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Mycology Flashcards

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Biology 101 flashcards
1
Q

What are the oxygen requirements of fungi?

A

Mostly obligate aerobes, sometimes facultative aerobes

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2
Q

What are the features of molds?

A
  • Growth occurs by production of multicellular branching cylindrical tubules called hyphae
  • The mass of intertwined hyphae is called a mycelium
  • Some hyphae are divided into cells by cross-walls called septa
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3
Q

What are examples of clinically significant molds?

A
  • Zygomycetes
  • Aspergillus
  • Dermatophytes
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4
Q

What are the features of yeasts?

A
  • Spherical or ellipsoid unicellular organisms
  • Reproduce by budding
  • Some species produce buds that do not detach and become elongated, producing chains of yeast cells called pseudohyphae
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5
Q

What are dimorphic fungi?

A

Fungi that are capable of growing as both yeasts (in vivo, at 37ºC) and molds (22ºC, e.g. in the lab)

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6
Q

How can hyphae and pseudohyphae be distinguished?

A

In pseudohyphae, there is a slight tapering of the cell near the hypha (appearing like a chain of sausages), while in true hyphae, it is a cleaner straight line

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7
Q

What are examples of clinically significant yeasts?

A
  • Candida albicans
  • Creptococcus neoformans
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8
Q

What are examples of clinically significant dimorphic fungi?

A
  • Blastomyces dermatidis
  • Coccidioides immitis
  • Histoplasma capsulatum
  • Sporothrix shenckii
  • Paracoccidioides brasiliens
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9
Q

How do fungi reproduce?

A

Spores (both sexual and asexual)

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10
Q

Define

Sporangiospores

A

A collection of asexual spores within a sac-like structure called a sporangium

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11
Q

What are the features of the fungal cell membrane and cell wall?

A
  • The cell wall contains chitin (unbranched polymer of N-acetylglucosamine), glucans, and mannans
  • The plasma membrane contains ergosterol instead of cholesterol
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12
Q

What are the types of reactions to fungi?

A
  • Infection
  • Hypersensitivity
  • Intoxication from mycotoxins
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13
Q

Which fungus is prominent in hypersensitivity reactions?

A

Aspergillus fumigatus

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14
Q

How do fungi cause hypersensitivity reactions?

A

Spores and toxins of fungi contain potent surface antigens that stimulate strong type I hypersensitivity (allergic) reactions, manifesting as eosinophilia and IgE-mediated bronchoconstriction

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15
Q

Can mycotoxins be inactivated by cooking?

A

No, as most of them are heat stable

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16
Q

Which species produce aflatoxin?

A
  • Aspergillus flavus
  • Aspergillus parasiticus
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17
Q

Which foods are typically contaminated with aflatoxin?

A
  • Peanuts
  • Corn
  • Grains
  • Tree nuts
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18
Q

What is the pathogenesis of aflatoxicosis?

A
  • Aflatoxin is metabolized in the liver to epoxides, which are carcinogenic
  • Aflatoxin B1 causes mutations in the tumor suppressor gene p53, leading to hepatocellular carcinoma
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19
Q

How are mycoses classified?

A
  • Superficial infections
  • Cutaneous mycoses
  • Subcutaneous mycoses
  • Systemic mycoses
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20
Q

How are mycoses diagnosed?

A
  • Clinical presentation: the first indication of a potential systemic mycosis is the failure to respond to antibacterial antibiotics
  • Laboratory diagnosis: microscopic examination, serology, PCR, fungal culture
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21
Q

What are the types of specimens collected for diagnosis of a mycosis?

A
  • Ringworm: skin scales, nail clippings, scalp scrapings with hair stubs and skin scales (folded into paper squares for transport)
  • Candidiasis: mucous membrane swabs (transported in clear transport media)
  • Subcutaneous infections: scrapings and crusts, aspirated pus, biopsies
  • Systemic infections: specimens collected from the affected sites (e.g. bronchoalveolar lavage fluid, urine, wounds, genital swabs)
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22
Q

How are mycotic specimens prepared for microscopic examination?

