Medical Mycology Flashcards

Question

25- The most common eumycotic organism in the US produces which color grains in its microcolony? A. White B. Black C. Red D. Yellow E. Green

Answer 1

►A The most common cause of fungal (eumycotic) eumycetoma in the US is Pseudallescheria boydii. This and Acremonium produce white colonies. Black colonies are caused by Exophilia, Madurella, and Curvalaria. Red colonies are created by Actinomadura pelletieri. Yellow colonies are made by Streptomyces and Nocardia, both causes of bacterial mycetoma.

Answer 2

►C Paracoccidioidomycosis is caused by Paracoccidioidomycosis brasiliensis, and is endemic to Central and South America, especially Brazil, Argentina, Venezuela, Ecuador and Colombia. Male agricultural workers are at greatest risk. Infection is most commonly caused by direct inoculation which leads to pulmonary disease. Lung disease may be followed by dissemination to mucocutaneous surfaces, gastrointestinal tract, spleen, adrenal glands, and lymph nodes. Cutaneous lesions are verrucous and/or ulcerative, and usually found on the face and in the nasal and oral mucosa. Primary mucocutaneous disease exists as well and is caused by direct inoculation. Biopsy specimens display multiple narrow-based budding yeast cells, described as a ―mariner‘s wheel.ǁ The treatment of choice is itraconazole.

Answer 3

►C Trichophyton rubrum is an anthropophilic dermatophyte that is a cause of T. pedis, T. manum, T. corporis, T. cruris, onychomycosis, Majocchiǁs granuloma, and rarely T. capitis. Colonies appear as fluffy to granular white to cream colored with reverse non-diffusible port-wine or red pigment. Macroconidia are rare, thin-walled pencil shaped. Microconidia are delicate teardrop shaped.

Answer 4

►A Microsporum canis os a zoophilic dermatophyte, which causes ectothrix invasion when infecting the hair. Colonies of M. canis are flat, spreading, white to cream-colored with a dense cottony surface, The reverse of the plate is a canary yellow. Wet mount of the fungus shows spindleshaped macroconidia with 5-15 cells and often have a terminal knob.

Answer 5

►D The diagnostic morphology of the Trichophytons overlap and may be difficult to differentiate. T. mentagrophytes produces a positive hair perforation test (wedges in the test hair).

Answer 6

►C All these organisms are dematiaceous, Fusarium is a hyalohyphomycete.

Answer 7

►C Southeast Asians and African Americans are at a higher risk for disseminated cocci, as are pregnant women and the immunocompromised. Approximately 60% of those contracting coccidiomycosis are asymptomatic, and the disease is infectious not contagious. The most common method of disease acquisition is inhalation from the soil during natural events (dust storms etc). Erythema nodosum is associated with a good prognosis and the first-line treatment during pregnancy is amphotericin B. (JAAD 2006 CME)

Answer 8

►B Trichophyton tonsurans is an anthropophilic dermatophyte that causes non-fluorescent endothrix hair invasion. It can cause black dot tinea capitis, tinea corporis, tinea pedis, and tinea unguium. An important identifying feature of T. tonsurans is its red-brown pigment that diffuses into the medium. Also, abundant tear-drop or club shaped microconidia can be found. It grows best in the presence of thiamine.

Answer 9

►C Causes white superficial onychomycosis.

Answer 10

►C Histoplasmosis is primarily a pulmonary infection that can disseminate to other organs. It is endemic to the Ohio, Missouri and Mississippi River Valleys where the bird and bat droppings in the soil contain the fungus. Primary cutaneous disease is extremely rare. At 25°C it displays septate hyphae and at 37°C H. capsulatum is a yeast. Itraconazole is the treatment of choice. On histopathological examination, intracellular organisms that display a halo are seen. The halo is not the result of a capsule but rather shrinkage artifact.

