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Bacteria growing like mould

They grow like mould in a cluster and can form spores. They are often confused with mould. They often cause a musty, earthy smell indoors. It has not yet been conclusively determined if they can be attributed to diseases. It is assumed that some of these bacteria can trigger allergies.

Adhesive film test

Analysing mould on surfaces by means of cultivation

During an adhesive film test, an adequately prepared culture medium is pressed onto a surface that is presumed to have been inflicted by a mould infestation. Spores and hyphal fragments remain stuck to the culture medium and grow into visible colonies. The adhesive film test is not suitable for monitoring the remediation success because settling spores are also captured.

Airborne bacteria measurement

Proof of mould spores in the ambient air

Mould spores are sucked up and with the help of a special collection head are isolated on a culture medium where they grow into visible colonies. As a general rule, 100 l of ambient air are taken per measurement. Lower amounts of air can be tested in the case of heavy contamination, otherwise the culture medium is overloaded and the counting of single colonies is no longer possible. If there is no visible infestation, 200 l of ambient air can be taken to analyse the spore contamination. It always makes sense to take measurements in several rooms of a building. At the same time as taking indoor measurements, it is always necessary to take an outdoor air measurement as the spores from outside are also found inside buildings. It is not practical to take outdoor air measurements in the rain or wind.
An airborne bacteria measurement is one of the most meaningful tests as defined amounts of air are used for verification purposes. It only registers living (germinable) spores.
The mould is cultured and counted on so-called agar plates after an airborne bacteria measurement. The laboratory can subsequently not only evaluate which types of mould are present but also the quantities of germinable spores in a defined area (m³). The quantities are determined using CFUs (colony-forming units).


A substance triggering allergies

It is now assumed that almost every mould species can trigger allergies regardless of their infectious or toxic potential. Certain types of mould are known for their great allergenic potential, such as types of the Alternaria species. The mould spores are generally the decisive factor in the occurrence of a mould allergy.


Biocides / fungicides

Substances to kill pests

Biocides are active ingredients (chemicals or microorganisms) that are used to combat harmful organisms (e.g. mould, bacteria, insects). Products that are particularly effective in combating mould (fungi) are called fungicides. Biocides are regulated in accordance with the Biocidal Products Directive. Users of biocidal products should bear in mind that some active ingredients may be harmful to health and dangerous. These hazardous substances should not be used. It is preferable to use user and environmentally friendly oxygen-releasing agents based on hydrogen peroxide that work with a concentration < 5% and are stabilised with fruit acids from the food sector.


Coliform bacteria

Information about faecal contamination

Escherichia coli and other lactose degrading enterobacteria living in the gut must never occur in drinking water. Danger caused by these bacteria, for example, in the case of a flood or after faecal contamination (burst pipes etc.)

Contact test

Analysing the types of mould on surfaces by means of adhesive film

Mould is transferred from the material directly onto a transparent adhesive film. Proof is established microscopically in a laboratory. It is not possible to assess whether the spores are living or dead. If mycelium can also be identified on the adhesive film in addition to spores, the mould growth on the material has been thereby proven.

Culture medium

Substrate for the cultivation of microorganisms

The use of malt extract medium (universal culture medium for fungi) and DG18 medium (special culture medium for fungi indoors adapted to the often slightly drier conditions) have become commonplace for the cultivation of mould from indoors. Through the addition of agar, the intrinsically liquid culture media solidify (in the same way as gelatin) and can be handled practically in petri dishes.



changing the microorganisms into a state in which they can no longer infect

Disinfection is defined as the killing of bacteria to the extent that not one of the original 100,000 replicable bacteria (so-called colony-forming units = CFUs) continues to survive following the disinfection. There are a variety of active ingredients and products in the area of disinfection. Active ingredients can have very different effects that can also be attributed to differences in the microorganisms to be controlled. It is advisable to always use the product that is the least harmful to the user and the environment, provided that it always achieves an adequate effect.



Cell threads of mould

The cell threads that form after the germination of the spores.


