Zygomycetes ("conjugating fungi") are strictly terrestrial fungi with airborne spores. To date, some 700 species have been described. Most grow on decaying plant material. The mycelium (filamentous network) of a zygomycete spreads over the substratum, growing forward by means of vegetative hyphae (thin threads). Zygomycetes produce sporangiophores, or spore-bearing hyphae, which can eject their spores as far as 6 feet.
Zygomycetes include ubiquitous, massively spore-forming groups Rhizopus and Mucor, the weeds of the fungus world, found worldwide on moldy bread. Other Zygomycetes include important pathogens of insects such as Entomophthora ("insect eater") and soil-dwelling predators and parasites of nematodes, amoebas, and protozoa.
Members of the genera Mucor, Rhizopus, and Absidia cause zygomycosis, a dangerous fungal disease. In animals it may take the form of necrotic placentitis resulting in abortion; lesions in various tissues of the body that closely resemble lesions of tuberculosis; gastroenteritis and ulceration of the alimentary tract; lesions in the abdomen and liver; pulmonary and subcutaneous infections.1
Many different fungi can cause zygomycosis including some that are often referred to as bread molds. In humans infection with Zygomycetes is associated with diabetes and other causes of metabolic acidosis, corticosteroid and deferoxamine therapy, skin and soft tissue breakdown from other causes, intravenous drug use, hematologic malignancy, solid organ transplant, burns, and malnutrition. Zygomycosis is acquired from environmental sources and there is no person to person transmission. Infections may be acquired by inhalation, ingestion, or contamination of wounds. although true zygomycetes infections are rare, the incidence of zygomycosis is on the rise. The most common sites of infection are sinus, lungs, and skin.2,3
Fluffy growth of Zygomycetes species superimposed on powdery, granular growth of Aspergillus species. Source: Case Rep Otolaryngol. 2011; 2011: 382473. doi: 10.1155/2011/382473
Diagnosis of zygomycosis can be made by microscopic observation of distinctive, ribbon-like, broad threads without cross walls in tissue sections and by culture of biopsy tissue.4 The clinical features of pulmonary zygomycosis are similar to those of invasive aspergillosis. Affected persons have persistent fever and pulmonary infiltrates that are unresponsive to antibacterial therapy. Pulmonary zygomycosis results from germination of inhaled fungal spores. The aggressive hyphae penetrates through the bronchial wall and grow into the blood vessels. The fatality rate is high and most people die from complications including massive bleeding from the lungs.5
- The Genesis of Germs: The Origin of Diseases and the Coming Plagues
- Surgical Pathology of the Gastrointestinal System: Bacterial, Fungal, Viral, and Parasitic Infections. Laura W. Lamps
- Clinical mycology. Elias J. Anaissie, Michael R. McGinnis, Michael A. Pfaller
- Burton's Microbiology for the Health Sciences, North American Edition. Paul G Engelkirk, Janet Duben-Engelkirk
- Dail and Hammar's pulmonary pathology: Nonneoplastic lung disease. David H. Dail, Philip T. Cagle, Samuel P. Hammar