Answer 11

►D Chromoblastomycosis is a chronic fungal infection of the skin and the subcutaneous tissue caused by traumatic inoculation of a specific group of dematiaceous (pigmented) fungi. Fonsecaea pedrosoi is the most common causative organism, but Fonecaea compacta, Rhinocladiella aquaspersa, Phialophora verrucosa, Exophilia jeanselmei and Cladosporium carrionii are pathogenic as well. It is found most commonly in agricultural workers in the tropics and subtropics, and it is notoriously resistant to therapy. It presents as verrucous papules and plaques that may coalesce. Histopathological findings include brown, thick-walled cells known described as ―copper pennies.ǁ Early in its course, limited disease may respond to surgical excision, electrodessication or cryosurgery. More extensive lesions may require systemic antifungal agents including itraconazole or terbinafine, which are the treatments of choice.

Answer 12

►A There is an increased risk of dissemination of Coccidiomycosis in pregnant women, especially during the third trimester and the post-partum period. In a review by Crum et al, maternal demise correlated with disease diagnosed later in pregnancy, with only 45% of patients diagnosed in the third trimester surviving (Am J Medicine 2006;119(11):Pages 993.e11-993.e17). Given that azoles have been shown to cause teratogenicity, amphotericin B is recommended as the therapy in pregnant women.

Answer 13

►A Favus is a chronic dermatophyte infection defined by the presence of yellowish crusts in the hair follicles called scutula. Prolonged infections lead to cicatricial alopecias of the scalp and glabrous skin. The infection is most commonly caused by Trichophyton schoenleinii.

Answer 14

►B "Black dot ringworm" is endothrix tinea capitis. Black dots are remnants of brittle hair broken at the surface of the scalp (cuticle intact). On KOH prep, spores are seen within the hair shaft. Causes are T. rubrum, T. gourvilli, T. yaounde, T. tonsurans, T. schoeleinii, T. soudanense, and T. violaceum ("Ringo Gave Yoko Two Squeaky Violins."). T. verrucosum causes nonfluorescent ectothrix tinea capitis. M canis, gypseum, and auddouinii also cause ectothrix tinea capitis.

Answer 15

►E Candidal infections may clinically present as thrush/leukoplakia, perleche/angular cheilitis, vulvovaginitis, balanitis, paronychia, onychomcosis, intertrigo, and folliculititis. Median rhomboid glossitis is now also associated with candidal infections. Mycetomas are caused by true fungi (eumycetoma) or filamentous bacteria (actinmycetoma).

Answer 16

►C Paracoccidioides brasiliensis causes a chronic progressive infection that is most commonly seen in rural areas of South America. Patients may have constitutional symptoms, lung involvement, ulcers of the upper respiratory and digestive tract, and verrucous/ulcerated cutaneous lesions. Classically, Paracoccidioides brasiliensis has a marinerǁs wheelǁ appearance.

Answer 17

►C Proximal White Subungual onychomycosis is an AIDS marker, nails have a characteristic white opaque appearance beginning in the region of the lunula and extending distally under the nail plate.

Answer 18

►E Formerly known as T. beigelii.

Answer 19

►E Pseudohyphae are seen in yeast and resemble true hyphae except that they are constricted at septations, branching occurs at septations, and the terminal cell is smaller than the others. They are septated.

Answer 20

►D White superficial onychomycosis of the fingernails is a marker for immunosuppresion and should prompt testing for HIV. Generally, T. mentag is the most common cause of white superfical onychomycosis. However, in immunosuppressed patients, T. rubrum is the more common dermatophyte.

Answer 21

►C Is a dematiaceous organism and is the only organism listed that does not produce creamy white colonies.

Answer 22

►A Patients with white piedra are infected with Trichophyton cutaneum also known as Trichophyton beigelii. The treatment should be oral azole antifungals and shampoos without shaving the scalp.

Answer 23

►B This is the only organism in this list that fits this description.

Answer 24

►A Hyphae are vegetative tube-like structures. In septate hyphae, transverse cross walls form within the hyphae. Pseudohyphae, seen in yeast, resemble true hyphae except that they are constricted at septations, branching occurs at septations, and the terminal cell is smaller than the others.

Answer 25

►A All other mycoses are primary pulmonary infections, which may disseminate to the skin.

Answer 26

►A Yeast cells in chains and a large thick walled round central yeast cell surrounded by several thinly attached budding smaller yeast cells p.18. This biopsy is describing Paracoccidioides brasiliensis, an organism endemic in Brazil. Its yeast form seen in tissue produces a Mariners wheel-like configuration. Generally this organism is inhaled and disseminates causing mucocutaneous lesions with lymphadenopathy.

