Mould Sampling and Mould Testing

mould testing

Mould sampling and testing in an integral part of any professional mould inspection. The inspector has a range of mould sampling techniques at his disposal. Each technique has its limitations and therefore it is very likely that during inspection a variety of different techniques will be used. Selection of technique depends of the ultimate goal of the investigation.

Swab, surface contact plate, and settled dust cassette surface samples are analysed by culture. Tape lifts are analysed by direct microscopic examination only, and bulk samples can be cultured and microscopically examined. In general, surface samples are collected to determine whether a surface is supporting fungal growth or if the surface is contaminated from growth site(s) elsewhere. Under normal circumstances fungal growth is obvious and visible but mould contamination may not be. Of course, almost all indoor surfaces are “contaminated” by fungal spores that settle out of the air. This contamination is a form of “background contamination.”

Mould Testing Kits

There is a variety of DIY mould test kit available on the market which may or may not include the identification of moulds. It is important to know how to use and correctly interpret the data from home mould testing kits otherwise it is just waste of your money. There are three basic types of mould test kits available on the market.

Mould swabs- Mould swabs are used to directly take a sample of the mould contaminated materials. This sample is them send to a laboratory for mould identification.

Mould settle plates- These kits work on the principle of passive settling of mould spores suspended in the indoor air onto the culture grown medium. Mould spores settle on the grown medium which contains all the nutrient mould need to grown. Settled mould spores, which are still invisible at this stage, start to grow to into visible mould colonies. Analytical laboratories call these initial colonies “colony forming units CFU”. Evaluating the number of colonies can provide some limited information about mould contamination of the air. Important points- Firstly, unless mould colonies are analysed by a professional laboratory growing mould cannot be identified with naked eye. Colour of the mould colonies is nothing to go by. Secondly, indoor mould colony counts have to be compared to the background concentration of spores in the same area at the same time otherwise the number of colonies has absolutely no meaning. Indoor count from settle plates can span from 1CFU to 100-150CFU per plate but without background comparison none of these reading tells you anything about the indoor air contamination.

Mould settle plate with identification- These kits work like the simple plate kits but are then send to a laboratory which cultures them , analyses them and provides conclusion based on the results.

Laboratory mould identification

There are several laboratories providing mould identification services. When selecting a laboratory to evaluate your mould samples the important point to consider how detail analysis is carried out by the laboratory. Laboratories can carry out mould testing from culturable samples (swabs, bulks and culture plates) to the genus levels or species level.  The genus level analysis tells you which genus the mould belong to e.g Penicillium or Alternaria. This is the basil level of analysis which does not tell you if your property is contaminated by toxic mould. For example genus penicillium contains over 300 different penicillium species from which only one is pathogenic in humans and handful of other are considered to be clinically significant.

Analysis to the species level is much more detailed and inevitably more time consuming and expensive. It tells you exactly which mould has contaminated your property. For example contamination of property by the genus Stachybotrys does not necessarily means toxic mould contamination. However Stachybotrys chartarum contamination is certainly toxic and such contamination needs to be taken seriously.

Mould bulk samples

Bulk samples or material samples are sampled from a great variety of liquid and solid. For example, pieces of wallboard, fibre board, or carpet can be analysed to determine whether hydrophilic (including cellulose degraders) or xerotolerant moulds predominate. This analysis may provide an indication of the previous moisture condition in the collected material (e.g., very wet or just damp). The presence of mostly xerotolerant Aspergillus versicolor and Aspergillus sydowii in the envelope wall samples suggests a previous damp condition as contrasted with a soaking wet condition where many hydrophilic fungi such as Acremonium and yeasts would be the most likely to dominate.

Surface Mould Testing

A sampling and analysis of settled dust especially from above floor surfaces provides an indication of microbial agents that were likely once airborne. Settled dust is heterogeneous, consisting of particles from people (e.g., skin scales), pets (e.g., Fel d1 allergen), textiles, paper, cooking and the outdoor air. The contaminant composition of settled dust can be highly variable depending on the location in a particular room or building.  Analysis of collected settled dusts for mould spore and other structures has been used forensically as a reliable indication of dampness or water damage history.

Cellotape sampling together with direct microscopy analysis provides a convenient method for identifying the types of moulds that may be present on a surface and  documenting whether mould particles on a surface are characterized as “normal deposition” or as growth, past or present, if the samples are expertly (normal deposition of spores and hyphal fragments that settle out from air). Cellotape sampling is useful in detecting the presence of fungal microcolonies (incipient mould growth) on surfaces where growth is not readily visible to the unaided eye.

Plate Mould Sampling

Plate mould samples are usually taken when the information about mould species contaminating the indoor environment. In plates samples the indoor air is either drawn across the grow plate and mould spores imbed themselves into the growth medium or are exposed to air and mould spores passively settle onto the plate surface.

Plate samples require laboratory identification of mould to get information about mould species present in the indoor environment.

Mould Spore Sampling

Spore traps are devices that collect both viable and nonviable spores as well as other morphologically distinct airborne particles (pollens, hyphal fragments, skin scales, plant hairs, textile fibres) by impaction onto a tape surface or sticky glass.

The particles collected in a spore trap are examined by direct optical microscopy in order to determine kinds of fungal genus or pollens that may be present. Mould spores can be identified by morphology at best to the genus or multigenus levels (e.g., Cladosporium, Alternaria, Penicillium– Aspergillus).

Filtration Mould Testing

Work on the principle of collecting airborne fungal elements into a collection fluid. The fluid can subsequently be concentrated by filtration to increase the detection limit of the method for organisms present as extremely low concentrations. Also, the collection fluid can be dilution plated simultaneously on different culture media selective for the growth of various kinds of fungi or bacteria.

Sampling strategies used by different laboratories can vary greatly mainly because of a variety of different sampling devices available on the market. When using culture plate impactors, it is desirable to collect a number of particles on the medium surface that is neither too high nor too low. If the concentration of moulds spores is right the mould testing can be carried out.