Opportunistic Mycoses

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Characteristics of opportunistic molds

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• Frequent laboratory contaminants
• abandon their saprophytic existence to cause opportunistic infections in immunocompromised patients
• Aspergillius and candida most common

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Mucormycosis - pathogenesis

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• caused by zygomycetes (Includes the genera Rhizopus, Mucor, and Absidia)
• Inhale spores
• Infects nasal sinuses (nasal discharge is black) and eyes
• Causes necrosis and blood clots
• Can migrate to brain: meningoencephalitis

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Mucormycosis - general ID

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• Rapid grower: 1-4 days
• Colony morphologyLid lifters
• Mycelium: White cottony (wooly) colony that turns gray when mature

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Absidia species

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• cause mucormycosis
• Internodal rhizoids (root-like hyphae)
• Typically have branching sporangiophores Sporangium tends to be pear shaped

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Mucor species

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• cause mucormycosis
• No rhizoids
• Typically have branched sporangiophores

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Rhizopus species

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• cause mucormycosis
• Nodal rhizoids
• Typically have unbranched sporagiophores

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Aspergillosis - general

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• Caused by aspergillus sp.
• Hyphae and/or conidia are light colored with septations
• Identification of genus/species is accomplished by macroscopic and microscopic examination

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Apergillosis - pathogenesis

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• Inhale conidia: develop sinusitis or bronchopulmonary disease
• can become systemic: rapid, fatal
• Can also be non-invasive in form of fungal ball and allergic fungal infections
• Most susceptible include bone marrow and transplant recipients, hematologic malignancies, and immunocompromised (90% mortality rate)

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Aspergillus - speciation

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• By evaluating colony morphology and microscopic arrangement of conidia on the phialides and vesicle to speciate.
• The phialides can directly attach to the vesicle which is called uniserate.
• The phialades may also be supported by a secondary structure called a metulae which is called biserate.

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Aspergillus fumigatus

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• Colony morphology: smoky, granular
• Microscopic exam: Uniserate, single row of phialides
• long chains of spherical conidia

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Aspergillus niger

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• Can cause swimmer’s ear
• Colony morphology: (salt and pepper appearance)
• Microscopic exam: Biserate and double row of phialides covering entire vesicle (radiate head)

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Mycotic keratitis - pathogenesis

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Fungal invasion of the corneal epithelium

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Fusarium sp

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• Most common cause of mycotic keratitis
• Rapidly growing

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Paecilomyces species

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• causes mycotic keratitis

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Scopulariopsis species

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• causes mycotic keratitis
• Tan colony with a brown center on its reverse
• lemon-shaped annelloconidia in chains which become spiny in age.

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Bipolaris

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• causes mycotic keratitis and Phaeohyphomycosis
• Conidiophores bend at the formation of each conidium, giving a knobby appearance.
• The conidia are oval, thick-walled, and contain four or five septations.

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Curvularia

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• causes mycotic keratitis and Phaeohyphomycosis
• Knobby conidiophores with boomerang shaped conidia that contain four cells

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Acremonium

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• causes mycotic keratitis and eumycotic mycetoma
• Unbranched tapering conidiophores support closely packed balls of sickle or elliptical shaped conidia.

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Mycotic otitis

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Invasion of the outer ear

caused by:

• Penicillium sp
• Aspergillus fumigatus
• Aspergillus niger
• Candida species
• Scopulariopsis species

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Penicillium species

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• cause mycotic otitis

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Alternaria species

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• causes opportunistic mycoses, Phaeohyphomycosis

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Nigrospora species

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• causes opportunistic mycoses

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Epicoccum species

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woolly to cottony colonies with rings of yellow, orange, and brown;

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Ulocladium species

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Bent-knee” shaped conidiophores lead to a zig-zag appearance and bear conidia that are dark round to oval (usually egg-shaped) that are usually more narrow at the base than at the apex. The conidia contain unconstructed horizontal and vertical septa.

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Cladosporium species

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• causes opportunistic mycoses

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Beauveria species

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• rarely causes keratitis.
• Known insect pathogen
• The surface is white to yellowish white or pale pinkish in color
• Single celled, tear-shaped conida appear as clusters on the tips of conidiophores that narrow at the tip

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Sepedonium species

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• Must distinguish from Histoplasma capsulatum, a dimorphic fungus
• Waxy and white colony rapidly becomes velvety with lemon color having a peripheral fringe

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Pneumocystis jiroveci Infection

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• (Interstitial Plasma Cell Pneumonia)
• Alveolar cells in the lungs are destroyed

Life cycle-3 stages:

• Trophozoite-irregular shaped
• Precyst
• Cyst-thick walled sphere that contains up to 8 intracystic bodies

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Pneumocystis jiroveci - Identification

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