Paecilomyces Species

By Karen A. Santo-Pietro, M.S., EMLab P&K Analyst

Paecilomyces species are fungi common throughout the world. They are found in substrates such as soil, food, optical lenses, paper and tobacco. They are important industrially as producers of citric and gluconic acids, and antifungal antibiotics (e.g. variotin). Some species are also important agriculturally as they can stimulate the growth of important crop seedlings like barley and corn. They are significant in the indoor environment as possible causative agents of Type I (hay fever, asthma) and Type III hypersensitivity pneumonitis.

In indoor environmental testing, microscopic differentiation of this group from other small chain-forming spores in air samples such as Penicillium and Aspergillus is not possible. (However, DNA based techniques such as PCR can be used for the detection of viable and non-viable Paecilomyces fungi.) They are also readily identifiable with culture-based methods if the spore-bearing structures (conidiophores) are present. The conidiophore may be branched in a simple arrangement with one phialide (the cell that produces the spores) or into whorls (multiple phialides that arise from the same base). The phialide is swollen at the base, gradually narrows into a long beak, and gives rise to chains of colorless or slightly pigmented conidia (spores). Depending on the species, the spores appear ellipsoidal to spindle-shaped, are smooth-walled to slightly roughened, and are about 2.5 to 8 µm in length. Thick-walled chlamydospores (spores that develop from the hyphae) may be present as a single spore or in short chains. They may also appear smooth-walled or ornamented. Paecilomyces species are the asexual forms of some ascomycetes, such as Thermoascus sp. and Talaromyces sp.

Microphoto of Paecilomyces.
Copyright © 2008 EMLab P&K

In fungal cultures, Paecilomyces colonies grow rapidly on malt extract agar (MEA) at 25°C, although they can grow at various temperatures. They grow in a variety of colors and appear white, brownish or in bright shades of pink, violet, or lilac. P.variotii, one of the more important species to humans, is a thermophilic (heat-loving) species and can grow between 50 to 60°C. It is initially buff, to tan and then develops into a powdery yellowish brown colony. P. variotii has been documented to cause infections of the eyes, skin, bones, and pulmonary system in immunocompromised patients. Ingestion of contaminated feed has also been reported to be toxic in ducks, rabbits, swine and chicken.

References:
1. De hoog, GS, J. Guarro, J. Gene, and M.J. Figueras. 2000. Atlas of Clinical Fungi, 2nd ed. Pp. 794-809.
2. Domsch, K.H., W. Gams, and T.-H. Anderson. 1993. Compendium of Soil Fungi. Volume I. P. 525-536.
3. Samson, R.A., E.S. Hoekstra, J.C. Frisvad (eds). 2004. Introduction to Food- and Airborne Fungi. Pp. 170-171.
4. Sutton, D.A., A.W. Fothergill, and M.G. Rinaldi. 1998. Guide to Clinically Significant Fungi. Pp. 290-293.