Medical Microbiology: Superficial, Cutaneous, and Opportunistic Mycoses

Flashcard study set covering Superficial, Cutaneous, and Opportunistic Mycoses from preclinical medical microbiology lectures at Addis Ababa University.

Mycosis

An infection caused by a fungus.

Superficial Mycoses

Fungal infections confined to the outermost dead layer of the skin (stratum corneum) and hair shaft that cause largely cosmetic problems and do not elicit an immune response.

Cutaneous Mycoses

Fungal infections affecting the keratinized layers of the epidermis, hair, and nails.

Subcutaneous Mycoses

Fungal infections involving the dermis and subcutis tissue layers.

Systemic Mycoses

Deep fungal infections involving internal organs.

Primary Fungal Pathogens

Fungi capable of causing infection in healthy, immunocompetent hosts.

Opportunistic Fungal Pathogens

Fungi of low virulence that cause disease primarily in immunologically compromised hosts.

Pityriasis (Tinea) Versicolor

A common superficial skin infection caused by lipophilic Malassezia species, characterized by hyper- or hypo-pigmented, well-demarcated macules on oily areas of the body.

Malassezia species

Lipophilic, dimorphic yeasts (including M. furfur, M. globosa, and M. sympodialis) that form part of the normal human and animal skin flora.

Seborrheic Dermatitis

An inflammatory skin condition and manifestation of Malassezia infection closely associated with dandruff.

Fawn-Colored Macules

The most common clinical presentation of lesions in Pityriasis Versicolor, typically appearing on the trunk and upper arms.

Spaghetti-Hyphae and Meatballs-Yeasts

The characteristic microscopic appearance seen on a $10\,\text{\%}\,\text{KOH}$ preparation of skin scrapings from a patient with Pityriasis Versicolor.

Tinea Nigra

A rare, chronic superficial fungal infection of the palms and soles characterized by dark brown-to-black macules.

Hortaea werneckii

A dematiaceous (pigmented), dimorphic saprophytic fungus of the phylum Ascomycota that serves as the etiologic agent of Tinea nigra.

Dematiaceous Fungi

Fungi that naturally contain melanin or dark pigment in their cell walls.

Traumatic Inoculation in Tinea Nigra

The non-contagious mode of transmission for Hortaea werneckii from environmental sources like soil, compost, and wood into skin breaches.

Black Piedra

A chronic superficial fungal infection of the scalp hair shaft characterized by hard, fusiform black nodules firmly attached to the hair shaft.

Piedraia hortae

A slow-growing, dematiaceous, non-dimorphic ascomycetous mold found in soil that acts as the etiologic agent of black piedra.

Asci in Black Piedra

Fungal reproductive structures contained within the pigmented center of hard black hair nodules seen during direct microscopic KOH examination.

White Piedra

A superficial cosmetic fungal infection of the hair shaft affecting scalp, axilla, facial, or genital hair, marked by soft white-to-brown swellings loosely adhering along the hair strand.

Trichosporon species

Non-pigmented, non-dimorphic yeasts of Basidiomycota (such as Trichosporon asahii) that produce hyphae, pseudohyphae, and arthroconidia.

Trichosporonosis

Opportunistic systemic infections caused by Trichosporon species, including fungemia, pulmonary infections, endocarditis, and peritonitis in vulnerable hosts.

Cycloheximide Sensitivity in Trichosporon

The growth property of Trichosporon species requiring mycologic media free of cycloheximide, as cycloheximide inhibits their growth.

Dermatophytes

Filamentous molds with septate hyphae that are keratinophilic and keratinolytic, digesting keratin via keratinases.

Ringworm (Tinea)

The clinical disease designation for cutaneous fungal infections caused by dermatophytes.

Genus Microsporum

A genus of dermatophytes that infects hair and skin (rarely nails), predominantly affects children, and frequently shows spontaneous remission.

Genus Trichophyton

A genus of dermatophytes that infects hair, skin, and nails in both children and adults, causing chronic infections.

Genus Epidermophyton

A genus of dermatophytes that infects skin and nails (rarely hair), primarily affecting adults.

Anthropophilic Dermatophytes

Dermatophyte species (such as Microsporum audouinii and Trichophyton tonsurans) that primarily infect human hosts.

