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Bacteriology > Fungi > Flashcards

Fungi Flashcards

1
Q

Morphologic characteristics of Aspergillus

A

Dichotomous (Y-shaped) branching and septated

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2
Q

Morphologic characteristics of Zygomycetes

A

Right angled (T-shaped) branching and non-septated

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3
Q

Morphologic characeristics of candida albicans

A

Hyphae, pseudohyphae, budding yeast (this triad is diagnostic of candida!)
If also germ tube positive = candida albicans

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4
Q

Morphologic characteristics of Malassezia

A

Clusters of yeast and strands of hyphae (spaghetti and meatballs)

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5
Q

Definition of dimorphism

A

Fungus exists in nature and room temp as a filamentous fungus (mold) and converts to yeast in tissue (NOTE that candida is the reverse)

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6
Q

Components of fungal cell wall

A

1-3 beta glucans, 1-6 beta glucans, mannans, chitin

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7
Q

Primary treatment for Zygomycetes

A

Amphotericin B

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8
Q

Primary treatment for Aspergillus

A

Voriconazole

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9
Q

Best stains for detecting fungi

A

Periodic acid-Schiff (PAS) and Gomorri’s Methenamine silver (GMS)
And always H&E

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10
Q

Presentation of Sporotrichosis

A

Subcutaneous, lymphocutaneous distribution, dimorphic pathogen, common in Maryland area when in contact with plants.
But other things present similarly so make sure to ask where person has been!

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11
Q

Superficial infections

A

Tinea versicolor

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12
Q

Mucocutaneous infections

A

Dermatophytosis, mucocutaneous candidiasis

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13
Q

Subcutaenous infections

A

Chromoblastomycosis, mycetoma, sporotrichosis

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14
Q

Deep mycosis

A

Opportunistic (candidiasis, aspergillosis, zygomycosis) and pathogenic (histoplasmosis)

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15
Q

What is the difference between conidia and sporangiospores?

A

Both are asexually produced propagation structures of fungi (what we actually inhale), but sporangiospores are from zygomyces and conidia are from aspergillus and all other fungi

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16
Q

Possible virulence factors of fungi

A 
Cell surface receptors
Hydrolytic enzymes
Host mimicry
Polysaccharide capsule
Melanin production (inhibits oxidative killing mechanisms)
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17
Q

What fungus has budding yeast and is encapsulated?

A

Cryptoccocosis

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18
Q

What molecule makes up the lipid portion of fungal cell membrane?

A

Ergosterol

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19
Q

What components of fungal cell wall can be detected in culture and used to diagnose fungal infections?

A

1-3 B glucan, mannas, galactomannan

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20
Q

What is the fundamental way in which many antifungal agents work?

A

Interrupting erogsterol biosynthesis

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21
Q

What are the main targets of antifungal agents in the pathway of ergosterol biosynthesis, and which antifungal agent affects each target

A

Squalene epoxidase - allylamines
Lanosterol 1,4 a-demethylase - azoles
Ergosterol itself - Ampho B

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22
Q

Mechanism of action of Ampho B

A

Binds directly to ergosterol in cell membrane to form ionic pores

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23
Q

Toxicity of ampho B

A

Kidney

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24
Q

Spectrum of Ampho B

A

Yeasts and moulds (filamentous fungi)

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25
Q

Mechanism of action of Azoles

A

Inhibit cytochrome P-450 dependent enzymes (lanosterol C14-demethylase) required to synthesize ergosterol

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26
Q

Toxicity of Azoles

A

Hepatic

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27
Q

Spectrum of Azoles

A

Yeasts and moulds (filamentous fungi)

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28
Q

What is the major azole used to treat aspergillus?

A

Voriconazole

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29
Q

What is the major azole used to treat candida and cryptococcus?

A

Fluconazole

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30
Q

Mechanism of action of echinocandins

A

Target fungal cell wall biosynthesis of 1-3 beta-glucans

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31
Q

Toxicity of echinocandins

A

Hepatic

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32
Q

Spectrum of echinocandins

A

Only Candida and Aspergillus (primary agents against Candida!)

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33
Q

Mechanism of action of 5-fluorocytosine (5-FC)

A

Inhibit synthesis of DNA and RNA (similar to the 5-FU used in cancer therapy)

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34
Q

Toxicity of 5-FC

A

Hepatic

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35
Q

Spectrum of 5-FC

A

Cryptococcus (primarily causes meningitis so this is primary agents against it)

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36
Q

Mechanism of action of Allylamines (Terbinafine)

A

Inhibits squalene epoxidase and ergosterol synthesis

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37
Q

Toxicity of Terbinafine

A

Hepatic

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38
Q

Spectrum of Terbinafine

A

Dermatophytes

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39
Q

What is the primary treatment for cryptococcal meningitis?

