6.1.1: Fungi

Fungi are eukaryotic heterotrophic, eukaryotic organisms, that are abundant in most habitats/ environments. Fungi exist in two forms; yeast and molds. Yeast typically exist as globular, single- celled organisms. Molds, on the other hand demonstrate a filamentous structure, made of long cylindrical tubules known as hyphae. The hyphae may be multicellular, with walls known as septae separating the cells. These molds are known as septate molds. Aseptate molds have hyphae that are not separated by septae, and instead are compose of multi-nucleated cells.

Most fungi are saprophytes, meaning that they acquire their nutrients from decaying plants and animals. There are some however that can cause disease. Diseases caused by fungi are known as mycoses. There are three categories of mycoses; fungal infections, fungal toxicoses, and allergies.

Fungal infections are infections resulting from fungi on or in the body, and may be systemic, superficial, cutaneous/subcutaneous. Systemic fungal infections are infections in which the fungal agent has spread throughout the body involving organs of various body systems. Some examples of systemic fungal infections include pneumocystis pneumonia, coccidioidomycosis, and candidiasis. Superficial fungal infections are those involving the skin, hair, or nails. Dermaphytoses are an example of a superficial fungal infection. Fungal infections that occur in the deeper layers of the dermis and/or in the hypodermis are referred to as cutaneous or subcutaneous infections. These infections are not as common as the superficial fungal infections which involve the dead cells of the integument.

Fungal toxicoses occur when toxins produced from fungi are ingested, such as the ingestion of poisonous mushrooms. Fungal allergies are hypersensitivity reactions, that usually occur in response to inhaled fungal spores. Fungal toxicoses and fungal allergies will not be part of the survey completed in this exercise.

In this exercise you will survey some clinically important yeast and molds that are known to cause fungal infections.

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