If you have ever submitted a bioaerosol, surface, bulk, or swab sample for fungal culture you have probably seen this terminology in a report and may have wondered why there was no further identification.
As a fungus grows on agar media, it typically produces hyphae and spores and these structures are used for identification (Fig. 1).
Lab analysts observe the color and growth pattern of the fungus on the media and then look at the hyphae and spores under the microscope. The color of the hyphae and the size, shape, and arrangement of spores help to identify the type of fungus. Sometimes a fungus fails to produce spores when growing in culture (non-sporulating). This can happen for a variety for reasons…it could be the incubation temperature or time, type of agar media, or amount of moisture or light. All fungi, even the common ones like Aspergillus or Cladosporium, may not sporulate all of the time. As part of the description of a non-sporulating fungus, we include the microscopic color of the hyphae, either hyaline (colorless, Fig. 2) or dematiaceous (brown/black pigmented, Fig 3).
Alternative methods for identification of non-sporulating fungi include mass spectrometry (MALDI-TOF) and genotypic methods (DNA sequencing). In our experience, these fungi can be difficult to identify by MALDI-TOF, with subsequent DNA sequence analysis revealing unusual fungi which are not in the MALDI-TOF database, such as Botryosphaeria, Articulospora, and Ascochyta to name a few. Definitive identification of non-sporulating fungi is often not necessary unless they have been isolated from critical cleanroom environments. Otherwise, the less definitive terms of non-sporulating hyaline fungi or non-sporulating dematiaceous fungi should suffice for identification.