatic parents, high fungal concentrations within the home in the first 3 months of life were showed as predictors of allergic rhinitis diagnosed in the first 5 years (20).

Patients sensitized this mold are at higher risk of severe asthma (14), and pre-existing asthma symptoms can be exacerbated by A. pullulans (15). The increased presence of spores of Ascomycota fungi was associated with thunderstorm-related asthma (9).

Aureobasidium pullulans was described as the cause of subcutaneous mycosis in a 66-year old immunocompromised patient who was undergoing chemotherapy (21). Fungemia and pulmonary embolism caused by A. pullulans was diagnosed and successfully treated in another 66-year old patient (22).

Diagnostics Sensitization

The presence of allergen-specific antibodies is determined by skin prick tests (SPTs) and serology for IgE and IgG specificities (8, 9, 16).

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 (9).

Prevention strategies

Complete avoidance is often not possible as A. pullulans is a very common mold. For certain professions (such as farmers) where some jobs carry higher risk of exposure, use of protective equipment such as filtered masks and respirators must be considered (16).

Molecular Aspects

Allergenic molecules

IgE from atopic patients bind to several allergens in A. pullulans extracts (8). In a later study, a 64 kDa and a 100 kDa allergen were identified by IgG immunoblot using serum from a farmer with hypersensitivity pneumonitis (16).

Cross-reactivity

Immunoblotting showed that A. pullulans extracts contain antigens that cross react with antibodies specific to certain antigens of the related mold Alternaria alternata (23). In a study carried out on 668 serum samples from patients who had previously recorded at least one IgE positivity to fungal antigens, associations were observed between the patterns of IgE sensitization and fungal phylogenetic relationships. Using a panel of 17 fungal extracts including A. pullulans, some samples were only positive to one fungal species, whereas many were multi-sensitized. The results suggest that the associations are likely due to antigen cross-reactivity between fungal species (24).

Compiled By

Author: RubyDuke Communications

Reviewer: Dr. Christian Fischer

Last reviewed: December 2022

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