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You are here: Home / Archives for primary colonizers

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

Jackson Kung'u

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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Filed Under: Fungi Tagged With: primary colonizers, secondary colonizers, tertiary colonizers, water activity

How Old Is The Mould In My House?

Jackson Kung'u

Often, people wonder if it was possible to tell how old mould growing in a house was and/or whether the mould was actively growing and what the source of the mould was. The answers to these questions would help in situations where say somebody buys a house and some months later they discover mould. If they would tell the mould was there before buying the property, they would follow it up with the seller for not disclosing the mould problem. Unfortunately there are no simple tests that can tell us the age of mould growing in a house, whether it is actively growing and the source. We can only speculate on a range of number of days since the current growth appeared and whether it was likely to be actively growing. It would be difficult to tell the source of the mould and how long it has been there before the growth was seen.

How moulds interact in nature

Mould propagules are ubiquitous in indoor environments and are well adapted to inhabit this ecological niche if just sufficient water is available. Based on the water activity (or equilibrium relative humidity) requirements, moulds can be divided into 3 broad groups:

  • Primary colonizers

Primary colonizers (also referred to as xerophiles) are the first to appear. They are capable of growing in relatively dry conditions at water activities of between 0.6-0.8. These kinds of conditions can be achieved through slow leaking pipes, condensation or other sources of moisture. At this low water activity viable propagules (spores and mycelial fragments) of species of Wallemia, Penicillium, Aspergillus and Eurotium would germinate and form growth.

  • Secondary colonizers.

As the water activity of the building material increases to between 0.8 and 0.9, the secondary colonizers would proliferate. Secondary colonizers include species of Cladosporium, Phoma, Ulocladium, Alternaria and also some species of Aspergillus such as A. flavus and A. versicolor. If nutrients are still available on the substrate and the water activity remains unchanged the secondary colonizers would gradually become the dominant moulds.

  • Tertiary colonizers.

At water activity of 0.9 and above, the water loving moulds (also called hydrophiles) would dominate as the tertiary colonizers. These levels of water activity are generally only met by incoming water as under flooding conditions and not just high humidity or condensation on indoor surfaces. Immediately after the flooding or serious water leakage, for example, all types of moulds would colonize the wet building material but with those that require higher water activity dominating. Presence of tertiary colonizers in a building is an indication of a serious water problem. Tertiary colonizers include moulds such as Stachybotrys, Chaetomium, Ulocladium, Trichoderma, Aureobasidium as well as actinomycetes and other bacteria.

 

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Filed Under: Fungi Tagged With: mould, primary colonizers, secondary colonizers, tertially colonizers

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