A
  • Wet mount after partial digestion of the tissue by 10–20% KOH
  • Addition of calcofluor white aids in identification of the fungal cell wall in fluorescence microscopy
  • Special stains include: methylene blue, lactophenol blue, PAS stain, ink
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23
Q

What are the components of a fungal cell culture?

A
  • Sabouraud’s dextrose agar, which supports fungi and restricts growth of bacteria
  • Supplementation with chloramphenicol to inhibit bacteria and cycloheximide to inhibit saprophytic molds
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24
Q

What are the classes of antifungal agents?

A
  • Polyene derivatives
  • Azoles
  • Griseofulvin
  • Flucytosine (5-fluorocytosine)
  • Allylamines
  • Echinocandins
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25
Q

What is the mechanism of action of most antifungal drugs?

A

Targeting the synthesis or incorporation of ergosterol into the cell membrane

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26
Q

What are the fungicidal antifungals?

A

The polyene derivatives: amphotericin B and nystatin

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27
Q

What are the polyene derivatives?

A
  • Amphotericin B
  • Nystatin
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28
Q

What are the features of amphotericin B?

A
  • The most effective drug for severe systemic mycoses due to its broad spectrum and low incidence of resistance
  • Administered IV only
  • Forms complexes with already formed ergosterol in the cell membrane, causing cell lysis (fungicidal)
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29
Q

What are the features of nystatin/

A
  • Similar mechanism of action to amphotericin B (fungicidal)
  • Used to treat local candidal infections of the mouth and vagina
  • Too toxic for parenteral administration
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30
Q

What are the azoles?

A
  • Ketoconazole
  • Fluconazole
  • Voriconazole
  • Itraconazole
  • Posaconazole
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31
Q

What are the features of the azoles?

A
  • Interfere with the synthesis of ergosterol (fungistatic)
  • Oral drugs used to treat a wide range of systemic and localized mycoses
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32
Q

What are the features of griseofulvin?

A
  • Administered orally
  • Interferes with fungal mitosis (fungistatic)
  • Used to treat dermatophytoses only—has no effect on other fungi
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33
Q

What are the features of flucytosine (5-fluorocytosine)?

A
  • Disrupts nucleic acid and protein synthesis (fungistatic)
  • Administered orally, usually in conjunction with amphotericin B to treat cryptococcosis and candidiasis
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34
Q

What are the allylamines?

A

Terbinafine

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35
Q

What are the features of terbinafine?

A

Inhibits ergosterol synthesis at the earliest stage (fungistatic)

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36
Q

What are the features of the echinocandins?

A

Inhibit ergosterol synthesis (fungistatic)

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37
Q

What are the features of superficial mycoses?

A
  • They affect the skin (stratum corneum) only
  • There is no tissue invasion, little tissue destruction, and therefore no immune response
  • The organisms are commensal microbiotal fungi in overgrowth
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38
Q

What diseases do Malassezia spp. cause?

A
  • Pityriasis versicolor
  • Seborrheic dermatitis (dandruff)
  • Catheter-associated infections
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39
Q

What are the morphologic features of Malassezia spp.?

A
  • Lipophilic yeasts that are round in shape
  • The single cell yeasts become hyphated molds, appearing in a “spaghetti and meatballs” shape. The hyphae are septate
  • Note: this is not true dimorphism as it does not relate to temperature
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40
Q

What species cause pityriasis versicolor?

A
  • Malassezia furfur
  • Malassezia globosa
41
Q

What are the features of pityriasis veriscolor?

A
  • Discrete, serpentine maculae on the chest, upper back, arms, or abdomen
  • The maculae are hyperpigmented in light-skinned patients and hypopigmented in dark-skinned patients
  • Depigmentation is caused by carboxylic acids produced by the yeasts
  • Maculae may coalesce, but show limited scaling, inflammation, or irritation
  • More common in the tropics (elevated temperature and humidity)
42
Q

How is pityriasis versicolor diagnosed?

