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Occurrence of the Mould Chaetomium in Indoor Environment: What Are the Implications?

Chaetomium is a cellulose degrading mould commonly found in soil, air, and decaying plant material. There are several species of Chaetomium. The most common ones are Chaetomium atrobrunneum, Chaetomium funicola, Chaetomium globosum, and Chaetomium murorum. In indoor environment the most common species of Chaetomium is Chaetomium globosum. Presence of Chaetomium species in indoor environment is a sign of serious water problem. Chaetomium may occur together with other water-loving moulds such Fusarium, Stachybotrys and Ulocladium. Species of Chaetomium are known to produce mycotoxins but to what extent these toxins contribute to poor indoor air quality or affect human health is not documented. In the medical literature some species have been reported to cause disease in immuno-compromised individuals.

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Moulds: How Are They Named?

Non-biologists often find names given to moulds difficult. The current system of naming fungi (the kingdom to which moulds belong) and other living organisms including plants and animals was introduced by Linnaeus in 1753. In this system (referred to as binomial nomenclature) an organism is identified by 2 names, i.e., the generic name and a specific name. For example, for Aspergillus niger, the generic name is Aspergillus and the specific name (or epithet) is niger. These names may be descriptive or given to commemorate the work of researchers or benefactors, or the place where the fungus was found; thus Aspergillus chevalieri is named after the French mycologist F.F. Chevallier (1796-1840), and Aspergillus amstelodami was originally discovered in Amsterdam. Aspergillus niger is descriptive. It refers to a mould with conidiophores (spore bearing structures) which are swollen at the apex, which produces chains of conidia (spores) and that the fungus is black (Latin: niger), and that it has the appearance of a mop (Latin: aspergillum).

Sometimes a fungus (plural is fungi) may have more than one name. For example Stachybotrys chartarum is still called by some people as Stachybotrys atra. This happens when the name of a fungus is changed. Name changing occurs if the original description of the fungus was inadequate so that the fungus is not recognizable to others and subsequently given new name(s) or through recognizing spurious differences between individuals as taxonomically significant. Much of the duplication is due simply to the enormous body of literature which must be searched through to find previously-published names which may be applied to apparently new species. A fungus may also be referred by more than one name if it exists in different forms (or states). Each form may have a different name.

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Cladosporium: A Common Allergenic Indoor Mould

Cladosporium is a leaf mould and one of the most common in outdoor and indoor air worldwide. It is a very common household mould in bathrooms, around tubs, shower stalls, or window frames and even bathroom walls and ceilings.  Like every other mould, it requires free water for growth.  Around the edge of the tub there is water from splashing or water running down the wall from the shower.  The water just sits around the edge of the tub and may evaporate very slowly.  On walls and ceilings  the steamy air results in condensate, especially on colder, outer walls.  The spores are ubiquitous and will germinate in this available water and  very quickly little dark brown colonies start to grow.  Eventually there will be an olive-brown to blackish brown growth of Cladosporium around the tub.

Some species of Cladosporium cause serious diseases to plants. The mold is commonly isolated from air, soil, foodstuffs, stored fruits, cereal grains, groundnuts, paint, and textiles. Cladosporium is a well known allergenic mould. The most common Cladosporium species in outdoor air are Cladosporium cladosporioides and Cladosporium herbarum. During summer there can be very high concentrations of airborne spores of Cladosporium cladosporioides and Cladosporium herbarum, and both contain allergenic proteins in their spores. Cladosporium cladosporioides and Cladosporium hebarum may be found colonizing painted metal surfaces of covering panels and vents of heating, air conditioning and ventilation systems.Cladosporium sp.

Cladosporium sphaerospermum is the most predominant species growing in buildings. Studies have shown it can outgrow Penicillium chrysogenum because of its ability to re-initiate growth from the hyphal tips much faster than Penicillium species. Cladosporium sphaerospermum and occasionally Cladosporium herbarum is frequently isolated from indoor surfaces such as in bathrooms, windowsills and damp painted surfaces. It is also commonly found colonizing wood.

Species of Cladosporium are not known to produce any serious mycotoxins.

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Water Damaged Homes: The Primary, Secondary and Tertiary Colonizers.

If a water problem in a building is not repaired and the water dried out within 48 hours, growth of mould and other microorganisms would naturally occur. The types of moulds predominant at anyone time would be determined by the level of moisture in the building material. This level of moisture is usually referred to as the water activity and it determines the order in which different categories of moulds appear. The first group of moulds to appear (at water activities less than 0.85) is referred to as the primary colonizers, the second group (at water activities of 0.85-0.90) is secondary colonizers and the third group (at water activities greater than 0.90) is the tertiary colonizers.

