Mycology

Mycology comes from the Greek μηκος meaning fungus and λογος meaning study of. Therefore mycology is the study of fungi (icky). Besides for infections, fungi are also responsible for penicillin and other antibiotics, mushrooms, poisons, bread, and alcohol! We’re only learning about the medically important part of fungi, there are maybe 100 medically important ones.

Fungi has it’s own kingdom because it has properties of plants, animals, and prokaryotes, in addition to its own unique properties.

Differences between Fungi and bacteria:

Fungi can be divided into two groups  yeasts {one cell}, and molds, {multicellular}. Dimorphic fungi lives as mold in nature but when they infect man they become yeast.

Some molds have no divisions between nuclei and some have lots of divisions, and some have a few nuclei and divisions between the few nuclei.

Yeast Ultrastucture  Cell wall  cell membrane  nucleus with membrane  nucleolus  ER  other structures. Mold is the same, but at the end of the mold cell (hyphae) we see lots of macrovesicles, which have the precursors for cell growth.

Cell Wall

1. Structure 

   1. Multilayered  can be 3,4,5 . . . layers depending on species, growth conditions, and age of culture. It’s important to know how many layers to know what drugs to give and how effective they’ll be.

   2. Composition  80-85% polysaccharides depending on species. 3 main polysaccharides:

      1. Chitin (NAG) unique because bacteria and animals don’t have it. There are 3 types of chitin synthase, which are targets for antifungals. Chitin is insoluble and gives structure to fungal cell, usually found closer to the inside of the cell, but this is not always true because membranes are fluid.

      2. Glucan  made of glucose, also closer to the inside.

      3. Mannan  made of mannose, closer to the outside, and generally responsible for the antigenicity of the fungal cell.

2. Function 

   1. Keeps cell shape (chitin and glucan).

   2. Protects from the environment (again chitin and glucan).

   3. Interaction with host  adhesion to binding sites of organism and host cells, no adhesion = no infection, also involved in phagocytosis.

   4. Growth and reproduction  chitin mostly, if you disturb the synthesis of chitin the fungus’ll grow abnormally and won’t divide.

Cell Membrane

1. Composition  phospholipids, proteins, and sterols. The sterols are synthesized similar to the way cholesterol is synthesized. Most antifungals act on the synthesis of ergostol. This changes the membrane permeability  leakage  death. Because of the similarity to cholesterol synthesis, these drugs have lots of side effects including liver failure and death. If the side effects are not too severe we can use the drugs, or if the drugs are specific to a certain step that is only in fungi.

2. Function  regulation of permeability.

Category: Microbiology Notes