Introduction to Mucormycetes

Mucormycetes (formerly known as the Zygomycetes) grow extremely rapidly both in vivo and in culture. They are often called "lid lifters" because of their fluffy and voluminous aerial mycelia that can lift the lid off of plates whose lids aren't taped on. Their hyphae are broad and have few septae, making them floppy and ribbonlike. Their branching is infrequent, haphazard, and nondichotomous (not comparable). Extreme care must be taken not to grind specimens prior to culture if zygomycosis is a consideration, as the grinding process can disrupt all of the viable hyphae. Instead, tissue specimens should be minced.

The most common types that cause mucormycosis are Rhizopus species and Mucor species. Distinct morphological features permit the identification of Mucormycetes and distinguish them from hyaline and dematiaceous molds. Of note, it is important to document the presence or absence of rootlike structures called rhizoids, and their location, and to determine whether the sporangiophores are branched or unbranched (simple).