A

Ampho B + 5-FC

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40
Q

What is the most superficial mycoses?

A

Tinea versicolor

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41
Q

What are the cutaneous mycoses?

A

Dermatophytoses and onchomycosis

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42
Q

What are the most common dermatophyte organisms?

A

Epidermophyton floccosum, Microsporum, Trichophyton

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43
Q

Dermatophyte infection of the foot?

A

Tinea pedis

44
Q

Dermatophyte infection of the capitis?

A

Tinea capitis

45
Q

Dermatophyte infection of the body?

A

Tinea corporis

46
Q

Dermatophyte infection of the groin?

A

Tinea cruris

47
Q

Dermatophyte infection of the nail?

A

Tinea unguium

48
Q

Dermatophyte infection of the hand?

A

Tinea manuum

49
Q

Which dermatophyte causes tinea pedis?

A

Trichophyton rubrum

50
Q

Which dermatophyte causes tinea capitis?

A

Trichophyton tonsurans

51
Q

Which dermatophyte predominates in US?

A

Trichophyton

52
Q

Which dermatophyte predominates in the rest of the world?

A

Microsporum

53
Q

Which tinea does Microsporum not cause?

A

Tinea ungugium (nails)

54
Q

Which dermatophyte causes tinea cruris?

A

Epidermophyton floccosum

55
Q

What is “black dot” alopecia?

A

Kerion forms where hair broke, get increased cell-mediated immune response

56
Q

What are the different mechanisms of hair invasion?

A

Ectothrix invasion - outside hair shaft, cuticle destroyed. Endothrix invasion - within hair shaft, cuticle intact.

57
Q

What is the primary method of diagnosis?

A

KOH or calcofluor preparation of scrape from leading edge of lesion

58
Q

What is the treatment for tinea capitis?

A

Oral antifungals (terbinafine, intraconazole); ketoconazole shampoo; selenium sulfide lotion for family members

59
Q

What is the treatment for tinea pedis, tinea corporis, tinea cruris, tinea manuum?

A

Topical antifungals (miconazole, clotrimazole, etc.); oral antifungals given if infection is extensive/severe

60
Q

What is onychomycosis?

A

Infection of nail plate/nail bed

61
Q

What causes onychomycosis?

A

Dermatophytes, usually Trichophyton rubrum. Increased risk in diabetics, HIV/AIDS, other compromised hosts

62
Q

Why is good foot care essential for diabetics?

A

If onychomycosis develops on toenail and penetrates into skin, can cause staph infection. Staph infection -> osteomyelitis -> amputation

63
Q

Three clinical types of onychomycosis

A

Proximal subungual (PSO), distal subungual (DSO), white superficial (WSO)

64
Q

Which is the most common type of onychomycosis?

A

DSO

65
Q

Mechanism of invasion of DSO

A

Hyphae enter distally under nail plate and spread proximally, digesting stratum corneum of nail bed and nail plate

66
Q

Mechanism of invasion of PSO

A

Infection enters at cuticle and involves proximal nail bed, can spread distally

67
Q

Mechanism of invasion of WSO

A

Dorsal surface of nail plate is attacked, minimal inflammation as viable tissue not involved

68
Q

Treatment for onychomycosis

A

Oral therapy (terbinafine, intraconzole)

69
Q

What causes tinea versicolor?

A

Malassezia furfur

70
Q

Treatment for tinea versicolor

A

Topical: econazole, ketoconazole, or selenium sulfide shampoo; Short course oral: itraconazole, fluconazole

71
Q

Dermatophytes from what source will cause muted inflammatory response?

A

Anthropophilic species (like T. tonsurans) because the immune system recognizes these as self

72
Q

Which dermatophyte causes tinea cruris?

A

Epidermophyton floccosum

73
Q

What is an early indicator of HIV infection?

A

Proximal subungual onchomycosis (PSO)

74
Q

What is the difference between opportunistic and pathogenic mycoses?

A

Opportunistic - only occur in compromised hosts; pathogenic - occur in host no matter the state of the immune system

75
Q

What are the morphological characteristics of candida?

A

Hyphae, pseudophyphae, budding yeast

76
Q

Treatment for mucocutaneous candidiasis

A

Topical azoles, or oral fluconazole

77
Q

What predisposes an individual to mucocutaneous candidiasis?

A

Immunosuppression by underlying diseases (HIV, diabetes), steroids, pregnancy, age, and receiving antibiotics

78
Q

What predisposes an individual to invasive candidiasis?