Primary colonizers
The primary colonizers are capable of growing at water activities below 0.85. This group may include Alternaria citri, Eurotium amstelodami, Aspergillus candidus, Aspergillus glaucus, Aspergillus niger, Aspergillus penicillioides, Aspergillus repens, Aspergillus restrictus, Aspergillus versicolor, Paecilomyces variotii, Penicillium aurantiogriseum, Penicillium brevicompactum, Penicillium chrysogenum, Penicillium commune, Penicillium expansum, Penicillium griseofulvum, and Wallemia sebi.

Secondary colonizers
Secondary colonizers grow best at water activities of 0.85 to 0.90. Secondary colonizers may include Aspergillus flavus, Cladosporium cladosporioides, Cladosporium herbarum, Cladosporium sphaerospermum, Mucor circinelloides, and Rhizopus oryzae.

Tertiary colonizers
At water activities greater than 0.90, tertiary colonizers appear. These may include Alternaria alternata, Aspergillus fumigatus, Epicoccum spp., Exophiala spp., Fusarium moniliforme, Mucor plumbeus, Phoma herbarum, Phialophora spp., Rhizopus spp., Stachybotrys chartarum, Trichoderma spp., Ulocladium spp., Rhodotorula spp., Sporobolomyces spp., and Actinomycetes.

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The Mould Stachybotrys chartarum: Why Is It So Feared?

The health effects due to the mould Stachybotrys chartarum are controversial. Stachybotrys chartarum, also known by an old name as Stachybotrys atra, is a cellulose degrading fungus commonly found in soil and on materials rich in cellulose such as hay, straw, cereal grains, plant debris, wood pulp, paper, and cotton. Although Stachybotrys chartarum mainly survives as a saprophyte (i.e., by feeding on dead organic material), it has also been reported to cause root lesions on soybean.

Why is Stachybotrys chartarum so feared?
The first reports associating Stachybotrys chartarum with ill-health dates back to the 1930s. Horses and other animals fed with straw and grains in Ukraine and other parts of eastern Europe were found to develop disease symptoms such as irritation of the mouth, throat, and nose; shock; dermal necrosis; a decrease in leukocytes; hemorrhage; nervous disorder; and death. Russian scientists, in 1938 conducted intensive studies and demonstrated that these symptoms were due to mycotoxins produced by Stachybotrys chartarum that had grown on the cellulose rich straw. The disorders were subsequently named stachybotryotoxicosis. Stachybotrys chartarum, conidiophores and spores as seen under a microscopeStachybotryotoxicosis has also been reported in farm workers who handled contaminated straw. Recent studies have shown spores of Stachybotrys chartarum to contain high concentrations of highly toxic mycotoxins. In 1993-1994 an outbreak of pulmonary hemorrhage in infants in Cleveland, Ohio,USA, was initially attributed to Stachybotrys chartarum. Since this incidence, this mould has received a lot of media attention in North America and has been given various names such as “toxic mould” and “black mould”. Although studies associating the outbreak with this mould were later reviewed and thought not to provide enough evidence to associate the disease with Stachybotrys chartarum, there are still no studies to date to prove or disapprove this claim.

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Salmonella food poisoning and symptoms

Salmonella food poisoning has been a growing concern in recent news. It has frequently lead to recalls of beef, salads and organic products and, even peanut butter products. Salmonella food poisoning occurs when one eats raw or undercooked foods such meat, poultry, eggs or egg products. Properly cooked food can get contaminated with Salmonella if […]

Legionella pneumophila – Guidelines for Laboratory Interpretation

Legionella pneumophila is a Gram negative, aerobic bacteria that is characterized as an opportunistic pathogen. It is the cause of Legionnaires’ Disease, a severe form of pneumonia and, it is the cause of Pontiac fever, a non-pneumonic form of L. pneumophila infection. Legionella spp.’s mode of transmission is through aerosols or aspiration of contaminated water. The Public Health […]

The Indoor Mold Is An Early Warning Device

The mold (or mould, in the Queen’s English) has been the victim of a bad press. Mention the word and it conjures up an image of something rotting or in the process of decomposition. And yet, were it not for the mold that inspired the discovery of penicillin millions of lives would have been lost. […]