Frightening fungi

It might have taken a while to pick up momentum. But it had to happen sometime in the world of fungi. Now it looks like fungi will benefit from the same process that led to a plethora of new bacterial names.

SEM of budding yeast cells with pseudohyphae extensions. Sketch based on SEM image, Musee Armand Frappier

SEM of budding yeast cells with pseudohyphae extensions. Sketch based on SEM image, Musee Armand Frappier

 

Time was when we had two main groups to choose from: yeasts and filamentous fungi. Three if you were clever and knew a bit about dimorphic fungi. But as some mycologists have pointed out,  the yeast currently known as Candida is only a genus on grounds of shape or form. When you study its genome, the species called Candida glabrata belongs to a distinct group, on a separate branch of the fungal family tree. Here is the filamentous fungus Aspergillus fumigatus:

Sporing bodies of Aspergillus. Drawing based on an original provided by Deanna Sutton at doctor fungus

Sporing bodies of Aspergillus. Drawing based on an original provided by Deanna Sutton at doctor fungus

The study of genetic relationships between fungi or phylogeny, distinguishes five major groups. In some branches of the family tree, species complexes are common. The naming of fungi is further complicated by the presence of different forms of the same fungi, depending on whether they reproduce sexually or asexually. There is a move to give these two forms the same species name, but clearly people have to agree which one to use. That may take a some time.

So why does it matter to medical practice ?

  1. multiple names for the same fungi are confusing to clinicians
  2. we need to use the same names when discussing the same infections
  3. different groups of fungi may have different antifungal sensitivity thresholds
  4. different groups of fungi may therefore need different approaches to treatment

One fungus-one name is the catch cry. If based on a strong molecular foundation, it is likely to speed up the conversion to rapid molecular identification and sensitivity methods for invasive fungal infections.

Acknowledgement:  Ian Arthur, PathWest Mycologist for his review of recent developments in the taxonomy of medically important fungi on 14th March, 2013.