14 Introduction to Fungi

“The best way to win a war is to know the enemy” * This applies to humans as well as fungus diseases (mycoses).

What are fungi?

1). Mushrooms over 15,000 species in the world - several are poisonous to man the “mushroom” is the “flower” of the fungus all mushrooms reproduce sexually by meiosis, the same as man the largest part of the mushroom is the root system which grows in soil, decaying wood. etc.

2). Hyphae and Spores Sabourauds agar Sabourauds + antibiotics Both plates air exposed for 5 minutes and incubated for 1 week

Thus, one way we identify fungi is by the gross appearance of the colony, i.e., the color, shape, texture, growth habit, etc.

The second method used to identify fungi is by examining the microscopic characteristics of the organism.

Here are few examples of how fungi appear microscopically Here are few examples of how fungi appear microscopically. Note the hyphae and spores.

Scopulariopsis, occasional onychomycosis

Dreschlera, a dematiaceous fungus

Nigrospora, a contaminant

Alternaria, rare pathogen

Rhizopus: zygomycosis/phycomycosis/mucormycosis

Syncephalastrum, contaminant

Aureobasidium, rare pathogen

Penicillium, one species is a pathogen

3). Yeast Cells These are single cells, usually 5-10 microns in diameter, which reproduce by forming buds (blastospores). The following are examples of yeasts:

Cryptococcus neoformans, a yeast surrounded by polysaccharide capsule.

Saccharomyces, a yeast used to make beer.

A yeast making buds at the end of long slender tubes.

An intracellular yeast as seen in histoplasmosis and penicilliosis

Why are we so concerned with hyphae and spores?

This is a picture of many cells in hyphae This is a picture of many cells in hyphae. These cells have a thick cell wall with much chitin. The cell membrane is composed of ergosterol which is similar to cholesterol found in our cell membrane. These facts are important in the treatment of patients with fungus diseases.

Now what about spores? These are the small airborne particles by which fungi reproduce. They are produced by mitosis and readily disseminate in the air. Remember the picture of the air-exposed media?

All of the fungal colonies seen here came from spores in the air. Sabourauds agar Sabourauds + antibiotics All of the fungal colonies seen here came from spores in the air.

What does this tell you about the ability of fungal spores to enter the human lung?

The sketch of the lung shows that fungal spores must be less than 5-6 microns in diameter to enter the human lung. Since many fungal spores are less than 6 microns in diameter the lung is an important way that fungi enter the lung.

Types of Mycoses Superficial Mycoses Dermatophytoses Systemic Mycoses

Conclusion Fungi are totally different from all other microorganisms that caused human diseases. It is important to know about the basic aspects of fungi if one wishes to know how to control, diagnose and treat the mycoses. Internet searches are an important way to keep up-to-date on such matters. I recommend the following search engine: http://www.pubmed.com

Thank You!