A

Usually seen in hospitalized patients (altered barriers like catheters, trauma, etc.); unresponsive to antibacterial antibiotic

79
Q

Pathogenesis of invasive candidiasis

A

Adherence and colonization
Penetration through barrier and angioinvasion
Hematogenous dissemination
Organ seeding
Replication in tissue yield necrosis +/- abscess formation with budding yeast and hyphae present

80
Q

Treatment of invasive candidiasis

A

First line - echinocandins, then fluconazole

81
Q

What clinical diseases are associated with Aspergillus?

A

Toxins, allergic syndromes, colonization (old TB cavity), infections (keratitis, invasive disease)

82
Q

Pathogenesis of invasive aspergillosis

A

Inhalation of conidia
Compromised host cannot phagocytose with macrophages
Germination of conidia with hyphal invasion of lung parenchyma
Angioinvasion with thrombus formation and tissue necrosis
Hematogenous dissemination from lung to elsewhere

83
Q

Morphological characteristics of Candida albicans?

A

Hyphae, pseudohyphae, and GERM TUBE

84
Q

Morphological characteristics of Aspergillus?

A

Septated, branching hyphae

85
Q

Treatment for Aspergillus?

A

Voriconazole, or liposomal AmphoB

86
Q

Pathogenesis of Zygomycosis

A

Inhalation/contact with sporangiospores (asexual spores)
Infection in paranasal sinuses
Tissue invasion of nerves and blood vessels may eventually invade orbit and eye
Direct extension of invasion to brain

87
Q

Morphological characteristics of Zygomycosis

A

Wide, nonseptated hyphae that branch at right angles (T shape)

88
Q

What clinical disease is frequently caused by Cryptococcus neoformans?

A

Meningioencephalitis

89
Q

What patients are at risk for Cryptococcus neoformans infection?

A

T cell compromised patients (on high dose steroids, on immunosuppressive agents, HIV+ patients with low CD4 count)

90
Q

Pathogenesis of Crytococcosis

A

Inhale yeast
Replicate in lung and recruit CD4, CD8 cells
Can clear pulmonary infection, but can also results in hematogenous dissemination across BBB
Replicate yeast and form gelatinous lesion
Breakdown meninges

91
Q

Morphological characteristics of Cryptococcus neoformans

A

Spherical yeast cells, pinched attachment between mother and daughter cells
Capsulated

92
Q

What is the capsule of Cryptococcus composed of?

A

Glucuronoxylomannan (used as antigen for rapid diagnosis)- Inhibits intracellular phagocytosis

93
Q

What is phenoloxidase

A

Enzyme in production of melanin, specific for C. neoformans

94
Q

Treatment for Cryptococcus

A

Ampho B plus 5-FCCan use fluconazole for maintenance

95
Q

Treatment for Pneumocystis carinii

A

Trimethoprim-sulfamethoxazole

96
Q

What are the fungi that cause deep mycoses?

A

Histoplasma capsulatum
Coccidiodes immitus
Blastomyces dermatitidis
Paracoccidiodes brasilensis

97
Q

Where is Histoplasma capsulatum found?

A

Soil and caves with bird or bat fecal material

Ohio-Mississippi river valley regions

98
Q

Where is Coccidiodes immitis found?

A

Desert soil in SW USA

Sonoran valley climates in Latin America

99
Q

Where is Blastomyces dermatitidis found?

A

Water in North Central and SE USA

100
Q

How do deep mycoses enter host?

A

Inhalation of asexual spores

Not transmitted person to person

101
Q

How does Histoplasmosis present?

A
  • 90-95% have asymptomatic or mild respiratory symptomology

- Disease of reticuloendothelial system - liver, spleen, lymp nodes, bone marrow, adrenals

102
Q

Pathogenesis of Histoplasmosis?

A

Inhalation of asexual spores (microconidia)
Conversion to yeast phase
Phagocytosed, but not killed, by alveolar macrophages
Replicate in macropage
Go to visceral organs and spread, especially if immunocompromised and can’t form granuloma

103
Q

Normal v. immunocompromised host presentation of Histoplasmosis (compare them)

A

Normal host - granulomas produced
- Can have necrosis (caseous necrosis) so almost indistinguisable from TB
Immunosuppressed host - no well formed granulomas, many intracellular yeasts in each macrophage

104
Q

Morphological characteristics of Histoplasma

A

3 um budding INTRACELLULAR yeast - in cytoplasm of macrophages, histiocytes, and lymphocytes

105
Q

Morphological characteristics of Blastomyces dermatidis

A

Large yeast with thick double refractal wall (no capsule), broad base budding

106
Q

Morphological characteristics of Coccidiodes immitis

A

Spherules

107
Q

What is the treatment for the deep mycoses?

A

Intraconazole (and can use fluconazole for Coccidiodes)

Bacteriology (19 decks)

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