Fungal Biology: Structure and Eukaryotic Traits

• Mycology comes from the Greek word "mykes" which means mushroom
• Mycology is the study of fungi
• Fungi are eukaryotic organisms
• The natural habitat of most fungi is the environment
• Candida albicans is an exception, as it is part of the normal human flora

Structure of Fungi

• Fungi are Eukaryotic organisms
• They have a true nucleus with a nuclear membrane
• They have membranous organelles, such as mitochondria and endoplasmic reticulum
• The cell membrane contains ergosterol, which is a target of many antifungal drugs
• Their cell wall mainly consists of polysaccharides, specifically chitin
• Fungi lack peptidoglycan, making them insensitive to antibiotics like penicillin

Prokaryotes vs. Eukaryotes

• Prokaryotes (Bacteria): 0.1-10 um, no nuclear membrane, single chromosome, no histones, binary fission, no organelles, peptidoglycan, no ergosterol, 70S ribosomes
• Eukaryotes (Fungi): 10-100 um, nuclear membrane, multiple chromosomes, histones, mitotic division, organelles, chitin, ergosterol, 80S ribosomes

Morphological Classification of Fungi

• Fungi can be classified into yeasts, molds, and dimorphic fungi

Molds (Filamentous Fungi)

• Molds are multicellular fungi
• Aspergillus is an example
• Molds produce hyphae, which are microscopic long branching filaments

Yeasts (Budding Fungi)

• Yeasts are unicellular fungi
• Candida is an example
• They reproduce by budding

Dimorphic Fungi

• Histoplasma is an example
• Some fungi can occur in two different forms
• In nature or culture at room temperature they exist as filamentous molds
• In infected tissues or when incubated at 37°C, they exist in a yeast form

Importance of Fungi

• Fungi have beneficial and harmful aspects

Fungi in medicine

• Fungi produce important drugs, antimicrobials, and vaccines
• Fungi are widely used as model organisms in genetic engineering

Fungi in food

• Fungi are used in the production of important foods like bread, cheese, and wine
• They are a common cause of damage to crops, foodstuffs, fabrics, and building materials
• Some species cause disease in humans and animals

Human Mycoses

• Human Mycoses are fungal infections that affect the skin, mucous membrane, hair, or nails

Superficial Mycoses

• Superficial mycoses include Candidiasis and Dermatophytosis

Candidiasis

• Candidiasis is a skin/mucous membrane infection, also known as Moniliasis
• Candida albicans is the normal flora of mucous membranes
• Candida albicans is an opportunistic fungi which dominate with impaired immunity and prolonged use of antibiotics
• Candida albicans affects warm & moist areas of the skin, like armpits, and mucous membranes like oral thrush.

Dermatophytosis

• Dermatophytosis, also known as Ringworm, causes Tinea
• Tinea is a contagious disease, characterized by itchy, red circular lesions.

Subcutaneous Mycoses

• Subcutaneous Mycoses is acquired when fungus is implanted into subcutaneous tissues by trauma
• Mycetoma "Madura foot" is an example of a Subcutaneous Mycoses

Systemic Mycoses

• Systemic Mycoses include Candidiasis and Aspergillosis

Systemic Candidiasis

• Systemic Candidiasis infection is mostly blood borne and disseminate to any organ

Systemic Aspergillosis

• Aspergillus Fumigatus causes pulmonary Aspergillosis
• Aspergillus Niger causes otomycosis, infection of the external ear
• Aspergillus Flavus produces aflatoxins, which can cause neoplasm in the liver

Mycotoxins

• Mycotoxins include poisonous mushrooms, aflatoxin, and ergotism

Poisonous Mushrooms

• Poisonous mushrooms, for example the Amanita mushroom, are potent hepatotoxins

Aflatoxin

• Aflatoxin, produced by Aspergillus flavus, causes neoplasm in the liver (Cancer Liver)

Ergotism

• Ergotism is caused by the mold Claviceps purpurea
• Claviceps purpurea infects grains and produces alkaloids, such as ergotamine, that cause vascular and neurologic effects