A number of methods can be used to test air for mold or other microbial contamination. One of the oldest methods of testing air for microbial contamination is the settle plates method. Though the method is semi-quantitative, it is still considered a useful method. In industries such as food, pharmaceutical and cosmetics the method is used to assess the likely number of microorganisms depositing onto the product or surface in a given time. The method involves opening and exposing petri dishes containing agar medium suitable for growth of microorganisms of interest. If one is interested in testing for mold, agar plates containing malt extract agar (MEA) supplemented with some antibiotics to suppress bacterial growth would be used. The agar plates are left open at table-top level at selected points in the room for half-hour to 4 hours. This allows mold spores and fragments to settle onto agar media by gravity. Mold test kits (involving growth media) are settle plates.

Settle Plates Results

The number of microorganisms deposited onto the agar surface of the plate over the period of exposure is determined by incubation of the agar plates at 25ºC for 5- 7 days and counting colonies that develop. The results can be expressed as number of colony forming units (CFUs) per unit time. The counted colonies can then be further characterised to genera or species. Higher numbers of CFUs and/or presence of potential pathogenic or toxigenic molds such Aspergillus fumigatus and Stachybotyrs chartarum are indicators of a problem.

Disadvantages of Settle Plates

Settle plate method is an extremely useful method for assessing air contamination by microorganisms. It is easy to conduct and very cost effective. However, only viable microorganisms would be detected by this method and hence it may give a false impression that the air is "clean" if most of the airborne microorgainisms are dead. False negatives may also be obtained from buildings with:

• very restricted mold growths.
• very still air in undisturbed rooms.
• species of poorly culturable molds (e.g., Stachybotrys chartarum).
• molds consisting of species with poor airborne dissemination (e.g., Aureobasidium on windowsills, Cladosporium on painted cold air vents, Fusarium and many other wet-spored fungi).

Mold Sampling

The mold sampling method one chooses should be determined by the objective of the investigation. One may sample air or surfaces for mold contamination. The standard method for sampling air is to use a volumetric sampler e.g. RCS or Andersen N6 for viable airborne spores and hyphal fragments and Air-O-Cell, VersaTrap, Allergenco and others such cassettes for total spore counts. Testing of surfaces may involve use of RODAC agar plates for smooth surfaces, and swabs and adhesive tape on all other surfaces. It is important to note that adhesive tapes may not work well on wet and porous surfaces. Bulk samples can also be taken and plated onto agar plates or analysed by direct microscopic examination. Dust samples can be collect from surfaces such as carpets, upholstered furniture and textiles.

Media For Mold Sampling

If one decides to collect viable air samples, the choice of media to use is very important. Generally, malt extract agar (MEA) is used. It is a "broad spectrum" medium that supports the growth of a wide range of fungal species. However, antibiotics may have to be incorporated to surpress bacteria growth. Its main disadvantage is that fast growing molds tend to overgrow slow growers making it difficult to count colonies. To overcome this problem, DG18 and Rose Bengal can be used. These media have compounds added to them to slow down fast growing fungi and inhibit bacterial growth. If one is sampling a relatively dry environment, MEA+40% sucrose would be recommended for detecting xerophilic (dry loving) fungi.

Mold Identification

Currently, the only reliable means for routine identification of mold species is to perform traditional mycological methods. This requires years of training and practice. Be sure to use a lab that has a qualified Mycologist on-board (preferably at PhD level). The lab should also be regularly participating in a recognised proficiency testing program such as the AIHA EMPAT program.

Performing Effective Mold Sampling

If you need to take mold samples, use properly trained personnel or to get yourself trained. If you decide to undergo training, select a mold training course that provides skills and background information to enable you recognize indoor mold, develop effective sampling strategies, and interpret laboratory results.

Mold Sampling

The mold sampling method one chooses should be determined by the objective of the
investigation. One may sample air or surfaces for mold contamination. The standard
method for sampling air is to use a volumetric sampler e.g. RCS or Andersen N6 for
viable airborne spores and hyphal fragments and Air-O-Cell, VersaTrap, Allergenco and others such cassettes for total spore counts. Testing of surfaces may involve use of RODAC agar plates for smooth surfaces, and swabs and adhesive tape on all other surfaces. It is important to note that adhesive tapes may not work well on wet and porous surfaces. Bulk samples can also be taken and plated onto agar plates or analysed by direct microscopic examination. Dust samples can be collect from surfaces such as carpets, upholstered furniture and textiles.

Media For Mold Sampling

If one decides to collect viable air samples, the choice of media to use is very
important. Generally, malt extract agar (MEA) is used. It is a "broad spectrum" medium that supports the growth of a wide range of fungal species. However, antibiotics may have to be incorporated to surpress bacteria growth. Its main disadvantage is that fast growing molds tend to overgrow slow growers making it difficult to count colonies. To overcome this problem, DG18 and Rose Bengal can be used. These media have compounds added to them to slow down fast growing fungi and inhibit bacterial growth. If one is sampling a relatively dry environment, MEA+40% sucrose would be recommended for detecting xerophilic (dry loving) fungi.

Mold Identification

Currently, the only reliable means for routine identification of mold species is to
perform traditional mycological methods. This requires years of training and practice. Be sure to use a lab that has a qualified Mycologist on-board (preferably at PhD level). The lab should also be regularly participating in a recognised proficiency testing program such as the AIHA EMPAT program.

Performing Effective Mold Sampling

If you need to take mold samples, use properly trained personnel or to get yourself
trained. If you decide to undergo training, select a mold training course that provides skills and background information to enable you recognize indoor mold, develop effective sampling strategies, and interpret laboratory results.