MICROBIOLOGY 2 MIDTERMS

Introduction to Mycology: Characteristics, Classification, and Diagnosis

• Fungi are eukaryotic organisms that do not contain chlorophyll and produce filamentous structures and spores.
• Fungi can be saprophytic, symbiotic, commensal, or parasitic, and mainly infect immunocompromised or hospitalized patients with serious underlying diseases.
• Medical mycology is concerned with the classification of medically-important fungi, the nature and mode of action of anti-fungal agents, and the pathogenesis of fungal infections.
• Fungal taxonomy relies heavily on morphology and mode of spore production, and they may be unicellular or multicellular.
• Fungi can exist in yeast and mold forms, and most pathogenic fungi are dimorphic, forming molds at ambient temperatures but yeasts at body temperature.
• Fungal diseases (mycoses) can be classified as cutaneous, subcutaneous, systemic, or opportunistic, and diagnosis involves wet mount, skin test, serology, fluorescent antibody, biopsy and histopathology, culture, and DNA probes.
• Direct microscopic observation involves using 10% KOH and gentle heat, and skin testing is limited to determining cellular defense mechanisms and epidemiologic studies.
• Fungal serology measures antibodies, and newer tests to measure antigen are being developed.
• Direct fluorescent antibody can be applied to histologic sections or cultures.
• Inflammatory reactions to fungi can be pyogenic, granulomatous, or necrotic.
• Isolation media for fungi include Sabouraud dextrose agar with or without antibiotics or cycloheximide, and they are incubated at body temperature or room temperature.
• Fungi are poor antigens, and DNA probes are species-specific but expensive and rapid.

Cutaneous Mycoses: Understanding Dermatophytosis

• Cutaneous mycoses are infections of the skin, hair, or nails caused by keratinophilic fungi called dermatophytes.
• Dermatophytosis, also known as ringworm, is a specific type of cutaneous mycosis that can affect the nails, hair, and stratum corneum of the skin.
• Dermatophytes use keratin as a subject to live and are resistant to cycloheximide.
• Dermatophytes are classified into three groups based on their usual habitat: keratophilic, which invade only keratinized layers; geophilic, which are usually found in soil and transmitted to humans by direct exposure; and zoophilic, which are associated with animals.
• Trichophyton, Microsporum, and Epidermophyton are the three genera of dermatophytes responsible for causing cutaneous mycoses.
• Clinical dermatophytosis is classified and named according to the anatomic location involved, such as tinea corporis, tinea pedis, tinea unguium, tinea capitis, and tinea barbae.
• Trichophyton species can cause infections on hair, skin, and nails, with four distinct patterns: small-spored ectothrix, large-spored ectothrix, black-dot endothrix, and favus hair endothrix.
• Microsporum species are characterized by their thick-walled, spindle-shaped, multicellular morphology and are the most common etiologic agent of tinea.
• Epidermophyton floccosum is a dermatophyte with bifurcated hyphae with multiple, smooth, club-shaped macroconidia.
• To diagnose dermatophytosis, clinical appearance and direct microscopic examination with 10-25% KOH can be used, as well as culture on mycotic agar, Sabouraud dextrose agar, or selective media containing cycloheximide and chlorampenicol.
• The source of the infection can be determined by identifying whether the dermatophyte is anthropophilic, zoophilic, or geophilic.
• Diagnosis is based on the anatomical site infected, the type of lesion, examination with a Woods lamp, examination of KOH-treated skin scales, and culture of the organism.

Subcutaneous Mycoses: Types, Causes, Clinical Findings, and Diagnosis

• Subcutaneous mycoses are chronic, granulomatous infections of the subcutaneous tissues usually on an extremity caused by fungi and bacteria-like fungi that live in soil.
• There are six types of subcutaneous mycoses: mycetoma, phaeohyphomycosis, chromoblastomycosis, sporotrichosis, lobomycosis, and rhinosporidiosis.
• Mycetoma, also known as Maduromycosis or Madura foot, is a slowly progressive granulomatous infection of skin and subcutaneous tissues commonly affecting the extremities.
• Madurella mycetomatis, Pseudallescheria boydii, Acremonium, Exophiala jeanselmei, Leptosphaeria, and Aspergillus are the causative agents of mycotic mycetoma, which is usually more common in men.
• Mycetoma usually results from trauma or puncture wounds to feet, legs, arms, and hands, usually on the feet.
• Clinical findings of mycetoma include abscess formation, draining sinuses containing granules, deformities, and dissemination to muscles and bones.
• Sporotrichosis is a subcutaneous mycosis that can develop after a finger thorn prick.
• Chromoblastomycosis is a chronic fungal infection caused by Fonsecaea pedrosoi, which can cause nodulose chromoblastomycosis in Senegal.
• Diagnosis of subcutaneous mycoses is difficult due to the nonspecific clinical findings.
• Identification of the infecting fungus is done through characteristics of the granule, colony morphology, and physiological tests.
• Laboratory diagnosis includes proper history of the patient, gross examination of the lesion by a microbiologist, specimen collection of grains or granules, and direct examination of KOH mount and gram stain.
• Culture of different sets of media is used for diagnosis, where Actinomycetoma is suspected on direct examination, while Eumycetoma is suspected after washing grains several times in NS with antibiotics and then inoculating it on SDA with antibiotics and incubating at 25° and 37°C.