Saprophytic Fungi Considered Contaminants
TECHNICAL UPDATE

DESCRIPTION/BACKGROUND INFORMATION

In nature, there are several hundred thousand species of fungi.  Of these, approximately 150 to 200 species are thought to be etiologic agents of disease.  This number and the field of medical mycology itself are constantly changing due to the increasing number of immunocompromised patients.  Organisms previously considered harmless have emerged as opportunistic pathogens as a result of AIDS and other immune diseases, organ transplants, hyperalimentation, chemotherapy and/or steroid treatments.    For this reason, it is extremely important to use collection methods that are most likely to recover actual causative agents.

CLINICAL APPLICATION

The appropriate collection, transport, and processing of a clinical specimen is the only way an organism can be clearly associated with disease.  Inappropriate specimen collection may result in the recovery of indigenous organisms and put the interpretation of culture results at risk.  The site of active infection is the best specimen for determining the presence of an etiologic agent.  Deeper specimens, such as skin scrapings or tissue biopsies, are preferred over swab cultures in most settings.  Nails and other specimens that may have bacterial or other superficial contamination should be thoroughly cleaned with 70% ethanol before collection.  For the proper specimen collection of various sources, refer to the Laboratory Services Manual or contact the microbiology department.

When determining whether the recovery of a fungal organism is indicative of an infection, the immune status of the patient should be considered.  As stated previously, fungi once thought to be non-pathogenic are now considered opportunistic pathogens.  Those patients who are immunocompromised, as well as those with severe burns, hematologic malignancies, diabetes mellitus, or other debilitating conditions are at greater risk to systemic infections by organisms usually thought of as contaminants.  In addition, the source from which the fungus is recovered should also be taken into account.  An organism may be considered a contaminant when recovered from one site, but may be a potential etiologic agent when located elsewhere.  For example, if a Gliocladium spp. was cultured from a corneal scraping, it would be considered a pathogen, whereas if it were recovered from a toenail, it would be thought of as a contaminant.

The following list includes several organisms considered to be contaminants in clinical specimens:

• Acremonium spp.
 
• Alternaria spp.
 
• Aspergillus spp.
 
• Beauveria spp.
 
• Bipolaris spp.
 
• Chaetomium spp.
 
• Chrysosporium spp.
 
• Cladosporium spp.
 
• Cunninghamella spp.
 
• Curvularia spp.
 
• Epicoccum spp.
 
• Fusarium spp.
 
• Gliocladium spp.
 
• Geotrichum spp.
 
• Mucor spp.
 
• Paecilomyces spp.
 
• Penicillium spp.
 
• Phoma spp.
 
• Rhizopus spp.
 
• Rhodotorula spp.
 
• Saccharomyces spp.
 
• Scopulariopsis spp.
 
• Streptomyces spp.
 
• Ulocladium spp.
 
• Verticillium spp.
 

These organisms can be associated with fungal disease when the conditions addressed previously are taken into consideration and if they are:

• visible in the clinical specimen when examined microscopically
• recovered from several clinical samples collected over a period of time
• able to grow at or near body temperature
• confirmed by serological tests if possible

REFERENCES:

1. Beneke, Everett S. and Alvin L. Rogers. Medical Mycology and Human Mycoses. Star Publishing Company; 1996: 5-24.
2. Larone, Davise H. Medically Important Fungi: A Guide to Identification. 3^rd ed. Washington, D.C.: American Society for Microbiology; 1995: 107-206.
3. Murray, P.R., E.J. Baron, J.H. Jorgensen, M.A. Pfaller, and R.H. Yolken, editors. 2003. Chs. 110-111, 116. Manual of Clinical Microbiology, 8^th ed. ASM Press, Washington, D.C.
4. St-Grermain, Guy and Richard Summerbell. Identifying Filamentous Fungi: A Clinical Laboratory Handbook. Star Publishing Company; 1996: 52-241.