VIDEO LECTURE

MYCOLOGY - CHAPTER  FIVE  

FILAMENTOUS FUNGI 

Dr Arthur DiSalvo 

CHROMOBLASTOMYCOSIS 

This is a chronic, localized infection infection of subcutaneous tissues caused by several species of dematiaceous fungi. The 3 most common agents are: 

• Fonsecaea pedrosoi (figure 1)
• Cladosporium carrionii (figure 2 and 4)
• Phialophora verrucosa (figure 3)

These fungi, recognized by a variety of names, are saprobes located in soil and decaying vegetation. The route of entry is usually by trauma. The lesions are sub-cutaneous and the surface can be flat or verrucous (figure 4A). The lesions take several years to develop. These organisms are called dematiaceous fungi, because they have a black color in the mycelium cell wall (in culture and in tissue). In tissue these fungi form sclerotic bodies which are the reproductive forms dividing by fission (figure 4B). These organisms induce a granulomatous reaction. The etiologic agents of chromoblastomycosis are septate, mold-like, branching, darkly pigmented which produce asexual fruits called conidia. We identify these fungi in culture by the shape and formation of the conidia. The fungi have a world-wide distribution especially in warmer climates like the tropics or the southern U.S. The melanin in the pigment may be a virulence factor. These organisms are distributed world-wide. There is no really successful therapy. Excision and local heat have been used with some success. Flucytosine (5-FC) and itraconazole have also been used to treat (or control) this disease. Posaconazole is showing some promise as a therapeutic agent. There are no serological tests to aid in the diagnosis.

Figure 4
Plate culture of Cladosporium carrionii, at four weeks growth. C. carrionii infection is a common cause of chromoblastomycosis, and is particularly prevalent in arid and semi-arid areas, most often in tropical and subtropical zones. CDC/Dr. Lucille K. Georg

Figure 4A
Chromoblastomycosis lesions are sub-cutaneous and the surface can be flat or verrucous
Dr Arthur DiSalvo

Figure 4B
Dematiaceous fungi:  In tissue these fungi form sclerotic bodies which are the reproductive forms dividing by fission
Dr Arthur DiSalvo
 

 Figure 6.
 Mycetoma with presence of geotrichum   © Bristol Biomedical Image Archive. Used with permission

MYCETOMA (Maduromycosis)

Mycetomas (fungous tumors) are also chronic, subcutaneous infections (figure 5). These are called eumycotic mycetoma (tumors caused by the TRUE fungi as opposed to those caused by actinomycetes) (figure 6). These tumors frequently invade contiguous tissue, particularly the bone. A diagnosis of the etiologic agent is essential for patient management because the prognosis and therapy differs. Mycetoma characteristics:

1. tumefaction - swelling

2. granules - a variety of colors (white, brown, yellow, black)

3. draining sinus tracts

The three most common etiologic agents are:

1. Madurella mycetomatis (figure 7 and 8)

2. *Exophiala jeanselmei (figure 9)

3. *Pseudallescheria boydii (figure 10 and 11)

*The most common in the US. These organisms are associated with the soil, thus you see many infections in the feet and legs.

 Clinical specimens for diagnosis:

1. pus -  with granules

2. tissue -  for histological examination

The color, size and texture of the granules are an aid in the diagnosis of mycetomas. The agents of mycetoma are all filamentous fungi which require 7-10 days for visible growth on the culture media and then another several days for specific identification. These fungi are identified by the colonial morphology, conidia formation and biochemical reactions. The species of fungi cannot be distinguished in histopathological tissue sections. Treatment is very difficult, but terbinafine and itraconazole have been used with some success. Posaconazole seems to be efficacious.

Figure 8.
Specimen of fibroadipose tissue containing “black grain” mycetoma due to the fungus Madurella grisea. Some Madurella spp. are a cause of mycetoma, a fungal infection characterized by sclerotia, or large black masses of hyphae. The fungus enters the human body via trauma, which usually affects the foot. This disease process may take several years.

Figure 9.
Conidiophores of the fungus Exophiala jeanselmei. Exophiala jeanselmei, is a well documented human pathogen. Clinical manifestations include mycetoma, localized cutaneous infections, subcutaneous cysts, endocarditis, cerebral involvement, and systemically disseminated infections. CDC/Dr. Libero Ajello.

Figure 10.
Conidiophores with conidia of the fungus Pseudallescheria boydii from a slide culture. Pseudallescheria boydii is pathogenic in humans, especially those who are immunocompromised, causing infections in almost all body regions, and which are classified under the broad heading of “Pseudallescheriasis”.

Figure 11.
Eumycotic mycetoma due to the fungus Pseudallescheria boydii. Pseudallescheria boydii is the most common etiologic agent associated with eumycetoma in the United States. The disease is a chronic cutaneous and subcutaneous infection with the foot being the most common site for lesions. CDC/Dr. Hardin
 

Figure 12.
 Histopathologic changes seen in zygomycosis due to Rhizopus arrhizus using FA stain technique. Rhizopus arrhizus, the most common Rhizopus spp., is known to be the cause of zygomycosis, an angiotropic disease, which means that it tends to invade the blood vessels, thereby, facilitating its systemic dissemination.

