What is Paecilomyces?

Paecilomyces is a fungal genus which can be found widely distributed around the world in dirt, food, and dead plant material. Many environments including homes naturally have some Paecilomyces species, and this fungus does not generally cause deleterious health effects, except in people with compromised immune systems. Superficially, Paecilomyces fungi can resemble Penicillium molds, but these two genera are quite different.

These fungi form filament-like structures, spreading to create a colony of powdery mold which can have a texture similar to that of suede or velvet in some species. The colony usually starts out creamy in color, and can develop red, yellow, brown, pink, and violet hues, among others. Unlike the physically similar Penicillium, Paecilomyces does not develop greenish colonies. Some species can develop a sweetish smell, especially in the case of mature colonies.

Fungi in this genus reproduce asexually by budding and producing spores which spread to the surrounding area. Several species are thermophilic, meaning that they thrive in high temperatures. This can be problematic for people trying to eliminate them, as heat is often used in the management of molds and fungi. However, many are vulnerable to fungicides, which can be used in situations where Paecilomyces species are causing a problem such as moldy walls.

These fungi are interesting to humans for a number of reasons. The first is that many prey on nematodes, which means that Paecilomyces can be used as a form of natural pest control. The fungi colonize the bodies of nematodes, eventually killing them with an overload of toxins. Some species also attack insects such as flies, gaining entrance to the body through one of the orifices such as the mouth.

In humans, Paecilomyces can sometimes cause mycoses, fungal infections of the body, usually in the case of people with a weakened immune system. These fungi have also been known to cause infections and ulcerations in the eye, especially in the case of contact lens wearers. A Paecilomyces infection can cause a variety of symptoms, including itching and unpleasant discharges. P. lilacinus is the species most likely to cause diseases in humans.

One species, P. hepiali, is sold in the form of Jinshuibao capsules in Traditional Chinese Medicine. The fungus is cultivated as an alternative to wild Cordyceps fungi. Another common species is P. variotii, commonly cultured in labs as an example of Paecilomyces fungus. In microscopic views, these fungi form colonies which are actually rather beautiful.