Material sample (mould)

Determining a mould infestation on carrier material

When identifying mould on an infested material, it is paramount to differentiate between the types of mould to assess the risk to health and the scope and urgency of the remediation. The material sample taken is crushed in a laboratory and suspended in a sterile solution, and then several dilutions are spread onto fungal culture media. The analysis of a weighed quantity is recommended in order to strive for an approximate comparability between the material samples analysed. When analysing the material, it is important to differentiate between the types of mould present in addition to determining the concentration in order to offer a well-grounded statement.


Microbial volatile organic compounds

Microorganisms release gases into the ambient air, not spores. These gaseous substances occur when there is a growth of fungi and bacteria and even a smell is perceptible in some cases. For example, various microorganisms produce geosmin, a strong-smelling compound. It is produced by many actinomycetes and exponents of the fungal species Chaetomium. Geosmin is often responsible for the musty smell in buildings. The term MVOC was formed on the basis of the acronym VOC, which describes volatile (easily migrating in the air) organic modules (indoors e.g. vapours from building materials etc.). MVOCs are essentially measured in the same way as VOCs.


Mass of hyphae

The mycelium is the vegetative part of the mould, consisting of hyphal threads that are spread by continuous growth and the formation of new hyphae if there is sufficient moisture and an adequate source of nutrients.


Toxic compounds produced by mould

Secondary metabolites produced by different types of mould. About 200 different toxins are known that are produced by over 300 different types of fungi. It is assumed that the formation of mycotoxins are dependent on a number of conditions. The toxins from Stachybotys chartarum and Aspergillus flavus are known and classified as dangerous. Mycotoxins pose a threat to humans primarily through mouldy food. The threat to humans from mycotoxins produced due to a mould infestation indoors is quite low because the toxic potential of the spores alone can generally be neglected. However, it is assumed with Stachybotrys chartarum that poisoning symptoms can be triggered by simply breathing in the spores.


Particle sampling

Collection and analysis of particles in the ambient air

With this type of ambient air measurement, the particular components of a defined volume of air are sucked in through a particle sampler and isolated on a slide with a special coating (slotted nozzle impaction). These particle traces are analysed microscopically for mould spores, where it is not possible to differentiate between living and dead spores. This method of ambient air measurement is performed after remediation measures for a mould infestation. Large numbers of spores and particle quantities indicate that no or insufficient deep cleaning measures have been carried out.


Sedimentation sampling

Collection of airborne mould spores

The sedimentation process (open petri dish process) is defined as the collection of airborne bacteria by means of an open petri dish. Mould spores in the air settle on the plates filled with culture medium. The plates are closed again after a certain period of time and the spores that had landed on them grow into visible colonies. As no specific volume of air is used for the sampling, the method is heavily dependent on random air movements and the results obtained are not very meaningful.


Mould reproduction form

Mould spores are not visible with the naked eye. They serve to reproduce mould. A single spore is enough to cause a mould infestation under the appropriate conditions (moisture, nutrients). In the case of a heavy mould infestation, millions of spores can be found in a single cm² depending on the type of mould. Mould develops different spores depending on the type with varying degrees of volatility. Many spores can be spread over an extensive area due to a small draught, others are carried by mites, insects etc. Mould spores can also be responsible diseases among humans and animals.


Thermal bridge

Area in components through which the heat is transported much quicker to the outside.

A distinction is made between structural, geometric and material thermal bridges. In the area of thermal bridges, the room-side surface temperature drops more sharply than in normal areas when the temperatures outside are cold. There is a risk of condensate forming with a subsequent mould infestation.

Types of mould

Types of mould are defined as fungi forming their spores directly on the mycelium (i.e. not on or in specially formed fruiting bodies). The number of types of mould spread globally is estimated at more than 100,000, a large number of which only occur in nature. About 20 species are largely found indoors. The most important exponents of these indoor pests can be found on our separate page on mould (specialist information). Here you will find explanations concerning mould species such as Aspergillus, Penicillium, Stachybotrys etc. and their different types.
Mould needs nutrients and water (moisture) in order to grow. Since the source of nutrients for mould is present almost everywhere, the avoidance of moisture is a crucial factor in preventing a mould infestation indoors. Excessive moisture is always the cause of mould damage in any form (water damage, building defects, user behaviour).