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Glossary of Mold Terms

   
 

Allergen

An allergen is a substance that elicits an IgE antibody response and is responsible for producing allergic reactions. Chemicals are released when IgE on certain cells come into contact with an allergen. These chemicals can cause injury to surrounding tissue - the visible signs of an allergy. Only a few fungal allergens have been characterized but all fungi are thought to be potentially allergenic. Click Here for More Information. . .

Biocide/Fungicide

Biocides and fungicides are chemicals that limit the growth of or kill microorganisms such as fungi.

"Black mold"

The poorly defined term “black mold” or “toxic black mold” has usually been associated with the mold Stachybotrys chartarum.  While there are only a few molds that are truly black, there are many that can appear black.  Not all mold that appears to be black is Stachybotrys.

Fungi

Fungi are neither animals nor plants and are classified in a kingdom of their own – the Kingdom of Fungi.  Fungi include a very large group of organisms, including molds, yeasts, mushrooms and puffballs.  There are >100,000 accepted fungal species but current estimates range to 1.5 million species.  Mycologists (people who study fungi) have grouped fungi into four large groups according to their method of reproduction.

Hidden mold

This refers to visible mold growth on building structures that is not easily seen, including the areas above drop ceilings, within a wall cavity (the space between the inner and outer structure of a wall), inside air handlers, or within the ducting of a heating/ventilation system. Click Here for More Information. . .

Microbial Volatile Organic Compounds (MVOCs)

Fungi produce chemicals as a result of their metabolism.  Some of these chemicals, MVOCs, are responsible for the characteristic moldy, musty, or earthy smell of fungi, whether mushrooms or molds.  Some MVOCs are considered offensive or annoying.  Specific MVOCs are thought to be characteristic of wood rot and mold growth on building materials.  The human nose is very sensitive to mold odors and sometimes more so than current analytical instruments. Click Here for More Information. . .

Mold

Molds are a group of organisms that belong to the Kingdom of Fungi (see Fungi).  Even though the terms mold and fungi had been commonly referred to interchangeably, all molds are fungi, but not all fungi are molds.

Mycotoxin

Mycotoxins are compounds produced by some fungi that are toxic to humans or animals.  By convention, the term “mycotoxin” excludes mushroom toxins.  Fungi that produce mycotoxins are called "toxigenic fungi”. Click Here for More Information. . .

Remediate

The term "remediate" simply means to fix a problem.  Related to mold contamination, remediation includes fixing the water/moisture problem, and the cleaning, removal and/or replacement of damaged or contaminated materials.

Spore

General term for a reproductive structure in fungi, bacteria and some plants.  In fungi, the spore is the structure which may be used for dissemination and may be resistant to adverse environmental conditions.

Stachybotrys

Stachybotrys is a genus that includes approximately 10 species.  These species occur mainly on dead plant materials.  Of these, Stachybotrys chartarum is the most common.  This species is cosmopolitan and one of its natural substrates is straw.  In the indoor environment, it is commonly found on cellulosic materials including paper, canvas and jute which are wetted to a water activity > 0.98.  This is a toxigenic mold Antigens to S. chartarum have been identified. Click Here for More Information...

“Toxic mold”

The term “toxic mold" has no scientific meaning since the mold itself is not toxic.  The metabolic byproducts of some molds may be toxic (see mycotoxin).

Toxigenic fungi

These are fungi that can produce mycotoxins (see above).

More Fungal Terms:

Conidium (plural, conidia)

An asexual spore of mold (Hyphomycetes), produced on the external surface of mycelium, not in a sporangium.

Conidiophore

A simple or branched hyphal structure bearing or consisting of cells that produce conidia/spores.

Fruiting structure

A general name for a spore-bearing organ both in macro-fungi (e.g. mushroom) or microfungi (e.g. a mold).

Hypha (plural, hyphae)

An individual fungal thread or filament of connected cells; the thread that represents the individual parts of the fungal body.

Mycelium

A mass of hyphae; not in the form of large spore producing parts such as mushroom.

Common Indoor Fungi:

Alternaria

Alternaria is a genus comprising approximately 50 species of which most are saprophytes or plant pathogens.  Alternaria alternata is an extremely common saprophyte found on plants, wood, wood pulp, textiles and food.  It is cosmopolitan in distribution [grows worldwide].  A. alternata grows on the surfaces of leaves [phylloplane] and occurs in outdoor air at modest levels peaking in July or August depending on the location (reaching perhaps 500 spores/m3).  The allergens of A. alternata can induce reactions at very low concentrations in sensitized individuals.  Phylloplane strains of A. alternata i.e. those found in air, do not produce AAL toxin.  Some produce the phytotoxin [compound toxic to plants] alternariol and related metabolites.

Aspergillus

Aspergillus is the asexual stage of a number of ascomycetes. Species of Aspergillus are distributed worldwide although they are somewhat more common in warmer climates.  These species grow on a vast array of organic materials.  Many species are cosmopolitan.  There are 182 accepted species although only 40 occur with any frequency.  Species of Aspergillus include several of considerable economic importance: A. flavus is the main producer of the potent carcinogen aflatoxin and A. fumigatus is an important cause of the invasive disease aspergillosis.  Several species are common on building materials including A. versicolorA. fumigatus is common in outdoor air in some regions in the fall, occurring on composting leaves and other materials.

