Mucormycetes, continued

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Mucormycetes, continued

The Rhizopus spp. produce rhizoids and unbranched sporangiophores that arise directly over the rhizoids. The sporangia (sack-like structures that contain spores) are prominent spherical structures full of spores (sporangiospores) that tend to collapse when they mature, imparting the appearance of a collapsed umbrella.
The Mucor spp. do not produce rhizoids. The sporangiophores can be branched or unbranched, but lack an apophysis (funnel-shaped swelling of sporangiophore). The sporangia of the Mucor spp. are large spherical structures that tend to fall apart, releasing their numerous spores.
Lichtheimia spp. (formerly referred to as Absidia) produces rhizoids, but its sporangiophores arise at points between rhizoids, rather than over the rhizoids. Sporangiophores are branched and form a conical apophysis at the top.
The Cunninghamella spp differ from most mucormycetes in that they have large vesicles on top of their branched sporangiophores. Their vesicles are covered with spines (denticles), each of which supports a single spore contained within a round sporangiolum.
Several forms of invasive infection are produced by the Mucormycetes: rhinocerebral, pulmonary, gastrointestinal and cutaneous. People most susceptible are the immunocompromised and important risk factors include uncontrolled diabetes (especially ketoacidosis), stem cell or solid organ transplantation, neutropenia, corticosteroid therapy, or severe burns.
The top right image shows an H&E stain of Mucor demonstrating broad, irregular, non-septate hyphae. The bottom right image is a Gomori-Methenamine-Silver (GMS) stain of Mucor also demonstrating irregular, non-septate hyphae.
Images courtesy of the CDC.