Guide to Terms Used for Mold and Indoor Air Quality

Actinomycetes - Heterogeneous group of gram-positive branching filamentous bacteria that are implicated in a variety of diseases (e.g., Streptomyces spp.).

Aerobic Bacteria - Solely depends on aerobic respiration and cannot grow in the absence of oxygen to generate ATP.

AIHA - American Industrial Hygiene Association

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.

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.

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.

Ambient Air - Outdoor air surrounding an object.

Amplification - Growing microorganisms to greater numbers in laboratory agar medium or on inanimate materials.

Anaerobic Bacteria - Microorganism that grow only in complete or nearly complete absence of air or molecular oxygen.

Ascospores - Sexual spores produced in a sac-like structure called an ascus and is characteristic of the Class Ascomycetes.

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. versicolor. A. fumigatus is common in outdoor air in some regions in the fall, occurring on composting leaves and other materials.

Asthma - Disease of bronchial tubes or airways; symptoms include shortness of breath, cough, tightening of chest and wheezing.  May be aggravated by any irritant (e.g., smoke, molds, etc.).

Bacillus - Rod-shaped bacterial cellular morphology (e.g., Bacillus spp.).

Bacteria - Microscopic organisms mostly single-celled; their DNA naked rather than being enclosed in nucleus. Using gram staining technique, bacteria are either gram-positive - blue/purple or gram-negative - pink/red

Basidiospores - Type of sexual spore formed externally on a basidium and is characteristic of the Class Basidiomycetes (e.g., mushrooms).

Bioaerosol - An airborne organic contaminant that is either generated by or is itself a living organism; examples of bioaerosols are fungi, bacteria, and pollen.

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.

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. cladosporoioidesand C. herbarumare the mostcommon 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.

Cleistothecium - An enclosed ascocarp (fruiting structure), lacking a pore or opening, containing ascospores characteristic of the Class Ascomycetes.

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.

Coccus - Round bacterial cellular morphology (e.g., Micrococcus spp.).

Dematiaceous - Presence of pigmentation (brown to black color) within the cell walls of hyphae or spores of the fungus (e.g., Alternaria spp.).

Dust Mite - Microscopic arachnid; ALLERGEN, allergenic proteins derived from dust mites.

EMLAP - Environmental Microbiology Laboratory Accreditation Program that is designed specially for laboratories involved in analyzing environmental samples to evaluate microbial exposures in a variety of workplaces.

EMPAT - Environmental Microbiology Proficiency Analytical Testing Program designed by AIHA to evaluate environmental laboratories that isolate and identify microorganisms.

Endotoxin - Substance containing lipopolysaccharide (LPS) complexes found in the cell wall of bacteria; principally gram-negative bacteria; believed to play important role in many complications of sepsis such as toxic shock syndrome, DIC, and thrombocytopenia.

Eukaryotic - All organisms with one or more nuclei in their cells bounded by a nuclear membrane.

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

Fungi - Fungi are neither animals nor plants and are classified in a kingdom of their own - the Kingdom of Fungi. Fungi are eukaryotic, chemoheterotrophic organisms with cell walls containing chitin and/or cellulose. They may be unicellular (yeast) or multicellular (molds) and include a very large group of organisms, including molds, mildew, yeasts, mushrooms, bracket fungi, rusts, smuts, 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.

Genus - Comprises different species that have several important features in common but differ sufficiently to still maintain their status as individual species.

Gram-Negative Bacteria - Stain a pink to red color by gram stain and is due to difference in constituents of bacterial cell walls.

Gram-Positive Bacteria - Stain a deep blue color by gram stain and is due to difference in constituents of bacterial cell walls.

HEPA - High-Efficiency Particulate Air: Refers to a filtering system capable of trapping and retaining at least 99.97 percent of all monodispersed particles 0.3 µm in diameter or larger.

Hidden Mold - This refers to visible mold growth on building structures that is not easily seen including for example, 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 an HVAC system.

HVAC - Heating, Ventilation, Air Conditioning Unit

Hyaline - Colorless, transparent; e.g., conidia/spore as it relates to molds.

Hypersensitivity Pneumonitis (allergic alveolitis) - An allergic reaction or inflammation of alveoli and bronchioles due principally to thermophilic actinomyces (bacteria); occurs in farmers, factory workers and others who are repeatedly exposed to these agents usually through inhalation.

Hypha (plural, hyphae) - An individual fungal thread or filament of connected cells; the thread that represents the individual parts of the fungal body.

Legionnaire’s Disease - Febrile and pneumonic illness with numerous clinical presentations cause principally by Legionella pneumophila. Other than L. pneumophila, the species most commonly associated with illness are L. micdadei, L. longbeachae, L. dumoffii, and L. bozemanii.

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.

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.

Mycelium - A mat-like structure of interweaving hyphae that constitutes the vegetative body of fungi.

Mycology - Scientific study of fungi/molds.

Mycotoxins - Mycotoxins are low molecular weight 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".

Nosocomial - Hospital-acquired infections

Penicillium - Penicillium is the asexual stage of a number of ascomycetes and species of Penicilliumare 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.

Perithecium - A type of ascocarp (fruiting structure) that usually possesses an ostiole (opening) through which the ascospores are freed.

Photosynthesis - Process by which green plants and certain other organisms use energy of light to convert carbon dioxide and water into simple sugar glucose.

Prokaryotic - Organisms lacking membrane-limited nuclei and not exhibiting mitosis.

Relative Humidity - RH, Ratio of the amount of water in the air at a given temperature to the maximum amount it could hold at that temperature; expressed as a percentage.

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.

Saprophytic - Nonpathogenic saprobe; fungi that obtain nutrition from dead organic matter.

Species - Collection of microbial strains that share many common physiologic and genetic features and as a group differ notably from other species.

Spore - General term for a reproductive structure in fungi, bacteria and some plants. A spore is a microscopic unit of propagation (unicellular or multicellular, asexual or sexual) that is capable of giving rise to a new organism.

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.

Taxonomy - Science of classification.

"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.

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

Yeast - Defined morphologically as a cell that reproduces by budding formation, a process whereby an old cell pinches off a portion of itself to produce a new cell. Yeasts are generally unicellular and produce circular, mucoid, creamy, opaque, or pasty colonies on agar media.

Virus - Composed of nucleic acid genome surrounded by a protein coat; strict intracellular parasites, reproducing or replicating only within a host cell.

VOC - Volatile Organic Compounds; Chemicals containing carbon are called organic.  Volatile means that they evaporate or get into the air easily which makes them easier to inhale. VOCs are produced by many species of bacteria and fungi and are often accompanied by a foul odor.