Mesophilic · Extended-panel species

Penicillium expansum

Postharvest 'blue mold' of apples and pears; documented indoors on gypsum board emitting patulin and chaetoglobosin guttation droplets.

Extended panelMesophilic · 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)
< 0.4 SE/mgMeklin AHHS threshold
Mycotoxin profile
6+ documented
Ecological role
Secondary colonizer

The < 0.4 SE/mg reference value is Meklin 2004's AHHS exclusion threshold: the paper retained species whose geometric mean was at least 2 spores per 5 mg dust (≈ 0.4 spores/mg) and eliminated the rest. This species was measured across the 1,096-home AHHS sample and characterized below that threshold, used here as a conservative ceiling on its true GM, not a percentile band. A detected value of X SE/mg implies an elevation factor of at least X ÷ 0.4 over the EPA reference, a lower bound, since the true GM is below 0.4. See the 82-species story for the math.

About Penicillium expansum

Penicillium expansum is the classical postharvest 'blue mold' pathogen of pome fruit (apples, pears, peaches, and hazelnuts) and a wound parasite that enters fruit through cuts and bruises. It is uncommon on standard residential ERMIs but has a striking indoor-mycotoxin emission profile: Salo et al. 2019 (J Appl Microbiol) documented strain CBS 145620 (isolated from a building with reported health complaints) growing on gypsum board, and (on laboratory medium) emitting guttation droplets containing chaetoglobosins and communesins A, B, and D at concentrations 100–1000× higher than previously reported from any fungus.

Taxonomy

Penicillium subgenus Penicillium, series Italica

Ecology and habitat

P. expansum is best known as a postharvest pathogen of apples, pears, peaches, and hazelnuts. It enters fruit through mechanical injuries (cuts, bruises, stem damage) and produces patulin as it expands through the tissue. Outside of fruit, the species is found in soil and on decaying plant material globally.

Indoor relevance

The species's indoor relevance was elevated by Salo et al. 2019 (J Appl Microbiol), a study of strain CBS 145620 isolated from an indoor building material from a building with reported health complaints. The strain grew on gypsum board (where its biomass toxicity stayed below the study's screening threshold), while on laboratory medium it produced visible guttation droplets containing chaetoglobosins (the same toxin family Chaetomium globosum produces) and communesins A, B, and D, with toxin concentrations 100–1000-fold higher than previously demonstrated from any fungus (note: patulin was not measured in that specific study, though the species is well-known for patulin biosynthesis in fruit). The Tannous et al. 2016 Food Sci Nutr work separately established that patulin production peaks at 16 °C, below the species's growth optimum. Together these papers mean P. expansum can be an unexpected indoor source of at least three distinct mycotoxin families. Detection in residential dust is uncommon, and the evidence on its toxin production from building materials rests mainly on that one study.

Cardinal physiology

Minimum water activity for growth: Aw 0.83[2]. Growth occurs across −2 to 35 °C with an optimum near 24 °C. Patulin production peaks at 16 °C[3] (notably below the growth optimum), which means cool indoor environments (basements, crawl spaces, refrigerated storage) favor toxin production relative to biomass accumulation.

Patulin production peaks at 16 °C, notably below growth optimum.

Secondary metabolites

The principal mycotoxin is patulin, an unsaturated lactone with broad biological activity. The species also produces citrinin, chaetoglobosins (cytoskeletal disruptors), communesins A/B/D, roquefortine C, and expansolides. The chaetoglobosin production is particularly notable: P. expansum is one of the few non-Chaetomium producers of this toxin family, and its co-production with patulin makes mycotoxin profiles from this species especially complex.

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

Patulin (major)CitrininChaetoglobosinsCommunesins A, B, DRoquefortine CExpansolides

DNA-based detection of a mycotoxin-producing species in household dust does not directly establish exposure to that mycotoxin at any specific concentration.

Lab availability

Some commercial dust testing labs offer this species as an extended-panel option. Specific lab coverage changes over time: check with your laboratory for current panel options.

Related

PatulinPrimary mycotoxin of this species; apple-juice regulatory marker.CitrininCo-produced nephrotoxin.ChaetoglobosinsCytochalasin family: unusual non-Chaetomium producer.Chaetomium globosumStandard-ERMI relative via chaetoglobosin production.Beyond the 36

References

  1. Meklin T, Haugland RA, Reponen T, Varma M, Lummus Z, Bernstein D, Wymer LJ, Vesper SJ. Quantitative PCR analysis of house dust can reveal abnormal mold conditions. J Environ Monit. 2004;6(7):615–620.
  2. Pitt JI, Hocking AD. Fungi and Food Spoilage. 2nd ed. London: Blackie Academic; 1997.
  3. Tannous J, Atoui A, El Khoury A, Snini SP, Lippi Y, El Khoury R, Atoui A, Lteif A, Oswald IP, Puel O. A study on the physicochemical parameters for Penicillium expansum growth and patulin production: effect of temperature, pH, and water activity. Food Sci Nutr. 2016;4(4):611–622.
  4. Puel O, Galtier P, Oswald IP. Biosynthesis and toxicological effects of patulin. Toxins. 2010;2(4):613–631.
  5. Moake MM, Padilla-Zakour OI, Worobo RW. Comprehensive review of patulin control methods in foods. Compr Rev Food Sci Food Saf. 2005;4:8–21.