Answer 27

►D White piedra is an infection of the hair shaft caused by Trichosporon beigelii. Unlike black piedra which is firmly adherent to the shaft, white piedra presents as light brown nodules composed of hyphae and arthroconidia, which move easily along the hair shaft. The most common sites of infection occur on the mustache, beard and pubic area.

Answer 28

►D Calcofluor white is the most sensitive microscopic test for fungal infection. It is a glucan specific immunofluorescent stain. The remaining options are useful in direct microscopic examination, but not the most sensitive.

Answer 29

►B The wet mount Epidermophyton floccosum shows smooth, thin-walled macroconidia without microconidia. The appearance is occasionally referred to as ―snow shoesǁ. Epidermophyton floccosum is incapable of hair invasion, and therefore, does not cause tinea capitis.

Answer 30

►E Produces a white cerebriform colony lacking any conidia. M. ferrugineum produces a rust colored colony with bamboo-like hyphae without conidia. The other organisms produce micro and macroconidia.

Answer 31

►A This patient has sporotrichosis. Sporotrichosis is mainly an occupational disease of farmers, gardeners, and horticulturists. Persons who handle thorny plants, sphagnum moss, or baled hay are at increased risk. Outbreaks have occurred in nursery workers who handled sphagnum moss, rose gardeners, children playing on baled hay, and greenhouse workers who handled bayberry thorns contaminated by the fungus. Classic treatment is with oral potassium iodide for 3-4 weeks. The most recognised side effect of treatment is gastrointestinal distress. Thyroid function tests should be performed during treatment as suppression can occur.

Answer 32

►B Cryptococcus neoformans is an encapsulated yeast with a worldwide distribution. Cryptococcosis is usually acquired by inhalation and subsequent dissemination to various organs including the meninges and the skin can occur. Immunosuppressed patients are particularly susceptible to infection. In approximately ten percent of disseminated cases, cutaneous lesions may develop. These present as acneiform papules or pustules and may progress to infiltrated plaques, nodules, or ulcers. Less commonly, cutaneous lesions can represent primary cutaneous cryptococcosis via direct inoculation of organisms into the skin. Diagnosis is made by direct microscopy and India ink stains can aid visualization. The organisms are large, encapsulated budding yeasts. In histopathologic sections, capsules stain with alcian blue and mucicarmine stains. In culture, C. neoformans is distinguished by production of urease as well as the ability to pigment on Guizotia seed medium. Colonies are described as slimy and mucoid. Serologic antigen-detection assays are also available. Treatment of disseminated cryptococcosis includes amphotericin combined with flucytosine.

Answer 33

►A Lobomycosis, also know as keloidal blastomycosis is caused by Lacazia loboi (formerly Loboa loboi). It is endemic to Brazil and the Caribbean and is associated with dolphins. Clinically, the disease presents with painless keloidal papules and plaques, ulcerative lesions and/or verrucous lesions. Biopsy specimens display multiple budding thick-walled cells attached with a bridge, often referred to as a ―chain of coins.ǁ Surgical treatment is necessary as antifungal medications are ineffective.

Answer 34

►B Chromoblastomycosis, or chromomycosis, is a cutaneous mycosis caused by dematiaceous, or pigmented, fungi. Several fungal species are associated with this infection including Phialophora verrucosa, Fonsecaea pedrosoi, F compactum, Exophiala (Fonsecaea, Wangiella) dermatitidis and Cladosporium carrionii. Infection is typically trauma-induced and involves the lower extremities. Lesions appear as verrucous papules, nodules and plaques, with occasional elephantiasis resulting from lymphatic blockage. Histopathologic findings include pseudoepitheliomatous epidermal hyperplasia and a dermal infiltrate composed of epithelioid histiocytes, multinucleated giant cells, and small clusters of inflammatory cells including plasma cells, neutrophils, eosinophils and lymphocytes. The characteristic histopathologic feature is the presence of dark brown, thick-walled, ovoid spheres in clusters or chains referred to as "copper pennies" or Medlar bodies. They are visible without the use of special stains.

