6.4 Penicillium

Penicillium is a very large group of fungi valued as a producer of antibiotics. Penicillium is commonly found in the soil; in the air; on living vegetation, seeds, grains, and animals; and on wet insulation. Penicillium has been associated with hypersensitivity pneumonitis in some individuals when it is present in high concentrations.

Penicillium is a source of antibiotic lines that have aided humanity. However, not all species of Penicillium are helpful. Some can cause allergic reactions and other adverse health effects when dispersed through indoor air. Currently, more and more is being learned about the effects of Penicillium and other microbiologicals in indoor air. This sec­tion represents a starting discussion of the risks associated with the growth of Penicillium within indoor air environments.

Penicillium is a fungus that grows when moisture, food, and just the right temperatures are available. Penicillium's spherical spores are produced in long, unbranched chains of each conidiophore. These usually fragment into individual spores, although chains of spores are seen periodically on slides. Although some species of Penicillium appear to reproduce solely by asexual means, some species of Penicillium are the anamorph (asexual) stage of the ascomycete genus Talaromyces.

6.4.1 What Do Samples Look Like?

When samples are freshly prepared from culture, the spores are pale green, although this fades with age. Their size ranges from 3 to 5 (ллп. When using visual methods of iden­tification, Aspergillus and Penicillium cannot be differentiated because the spores are so sim­ilar that they are grouped together into the Aspergillus IPenicillium group. Spores from this group are found almost all year-round.

6.4.2 What Species of Penicillium Are Used to Produce Antibiotics?

Penicillin, as produced by Alexander Fleming in 1929, was a product of Penicillium notatum. Since that time, other species of Penicillium have been used to form other antibi­otics. As an example, Griseofulvin is an antifungal antibiotic formed from a species of Penicillium.

6.4.3 What Other Fungi Grow Where Penicillium Grows?

Aspergillus, Penicillium, Verticillium, Alternaria, and Fusarium are all found in the order Moniliales and have similar morphology. Thus, where Aspergillus is found, one may expect to find Penicillium and vice versa. The key here is the relative presence of moisture that may accelerate the growth of one particular fungus rather than another.

6.4.4 If Penicillium Grows Everywhere, What Is the Concern?

The concern is that, in most cases, we do not want Penicillium growing inside us. This warning is especially true if an individual is immune compromised.

People sensitized to Penicillium, the very young, the aging population, and people with certain illnesses, could be considered immune compromised. These individuals may react more strongly (and often more negatively) to some Penicillium species entering their bodies.

6.4.5 How Does Penicillium Enter the Body?

The route of entry into the body is unknown. However, the respiratory route is used by many other fungi with abundant conidia. Penicillium may have abundant conidia; thus, the respiratory route of entry is expected. Skin trauma has been associated with local infection, but not with systemic disease. Infection via the digestive route is unusual for filamentous fungi.

6.4.6 Are There Particular Species of Penicillium about Which I Should Be Concerned?

Within current medical literature, the primary concern is with Penicillium marneffei (P. marneffei). This species has two life formations and is the only Penicillium species that is termed dimorphic. The prevalence of one form over another is dependent on temper­ature. At 37°C the fungus grows as yeasts forming white-to-tan, soft, or convoluted colonies. Microscopically, the yeasts are spherical or oval and divide by fission rather than budding.

At 25°C the fungus produces a fast-growing, grayish floccose colony. Microscopic examination reveals septate branching hyphae with lateral and terminal conidiophores that produce unbranched, broomlike chains of oval conidia.

Inside the body P. marneffei first proliferates in the reticuloendothelial system and then is disseminated. The lungs and liver are usually the most severely involved organs. Other commonly involved organs include skin, bone marrow, intestine, spleen, kidney, lymph nodes, and tonsils.

The reticuloendothelial system is made up of special cells called phagocytes located throughout the body; they can be found in the liver, spleen, bone marrow, brain, spinal cord, and lungs. When functioning correctly, phagocytes destroy disease-causing organ­isms by ingesting the organisms. An example of these cells are histiocytes. Histiocytes try to ingest and kill P. marneffei. Unfortunately when the P. marneffei do not die, the histiocytes carry them throughout the body.