Pollen | Microorganism of the Month: Scopulariopsis species
By Dr. Harriet Burge, EMLab P&K Chief Aerobiologist and Director of Scientific Advisory Board
The presence of an abundance of arthropod fragments on a spore trap sample may indicate the existence of an infestation and be an indication that allergen exposure is occurring. An entomologist could probably give a good indication of which arthropods are involved, but most analysts can only recognize the particles as arthropod-derived. Although allergens in themselves are not visible on spore trap samples because they dissolve in the mounting medium, the particles on which they are borne may be visible. Dust mite fecal balls, which contain most of the dust mite allergen, may appear on spore trap samples if the samples were collected during disturbance.
Animal hair and bird feathers are generally not allergenic, although they may carry allergens. The presence of animal hair and/or feathers is an indication of the presence of the creatures, and could also indicate the presence of allergens. However, specific allergen assays are available that are more reliable indicators of allergen exposure. Again, spore trapping is not the ideal way to evaluate exposure since good immunoassays are available.
Pollen is the one allergen source that is readily recognized on spore trap samples. Pollen grains are distinctive, and can be specifically identified by some analysts. Pollen is shed from wind-pollinated plants with inconspicuous flowers. In the eastern USA, the golden yellow flower heads of goldenrod (Solidago sp.) is often blamed for fall allergy symptoms when, in fact, it is the inconspicuous ragweed plant (Ambrosia sp) that is producing the sensitizing pollen. In the western USA, Acacia (genus of shrubs and trees) is often blamed for juniper pollen allergies. In general, if a flower is pretty enough to bring indoors, it is insect pollinated and produces little or no airborne pollen. On the other hand, I have encountered people who have become sensitized to, for example, daffodils, because of intense exposure in flower farming situations.
In more than 40 years of viewing spore trap slides, I have seen only one case of indoor pollen production, and that sample was collected while the homeowner was vigorously brushing the surface of a flowering Impatiens plant while the sample was being collected. The vast majority of indoor pollen has penetrated from outdoors. The grains are relatively large (10-50 microns in diameter with an average of about 20). Thus they are readily filtered from the air in closed buildings, and indoors they settle quickly. Pollen exposure is highly seasonal, and therefore most people know to which pollens they are sensitized. Newly sensitized people may blame other factors for symptoms (e.g., their home or office environment) when, in fact, they have developed a new sensitivity. It generally takes several years of exposure to a new pollen type before symptoms begin to occur.!
Human skin scales are always abundant in indoor dust, and may be trapped on air samples. They are relatively large, and tend to settle quickly. They can become fragmented, but these fragments are not generally identifiable as such. Human skin scales in themselves are not allergenic. Human to human allergies are extremely rare, and would convey a strong evolutionary disadvantage. One study estimates that animal proteins must have a similarity to the equivalent human protein of less than 54% in order to be allergenic. Note that developing sensitivity to ones own body components is not rare, and is called autoimmune disease. Skin scales do carry bacteria (an average of about 5/scale) and serve as a food source for some fungi.
Ash and other particles released from the combustion of biological material may become abundant indoors. Burning candles, cigarettes, cigars, wood, oil, etc., will produce these particles and they will be obvious on spore trap samples. The very tiniest of these particles are considered to carry the most risk of illness, and these are not visible or countable on spore traps. The larger particles that could be counted are less likely to have serious health effects. The presence of these larger particles may, however, indicate that activities generating the smaller particles are occurring.
Wood and other plant fibers and particles may also be recovered on indoor spore trap samples. Trichomes are plant hairs that are often recovered in outdoor air especially where oak trees are abundant. During harvesting operations, sharp hairs from the surface of soybean leaves may reach millions/cubic meter of air, and may cause significant skin and mucous membrane irritation. As with pollen, these fibers are unlikely to have indoor sources.
Many fibers may be present in indoor air, although some disturbance is usually necessary to make them airborne. Our fabrics are constructed of biological fibers (cotton, wool, linen) or fibers made of biological materials. These fibers are generally not sufficiently abundant indoors to cause problems. Note that people who consider themselves hypersensitive tend to be able to wear cotton, the fibers of which are quite short (an inch or less) and do shed into the air.
Sawdust contains small particles that can become airborne and can cause respiratory irritation and even allergies if exposure occurs over a long period of time. Short term remediation efforts are unlikely to produce this kind of sensitivity, but using (for example) a table saw in a basement that shares ventilation with the rest of a home, could cause problems.
Starch grains can be abundant indoors, primarily because many carpet cleaners contain large quantities of cornstarch. These grains are distinctive and can be recognized on spore trap slides. Pure starch is unlikely to be allergenic, but may cause irritation. Note that starch granules released from grass pollen have been shown to carry grass pollen allergens. Cornstarch has also been used in latex gloves (as has talc) and latex proteins (allergens) tend to coat the starch and talc particles. These particles, then, are inhalable and may cause severe allergies.
By Diane Green, EMLab P&K Analyst
In 1907, Bainier made the initial identification of Scopulariopsis with the species S. brevicaulis. Since then several other species have been identified, including S. acremonium, S. asperula, S. brumptii, S. flava, S. fusca, and S. koningii.
Scopulariopsis is a fungus that produces one-celled, colorless to brown, pear-shaped spores in chains. The characteristic that usually makes these spores easy to identify on a spore trap (versus other chain producing fungi such as Penicillium, Aspergillus, and Paecilomyces, which are hard to distinguish from one another) is the distinctly truncated base. These spores can be smooth or roughened, depending on the species and also on the age of the spores. As the spores of different species spores mature, they may become finely to coarsely roughened.
Figure 1: Close up view of distinctive Scopulariopsis spores.
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The spore-bearing structure of Scopulariopsis is called an annellophore, a word that describes the way the spores are formed. The spores are produced in chains, and as the second spore is produced, the first is pushed away from the annellophore leaving a cylinder of cell wall material attached to the annellophore opening. When the third spore is produced, the second spore is pushed away leaving a second ring, and so forth. These rings accumulate and are characteristic of annellophores.
Scopulariopsis may produce a single annellophore or a broom-like structure called a scopula. The scopula is similar in appearance to the penicillus in Penicillium. However, the spores of Penicillium are produced on phialides, which do not have the characteristic apical rings of annellophores. The colonies of Scopulariopsis grow at a moderate to rapid rate. They have a velvety to powdery texture, and the surface color is white, cinnamon, grayish or black, never blue or green as in Penicillium. Many species of Scopulariopsis are known to have a sexual stage in the ascomycetous genus Microascus.
Figure 2: Scopulariopsis spores growing from a scopula (arrow).
Copyright © 2008 EMLab P&K
Several Scopulariopsis species are associated with infections causing skin lesions, affecting the nails (especially toenails) and causing opportunistic infections in immunocompromised people. Certain species are also known to attack bee larvae and silkworms.
Scopulariopsis is occasionally recovered from house dust where it probably uses skin scales for food. It is also occasionally recovered from both indoor and outdoor air.
1. Barron, George L. (1968): The Genera of Hyphomycetes from Soil. The Williams and Wilkins Company, Baltimore. Pp 275-278.
2. de Hoog, G.S., Guarro, J., Figueras, Gene and M.J (2000): Atlas of Clinical Fungi, Second Edition. Centraalbureau voor Schimmelcultures, The Netherlands. Pp 902-916.
3. Ellis, M.B. (1971): Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew. Pp 326-329.
This article was originally published on March 2008.