About Aureobasidium pullulans
Aureobasidium pullulans is a remarkable polymorphic fungus that can appear as a yeast, as a filamentous mold, or a combination of both, ranging in color from white through pink to dark black. Indoors it is most commonly found on painted wood surfaces, window frames, caulking, grout lines, and damp building materials, often mistaken for Stachybotrys on painted surfaces. While not typically a significant mycotoxin producer, it is allergenic and has been associated with hypersensitivity reactions.
Ecology and water requirements
Aureobasidium pullulans is classified as a secondary colonizer with mesophilic moisture requirements: capable of growing at water activity in the range Aw 0.88 and above[2], typical of condensation surfaces and freshly damp materials. Secondary colonizers follow primary xerophilic species in the ecological succession that develops on damp building materials. Detection of elevated Aureobasidium pullulans on an ERMI suggests intermittent or recent moisture conditions consistent with condensation, vapor permeation, or short-lived water events: chronically cool surfaces (uninsulated walls, single-pane windows, plumbing chases) and bathrooms or kitchens with insufficient ventilation are typical contexts.
Mycotoxin biology
Aureobasidium pullulans is not currently documented as a significant mycotoxin producer in the indoor environment context. Its primary health relevance indoors is generally as an allergen. Fungal spores and hyphal fragments are documented triggers for allergic rhinitis, asthma exacerbation, and hypersensitivity reactions in sensitized individuals. Allergen production and inflammatory potential vary by strain, growth substrate, and environmental conditions. As with all ERMI species, a positive DNA detection in dust indicates that spore material is present in the home but does not directly measure airborne exposure or sensitization status.
Detection in dust versus visual inspection
DNA-based detection of Aureobasidium pullulans in settled household dust (the basis of the ERMI panel[1]) integrates spore material from current and recent growth in the home, capturing exposure history over weeks to months. A positive detection in dust does not necessarily indicate currently-active growth at the time of sampling; conversely, an active growth site can produce relatively low dust spore counts if the spores are not being aerosolized (sealed wall cavities, behind vapor barriers, or under flooring). Interpretation requires considering the dust signal alongside building inspection, occupant symptom history, and the broader pattern of species detected on the panel.
Where it’s typically found
Aureobasidium pullulans is documented on the following substrates and locations:
- Painted wood
- window frames
- caulking
- grout lines
- damp building materials
- wood and plywood
Mycotoxins
No mycotoxins documented for this species in our reference literature.
On your ERMI report
Aureobasidium pullulans is one of the 26 EPA water-damage indicator species used to compute the SLG1 component of the ERMI score (sometimes labeled "Group 1" in EPA documentation). Whether the level detected in any specific home is concerning depends on the broader pattern: which other species are elevated, the water-activity profile of the elevated species, the home's climate context, and (where relevant) the occupant's sensitivity history. Our interpretation report puts Aureobasidium pullulans in that broader pattern.