Answer 35

►C The structures formed during asexual propagation of fungi are termed either spores or conidia depending on their mode of production and they arise following mitosis of a parent nucleus. Conidia arise either by budding off conida-producing hyphae (on the sides or ends) or by differentiation of preformed hyphae. The size and shape are generally characteristic of the organism. Dermatophytes produce conidia. Arthroconidia are produced when hyphae fragment or lyse. They may appear as thick- or thin-walled cells and are typically larger than the hyphae from which they came. The separation occurs at the septae. The mold form of Coccidioides immitis reproduce in such a fashion. Sporangia are sacs or cases that are multicellular structures in which spores are produced. Zygomycetes reproduce in this way. Chlamydoconidia are thick walled, round conidia that are formed during unpleasant environmental conditions. Trichophyton tonsurans produces these structures.

Answer 36

►E Trichophyton verrucosum is a zoophilic fungus that requires thiamine and sometimes inositol for growth. T. violaceum and tonsurans only have a partial requirement for thiamine. Trichophyton equinum requires niacin. (Horses are nice).

Answer 37

►E Sabouraud Dextrose Agar (SDA) Emmons Modification does not contain cycloheximide. Mycosel/ Mycobiotic (SDA with cycloheximide and chloramphenicol) and Dermatophyte Test Media contain cycloheximide. Cycloheximide inhibits rapidly growing nonpathogenic molds and some pathogens (Cryptococcus neoformans, some Candida species, Prototheca, Scytalidium species, yeast forms of Histoplasma and Blastomyces). Chloramphenicol inhibits bacterial flora.

Answer 38

►D Pseudohyphae are products of yeast, which produce elongated yeast cells that do not pinch off, branching and pinching in at the points of septations.

Answer 39

►A The biopsy describes Blastomyces dermatitidis, the negative mucicarmine rules out Cryptococcus. Chicago is an endemic area for Blastomyces. The colony morphology also describes Blastomyces.

Answer 40

►B Trichosporon asahii can cause disseminated disease in immunocompromised patients, especially those with neutropenia. Patients develop nodular and then necrotic lesions and require systemic antifungal agents. Malassezia globosa is the most common cause of tinea versicolor, not M. furfur. M. pachydermatis, M. dermatis, M. obtuse, M. restrica, M. sympodialis and M. slooffiae are all thought to be medically important as well. M.sympodialis is part of the skin‘s normal flora. Trichosporon beigelii and Piedraia hortae are the etiological agents of white and black piedra respectively. Several Malassezia species have been implicated in neonatal cephalic pustulosis (‗neonatal acne‘).

Answer 41

►D T. tonsurans and T. violaceum cause the endothrix infection "Black Dot Ringworm". All other choices cause Grey Patch Ringworm.

Answer 42

►A There is a resistance due to a prior exposure.

Answer 43

►C On artificial media the mould form of Histoplasmosis produces hyphae with tear drop microconidia and round thick wall tuberculate macroconidia.

Answer 44

►C Dermatophytes utilize protein as a carbon source producing alkaline by-products causing Dermatophyte Test Media to turn from amber to red. Nondermatophytes cause the media to turn yellow due to acid by-products.

Answer 45

►A Wood's light positive dermatophytes (M. canis, M. audouinii, M. distortum, M. ferrugineum, M gypseum, and T. schoenleinii) fluoresce secondary to pteridine. Corynebacterium can fluoresce as well due to coproporphyrin III. Pseudomonas fluoresces from production of pycyanin. The other organisms do not react with a Wood's light.

Answer 46

►B KOH and culture are the best and most reliable lab tests to diagnose a fungal infection. M. canis is frequently found in kittens and puppies and is a common cause of tinea faciei in children. An oral antifungal should be prescribed when a fungal infection involves hair.

Answer 47

►D Cycloheximide in Mycosel or Mycobiotic media (SDA with cycloheximide and chloramphenicol) inhibits rapidly growing nonpathogenic molds and some pathogens (Cryptococcus neoformans, some Candida species, Prototheca, Scytalidium species, yeast forms of Histoplasma and Blastomyces).

