Introduction

There are many different organisms in the fungal lineage which include mushrooms, rusts, smuts, puffballs, truffles, morels, moulds and yeasts, as well as many lesser known organisms. fungi are eukaryotic and heterotrophic organisms which posess a chitinous cell wall. Sexual and asexual reproduction of the fungi is commonly via spores, often produced on specialized structures or in fruiting bodies. Some species have lost the ability to form reproductive structures, and propagate solely by vegetative growth.

Fungi are abundant in soil, vegetation, water and on decaying material and wood. Fungi have a eukaryotic cell structure and are able to grow as branching or filamentous forms (mycelia) or as single cells (yeasts).

The study of fungi is called mycology. Fungi are fundamental for life on earth in their roles as symbionts and by playing a role in xenobiotics, a critical step in the global carbon cycle. Many fungi produce toxins, antibiotics, and other secondary metabolites, some of which cause diseases of animals (as well as plants).

Although there are over 50,000 identified species of fungi, only a few hundred are known to be pathogenic, causing infections known as mycoses (mycology being the study of fungi). Fungi are nonphotosynthetic organisms (lack chlorophyll) which are restricted to a parasitic or saprophytic existence. They are abundant in soil, vegetation, water and on decaying vegetation and wood. Fungi have a eukaryotic cell structure and are able to grow as branching or filamentous forms (mycelia) or as single cells (yeasts).

Fungal Structure

Types of Fungi

Fungal Reproduction

Immunity to Fungi

Major pathogenic fungi

Superficial: These infections affect only the skin, hair, nails etc.

• Generally not dangerous
• Examples- Hortaea werneckii, causing tinea nigra, and Piedraia hortae, causing black piedra

Cutaneous: including dermatophytoses

• Only affect superficial keratinized tissue- skin, hair and nails
• Again generally not dangerous
• Examples- Candida albicans, causing candidiasis of the skin and nails and Microsporum species

Subcutaneous: Usually cause chronic localised infections of the skin and underlying dermis

• Normally reside in soil and vegetation, entering the skin through cuts and grazes
• Can occasionally affect the deep tissues, e.g. bones and muscles
• Examples- Sporothrix schenkii, causing sporotrichosis, Madurella mycetomatis causing mycetoma

Systemic: Also known as deep, endemic or primary

• Usually serious
• Sometimes fatal
• Examples- Histoplasma capsulatum causing histoplasmosis, Blastomyces dermatitidis causing blastomycosis

Opportunistic: Ubiquitous fungi that affect only susceptible hosts; immunocompetent individuals are normally resistant

• Examples- Aspergillus fumigatus, causing aspergilliosis, Cryptococcus neoformans, causing cryptococcosis

Further Links

• Fungi Flashcards

Fungal Diseases

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References

Special accreditation for the use of lecture notes, images and input from:

Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

Other Sources

• Carter and Chengappa: Essentials of Veterinary Bacteriology and Mycology, Fourth edition