**14.2 Mucormycosis**

Mucormycosis (zygomycosis) is infection by the class *Zygomycetes*, mainly *Mucor ramosissimus, Rhizomucor pusillus* and *Rhizopus oryzae*. Sixteen species of *Zygomycetes* infect the human. *Zygomycetes* (mucoral fungi) are common molds growing in a moist environment. Fungi commonly have chitin as structural polysaccharide, but *Zygomycetes* synthesize chitosan, a deacetylated homopolymer of chitin. Hence, serum β-D-glucan, a laboratory marker of fungal infection, is negative in case of mucormycosis [150].

The main sites of localized mucormycosis are the lung and paranasal cavity. Formation of conidiophores is rarely encountered in case of paranasal cavity infection. The gross features of systemic mucormycosis represent hemorrhagic infarction of the involved tissues and organs [151]. Microscopically, faintly basophilic and wide hyphae, showing the lack of septum formation and wide angle of lamification, are seen in the mycotic thrombus. Stamp smear preparations (**Figure 53**) reveal typical microscopic morphology of mucormycosis. Infection of *Zygomycetes* is microscopically featured by angioinvasiveness and weak reactivity with Grocott

staining, as illustrated in **Figure 54**. However, some lesions of mucormycosis reveal clear basophilia with strong Grocott reactivity (refer to **Figure 57**, displaying

*Mucormycosis. Formation of conidiophores in the paranasal cavity and stamp cytology preparation of cerebral mucormycosis in a pediatric acute leukemia case. Aerated growth condition within the cavity is essential for conidiophore formation (H&E and immunostain for* Rhizomucor *antigen). Non-septating hyphae show variable thickness. Wide angle of lamification is distinct from* Aspergillus *hyphae (PAS and Giemsa, the courtesy by Dr. Suzuko Moritani, a pathologist at Shiga Medical University Hospital, Otsu, Japan).*

Cutaneous mucormycosis is infrequently encountered as skin manifestation of

systemic mucormycosis [152, 153]. A rare lethal variant is craniofacial

*Angioinvasive mucormycosis (H&E, Grocott, and immunostain).* Zygomycetes *frequently shows angioinvasion, resulting in hemorrhagic infarction of the organ and tissue. Weak reactivity with H&E and Grocott stain is characteristic of this opportunistic fungus, as arrowheads indicate. The hyphae are clearly immunoreactive with anti-*Rhizomucor *monoclonal antibody, which is cross-reactive with* Zygomycetes *but*

neonatal intestinal mucormycosis).

**Figure 53.**

*Pathology of Gangrene*

*DOI: http://dx.doi.org/10.5772/intechopen.93505*

**Figure 54.**

**131**

*not with* Aspergillus *or* Candida*.*

#### **Figure 52.**

*Malignant otitis externa (H&E and Gram stain on smear preparation). In this lethal diabetic case (a female patient aged 40's) accompanying pseudomonal septicemia, Gram-negative rods densely colonize the necrotic debris in necrotizing petrositis. Myxoid matrix of the colony indicates biofilm infection. Gram-negative rods are demonstrated in the smear preparation.*

#### **Figure 53.**

diabetic patients. Those immunocompromised patients who suffer from acquired immunodeficiency syndrome, undergo chemotherapy, and take immunosuppressant medications such as glucocorticoids may also be vulnerable to this serious disease [145–149]. Once infection becomes established in the external meatus of the susceptible patient, the bacteria invade the underlying structures of the soft tissue and destroy the temporal bone, and finally resulting in septicemia. Malignant otitis externa should be suspected if tenderness, erythema, and/or edema of the external ear and adjacent tissues are noted on physical examination. *Pseudomonas aeruginosa* is the inciting organism in the vast majority of cases. Features of biofilm infection by Gram-negative rods are characteristic. The biopsy histology is illustrated in **Figure 52**. Much less frequently it is caused by *Staphylococcus aureus* and group A βhemolytic *Streptococcus*. Fungal etiology is also known, and *Aspergillus* and *Candida* can be the causative microbes. When untreated, the mortality rate is around 50%.

Mucormycosis (zygomycosis) is infection by the class *Zygomycetes*, mainly *Mucor ramosissimus, Rhizomucor pusillus* and *Rhizopus oryzae*. Sixteen species of *Zygomycetes* infect the human. *Zygomycetes* (mucoral fungi) are common molds growing in a moist environment. Fungi commonly have chitin as structural polysaccharide, but *Zygomycetes* synthesize chitosan, a deacetylated homopolymer of chitin. Hence, serum β-D-glucan, a laboratory marker of fungal infection, is negative in case of

The main sites of localized mucormycosis are the lung and paranasal cavity. Formation of conidiophores is rarely encountered in case of paranasal cavity infection. The gross features of systemic mucormycosis represent hemorrhagic infarction of the involved tissues and organs [151]. Microscopically, faintly basophilic and wide hyphae, showing the lack of septum formation and wide angle of lamification, are seen in the mycotic thrombus. Stamp smear preparations (**Figure 53**) reveal typical microscopic morphology of mucormycosis. Infection of *Zygomycetes* is microscopically featured by angioinvasiveness and weak reactivity with Grocott

*Malignant otitis externa (H&E and Gram stain on smear preparation). In this lethal diabetic case (a female patient aged 40's) accompanying pseudomonal septicemia, Gram-negative rods densely colonize the necrotic debris in necrotizing petrositis. Myxoid matrix of the colony indicates biofilm infection. Gram-negative rods are*

**14.2 Mucormycosis**

*Pathogenic Bacteria*

mucormycosis [150].

**Figure 52.**

**130**

*demonstrated in the smear preparation.*

*Mucormycosis. Formation of conidiophores in the paranasal cavity and stamp cytology preparation of cerebral mucormycosis in a pediatric acute leukemia case. Aerated growth condition within the cavity is essential for conidiophore formation (H&E and immunostain for* Rhizomucor *antigen). Non-septating hyphae show variable thickness. Wide angle of lamification is distinct from* Aspergillus *hyphae (PAS and Giemsa, the courtesy by Dr. Suzuko Moritani, a pathologist at Shiga Medical University Hospital, Otsu, Japan).*

staining, as illustrated in **Figure 54**. However, some lesions of mucormycosis reveal clear basophilia with strong Grocott reactivity (refer to **Figure 57**, displaying neonatal intestinal mucormycosis).

Cutaneous mucormycosis is infrequently encountered as skin manifestation of systemic mucormycosis [152, 153]. A rare lethal variant is craniofacial

#### **Figure 54.**

*Angioinvasive mucormycosis (H&E, Grocott, and immunostain).* Zygomycetes *frequently shows angioinvasion, resulting in hemorrhagic infarction of the organ and tissue. Weak reactivity with H&E and Grocott stain is characteristic of this opportunistic fungus, as arrowheads indicate. The hyphae are clearly immunoreactive with anti-*Rhizomucor *monoclonal antibody, which is cross-reactive with* Zygomycetes *but not with* Aspergillus *or* Candida*.*

(rhinocerebral) mucormycosis, which is encountered as a complication of poorly controlled diabetes mellitus [154, 155]. Angioinvasive colonization of *Zygomycetes* aggressively progresses from the paranasal cavity to the overlying facial skin and to the lower part of the frontal lobe of the brain (**Figure 55**).