Answer 48

►A Conidia are cells produced on the end or sides of hypha or conidiophore, the size and shape arrangement are generally characteristic of the organism. The remaining descriptions are of specific types of conidia. Spores produced in a sac are sporangia, thick-walled round cells that are resistant to the environment are chlamydoconidia, blastoconidia are formed by budding and arthroconidia are formed by fragmentation of hyphae.

Answer 49

►B T. soudanense produces an apricot colored colony with reflexive branching. It is an anthropophilic organism causing an endothrix tinea capitis. T. verrucosum produces a white colony and requires thiamine and inositol for sporulation, T. violaceum produces a purple colony and has a partial requirement for thiamine

Answer 50

►E All of the listed features are those of molds. Yeast are unicellular, oval to round cells that reproduce by budding or fission. They form moist colonies, not smooth or fuzzy colonies.

Answer 51

►B The etiologic agents of actinomycotic mycetoma are filamentous bacteria that require antibiotics, whereas fungal agents causing eumycotic mycetoma require antifungal therapy.

Answer 52

►C E. floccosum does not infect hair; M. audouinii and M. canis cause fluorescent ectothrix T. capitis, T. mentagrophytes ectothrix T. capitis. T.Schoenlinii can cause endothrix or ectothrix, fluoresces blue white. It causese favus with hyphae with air spaces in them.

Answer 53

►B Arthroconidia are formed by fragmentation of hyphae and may appear as thick or thin walled rectangular cells. An example would be the mould form of Coccidioides immitis. The remaining options are incorrect.

Answer 54

►E All three organisms are seen in AIDS patients and can produce molluscum-like lesions.

Answer 55

►D Mycetoma is a granulomatous infection of dermal and subcutaneous tissues usually occurring on the foot. Draining sinuses containing grains characterize such infections. Three types of mycetoma exist: eumycotic (true fungal), actinomycotic (filamentous organisms) and botryomycotic (bacterial infections). Madurella and Leptosphaeria species produce black grains. Pseudallescheria and Acremonium species, along with dermatophytes, make white grains. Nocardia brasiliensis and N. asteroides produce white grains, while Nocardia caviae and Actinomyces israelii tend to have yellow-white grains. Actinomadura madurae produce pink or white grains and Actinomadura pelleteri make red grains. Streptomyces somaliensis produce brown or yellow grains.

Answer 56

►E Organisms that cause an ectothrix pattern of tinea capitis include M. canis, M. audouinii, M. ferruginosum, M. distortium, M. gypseum and occasionally T. rubrum. T. tonsurans, T. violaceum, T. soudanense, T. gourvilli, T. yaoundei, and occasionally T. rubrum cause an endothrix pattern. T. schoenleinii causes favus in which hyphae and air spaces are seen in t he hair shaft. A bluish-white fluorescence pattern is seen with Wood‘s lamp. Clinically, patients have thick, yellow, cup-shaped crusts (scutula); scarring and secondary infection may result. M. canis, M. audouinii, M. ferruginosum, M. distortium display a yellow fluorescence on Wood‘s lamp examination.

Answer 57

►D Penicillosis is a recently recognized disease caused by infection with Penicillium marneffei, a dimorphous fungus that is contracted through inhalation. Cases have been described in Vietnam, China, and Thailand as well as imported cases in the U.S. in veterans returning from Vietnam. Bamboo rats in these areas have been shown to be infected with P. marneffei and may represent a reservoir. Although penicillosis has a tendency to occur in immunocompromised hosts opportunistically, it has also been described in normal hosts. Clinical presentation is typically with pulmonary or disseminated disease which can affect the skin, gastrointestinal tract, spleen, lymph nodes, skin, and bone marrow. Cutaneous features include multiple umbilicated papules which can enlarge and ulcerate occurring commonly on the face and trunk. Diagnosis is by culture or histopathology. Treatment is with itraconazole. Severe cases may require amphotericin B.

Answer 58

►B White piedra is cause by Trichosporon beigelii, or Trichosporon ovoides and T. inkin (new nomenclature). It presents with tan to white soft, nonadherent small concretions ~1mm, seen on the scalp, beard, moustache, and pubic areas. The hairs may fluoresce.