Figure 13.
 Histopathologic changes seen in a heart valve due to zygomycosis caused by Mucor pusillus. Using methenamine silver stain, one can detect the presence of fungal elements associated with zygomycosis, including sparsely septate hyphae, amongst a mostly acute inflammatory process with some island of chronic granulomatous inflammation. CDC/Dr. Libero Ajello

Figure 14
Mucor sp. enter the brain via the blood vessels
Dr Arthur DiSalvo

MUCORMYCOSIS 

Also known as zygomycosis and phycomycosis. Mucormycosis is an acute inflammation of soft tissue, usually with fungal invasion of the blood vessels. This rapidly fatal disease is caused by several different species in this class. The zygomycetes, like the Candida species, are ubiquitous and rarely cause disease in an immunocompetent host. Some characteristic underlying conditions which cause susceptibility are: diabetes, severe burns, immunosuppression or intravenous drug use. 

The three most common genera causing this clinical entity are:

• Rhizopus species (figure 12)
• Mucor species (figure 13)
• Absidia species

Characteristics
These fungi are found world-wide, commonly in soil, food, organic debris etc. They are seen on decaying vegetables in the refrigerator and on moldy bread. Rhinocerebral infections are common. This disease is frequently seen in the uncontrolled diabetic patients.

Typical case
An uncontrolled diabetic patient comes to ER (may be comatose depending on the state of diabetes) and a cotton-like growth is observed on the roof of the mouth or in the nose. These are the hyphae of the organism. If untreated, the patient will die within a few hours or days. What do you do to help this patient first? Controlling the diabetic state is most important before administering amphotericin.

These fungi have a tendency to invade blood vessels (particularly arteries) and enter the brain via the blood vessels and by direct extension through the cribiform plate (figure 14). This is why they cause death so quickly.

Culture
A rapid growing, loose, white mold  is visible within 24 to 48 hours. With age, and the formation of sporangia, the colony becomes dark gray. The sporangia contain the dark spores (figure 16). The mycelium is wide (10-15 microns), ribbon-like and non-septate (coenocytic). This same appearance is clear in tissue sections. The species are identified by the morphology in culture. 

Treatment
Treatment consists of debridement and amphotericin

Identification
There is an immunodiffusion test available, but the physician cannot wait for these results before instituting rapid, vigorous intervention. The diagnosis and treatment must be immediate and based primarily on clinical observations.

Figure 17
This photomicrograph shows the conidial head of an Aspergillus niger fungus. Conidial heads of Aspergillus niger are large, globose, and dark brown, and contain the fungal spores, facilitating propagation of the organism. This is one of the most common species associated with invasive “pulmonary aspergillosis”.  CDC/Dr. Lucille K. Georg

Figure 18
This photomicrograph depicts the appearance of a conidiophore of the fungus Aspergillus flavus. Aspergillus spp. are filamentous, cosmopolitan and ubiquitous fungi found in nature, are commonly isolated from soil, plant debris, and indoor air environments, and are the most commonly isolated filamentous fungi in invasive infections. CDC/Dr. Libero Ajello

ASPERGILLOSIS 

Aspergilli produce a wide variety of diseases. Like the zygomycetes, they are ubiquitous in nature and play a significant role in the degradation of plant material as in composting. Similar to Candida and the Zygomycetes, they rarely infect a normal host. The organism is distributed world-wide and is commonly found in soil, food, paint, air vents. They can even grow in disinfectant. There are more than one hundred species of aspergilli The most common etiologic agents of aspergillosis in the United States:

• Aspergillus fumigatus (figure 16)
• Aspergillus niger (figure 17)
• Aspergillus flavus (figure 18)

There are three clinical types of pulmonary aspergillosis:

• Allergic hypersensitivity to the organism. Symptoms may vary from mild respiratory distress to alveolar fibrosis.
   
• Aggressive tissue invasion. Aspergillosis is primarily a pulmonary disease, but the aspergilli may disseminate to any organ. They may cause endocarditis, osteomyelitis, otomycosis and cutaneous lesions.
   
• Fungus ball  which is characteristically seen in the old cavities of TB patients. This is easily recognized by x-ray (figure 19), because the lesion (actually a colony of mold growing in the cavity) is shaped like a half-moon (semi-lunar growth). The patients may cough up the fungus elements because the organism frequently invades the bronchus. Chains of conidia can sometimes be seen in the sputum.

Culture
Aspergilli require 1-3 weeks for growth. the colony begins as a dense white mycelium which later assumes a variety of colors, according to species, based on the color of the conidia. The hyphae are branching and septate. Species differentiation is based on the formation of spores as well as their color, shape and texture. 

Histopathology
The septate hyphae are wide and form dichotomous branching, i.e., a single hypha branches into two even hyphae, and then the mycelium continues branching in this fashion (figure 20).

Serology
There is an excellent serological test for aspergillosis which is an Immunodiffusion test. There may be 1 to 5 precipitin bands. Three or more bands usually indicate increasingly severity of the disease. i.e., tissue invasion.

Treatment
Voriconazole and Amphotericin B.

  Figure 20
Branching of aspergillus hyphae
Dr Arthur DiSalvo

Lung: Aspergillus hyphae in fungal pneumonia  © Bristol Biomedical Image Archive. Used with permission

  Nasal aspergillosis  © Bristol Biomedical Image Archive. Used with permission

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