Geophilic Dermatophytes

Soil saprophytic dermatophyte species (such as Microsporum gypseum and Trichophyton ajelloi) that occasionally infect humans or animals.

Zoophilic Dermatophytes

Dermatophyte species (such as Microsporum canis and Trichophyton verrucosum) that primarily infect animals.

Tinea Capitis

Ringworm of the scalp, eyebrows, and eyelashes characterized by scaly bald patches, moist papules to pustules, and friable hair.

Tinea Barbae

Ringworm infection of beard hair, commonly presenting as edematous, erythematous lesions caused by Trichophyton mentagrophytes or Trichophyton verrucosum.

Ectothrix Hair Invasion

Dermatophyte invasion pattern characterized by the formation of arthrospores on the external surface of the hair shaft (e.g., M. canis, T. mentagrophytes).

Endothrix Hair Invasion

Dermatophyte invasion pattern where fungal growth occurs strictly inside the hair shaft, creating a 'black-dot' clinical appearance (e.g., T. tonsurans, T. violaceum).

Favic Hair Invasion (Favus)

Specialized endothrix hair infection caused by Trichophyton schoenleinii, producing a honeycomb pattern of damage on the hair shaft surface.

Tinea Corporis

Ringworm of non-hairy, smooth skin presenting as pruritic, circular patches with advancing red vesiculated borders and central scaling.

Tinea Cruris

Ringworm of the groin (jock itch) presenting as dry, pruritic, erythematous scaling lesions in intertriginous areas.

Tinea Pedis

Ringworm infection of the foot (athlete's foot), characterized by acute itching with red vesicles or chronic scaling, fissures, and interdigital maceration.

Tinea Unguium (Onychomycosis)

Ringworm infection of nails resulting in thickened, discolored, lusterless, or distally crumbling nails.

Dermatophytid (Id Reaction)

Pruritic vesicular-to-bullous skin lesions (commonly on fingers or palms) containing no fungi, representing a secondary allergic immune response to a distant dermatophyte infection.

Wood's Lamp Examination

A diagnostic tool using ultraviolet light that causes hair infected by certain Microsporum species to fluoresce bright greenish.

KOH (Potassium Hydroxide) Preparation

A rapid bedside test that dissolves host keratin in skin scrapings, hair, or nail samples to reveal branching septate fungal hyphae under microscopic examination.

Sabouraud Dextraud Agar (SDA)

A standard routine mycological medium used to culture fungal isolates, often supplemented with chloramphenicol or cycloheximide.

Candida species

Commensal yeast-like fungi capable of forming true hyphae and pseudohyphae, representing the leading cause of opportunistic mycoses in immunocompromised hosts.

Candida albicans

The principal human pathogenic Candida species, distinguished by its ability to form germ tubes, biofilms, and tissue-invasive hyphae.

Phenotypic Switching in Candida

The reversible capability of Candida albicans to transform between yeast forms and hyphal structures to facilitate tissue attachment and deep invasion.

Secreted Proteinases and Phospholipases

Extracellular digestive enzymes produced by Candida albicans hyphae that promote host cell membrane destruction and tissue penetration.

Oropharyngeal Candidiasis (Thrush)

A mucosal Candida infection of the oral cavity featuring white pseudomembranous plaques, affecting $80\,\text{\%}\text{--}90\,\text{\%}$ of HIV patients during disease progression.

Laryngeal Candidiasis

A mucosal Candida infection seen primarily in HIV-infected individuals and patients with underlying hematologic malignancies.

Vulvovaginal Candidiasis (VVC)

A common fungal mucosal infection experienced by $75\,\text{\%}$ of women at least once in their lifetime, with high rates of recurrence.

Glycosuria Predisposition to Candiduria

Urinary excretion of glucose in diabetic patients that directly promotes fungal multiplication while impairing host phagocytic immune responses.

Fungus Balls (Bezoars)

Aggregates of fungal hyphae and debris that accumulate in the upper urinary tract, posing a major risk of urinary outflow obstruction.

Ascending Urinary Tract Route

The primary pathway by which Candida organisms enter and colonize the bladder, usually associated with indwelling urinary catheters.

Hematogenous Spread in Renal Candidiasis

The primary route by which Candida organisms reach and infect the kidney parenchymal tissue during systemic dissemination.