Answer 59

►D Pityriasis versicolor is primarily caused by the yeast M. furfur. M. furfur is a dimorphic, lipophilic organism that can produce metabolites such as azaleic acid (a dicarboxylic acid) that can inhibit tyrosinase and injure melanocytes

Answer 60

►C M. canis and T. tonsurans both cause tinea capitis. M. canis is more commonly associated with inflammatory tinea capitis and kerion formation.

Answer 61

►C Tinea imbricata or Tokelau, an unusual type of tinea corporis causing polycyclic scaly lesions, is endemic in the South Pacific Islands, Far East and C. & S. America.

Answer 62

►E The endemic area for Histoplasmosis includes: the Ohio, Mississippi and Missouri River Valleys Syracuse NY area and the Caribbean. This organism prefers soil with a high nitrogen content such as that enriched with bird and bat guano.

Answer 63

►E All organisms listed other than S. apiospermum cause black granules. S. Apiospermum which is the filamentous mold form of pseudallescheria boydii has white granules.

Answer 64

►A Chlorazol black E is chitin specific. Calcofluor white is glucan specific. Gomori Methenamine Silver (GMS) and Fontana-Masson are histology stains. KOH is a rapid, easy, reliable method for diagnosing fungal infections, but is not chitin-specific.

Answer 65

►B Mycelium does not have reproductive capabilities. The remaining statements are correct.

Answer 66

►B Mycetomas may be subdivided into eumycetoma and actinomycetoma . Mycetomas generally begin as subcutaneous swellings occurring on the feet. Later, sinuses, granules, and nodules may be seen. The skin and subcutaneous tissue may also become involved. Treatment is difficult in later stages.

Answer 67

►C Sporothrix schenckii produces tiny yeast cells 4-6 um difficult to demonstrate on biopsy unless there is an overwhelming infection. Asteroid bodies are seen on H & E and PAS as radiating fingers of eosinophilic material.

Answer 68

►D Eumycotic mycetoma is fungal and can be caused by Pseudallescheria boydii (most common in US), Madurella, Acremonium, curvalaria, and Exophilia jeanselmei. Actinomycotic mycetoma is bacterial and maybe caused by Nocardia asteroids or brasiliensis, Streptomyces, and Actinomyces.

Answer 69

►C M. gypseum may occasionally produce a dull fluorescence. M. canis is fluorescent.

Answer 70

►A This child is presenting with the characteristic scutula of favus. Favus is most often caused by T. schoenleinii, T. violaceum, and M. gypseum.

Answer 71

►A Pityriasis versicolor (Tinea versicolor) is caused by Malassezia furfur, M. globosa (most common cause), M. pachydermatis, M. dermatis, M. obtuse, M. restrica, M. sympodialis, and M. sloofiae. The organisms that cause Pityriasis versicolor are difficult to grow. The culture requires olive oil overlay.

Answer 72

►B Coccidioidomycosis: Primary inoculation is pulmonary. Erythema nodosum is a favorable prognostic sighn. Dissemination from the localized pulomary lesions may occur in less than 1% of infections. Target ogans of dissemination include the bones, joints, viscera, brain, meinnges, and skin. The causative organisms is Coccidioides immitis, is a nonbudding, thick-walled spherule, with a polysaccharide capsule demonstrated with Gridley or Gomori methanamine silver stain. It is endemic in northern Mexico, Venezuela, and in southwest US, especially California

Answer 73

►E Only T. soudanense in this group of choices produces an endothrix type of tinea capitis. Endothrix do not fluoresce. Trichophyton mentagrophytes, Microsporum nanum and Trichophyton verrucosum produce nonfluorescent ectothrix tinea capitis. Microsporum gypseum may produce a fluorescent or nonfluorescent ectothrix tinea capitis.

Answer 74

►C Racket forms (club-shaped cells), favic chandeliers (terminal hyphal branches having an antlerlike appearance), pectinate bodies (hyphae resembling a comb), spiral hyphae (hyphae forming corkscrew-like turns), and nodular bodies (knot-like structure of hyphae) are among the types of mycelia.

