Xerophilic

Aspergillus ochraceus

Aspergillus ochraceus is best known as a producer of ochratoxin A: a nephrotoxic, immunosuppressive, and potentially carcinogenic mycotoxin classified as a Group 2B possible human carcinogen.

Water-damage indicatorXerophilic · Aw ≥ 0.77

Moisture niche · where this species can grow

XerophilicAw < 0.80
MesophilicAw 0.80–0.89
HydrophilicAw ≥ 0.90
Min Aw 0.77
← Drier conditions toleratedRequires liquid water →
Minimum Aw
0.77
EPA reference (GM)
2 SE/mg
Mycotoxin profile
3+ documented
Ecological role
Primary colonizer

About Aspergillus ochraceus

Aspergillus ochraceus is best known as a producer of ochratoxin A: a nephrotoxic (kidney-damaging), immunosuppressive, and potentially carcinogenic mycotoxin classified as a Group 2B possible human carcinogen. Some studies have reported ochratoxin A in the blood and urine of people living in mold-contaminated buildings, although food is the main source of ochratoxin A for most people. Effects reported for ochratoxin exposure include kidney dysfunction, fatigue, immunosuppression, and neurological effects. Whether any value here is clinically meaningful for any specific person is a question for a qualified clinician.

Ecology and water requirements

Aspergillus ochraceus is classified as a primary colonizer with xerophilic adaptations: capable of germinating and growing at water activity as low as Aw 0.77[2], well below what most molds tolerate. Primary colonizers establish first in damp or even mildly humid environments, often before any visible moisture problem is apparent. Elevated Aspergillus ochraceus on an ERMI test is more often associated with long-term high humidity than with a sudden water event[3]. Common contexts include poorly ventilated areas, conditioned-vs-unconditioned boundary zones (attics, crawl spaces, unfinished basements), and dusty environments where ambient relative humidity is sufficient to support growth on settled organic material.

Mycotoxin biology

Aspergillus ochraceus 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[4]. The same isolate may produce substantially different metabolite profiles on drywall paper versus wood versus settled dust[5]. 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 ochraceus 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 ochraceus is documented on the following substrates and locations:

  • Damp walls
  • wallpaper
  • stored foods (cereals
  • dried fruits
  • coffee
  • spices)
  • HVAC systems
  • house dust

Mycotoxins

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

Ochratoxin A & BPenicillic acidDestruxin B

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 ochraceus 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 Aspergillus ochraceus in that broader pattern.

Mycotoxins and extended panels

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

MycotoxinOchratoxin APrimary warm-climate OTA producer indoors.Extended speciesP. aurantiogriseum / P. viridicatumHistorical Penicillium OTA route.

Related species

Aspergillus flavus/oryzaeAw ≥ 0.78 · XerophilicAspergillus fumigatusAw ≥ 0.82 · MesophilicAspergillus nigerAw ≥ 0.77 · XerophilicAspergillus penicillioidesAw ≥ 0.73 · 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. World Health Organization. WHO Guidelines for Indoor Air Quality: Dampness and Mould. Copenhagen: WHO Regional Office for Europe; 2009.
  4. Nielsen KF. Mycotoxin production by indoor molds. Fungal Genet Biol. 2003;39(2):103–117.
  5. Miller JD, McMullin DR. Fungal secondary metabolites as harmful indoor air contaminants: 10 years on. Appl Microbiol Biotechnol. 2014;98(24):9953–9966.