Abdominal Candidiasis

Peritoneal Candida infection secondary to gastrointestinal tract perforation, acute pancreatitis, or surgical abdominal procedures.

Chronic Mucocutaneous Candidosis (CMC)

A severe, persistent, granulomatous or erythematous Candida infection of mucous membranes, skin, and nails occurring in individuals with congenital immunological or endocrine disorders.

Germ Tube Test

A rapid diagnostic screening test where incubation of yeast in serum and glucose produces short outgrowths without constrictions, identifying Candida albicans and Candida dubliniensis.

Non-Albicans Candida Species

Species including C. glabrata, C. krusei, C. tropicalis, and C. auris that often display higher resistance to azole antifungal agents.

Aspergillus species

Ubiquitous, non-dimorphic, filamentous molds with septate hyphae that constitute the second most common cause of opportunistic fungal infections.

Aspergillus fumigatus

The primary pathogenic Aspergillus species responsible for invasive aspergillosis, demonstrating excellent growth at $37\,^\circ\text{C}$ and thermal tolerance up to $\sim 50\,^\circ\text{C}$.

Aspergillus flavus

A pathogenic Aspergillus species associated with sinusitis, keratitis, and the production of carcinogenic aflatoxins.

Aflatoxin

A potent carcinogenic mycotoxin produced by Aspergillus flavus in contaminated grains that induces liver cell necrosis and hepatocellular carcinoma.

Aspergillus niger

An opportunistic Aspergillus species with moderate growth at $37\,^\circ\text{C}$ that commonly causes otomycosis (ear infections) and aspergilloma.

Secreted Elastases and Proteases in Aspergillus

Extracellular enzymes produced by tissue-invasive Aspergillus species that digest structural proteins to facilitate systemic dissemination.

Allergic Bronchopulmonary Aspergillosis (ABPA)

A hypersensitivity lung response triggered by the inhalation and transient growth of Aspergillus conidia in susceptible asthmatic or cystic fibrosis patients.

Aspergilloma (Fungus Ball)

A dense mass of Aspergillus hyphae, fibrin, and cellular debris colonizing a pre-existing pulmonary cavity without invasive tissue destruction.

Microscopic Features of Aspergillus in Tissue

Long, hyaline, septate hyphae measuring approximately $3.0\,\mu\text{m}$ in diameter that branch dichotomously at acute angles.

Blood Culture Limitations in Invasive Aspergillosis

The diagnostic property where sputum and blood cultures are frequently negative because Aspergillus invades deep vessel walls without circulating freely as yeast cells.

Temperature Tolerance Differential in Aspergillus

The laboratory principle where pathogenic Aspergillus species grow at $37\,^\circ\text{C}$, while non-pathogenic environmental species (e.g., A. glaucus, A. restrictus) fail to grow at $37\,^\circ\text{C}$.

Cryptococcus neoformans

An encapsulated, non-dimorphic yeast found worldwide in soil enriched with aged pigeon droppings, acting as an opportunistic pathogen in immunocompromised hosts.

Cryptococcus gattii

An encapsulated yeast associated with eucalyptus tree debris that acts as a primary pathogen, causing infections mostly in immunocompetent individuals.

Polysaccharide Capsule of Cryptococcus

The primary virulence factor of Cryptococcus species, possessing essential antiphagocytic properties that shield the yeast from host immune clearance.

India Ink Stain

A simple microscopic technique applied to CSF samples to highlight the prominent unstained capsule halo around Cryptococcus yeast cells.

Subacute Cryptococcal Meningitis

A central nervous system syndrome resulting from hematogenous dissemination of Cryptococcus from the lungs, presenting with subacute or intermittent headaches and fever.

Cryptococcoma

A localized, solid, tumor-like brain mass created by Cryptococcus fungal elements in the cerebral hemispheres or cerebellum.

Cryptococcal Antigen Test

A sensitive and specific latex agglutination or EIA laboratory assay that detects cryptococcal capsular polysaccharide antigen in CSF or serum.

Pneumocystis jirovecii

An obligate extracellular fungal organism adapted specifically to human lungs, causing life-threatening pneumonia in immunosuppressed individuals.

