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.
Epidemiology
Worldwide distribution
Aureobasidium pullulans causes allergic disease in multiple locations worldwide; including in Poland, Mexico, Norway, North America.
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.
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.
Risk factors
Being male was associated with poorer control of asthma symptoms in patients exposed to indoor molds, including A. pullulans.
Certain occupations (e.g. farmers) appear to be at higher risk of developing hypersensitivity pneumonitis following exposure to this mold.
Night-time, rainy and windy weather were associated with peaks of hyaline conidia concentrations.
Immunocompromised patients are more likely to develop opportunistic A. pullulans infections.
Route Of Exposure
Main
Inhalation of mold components, mostly conidia
Clinical Relevance
Aureobasidium pullulans is a recognized cause of hypersensitivity pneumonitis (HP) in certain professions (farmers), but also in children. The symptoms of HP include fatigue, fever, cough and dyspnea, other flu-like symptoms, headache and weight loss. “Humidifier lung” is a type of HP that has been associated with A. pullulans infection. 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.
Patients sensitized this mold are at higher risk of severe asthma, and pre-existing asthma symptoms can be exacerbated by A. pullulans. The increased presence of spores of Ascomycota fungi was associated with thunderstorm-related asthma.
Aureobasidium pullulans was described as the cause of subcutaneous mycosis in a 66-year old immunocompromised patient who was undergoing chemotherapy. Fungemia and pulmonary embolism caused by A. pullulans was diagnosed and successfully treated in another 66-year old patient.
Diagnostics
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. Controlled emission chambers have also been used to determine the source of fungal aerosols
The presence of allergen-specific antibodies is determined by skin prick tests (SPTs) and serology for IgE and IgG specificities.
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.
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.
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. 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.
References
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