While we are enjoying the summer, it can be a tough time for allergy sufferers. The concentrations of pollen and mold spores in outdoor environment is highest in summer months. Since mold spores and pollen tend to infiltrate into indoor environment their concentration indoors can also be very high in summer. Molds and pollen capable of causing allergic reactions in sensitive individuals are said to be allergenic. Allergy follows inhalation of large amounts of spores or pollen grains. The amounts capable of triggering allergy depends on the specific allergen and the sensitivity of the individual.
Types Of Mold Allergy
Molds as causative agents of respiratory allergy and asthma have been known since the 18th century. Allergic reactions to molds may be either immediate, developing within minutes of exposure (Type I), or delayed, occurring 4 – 8 h later (Type 111). Two of the most important allergenic molds are Alternaria alternata and Cladosporium herbarum. Concentration of these two molds are usually highest outdoors from June to October.
Fungi produce huge amounts of spores. In his book, “The Fifth Kingdom”, Dr. Bryce Kendrick, gives the following examples:
- One specimen of the common bracket fungus discharges 30,000,000,000 spores per day every day from beginning of May to the end of September
- A 2.5 cm diameter colony of the green mold, Penicillium, can produce 400,000,000 spores.
Fortunately, these huge numbers are diluted by air and we inhale far much less spore concentrations.
Allergenic Pollen
Among the well known allergenic pollen is the ragweed pollen. Individuals sensitive to ragweed pollen are also sensitive to other pollen grains such as those of poverty weed and false ragweed. Concentrations of these pollens are highest within the months of June to September depending on the flowering time of the particular weed.
The problem of using a single type of media is that some molds may not grow well (or may not grow at all) in the selected media. Hence, although such molds may be the dominant contaminants in the air, they may end up being missed or underestimated. The solution, therefore, is to use more than one type of mold sampling media or select one that is known to support a wide range of environmental molds. A good example is Malt Extract Agar (MEA). The problem with this media is that it also supports the growth of bacteria to some extent. 
If the environment sampled is contaminated with bacteria, the bacteria grow faster than molds and interfere with mold growth. This problem can be overcome by incorporating a suitable antibiotic or other suitable compounds (e.g., Rose Bengal) into MEA to suppress bacterial growth. Rose Bengal not only suppresses the growth of bacteria but also restricts the spread of fast growing molds thus making it easy for colony counting.
Direct microscopy allows identification of the dominant contaminant (at least to genus level) regardless of whether the mold is dead or cannot grow on media used.
After plating onto DG18 and MEA and incubation (see petridishes marked “B”), Stachybotrys appeared on MEA but not on DG18. These observations clearly indicate how wrong conclusions can be made if the right type of media is not used either in air sampling or culturing of bulk samples.