Fungal Classification Evidence for Pneumocystis

Biochemical and genetic features—including cell wall glucan, chitin subunits, elongation factor 3, and ribosomal RNA sequence homology—that confirm Pneumocystis is a fungus.

Membrane Cholesterol in Pneumocystis

An atypical feature of the Pneumocystis cytoplasmic membrane, which contains cholesterol instead of ergosterol as its predominant sterol.

Trophic Form (Trophozoite) of Pneumocystis

Single-nucleated, thin-walled extracellular life forms lacking cell wall $\beta$-glucan that adhere directly to type 1 alveolar epithelial cells.

Cyst Stage of Pneumocystis

An ascus-like life stage containing multiple intracystic sporozoites protected by a thick fungal cell wall composed of $\beta\text{-}1,3$ and $\beta\text{-}1,6$ glucans.

CD4+ T Cell Threshold for PCP Risk

A peripheral CD4+ T cell count of $200\,\text{cells}/\mu\text{l}$ or lower, marking an exceptionally high clinical risk for developing Pneumocystis pneumonia.

Major Surface Glycoprotein (MSG)

An abundant cell-surface protein expressed by Pneumocystis jirovecii that functions as an attachment ligand to alveolar tissues and undergoes antigenic variation.

Foamy Eosinophilic Alveolar Exudate

The characteristic histopathologic alveolar finding in Pneumocystis pneumonia that impairs gas exchange and causes severe progressive hypoxemia.

Non-Culturable Status of Pneumocystis

The diagnostic constraint that Pneumocystis jirovecii cannot be grown on artificial laboratory culture media, necessitating direct staining or molecular detection.

Methenamine Silver Stain for PCP

A histochemical stain applied to BAL or lung tissue specimens to highlight the typical cup-shaped or crushed ping-pong ball-like cysts of Pneumocystis jirovecii.

Trimethoprim-Sulfamethoxazole (TMP-SMX)

The primary first-line antimicrobial drug combination utilized for both treatment and primary prophylaxis of Pneumocystis jirovecii pneumonia.

Primary Prophylaxis Criteria for PCP

Indicated preventive treatment with TMP-SMX for HIV patients with CD4 count $< 200\,\text{cells}/\text{mm}^3$, CD4 percentage $< 14\,\text{\%}$, oral thrush history, or organ transplant recipients.

Mucormycosis (Zygomycosis)

A rapidly progressive, life-threatening opportunistic fungal infection caused by environmental molds of the order Mucorales (such as Rhizopus, Mucor, and Rhizomucor).

Angioinvasion in Mucormycosis

The hallmark pathogenic mechanism of Mucorales hyphae invading host blood vessels, resulting in extensive vascular thrombosis, tissue infarction, and black necrotic eschars.

COVID-Associated Mucormycosis (CAM)

A dramatic surge of mucormycosis infections observed in COVID-19 patients, driven by immune dysregulation, corticosteroid-induced immunosuppression, hyperglycemia, and hypoxia/acidosis.

Rhino-Orbital-Cerebral Mucormycosis

The most common clinical form of mucormycosis, presenting with severe sinusitis, facial swelling, palate/nasal black necrotic eschars, and rapid invasion of the orbit and brain.

Diabetic Ketoacidosis Risk in Mucormycosis

A metabolic condition where high blood glucose and acidosis impair phagocyte chemotaxis and release unbound serum iron, fostering rapid Mucorales proliferation.

Broad Aseptate Hyphae with Right-Angle Branching

The key microscopic morphological features of Mucorales fungi observed in direct KOH mounts or histopathological tissue sections.

Liposomal Amphotericin B

The preferred high-dose intravenous antifungal formulation used for immediate medical management of invasive mucormycosis.

Emergency Surgical Debridement

The mandatory non-pharmacological procedure performed urgently to physically remove devitalized, necrotic tissue in patients with mucormycosis.

Posaconazole and Isavuconazole in Mucormycosis

Broad-spectrum triazole antifungal agents utilized as step-down oral therapy or salvage options following initial amphotericin B therapy.

Whitfield Ointment

A topical therapeutic formulation containing benzoic and salicylic acid used in treating superficial fungal skin infections like Tinea nigra.

Griseofulvin

An oral systemic antifungal medication used to treat extensive or refractory dermatophyte infections involving hair, skin, or nails.