Introduction

Fungi are a diverse group of eukaryotes that includes yeasts, molds, mushrooms, rusts, smuts, and the recently reclassified microsporidia. They constitute one of the five kingdoms of life (Prokaryotae, Fungi, Protista, Plantae, and Animalia) in the current classification system. Like other eukaryotic organisms, fungi have membrane-bound nuclei, membrane-bound cytoplasmic organelles, and 80S ribosomes contained within a plasma membrane. Their membranes contain sterols, namely ergosterol, which determines cell membrane fluidity and acts as boundary lipid. Fungi lack chloroplasts, found in plants and some protists, and have cell walls that contain chitin, unlike other eukaryotes. Many can reproduce both sexually (teleomorphic state) and asexually (anamorphic state). There are several valid and recognized classification schemes for the kingdom Fungi. Recent phylogenetic analysis, based on ribosomal RNA and associated genes, divides the kingdom Fungi into one subkingdom, the Dikarya including the phyla Ascomycota and Basidiomycota, and five additional phyla composed of Chytridiomycota, Neocallimastigomycota, Blastocladiomycota, Glomeromycota, and the Microsporidia.^1,2 Taxonomy based on molecular detection of genetic sequences has had little effect on the commonly known genus and species names of fungi, but did substantially change their higher taxonomic relationships. From a classical medical perspective, pathogenic fungi can also be classified into the dermatophytes, yeasts, dimorphic fungi (having two anamorphic forms), hyaline hyphomycetes (e.g., Aspergillis spp.), dematiaceous hyphomycetes (a disparate group of melanin-pigmented fungi), coelomycetes (anamorphic fungi that form conidia in a cavity called pycnidia), zygomycetes (aseptate fungi), and the basidiomycetes (a large group of fungi including puffballs, shelf fungi, rusts, smuts, and mushrooms that bear sexually produced spores on specialized cells called basidia).³ Additionally, based on morphology and reproductive features fungi have been historically classified into the Ascomycota (sac fungi), Basidiomycota (club fungi), Zygomycota (conjugation fungi, aseptate), Deuteromycota (fungi imperfecti, with no known sexual state), and the Mycophycophyta (lichens and symbiotic fungi).⁴ At a very basic level, fungi are easily separated into two major morphologic categories: the filamentous or true fungi and yeasts. Most fungi are ubiquitous saprophytes in the environment, which feed on and recycle decaying organic matter. They prefer dark moist environments in which to grow. Filamentous saprophytic fungi, represented by the hyaline hyphomycetes, dematiaceous hyphomycetes and the zygomycetes, are by far the most commonly encountered agents producing bovine mycotic abortion.