A
  • Skin scrapings are examined under a microscope using KOH and ink stains
  • Short unbranched, nonpigmented hyphae and spherical cells are observed
  • The lesions fluoresce under Wood’s lamp (UV irradiation), giving a pale green color
43
Q

What species cause seborrheic dermatitis (dandruff)?

A

Malassezia furfur

44
Q

What are the features of seborrheic dermatitis (dandruff)?

A
  • Skin hyperproliferation
  • Red lesions on the scalp covered with greasy scales, causing itching
45
Q

How are Malassezia infections treated?

A
  • Some cases resolve spontaneously
  • Topical azoles (as a cream or shampoo) are applied for 2 weeks for cosmetic reasons
  • In severe cases, oral azoles are used
  • There is a high recurrence rate
46
Q

What are the features of cutaneous mycoses?

A
  • Affect the skin and dermis only
  • Do trigger an immune response, resulting in localized symptoms
47
Q

Which genera are collectively known as dermatophytes?

A
  • Microsporum
  • Trichophyton
  • Epidermophyton
48
Q

What is the common name of dermatophytes?

A

Ringworm

49
Q

How are dermatophytes transmitted?

A
  • Contact with contaminated soil (geophilic species)
  • Direct contact (anthropophilic species)
  • Contact with infected animals (zoophilic species)
  • Any underlying skin conditions may increase risk of infection as the skin is the most important barrier to infection
  • Heat and humidity enhance infection
50
Q

What are the diseases caused by dermatophytes?

A
  • Tinea pedis (athlete’s foot)
  • Tinea unuguium (nail)
  • Tinea corporis (body)
  • Tinea cruris (groin area)
  • Tinea manus (hand)
  • Tinea capitis (head)
  • Tinea barbae (bearded region)
51
Q

What are the features of tinea pedia (athlete’s foot)?

A
  • Most prevalent dermatophytosis
  • Chronic infection of the toe webs
  • Initially, there is itching between the toes and the development of small vesicles that rupture and discharge a thin fluid
  • The skin of the toe webs becomes macerated and peels, and the cracks that appear are prone to secondary bacterial infection
  • Rarely, severe maceration and loss of foot volume can occur
52
Q

What are the features of tinea unguium?

A
  • Oftentimes follows prolonged tinea pedis or tinea manus
  • The nails become yellow, brittle, thickened, and crumbly
  • This is painless, unlike paronychia associated with candidiasis
53
Q

What are the features of tinea corporis?

A
  • Ring-like lesions with a clearing, scaly center surrounded by a red advancing border that may be dry or vesicular
  • Fungal metabolites, enzymes, and antigens diffuse through the epidermis leading to erythema, vesicle formation, and pruritus
54
Q

What are the features of tinea capitis?

A
  • Infection begins in the skin of the scalp and spreads down the keratinized wall of the hair follice
  • Tinea favus is an acute inflammatory infection of the hair follice, which may lead to permanint hair loss and black spots on the affected area
55
Q

How are dermatophytes diagnosed?

A
  • Microscopic examination
  • Culture
56
Q

How are dermatophyte samples prepared and examined microscopically?

A
  • Specimens are scrapings from the skin, nails, and hair
  • Specimens are prepared in a wet mount using 10% KOH
  • The fungi appear as branching hyphae
  • Hyphae or spores are detected either in the hair (endothrix) or around the hair (ectothrix)
57
Q

How are dermatophytes identified in culture?

A
  • Specimens are grown on Sabouraud’s dextrose agar at room temperature for 4 weeks
  • The arising colonies are examined microscopically after staining with lactophenol cotton blue
58
Q

How are species of dermatophyte distinguished?

