Pathophysiology
Clinical meaning
Fungal infections (mycoses) represent a diverse group of diseases caused by eukaryotic organisms that possess cell walls containing chitin and cell membranes containing ergosterol -- key molecular targets that distinguish fungi from human cells and form the basis for antifungal pharmacotherapy. Fungi are classified into three major morphological groups relevant to clinical practice: yeasts (unicellular organisms that reproduce by budding, such as Candida and Cryptococcus), molds (multicellular organisms that grow as branching filamentous hyphae, such as Aspergillus and Mucor), and dimorphic fungi (organisms that exist as molds in the environment at 25 degrees Celsius and convert to yeast forms at body temperature of 37 degrees Celsius, such as Histoplasma, Blastomyces, and Coccidioides). This thermal dimorphism is remembered by the mnemonic: mold in the cold, yeast in the heat (or beast). Fungal infections are categorized by depth of tissue involvement. Superficial mycoses affect only the outermost layers of skin and hair (tinea versicolor caused by Malassezia furfur). Cutaneous mycoses (dermatophytoses) involve the keratinized layers of skin, hair, and nails, caused by three genera of dermatophytes: Trichophyton, Microsporum, and Epidermophyton. These organisms...