Cladosporium

Cladosporium is a genus comprising approximately 500 species most of which are saprophytes or plant pathogens of which perhaps 20 are common.  Cladosporium sphaerosphermum, C. cladosporoioides and C. herbarum are the most common species. All are found on plants, wood, wood pulp, textiles and food. Of the three, C. sphaerospermum is the species typically found on building materials. The other two are phylloplane species that occur in outdoor air at high levels, peaking in June, July or August depending on the location (reaching perhaps 10,000 spores/m3). Cladosporium herbarum produces a wide variety of allergens and approximately 10% of the population is sensitized to Cladosporium. Phylloplane strains of Cladosporium do not produce metabolites with material toxicity.

Penicillium

Penicillium is the asexual stage of a number of ascomycetes and species of Penicillium are distributed worldwide although they are somewhat more common in temperate climates.  These species grow on a vast array of organic materials.  Many species are cosmopolitan.  There are 225 accepted species although only 70 occur with any frequency.  Species of Penicillium include several of considerable economic importance: P. verrucosum produces ochratoxin on cereals and P. chrysogenum produces penicillin.  Many Penicillium species cause damage in damp building materials including the toxigenic species P. aurantiogriseum.

Additional Facts:

Allergen

An allergen is a substance that elicits an antibody response and is responsible for producing allergic reactions by inducing IgE formation, one of a group of immune system mediators. IgE antibodies when bound to basophiles in circulation or mast cells in tissue, cause these cells to release chemicals when they come into contact with an allergen.  These chemicals can cause injury to surrounding tissue - the visible signs of an allergy.  Fungal allergens are proteins found in either the mycelium or spores.  Only a few fungal allergens have been characterized but all fungi are thought to be potentially allergenic.

Fruiting structure

A general name for a spore-bearing organ both in macro-fungi (e.g. mushroom) or microfungus (e.g. a mold).  More specific terms have been use for fruiting structures, such as ascocarp, basidiocarp, perithecium, sporocarp, etc.

Hidden mold

This refers to visible mold growth on building structures not easily seen including for example, above drop ceilings, within a wall cavity [the space between the inner and outer structure of a wall], inside air handlers, or within the ducting of a ventilation system.  Visible mold within a ventilation duct is in immediate contact with the occupied space and release of spores from such growth are known to be affected by air-movement and air relative humidity.  Spores of mold growth in wall cavities are released as a function of air exchange between the wall cavity and the occupied space.  The rate of spore movement between such spaces is typically slow.  Volatile gases produced by visible mold growth in wall cavities is also known to occur including through air barriers.

Microbial Volatile Organic Compounds (MVOCs)

Bacteria and fungi produce odors as a consequence of their metabolism.  More is known about fungal volatiles which are involved in inter specific competition especially amongst the fungi resulting in wood decay.  Fungi produce many metabolites that have boiling points around room temperature, the most common of which is ethanol but the list is long including many chemicals that arise also from man-made materials.  These compounds are responsible for the characteristic smell of fungi whether mushrooms or molds.  Some molds have characteristic odors.  Particular patterns of fungal volatiles are somewhat diagnostic for wood rot and mold growth on building materials.  The human nose is very sensitive to mold odors and sometimes more so than current analytical instruments.

Mycotoxin

Mycotoxins are low molecular weight compounds produced by fungi that are toxic to humans or animals.  By convention, the term “mycotoxin” excludes mushroom toxins.  The ordinary use of the term mycotoxin refers to compounds of importance in agriculture and includes a small number of very potent compounds.  This includes deoxynivalenol, aflatoxin, fumonisin, ochratoxin, zearalenone and the much less common nivalenol, T-2/HT-2 toxins, as well as some other Penicillium and Aspergillus toxins and toxins from S. chartarum and Pithomycetes chartarum.  By convention, the term does not include compounds of low potency or toxicity only in in vitro systems.  The biochemical targets of mycotoxins are usually many but the mechanism of toxicity, even within families of toxins are typically different.

The genetic property to produce mycotoxins is particular to given species.  Fungi that produce mycotoxins as defined here are called "toxigenic" fungi.  Some species including Fusarium graminearum and S. chartarum have genetic sub-populations called chemotypes that produce different mixtures of compounds.  In the case of F. gramineaum, these chemotypes are distributed by continent.  In the case of S. chartarum, both chemotypes occur together.  The occurrence of fungi on different substrates including building materials is determined by the composition, water content, and temperature.  Should a toxigenic fungus grow in nature, one or more of the toxins for which it has the genetic potential are typically produced.

Stachybotrys

Stachybotrys is a genus that includes approximately 10 species.  These species occur mainly on dead plant materials.  Of these, Stachybotrys chartarum is the most common.  This species is cosmopolitan and one of its natural substrates is straw.  In the indoor environment, it is commonly found on cellulosic materials including paper, canvas and jute which are wetted to a water activity > 0.98.  This is a toxigenic mold.  There are two chemotypes of this species that produce either trichothecenes plus spirolactones or atranones plus spirolactones; these toxins have been demonstrated on mold-damaged building materials.  The closely related species Memnoniella echinata occurs on the same materials but does not produce potent trichothecenes.  Both chemotypes of S. charatum and M. echinata typically occur together on samples of very wet cellulosic materials with M. echinata being more important in warmer climates.  This fungus does not cause invasive disease.  Antigens to S. chartarum have been identified.


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