Aureobasidium pullulans is a common and widespread fungus found globally in diverse environments, both outdoors (like on plant surfaces) and indoors where moisture is present. The level of risk associated with this mold depends heavily on the circumstances of exposure and the underlying health of the individual. While most people coexist with A. pullulans without issue, it can trigger health concerns in specific populations.
Defining Aureobasidium pullulans
Aureobasidium pullulans is a saprophytic mold that obtains nutrients from dead or decaying organic matter. It is highly adaptable, exhibiting phenotypic plasticity that allows it to exist in both yeast-like and filamentous forms depending on the environment. This species is often referred to as a “black yeast” due to its characteristic dark pigmentation.
The appearance of A. pullulans changes noticeably as it matures. Young colonies are typically smooth and may appear white, creamy, or light pink. Over time, the fungus produces thick-walled, dark spores called chlamydospores, which cause the colony to turn black or dark brown. This mold tolerates varied conditions, including cold temperatures, low nutrient environments, and fluctuating water activity, making it common even in Arctic regions.
Health Risks and Pathogenicity
The primary concern regarding Aureobasidium pullulans relates to its potential for allergic reactions and, in rare instances, infection. As a known allergen, exposure occurs mainly through the inhalation of its airborne spores. Breathing in the large number of spores produced by the mold can trigger hypersensitivity reactions in sensitive individuals.
Allergic responses commonly associated with exposure include asthma, allergic rhinitis, and the exacerbation of pre-existing respiratory conditions. Chronic, high-level exposure, such as through contaminated humidifiers, can lead to a more severe condition known as hypersensitivity pneumonitis. This inflammatory lung reaction is characterized by symptoms like fever, cough, and shortness of breath.
While generally non-pathogenic to healthy people, A. pullulans can act as an opportunistic pathogen, particularly in vulnerable populations. Individuals with severely compromised immune systems, such as organ transplant recipients or those undergoing chemotherapy, are at risk for more serious infections. These infections, classified as phaeohyphomycoses, can manifest as localized issues like keratitis or cutaneous infections. In severe cases, the fungus can cause systemic infections, fungemia, or pulmonary mycosis, colonizing internal organs.
Exposure Contexts and Remediation
People encounter high concentrations of Aureobasidium pullulans most frequently in indoor environments that provide consistent moisture and organic material. This mold thrives in damp, high-cellulose settings like window sills, bathrooms, and basements. It is often the cause of the black discoloration seen on shower tiles, grout, and damp painted surfaces.
Minimizing exposure begins with aggressive moisture control, which is the most effective way to inhibit fungal growth. In moisture-prone areas like bathrooms, ensure adequate ventilation, such as running an exhaust fan after showering. For small, visible surface growth, a simple cleaning solution can be effective. A solution of 10% bleach combined with a non-ammoniated detergent can be applied to the affected area, left wet for about 15 minutes, and then rinsed.
For cleanup, appropriate personal protective equipment, such as gloves and a respirator, should be worn to prevent the inhalation of dislodged spores. If the mold growth is extensive, covering more than ten square feet, or if it appears to be a deep structural infestation, professional remediation is advised. Professionals can isolate the affected area to prevent spore spread and safely remove contaminated materials, ensuring the source of the moisture problem is also addressed.