A

Their microscopic morphology:

  • Microsporum: thick-walled, multicellular, spindle-shaped
  • Trichophyton: large, smooth, thin wall, pencil-shaped, septate hyphae
  • Epidermophyton floccosum: bifurcated hyphae with 2–4 cells; multiple smooth club-shaped spores (macroconidia)
59
Q

How are dermatophytes treated?

A
  • Local antifungal cream (e.g. miconazole)
  • Oral terbinafine for weeks to months
60
Q

What are the features of subcutaneous mycoses?

A
  • The causative agents typically reside in soil or on vegetation
  • Infection occurs often by traumatic implantation, with lesions expanding slowly from the area of inoculation
  • Inflammation and cell damage are triggered
61
Q

What is the causative agent of sporotrichosis?

A

Sporothrix schenkii

62
Q

What disease does Sporotrhix schenkii cause?

A

Sporotrichosis

63
Q

How is sporotrichosis transmitted?

A

A variety of plants, but especially rose bushes

64
Q

What are the features of sporotrichosis?

A

Granulomatous infection—either skin nodules or pulmonary sporotrichosis

65
Q

What is the causative agent of fungal mycetoma (Madura foot; maduromycosis)

A

Madurella mycetomatis, a mold with septate hyphae

66
Q

What disease does Madurella mycetomatis cause?

A

Fungal mycetoma (Madura foot; maduromycosis)

67
Q

What are the features of fungal mycetoma?

A
  • Affects subcutaneous tissues of the feet
  • Swelling follows trauma, with purplish discoloration and multiples sinuses that drain pus containing yellow, white, red, or black granules
  • In fungal mycetoma, the abscesses are not painful
68
Q

How is fungal mycetoma diagnosed?

A
  • Culture on SDA
  • Clinical presentation: black granules are typical of fungal mycetoma
  • Microscopic examination: septate hyphae with intercalary chlamydospores—spores in the middle of hyphae
69
Q

How is fungal mycetoma treated?

A
  • Chemotherapy: itraconazole, ketoconazole, amphotericin B
  • Surgical debridement or excision
70
Q

In which group do opportunistic mycoses occur?

A
  • Immunosuppressed patients
  • Patients with immunodeficiencies (e.g. AIDS patients with CD4+ T cell counts of <100 µL–1)
  • Pregnant women
  • Patients who have undergone extensive broad-spectrum antibiotic therapy
71
Q

What are the predisposing and risk factors for candidiasis?

A
  • Certain diseases, e.g. AIDS, diabetes mellitus
  • Persistent use of antibiotics or corticosteroids
  • General debility (e.g. ICU patients)
  • Urinary, venous, or arterial catheters
72
Q

What is the most clinically significant Candida species?

A

Candida albicans

73
Q

What are the diseases caused by Candida?

A
  • Cutaneous/mucosal candidiasis: thrush, vulvovaginitis, skin infection, diaper pseudorash
  • Candidemia
74
Q

Where are the typical locations of skin infection with Candida?

A
  • Axillae
  • Groin
  • Intergluteal folds (diaper pseudorash in newborns)
  • Inframammary folds
75
Q

What are the features of skin candidiasis?

A
  • Infected areas become red and may develop “weeping” vesicles
  • Paronychia: erythematous swelling of the nail fold
  • Interdigital candidiasis: forms a web between fingers. Prominent in those who skin hands in water extensively, e.g. homemakers, bartenders, cooks
76
Q

What is thrush?

A

Mucosal candidiasis on the tongue, lips, gums or palate, causing whitish pseudomembranous lesions

77
Q

What is vulvovaginitis?

A

Mucosal candidiasis of the vagina, characterized by irritation, pruritus, and vaginal discharge

78
Q

What are the features of candidemia?

A
  • Caused by indwelling catheters, surgery, intravenous drug abuse, aspiration, or damage to the skin or GI tract
  • Lesions may occur anywhere, especially the kidney, skin, respiratory tract, eye, heart, and meninges
79
Q

How are Candida samples identified microscopically?

