6.3 Aspergillus

Aspergillus and Penicillium are molds prevalent in soils. These molds can cause asthma-like symptoms or other lung irritation in humans and deterioration in buildings and other materials. When conditions within buildings cause the buildup of moisture on surfaces and temperatures are right, Aspergillus grows well and is evidenced by a black deposit.

Aspergillus is a type of mold called Ascomycota or sac fungi. Sac fungi have sexual spores that are produced in an ascus or saclike structure. Their asexual spores, called coni-diospores (from the word conidia, which means "dust"), are produced in long chains from a conidiophore. The characteristic arrangement of the conidiospores is used to identify the different molds. Penicillium is another mold that is also called Ascomycetes.

6.3.1 What Color Are These Molds?

Aspergillus is black, and Penicillium is white. Also, Aspergillus is not the black mold on bread. That mold is Rhizopus nigricans. The difference is evident in the differing structures for black asexual spores (sporangiospores).

6.3.2 How Is Aspergillus Spread?

Aspergillus spores are carried in the wind and through ventilation airstreams in homes. The asexual spores freely detach from the conidiophore chain and, with the slightest dis­turbance, float in the air like dust. The easiest way to get Aspergillus started in the home is to bring the spores in on shoes and deposit the spores on carpet fibers.

6.3.3 How Does Aspergillus Grow/Amplify?

When the spores are placed on wet surfaces, the spores grow hyphae. The hyphae grow, form a mass, and are soon visible to the naked eye. The vegetative mycelium process foods, and reproductive mycelium create more spores. At this time the mold /fungi appears as a black fuzzy mass. (Amplification is the process whereby Aspergillus or other biological organisms continue to increase in number over time.)

6.3.4 What Conditions Help Aspergillus Grow/Amplify?

Fungi generally grow better with an acidic pH. The growth is usually on the surface rather than embedded within a substrate (under the surface).

Fungi are able to grow on surfaces with a low moisture content, in contrast to the mois­ture required for bacterial growth. Therefore, even a slight difference in temperature and surface moisture facilitates the growth of fungi.

Fungi are capable of using complex carbohydrates, such as lignin (wood). Thus, with a little moisture, fungi can easily grow on wood or other complex organic materials. These adaptations allow fungi to grow readily on painted walls and shoe leather.

6.3.5 Can Mold/Fungi Make You Sick?

Fungal diseases are called mycoses, which are chronic, long-lasting infections. Aspergillosis is an opportunistic infection that can become pathogenic (disease-causing) in a weakened individual host. The inhalation of spores is a possible mode of entry into the body as spore size ranges from 2 to 10 |xm.

6.3.6 What Are the Symptoms of Aspergillosis?

The incubation period varies with different individuals. People with other weakening medical problems or general ill health are most susceptible. Aspergillus niger (A. niger) pro­duces mycotoxins that can induce asthma-like symptoms. In situations when A. niger was found growing with Penicillium sp., massive inhalation of spores has been documented as causing an acute, diffuse, self-limiting pneumonitis (lung irritation). Healthy individuals can exhibit otitis externa (inflammation of the outer ear canal) as a result of Aspergillus growth.

6.3.7 Does Aspergillus Cause Deterioration of Materials?

Members of the Aspergillus genus are known as biodeteriogens (organisms that cause deterioration of materials). A. niger causes damage, discoloration, and softening of the sur­faces of woods, even in the presence of wood preservatives. A. niger also causes damage to cellulose materials, hides, and cotton fibers. A. niger can also attack plastics and polymers (i.e., cellulose nitrate, polyvinyl acetate, polyester type polyurethanes).

6.3.8 What Happens If Aspergillus Colonies Grow inside Construction Layers?

In cases of extensive growth, colonies will grow into wood, plaster, and/or dry-wall, causing a soft bulging area. This area lacks structural integrity and is subject to early deterioration.

6.3.9 How Is Aspergillus Identified?

Soy agar will grow Aspergillus and a wide range of other microbiologicals. Thus, Tryptic Soy Agar or Potato Dextrose Agar is the original screening tool used to determine the presence of biologicals. Once biological contamination has been established, selective media can be used to grow suspect organisms for identification. Using a special type of pro­tein gelatin (called Rose Bengal Agar) that has been made with special nutrients, Aspergillus cultures can be selectively and quickly grown.

6.3.10 How Are Levels of Aspergillus Communicated?

Aspergillus is reported in terms of colony forming units per cubic meter. The presence of any one fungi in excess of 200 CFU/m³ is indicative of an indoor source of fungal amplification. The presence of any colony forming units per cubic meter is indicative of transmission of fungal spores from surface to surface and/or from exterior to interior locations.

6.3.11 Why Do Aspergillus Colonies Look Black?

Aspergillus is black or brown-black. Also, active biological contamination creates a sur­face to which dusts and other debris "stick." If biological contamination is extensive and characterized by amplification and "kill" cycle condition, the fungi/molds will decay and produce toxins. These toxins can be identified with Aspergillus contamination as a black stain or tarlike liquid residue.

6.3.12 What Will Biotesting of the Air Show?

Biotesting using a BIOTEST air monitor will reveal whether colony forming units are found in the air. Biotesting by surface culturing on agar reveals the presence of biologicals on surfaces and in waters.

6.3.13 What Can Be Done to Prevent Aspergillus Growth?

Keep the air dry, provide filtered replacement air, and have sufficient air exchanges. Prevent accumulation of standing water or leaks.