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Introduction to Clinical Mycology

Part 4



Identification of Molds

Slide 5

March 2012

Identification of molds is made up of several criteria. When we sit down to try to identify a mold, one of the things that we first start off with is to see if it is an organism that has hyphae that are septate or nonseptate or pauciseptate (having few septations). The next thing we look for, is this organism pigmented or not. If it is pigmented, it is called dematiaceous, if it is not, it is called hyaline. This happens to be pigment in the hyphae or the spores.

The other thing we look for is to see if the organism is monomorphic or dimorphic, not always easy to tell at first glance. Sometimes, you will see, you have to work at trying to get the second form to be there. But you have criteria that you look at, for example, the spores, the type of spores that are produced, and the arrangement of those spores, gives you an idea of what the organism might be in terms of the dimorphic fungus too. And then the growth rate–the growth rate is something that we seem to rely on probably more than we should. The growth rate in text books says, for example, the dimorphic molds like Histoplasma or Blastomyces are slow growing and may take up to 4 to 6 weeks and so on. We actually have seen things like Blastomyces grow up in a shorter period of time, in just 2 days. Well, the reason for that is the growth rate is influenced by how much organism happens to be in the initial specimen that is cultured. If there are a few organisms in the specimen, the culture is going to grow very slowly; you won’t see it for several days or several weeks. If there are lots of cells in there in the original inoculant, the organism will grow very quickly and you would be able to make an identification much earlier. So the growth rate is not an absolute criterion for making an identification, but it is helpful.

Identification of Molds

 


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