Introduction to Medical Mycology

Fungi are a diverse group of eukaryotic organisms that play important roles in ecosystems and human health. They are heterotrophic, meaning they obtain nutrients from organic sources like dead plants and animals. Fungi are distinguished by their cell walls made of chitin and their ability to produce spores for reproduction. They are also known for their ability to break down complex organic matter, contributing to nutrient cycling.

The morphology of fungi describes their appearance, structure, and form. They can exist as single-celled yeasts or multicellular molds. Yeasts are oval-shaped, reproduce by budding, and are often associated with infections like candidiasis. Molds are filamentous, growing as a network of hyphae, which can form complex structures called mycelia. Different fungal species exhibit unique morphologies.

Medical mycology focuses on fungi that cause diseases in humans (mycoses). Fungal infections range from superficial skin infections to life-threatening systemic diseases.

Mycoses are diseases caused by fungal infections. These range from superficial skin infections like athlete's foot to serious invasive infections that can affect internal organs. The type of mycosis depends on the fungal species and the site of infection.

Direct microscopic examination is a rapid diagnostic tool used to identify fungal elements in clinical specimens. It involves examining samples under a microscope, typically using a wet mount preparation with a drop of potassium hydroxide (KOH) to clear debris and allow better visualization of fungal structures. This helps to identify fungal elements like hyphae, spores, and yeasts.

Fungal culture on specific media is a crucial step in identifying fungal species. It involves growing the fungus in a controlled laboratory setting, typically using Sabouraud's dextrose agar (SDA). This media provides optimal conditions for fungal growth, allowing identification based on colony morphology and microscopic features.

Serological tests are utilized to detect specific fungal antigens or antibodies in patient samples. This is particularly helpful in identifying invasive fungal infections. The detection of certain antigens, like β-D-glucan, is a strong indicator of invasive fungal infection. Likewise, specific fungal antibodies can be identified to confirm the diagnosis of systemic fungal infections.

Antifungal therapy aims to eliminate or control fungal infections. These drugs work by targeting key aspects of fungal biology, like interfering with cell wall synthesis, blocking ergosterol synthesis (essential for fungal cell membrane function), or inhibiting DNA synthesis. Common antifungal classes include azoles (fluconazole), polyenes (amphotericin B), and echinocandins (caspofungin).

Ergosterol is a sterol, a type of lipid, that is a crucial component of the cell membrane in fungi. It is involved in maintaining cell wall integrity and permeability. It is a key target for some antifungal drugs like azoles and polyenes, which block its synthesis.

Chitin is a complex carbohydrate found in the cell walls of fungi. It provides structural support and helps maintain the rigidity of the cell wall, enabling the fungus to maintain its shape and withstand environmental pressures.