Mesophilic

Aspergillus ustus

Aspergillus ustus is an emerging opportunistic pathogen that has gained attention in clinical settings due to its resistance to multiple antifungal medications, including triazole antifungals like voriconazole commonly used to treat aspergillosis.

Environmental referenceMesophilic · Aw ≥ 0.83

Moisture niche · where this species can grow

XerophilicAw < 0.80
MesophilicAw 0.80–0.89
HydrophilicAw ≥ 0.90
Min Aw 0.83
← Drier conditions toleratedRequires liquid water →
Minimum Aw
0.83
EPA reference (GM)
2 SE/mg
Mycotoxin profile
4+ documented
Ecological role
Secondary colonizer

About Aspergillus ustus

Aspergillus ustus is an emerging opportunistic pathogen that has gained attention in clinical settings due to its resistance to multiple antifungal medications, including triazole antifungals like voriconazole commonly used to treat aspergillosis. Infections are rare in healthy individuals. In immunocompromised patients, the infections it causes can be difficult to treat. Whether any value here is clinically meaningful for any specific person is a question for a qualified clinician.

Ecology and water requirements

Aspergillus ustus is classified as a secondary colonizer with mesophilic moisture requirements: capable of growing at water activity in the range Aw 0.83 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 Aspergillus ustus 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

Aspergillus ustus produces a range of secondary metabolites with biological activity. The compounds documented in the literature for this species are listed in the chips below. Mycotoxin production is not uniform across all strains and is influenced by substrate, temperature, and water activity[3]. The same isolate may produce substantially different metabolite profiles on drywall paper versus wood versus settled dust[4]. DNA-based detection via the ERMI panel identifies species presence but does not directly measure mycotoxin presence; detection of a mycotoxin-producing species in household dust does not establish exposure to that mycotoxin at any specific concentration.

Detection in dust versus visual inspection

DNA-based detection of Aspergillus ustus 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

Aspergillus ustus is documented on the following substrates and locations:

  • House dust
  • water-damaged building materials
  • soil
  • HVAC filters
  • carpets

Mycotoxins

Compounds documented as produced by Aspergillus ustus (presence and quantity vary by chemotype, strain, and substrate):

AustdiolAustamideAustalide· cytotoxicLimited indoor production data

Mycotoxin production is not uniform across all strains and is influenced by substrate, temperature, and water activity. Detection of a mycotoxin-producing species in household dust does not directly establish exposure to that mycotoxin at any specific concentration.

On your ERMI report

Aspergillus ustus is one of the 10 EPA environmental reference species used to compute the SLG2 component of the ERMI score (sometimes labeled "Group 2" in EPA documentation). Group 2 species are commonly found in outdoor air; their levels are subtracted from the indicator-species sum, which means high outdoor-reference detections actually reduce the final ERMI. A low-level detection of Aspergillus ustus is common, because these species are also found in outdoor air. Our interpretation report reads its level alongside the indicator species.

Mycotoxins and extended panels

Related reference pages: the mycotoxins Aspergillus ustus can produce, and the extended-panel species most closely related to it:

MycotoxinSterigmatocystinAustocystins from A. ustus are structurally related compounds.

Related species

Aspergillus flavus/oryzaeAw ≥ 0.78 · XerophilicAspergillus fumigatusAw ≥ 0.82 · MesophilicAspergillus nigerAw ≥ 0.77 · XerophilicAspergillus ochraceusAw ≥ 0.77 · Xerophilic

References

  1. Vesper SJ, McKinstry C, Haugland RA, et al. Development of an Environmental Relative Moldiness Index for U.S. homes. J Occup Environ Med. 2007;49(8):829–833.
  2. Pitt JI, Hocking AD. Fungi and Food Spoilage. 3rd ed. New York: Springer; 2009.
  3. Nielsen KF. Mycotoxin production by indoor molds. Fungal Genet Biol. 2003;39(2):103–117.
  4. Miller JD, McMullin DR. Fungal secondary metabolites as harmful indoor air contaminants: 10 years on. Appl Microbiol Biotechnol. 2014;98(24):9953–9966.