THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER Vol. 25, No. 05
Tuesday, March 7, 2006
A. Provided by Sharon Wallace, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.
8 outbreaks were reported to DHMH during MMWR Week 8 (February 19 25, 2006):
7 Gastroenteritis outbreaks
6 outbreaks of GASTROENTERITIS associated with an Assisted Living Facility (Baltimore Co.),
a College (Baltimore Co.), and Nursing Homes (Washington Co., Prince George's Co., Montgomery
Co., & Baltimore Co.)
1 outbreak of GASTROENTERITIS/SHIGELLA associated with a Private Home (Harford Co.)
1 Foodborne Gastroenteritis outbreak
1 outbreak of FOODBORNE GASTROENTERITIS associated with a Worksite (Frederick Co.)
B. The Johns Hopkins Hospital, Department of Pathology, Information provided by,
Natasha Rekhtman, M.D., Ph.D.
Clinical History: The patient is a 47-year-old man with history of orthotopic liver transplant in December 2005 for Hepatitis C cirrhosis. His medications include Tacrolimus and Prednisone. In January 2006, the patient noticed a scratch over his left forearm that continued to progress significantly of the period of two weeks. At the time of his presentation to the clinic, the lesion measured 9 cm by 6.5 cm and appeared as a gangrenous ulcer with eschar and purpuric edges. The biopsy was obtained and material was submitted to dermatopathology and microbiology labs. Histopathology and direct examination of microbiology specimen with Calcofluor white revealed invasive fungal hyphae, which were aseptate, wide, ribbon-like with wide-angle branching (shown below).
Calcofluor White stain
Based on morphologic examination, the organisms were consistent with Zygomycetes. Unfortunately, the microbiologic cultures were negative (for unclear reason) and the exact speciation of the organism was not possible. The patient was treated with AmBisome. He also underwent two debridements with a graft placement. At the time of discharge, the patient was stable.
Organism: Zygomycosis (also known as Mucormycosis or Phycomycosis) is the diseases caused by fungi belonging to the taxonomic group Zygomycetes. Zygomycosis is currently the preferred term. The three most common genera in this group are Mucor (or Rhizomucor), Rhizopus and Absidia. Zygomycetes are saprophytic molds, which are found almost ubiquitously in nature. These organisms rarely cause disease in immunocompetent host, but they may cause devastating opportunistic infections in immunosuppressed patients and patients with uncontrolled diabetes.
Organism Identification in the Laboratory:
- Direct microscopic examination: Calcofluor white is a florescent dye used for rapid morphologic detection of fungi in microbiology laboratory. This dye binds to chitin present in fungal walls and it fluoresces when viewed in a UV miscroscope. Calcofluor white stain may provide an immediate presumptive diagnosis prior to culture. Zygomycetes have a distinctive appearance when visualized with Calcofluor white. Defining features are nonseptate or sparsely septate broad (6-25 µm thick) ribbon-like hyphae with irregular branching at right angles. Similarly, the organism detection may be performed in tissue biopsy, wherein a similar morphology is observed. Zygomycetes have a propensity to invade blood vessels, which causes tissue hemorrhage and necrosis. As for other fungi, GMS and PAS may aid in the visualization of Zygomycetes in tissue.
- Macroscopic examination of cultured organisms: All Zygomycetes grow very rapidly in culture (2-3 days). They generously cover the entire surface of the plate, earning a name as “lid-lifters”. The texture of colonies is typically cotton-candy like.
- Microscopic examination of cultured organisms: Genus assignment is based on the arrangement rhizoids (root-like hyphae) in relation to sporangiophores. Rhizopus is characterized by sporangiophores arising directly over the rhizoids. In contrast, sporangiophores arising between rhizoids are characteristic of Absidia. Mucor does not produce any rhizoids.
As stated above, invasive Zygomycosis affects almost exclusively immunocompromised patients and patients with uncontrolled diabetes, particularly those in ketoacidosis. It is thought that hyperglycemia in combination with acidosis provides the ideal nutritional and metabolic milieu for the growth of the organism. Therefore an essential step in treatment of Zygomycosis is the correction of hyperglycemia and ketoacidosis. In addition, zygomycosis has been reported in patients with iron overload who are receiving deferroxamine therapy. The growth of Zygomycetes appears to be enhanced in the presence of increased concentration of iron.
Invasive zygomycosis may affect almost any organ. In addition, widely disseminated disease may develop in severely immunocompormized patients. Most commonly involved sites are rhinocerebral, pulmonary, cutaneous, and gastrointestinal. Patients with rhinocerebral disease may present with facial pain, black nasal discharge, and fever. Intracranial invasion is the feared complication, which may occur by direct extension through the cribriform plate or via ophthalmic vessels. Without urgent surgical debridement and antifungal therapy Zygomycetes may be rapidly fatal. In addition, similarly to Aspergillus, Zygomycetes may act as non-invasive colonizer in an immunocompetent host, forming “fungus balls” in the pre-existent cavitary lung lesions.
Pathogenesis: Spores are inhaled from the environment and may deposit in the sino-nasal sites and may pass into alveolar spaces. In the case of primary cutaneous zygomycosis, spores are introduced directly into injured skin. Hyphae are generated in tissue after germination of spores.
Therapy: Extensive surgical debridement of affected tissue and treatment with Amphotericin B, especially liposomal formulations, is recommended. It is important to note that Zygomycetes are resistant to available azole derivatives, such as voriconazole. Posaconazole does have activity. In addition, correction of the underlying disorder, including correction of hyperglycemia and acidemia or decreasing doses of immunosuppressive drugs if possible is critical in treating Zygomycosis.
Koneman et al Color Atlas and Textbook of Diagnostic Microbiology, 6th ed, Lippincott-Raven, 2006
Sugar AM. Agents of mucormycosis and related species. In Mandel GL. et. al. Principals and Practice of Infectious Diseases, New York: Churchill Livingstone; 1995;1351-64.