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739) Which one of the following statements most accurately describes the standard practice required to ensure a safe environment when processing specimens and/or cultures of potentially pathogenic fungi in the mycology laboratory?

It is standard practice that all yeast and filamentous fungi (molds) are handled and processed under a biologic safety cabinet (BSC). Tape or shrink seals are required to seal all agar and broth media to protect against contamination or infection with dimorphic fungi (e.g., Coccidioides immitis). The use of a BSC is required for processing and handling molds, not yeast. Tape or shrink seals are required when using plated agar media; however, petri plates should not be used if C. immitis is suspected. The required location of the BSC used for handling fungal specimens and cultures is a confined access mycology facility. All agar slants and plates are required to be sealed by tape or shrink seals to prevent contamination. Slide cultures of suspect dimorphic fungi, in lieu of wet mount preparations, must be prepared in a BSC located within a confined access room. Mold species, such as Aspergillus and Candida species, are less infectious to laboratory workers; therefore, they can be handled and processed outside of a BSC.

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• Accurate data regarding laboratory-acquired mycoses are not available due to a general lack of required reporting to public health agencies. Reporting acquired infections in laboratories is currently required coccidioidomycosis in California and Arizona, blastomycosis in Louisiana and Wisconsin, and histoplasmosis in Kentucky and Wisconsin.

• Because filamentous fungi produce conidia or spores that can easily become airborne, special safety precautions specific to mycology are required. Examination of molds should be performed in a biologic safety cabinet (BSC), not only to prevent contamination of the laboratory environment, but also to avert acquisition of dimorphic fungi, such as Coccidioides immitis, Blastomyces dermatitidis, and Histoplasma capsulatum. Because yeast do not produce airborne spores, they can be processed on the open work bench.

• Standard safety precautions in mycology require that slide cultures never be prepared if dimorphic fungi are suspected. Slide culture procedures are reserved for the workup of low-virulence fungi. Wet mount preparations are recommended for presumptive identification of dimorphic fungi, and screw-cap tubes of slanted media or plated media can be used to grow nondimorphic molds. However, when the latter are used, oxygen-permeable tape or shrink seals must be used to contain the spores within the plate.

• Although it is recommended that a designated laboratory under negative pressure be used to safely culture and identify molds, it is not a requirement. Handling and processing fungal isolates, including molds, can be safely performed using a certified BSC in the open microbiology laboratory.

• Yeast are routinely identified by commercially prepared biochemical-based assays. Identification of molds includes DNA probe assays for dimorphic fungi, microscopic morphology, and differential or selective media. Molecular methods for identification are rapidly replacing phenotypic assays, such as gene sequencing, nucleic acid amplification, and mass spectrophotometry.

Chosewood LC, Wilson DE, eds: Centers for Disease Control and Prevention and National Institutes of Health. Biosafety in microbiological and biomedical laboratories. 5th ed. Washington, DC: US Department of Health and Human Services; 2006.

Fleming DO, Hunt SL, eds: Mycotic agents of human disease. In Biological safety principles and practices, 4th ed. W.A. Schell: pp 163-178.

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Clinical Pathology: General Principles, Microbiology

739) Which one of the following statements most accurately describes the standard practice required to ensure a safe environment when processing specimens and/or cultures of potentially pathogenic fungi in the mycology laboratory?

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