A
  • Specimens include swabs and scrapings from superficial lesions, tissue biopsies, and exudates
  • Appear as oval, buding yeast cells; some form pseudohyphae
80
Q

How are Candida samples identified in culture?

A

Appear as creamy colonies on SDA agar:

  • Gram-positive
  • Produce germ tubes in human serum at 37ºC for 30 minutes
  • Form chlamydospores on cornmeal agar
  • Ferment glucose and maltose with acid and gas formation
81
Q

What is the causative agent of cryptococcosis?

A

Cryptococcus neoformans

82
Q

What disease does Cryptococcus neoformans cause?

A

Cryptococcosis

83
Q

How is cryptococcosis transmitted?

A
  • Inhalation of desiccated yeast cells from dry pigeon feces, trees, soil, etc.
  • The yeasts migrate to the central nervous system where they cause meningoencephalitis, or to the lungs
84
Q

How is cryptococcosis diagnosed?

A
  • Microscopic examination of CSF samples in wet mounts with or without India ink
  • Culture: either SDA or bird seed culture
  • PCR
85
Q

What are the diseases caused by Aspergillus spp.?

A
  • Allergic aspergillosis
  • Invasive aspergillosis
86
Q

What are the features of allergic aspergillosis?

A
  • Immediate asthmatic reaction upon second exposure after sensitization (mostly for A. fumigatus)
  • In others, the conidia germinate and hyphae colonize the bronchial tree without invading the lung parenchyma—allergic bronchopulmonary aspergillosis
  • Normal hosts exposed to massive doses of conidia can develop extrinsic allergic alveolitis
  • People with preexisting pulmonary lesions develop cavitary lesions filled with aspergillomas/fungomas
87
Q

What are the features of invasive aspergillosis?

A
  • Occurs in AIDS patients, people taking corticosteroids, or people with lymphomas and leukemias
  • Hyphae invade the lumens and walls of blood vessels, causing thrombosis, infarction, and necrosis
  • From the lungs, the disease may spread to the GI tract, kidney, liver, or brain, causing abscesses and necrotic lesions
88
Q

What is the causative agent of mucormycosis (zygomycosis)?

A

Molds of the order Mucorales, especially Rhizopus, Mucor, and Absidia

89
Q

What is the pathogenesis of mucormycosis (zygomycosis)?

A

Air contaminants enter the nose, eyes, heart, and brain of susceptible individuals

90
Q

How is mucormycosis (zygomycosis) diagnosed?

A

Direct examiantion or culture of nasal discharge, tissue, or sputum by direct smear

91
Q

How is mucormycosis (zygomycosis) treated?

A
  • Aggressive surgical debridement
  • Rapid administration of amphotericin B
  • Control of the underlying disease (e.g. diabetes)
92
Q

What is the causative agent of pneumocystis pneumonia?

A

Pneumocystis jiroveci

93
Q

How is pneumocystis pneumonia diagnosed?

A
  • BAL, lung biopsy, or induced sputum samples are stained and examined for presence of cysts or trophozoites
  • Stained with eosin methylene blue or silver stains
  • Cannot be culture in vitro
94
Q

How is pneumocystis pneumonia treated?

A

Trimethoprim-sulfamethoxazole (cotrimoxazole)

95
Q

What are the endemic mycoses?

A
  • Coccidiodiomycosis
  • Histoplasmosis
  • Blastomycosis
  • Paracoccidiodiomycosis
96
Q

What are the features of the endemic mycoses?

A
  • Most infections are asymptomatic or mild and resolve without treatment
  • A small number of patients develop pulmonary disease
97
Q

What are the types of fungi, by growth form?

A
  • Molds
  • Yeasts
98
Q

What are the types of fungi, by growth location?

A
  • Saprophytic: live on dead and decaying tissue
  • Parasitic: live on living organisms

Microbiology and immunology (33 decks)

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