Answer 75

►D Chlorazol Black E is a chitin specific stain. The remaining options are useful in direct microscopic examination for fungal elements, but are not chitin specific.

Answer 76

►A SDA Emmons Modification is the gold standard medium. It is nutritionally poor, containing dextrose, peptones, water, and agar, and encourages sporulation. Phenol red, gentamicin, and cycloheximide are found in dermatophyte test media (DTM). Chloramphenicol and cycloheximide are found in Mycosel/Mycobiotic.

Answer 77

►C Trichophyton mentagrophytes is the dermatophyte primarily responsible for bullous tinea pedis. It typically has septate, spiral hypahe with cigar or grape like thin-walled microconidia.

Answer 78

►E Polymorphous lesions have been reported in Cryptococcosis

Answer 79

►C Aspergillus and Fusarium produce similar appearing morphology in biopsy. Coccidioidomycosis produces spherules, very few if any septations are seen in Zygomycosis, dark hyphae, yeast cells are seen in Phaeohyphomycosis.

Answer 80

►C Chlamydoconidia are thick-walled round cells, resistant to the environment. Arthroconidia are formed by fragmentation of hyphae, and may appear as thick or thin-walled rectangular cells. Blastoconidia are formed by budding. Sporangia are spores that are produced in a sac.

Answer 81

►D Calcofluor white is a glucan specific stain. Chlorazol black E is chitin specific. KOH is a rapid, easy, reliable method of diagnosing fungal infections but is not glucan specific; Swartz Lamkins contains a counterstain but is not glucan specific. Mayer's mucicarmine is a histology stain.

Answer 82

►B Tinea imbricata is characterized by concentric, annular, scaly rings resembling erythema annulare centrifugum. The causative agent is T. concentricum, which is endemic to the South Pacific, South and Central America and Asia. The infection is usually chronic.

Answer 83

►B Malassezia species fluoresce pale yellow with Wood‘s lamp examination. Trichosporon beigelii (not trichophyton) causes white piedra, an infection that causes tan to white, soft non-adherent concretions on head and pubic hairs. Piedraia hortae causes black piedra, which forms dark concretions that are adherent to scalp, beard, and pubic hairs. Micrococcus sedentarius is a bacterium that is responsible for pitted keratolysis, which is characterized by crateriform pitting that primarily affects the pressure-bearing aspects of the plantar surface of the feet and, occasionally, the palms of the hands. Tinea nigra (superficial phaeohyphomycosis) presents with asymptomatic brown to black, macular, non-scaly macules and patches on the palms or soles. Phaeoannellomyces werneckii is causative.

Answer 84

►B Aspergillus is seen as wide (3 um) septate dichotomously branching (45ǁ angles) hyphae.

Answer 85

►C C. albicans is responsible for approximately 50% of all Candidemia, but C. tropicalis is seen with increasing frequency among patients with dissemination and cutaneous manifestations.

Answer 86

►C M. gypseum is a geophilic organism, all others listed are anthropophilic.

Answer 87

►C Having diabetes is a risk factor for Mucormycosis, ring forms in the biopsy are the x-section of the wide sparsely septate hyphae.

Answer 88

►C Fluorescent-positive infections are caused b y:"Dogs And Cats Fight Some Gypsies" M. Distortum M. audouinii M canis M. ferrugineum T. schoenleinii M. gypsium (occasionally)

Answer 89

►A Chlorazol Black-E is a stain specific for chitin and is used in direct examination, not histologic preparations. The remaining options are histology stains useful in fungal identification in tissue.

Answer 90

►B This fungus is very difficult to treat due to its resistance to most antifungals. It is sensitive to cylcoheximide so it should be cultured on media free of this antifungal.

Answer 91

►A Nocardia brasiliensis is a common cause of actinomycotic mycetoma and the ulcerative, draining lesions can be misdiagnosed as sporotrichosis.

Answer 92

►C Trichosporon beigelii (new nomenclature: Trichosporon ovoides and Trichosporon inkin) causes white piedra as well as other superficial infections, including post-operative wound infections, paronychia, and onychomycosis. It grows as cream to yellow-colored pasty colonies when cultured. Treatment is with topical amphotericin B lotion, benzoic acid, salicylic acid, or cutting off affected hair. Black piedra is caused by Piedraia hortae, which grows as small, compact, black-greenish velvety colonies when cultured, and can be treated only by cutting off affected hairs.

