Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1355 page)

FUNGAL CULTURE (MOLD, YEAST, DIMORPHIC, AND DERMATOPHYTE PATHOGENS)

   Definition and Use

   Fungal cultures are indicated when clinically significant fungal infection is suspected. Symptomatic fungal infections commonly can be characterized as follows:

   Superficial (skin/nail/hair)

   Subcutaneous (chromoblastomycosis, mycetoma, phaeohyphomycotic cyst, sporotrichosis)

   Systemic mycosis (e.g., coccidiomycosis)

   Opportunistic mycosis (e.g., aspergillosis)

   Fungal cultures are used as the most sensitive routine laboratory method for detection of fungal infections.

Method

   The media inoculated vary, depending on the specimen submitted and type of pathogen suspected.

   Direct examination, such as wet mount or calcofluor white staining, should be performed for most specimen types; see
Fungal Wet Mount
. Specimens for routine fungal culture are inoculated onto nonselective media, such as BHI or Sabouraud dextrose–BHI agar. For specimens likely to be contaminated, selective media, such as inhibitory mold agar, are inoculated. An enriched medium, such as BHI blood agar, is inoculated to improve recovery of dimorphic fungal pathogens.

   Special media may be inoculated for some types of specimens or suspected pathogen, like Bird (niger) seed agar for
Cryptococcus neoformans
, chromogenic agar for differentiation of
Candida
isolates, or dermatophyte test medium for dermatophytes. If
Malassezia furfur
is suspected, medium supplemented with a source of long-chain fatty acids (like olive oil) is inoculated.

   Inoculated media are typically incubated at 25–30°C in room air for up to 4 weeks. Cultures for isolation of systemic, dimorphic pathogens may be incubated at 35–37°C, but the incremental yield, versus 30°C incubation, is minimal. Cultures for fastidious pathogens are incubated for up to 8 weeks.

   Media inoculated for aerobic bacterial culture will support the growth of the common yeast pathogens,
Candida
species, so specific culture for yeast is not usually required.