Nevertheless, the taxonomic status of such an important group of fungi is still very confusing and many new species as well as lineages have been elucidated recently. The dermatophytes are a group of molds that cause superficial mycoses of the hair, skin, and nails and utilize the protein keratin, that is found in hair, skin, and nails, as a nitrogen and energy source.Members of Fusarium solani species complex (FSSC) have been known as plant, animal, and human pathogens. Molds are commonly cultured on fungal-selective or enriched media such as Saboraud Dextrose agar (SDA), Corn Meal agar, and Potato Dextrose agar. This gives rise to a new sporangium producing sporangiospores having DNA that is a recombination of the two parent strain's DNA. During sexual reproduction (see Figure 8), hyphal tips of (+) and (-) mating type join together and their nuclei fuse to form a sexual spore called a zygospore (see Figure 9). Other mycoses include pulmonary, cutaneous, and gastrointestinal. The most common infection is a severe infection of the facial sinuses, which may extend into the brain. Rhizopus species are the most common causative organisms. Mucormycoses are infestions caused by fungi belonging to the order of Mucorales. Scanning electron micrograph of the conidiospores of Rhizopus courtesy of Dennis Kunkel's Microscopy.Anchoring structures called rhizoids are also produced on the vegetative hyphae. Its sporangiospores, typically brown or black, are produced within the sporangium (see Figure 7). At the end of its sporangiophore is dome-shaped end called a columella that extends into a sac-like structure called a sporangium. Although usually nonpathogenic, it sometimes causes opportunistic wound and respiratory infections in the compromised host. Rhizopus is an example of a mold that produces sporangiospores. In highly immunosuppressed individuals, however, Aspergillus may disseminate beyond the lung via the blood. Scanning electron micrograph of the conidiospores of Aspergillus courtesy of Dennis Kunkel's Microscopy.Īlthough generally harmless in most healthy individuals, Aspergillus species do cause allergic bronchopulmonary aspergillosis (ABPA), chronic necrotizing Aspergillus pneumonia (or chronic necrotizing pulmonary aspergillosis ), aspergilloma (a mycetoma or fungus ball in a body cavity such as the lung), and invasive aspergillosis.Scanning electron micrograph of the conidiospores of Penicillium courtesy of Dennis Kunkel's Microscopy.The form and manner in which the spores are produced, along with the appearance of the hyphae and mycelium, provide the main criteria for identifying and classifying molds. Molds may also reproduce by means of sexual spores such as ascospores and zygospores, but this is not common. These spores are disseminated by air, water, animals or objects and upon landing on a suitable environment, germinate and produce new hyphae (see Figure 1). Molds reproduce primarily by means of asexual reproductive spores such as conidiospores, sporangiospores, and arthrospores. Molds possess a rigid polysaccharide cell wall composed mostly of chitin and, like all fungi, are eukaryotic (see Figure 2). The portion of the mycelium that anchors the mold and absorbs nutrients is called the vegetative mycelium the portion that produces asexual reproductive spores is termed the aerial mycelium (see Figure 1). The total mass of hyphae is termed a mycelium. A hypha is a branching, tubular structure from 2-10 µm in diameter and is usually divided into cell-like units by crosswalls called septa. Molds are multinucleated, filamentous fungi composed of hyphae.
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