Answer 93

►E This patient has molluscum-like lesions on the face in the setting of immunosuppression. The differential for such papules includes cryptococcus, histoplasmosis, coccidiomycosis, and penicilliosis. Blastomycosis can cause sporotrichoid lesions, warty vegetations, papillomatous proliferations, and osteomyelitis; it usually does not produce molluscum-type papules.

Answer 94

►E Yeasts and molds are not mutually exclusive. Dimorphism can occur - a dimorphic fungus will be in a mold form in the environment at 25 degrees and in a yeast/spherule form at 37 degrees C.

Answer 95

►B Lobomycosis, also called Keloidal blastomycosis, is caused by Loboa loboi. Lesions characteristically appear keloidal with or without fistulas. A common location for the infection is on the ears and has been associated with dolphins. Histologically, double contoured refractile spherules with budding may be seen.

Answer 96

►E At room temperature Histoplasma capsulatum produces round thick walled spiny macroconidia and pear shaped microconidia.

Answer 97

►D Mucicarmine stain is used to stain adenocarcinoma in addition to infectious organisms including Cryptococcus and Rhinosporidium. The Cryptococcus capsule stains red. Periodic Acid Schiff (PAS) is useful in identifying fungi, parasites, glycogen and the basement membrane. The wall of the organism stains red. Fontana-Masson stains melanin black and therefore helps identify dematiaceous (melanin-producing) fungi. Gormori methenamine silver stains fungi, parasites, Donovan bodies and Rhinoscleroma black. Von Kossa stain is used to identify calcium by staining it black.

Answer 98

►C This organism is ubiquitous and is abundant in soil enriched with pigeon droppings.

Answer 99

►C Sucrose hydrolysis is not a useful parameter to distinguish dermatophytes from one another. Growth temperature, colony morphology, hair fluorescence and nutritional requirements can be used to identify dermatophytes.

Answer 100

►E This is the only organism in this list that fits this description.

Answer 101

►C A mass of hyphae (vegetative tube-like structures) is known as a mycelium. Sporangia, Conidia, and Chlamydoconidia are structures formed through different types of asexual reproduction. Pseudohyphae are seen in yeast.

Answer 102

►B Cycloheximide is used in fungal culture media to reduce contaminants.

Answer 103

►C The large size of the spherule and the rough endospores describe this organism along with the clinical symptoms. The other organisms that produce spherules are Prototheca (8-20 um) and Coccidioides immitis (10-80 um)

Answer 104

►B M. audouinii was previously the primary cause of T. capitis in the US.

Answer 105

►C Organisms that cause an ectothrix pattern of tinea capitis include M. canis, M. audouinii, M. ferruginosum, M. distortium, M. gypseum and occasionally T. rubrum. T. tonsurans, T. violaceum, T. soudanense, T. gourvilli, T. yaoundei, and occasionally T. rubrum cause an endothrix pattern. T. schoenleinii causes favus in which hyphae and air spaces are seen in the hair shaft. A bluish-white fluorescence pattern is seen with Wood‘s lamp. Clinically, patients have thick, yellow, cup-shaped crusts (scutula); scarring and secondary infection may result. M. canis, M. audouinii, M. ferruginosum, M. distortium display a yellow fluorescence on Wood‘s lamp examination.

Answer 106

►D These lesions often have a deeper pigment at the advancing border. The other organisms are dematiaceous but are not the etiologic agent of tinea nigra.

Answer 107

►C Although fairly uncommon, S. apiospermum is the most frequently recovered organism causing eumycotic mycetoma in the US. This name represents the asexual stage of the organism which grows as a filamentous mould, the sexual state, Pseudallescheria boydii, grows as a cleistothecia (round sac containing ascospores).

Answer 108

►B Tinea corporis gladiotorum is caused by Trychophyton tonsurans. Clinically, it appears as well- defined, scaly plaques usually located on the arms, neck, and head.

Medical Mycology Flashcards

(146 cards)