Zygomycetes (Mucorales) - Mucormycosis: Microscopic exam; Culture; Molecular diagnosis (PCR); Molecular Identification (sequencing); Antifungal susceptibility. 

Information 2020-03-03.

Zygomycetes are very old filamentous fungi, with a very wide evolutionary distance between species. They have hyphae without septa (non-septate or cenocitic) and reproduce by asexual endospores (sporangiospores) or by sexual zygospores after the fusion of two cells of the same mycelium (homothallic) or from different mycelia (heterothallic). They are fast-growing fungi and are widely distributed in nature, mainly in soil and in decomposing organic matter. Therefore, sometimes they find themselves breaking down food, such as fruits or vegetables, altering their organoleptic characteristics (color, smell, taste, texture, etc.).

Within this complex group of fungi there are parasitic or pathogenic species of plants and animals, including humans. These are mainly opportunistic pathogens that infect people who have a weakened immune system, such as patients with diabetes mellitus, infected with human immunodeficiency virus (HIV), who have malignant neoplasms, have suffered organ or other tissue transplants, as well as traumatic patients who present with cuts, burns or skin lesions.

The most common route of infection is the inhalation of spores, followed by ingestion of contaminated food and skin exposure. Infections caused by this complex group of fungi are called mucormycosis and depending on the location of the infection and the type of underlying disease of the patient who presents it, there are several types:

-        Cutaneous (skin): It occurs after the entrance of the fungus through a skin lesion. It is the most common type in people with a good immune system.

-        Gastrointestinal: Common in premature and low birth weight babies who have been in surgery, or received broad-spectrum antibiotics, or immunosuppressive medications.

-        Pulmonary: It is the most common type in patients who have received a stem or organ cell transplant, and in people with cancer.

-        Rhinocerebral (brain and sinuses): Mainly affects people with uncontrolled diabetes and people who have received a kidney transplant.

-        Disseminated: It is the most lethal. The infection spreads through the bloodstream. The most common condition is cerebral, but it can also affect other organs.

Currently, mucormycosis is considered the most common fungal infection caused by filamentous fungi, after aspergillosis. The most common species that cause this disease belong to the following genera: Rhizopus, Mucor, Rhizomucor, Syncephalastrum, Cunninghamella, Apophysomyces, and Lichtheimia. This infection has a high associated mortality (50% of total cases and 90% of disseminated infections), and one of the main reasons is that these fungi have a high rate of resistance to the main antifungals for clinical use.

The definitive diagnosis of mucormycosis is based on optical microscopy to observe the cenocitic hyphae (of uneven diameter and contour and invading blood vessels) and the isolation in microbiological culture media of respiratory, gastric or biopsied or excised lesions with surgery. On some occasions, due to the type of hyphae that these fungi present, it is difficult to achieve their correct growth in culture for subsequent identification, and the alternatives to this are based on the use of molecular methods of amplification, by PCR or real-time PCR (rt-PCR).

The treatment of this type of infections is mainly based on rapid diagnosis, control of predisposing factors, improvement of the patient´s immune status and the use of antifungals (liposomal amphotericin B, voriconazole or isavuconazole) in combination with extensive surgery, with injury exeresis.

Tests performed in IVAMI:

  • Microscopic examination to observe the cenocitic hyphae.
  • Culture for isolation and microscopic identification.
  • Molecular diagnosis (PCR).
  • Molecular identification of species (sequencing).
  • Antimicrobial susceptibility test.

Recommended samples:

  • Respiratory sample: sputum, bronchoaspirate or bronchoalveolar lavage.
  • Gastric sample: Gastric fluid; Biopsies

Storage and shipment of the sample:

  • Refrigerated (preferred) for less than 2 days.
  • Frozen: more than 48 hours.
  • Paraffin biopsies can be stored and sent at room temperature or refrigerated.
  • Fresh biopsies should be kept mainly frozen.

Delivery of results:

  • Microscopic examination to observe the cenocitic hyphae: 24 hours.
  • Culture for isolation and microscopic identification: 48 to 72 hours.
  • Molecular diagnosis (PCR): 48 to 72 hours.
  • Molecular identification of species (sequencing): 4 to 5 days.
  • Antimicrobial susceptibility test: 7-10 days.

Cost of the tests:

  • Microscopic examination to observe the cenocitic hyphae: consult ivami@ivami.com.
  • Cultivation for isolation and microscopic identification: consult ivami@ivami.com.
  • Molecular identification of species (sequencing): consult ivami@ivami.com.