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AP/CP Boards > Mycology > Flashcards

Mycology Flashcards

1
Q

Basic characteristics of fungi

  • Eukaryotic/Prokaryotic?
  • Energy and nutrition?
  • Reproduce?
  • Cell walls made of?
  • Principal cell wall sterol?
  • How do they grow?
A

Basic characteristics of fungi

  • Eukaryotic (membrane-bound nucleus, complex organelles)
  • Energy and nutrition - parasitic or saprophytic.
  • Reproduce by budding, fission or spore formation
  • Cell walls (polysaccharide and glycoproteins).
  • Principal cell wall sterol is ergosterol
  • Can grow as yeast-like cells or as molds
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2
Q

Traditional Classification (4)

A

Traditional Classification

  • Mucormycetes ( Rhizopus , Mucor , Absidia , Basidiobolus )
  • Ascomycetes ( Histoplasma , Blastomyces , some Candida )
  • Basidiomycetes ( Cryptococcus )
  • Deuteromycetes (most pathogenic Candida species, pathogenic Aspergillus species, Coccidioides )
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3
Q

Morphologic Classification (3)

A

Morphologic Classification

  • Yeast
    • grows as single cells
    • Candida , Cryptococcus
  • Molds
    • Multicellular filaments (hyphae), multiple genetically identicle nuclei, colony
    • Aspergillus, Mucormycetes, many others
  • Dimorphic fungi
    • yeasts/spherules at 37°C, molds at 25°C
    • Histoplasma, Blastomyces, Coccidioides, Paracoccidioides, Sporothrix
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4
Q

Diagnosis of Fungal Diseases

A

Diagnosis of Fungal Diseases

  • Culture causative fungus.
  • Microscopic morphology
  • Demonstrate specific host immune response
  • Demonstrate fungal antigen(s)
  • Demonstrate fungal nucleic acid sequence(s)
  • Demonstrate distinctive fungal metabolite(s)
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5
Q

How do you culture fungi?

A

Culture

  • Yeast-like fungi ( Candida spp. and related)
    • grow on routine bacterial media
  • Filamentous fungi (molds)
    • may grow on routine media
    • should be cultured on mycologic media for optimum recovery
    • special requirements ( M. furfur )
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6
Q

Mycologic Media (6)

A

Mycologic Media

  • Culture media for primary isolation): selective & non-selective agars, that can include:
    • Sabouraud’s glucose agar (SAB), non-selective
    • Selective SAB, with chloramphenicol
    • Selective SAB, with chloramphenicol plus cycloheximide (Actidione)
    • Blood Brain Heart Infusion (BBHI), non-selective
    • BBHI with gentamicin (G) & chloramphenicol (C)
    • Selective BBHI with G, C & Actidione
  • Usually incubated at 30oC
    • For possible dimorphs sub at 37 to convert to yeast
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7
Q

Fungal Identification

A

Fungal Identification

  • Yeasts: biochemical, supplemented by morphology
  • Molds and dimorphs: morphology, supplemented by biochemical and sequencing
  • MALDI-TOF is becoming widely used for yeasts; very promising for the rest.
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8
Q

Can We Do Fungal Blood Cultures?

A

Can We Do Fungal Blood Cultures?

  • Yes!
  • 90% of the time looking for yeast fungemia; usually from a urinary source
    • Conventional blood culture is perfectly adequate
    • Some conventional systems are insensitive for Cryptococcus
  • Occasionally looking for fungemia with a mold or dimorph; Aspergillus, Fusarium, Histoplasma
    • Special culture procedures
    • Biphasic bottle
    • Lysis-centrifugation (Isolator) system
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9
Q

Can you see fungi on Gram stains?

A

Microscopy

  • Budding yeast or mycelia are often evident on Gram stains
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10
Q

Diagnostically-useful fungal antigens

A

Diagnostically-useful fungal antigens

  • Commonly Used
    • Cryptococcus neoformans galactoxylomannan
    • Histoplasma capsulatum surface antigens
  • Used in specific/complex situations
    • Candida albicans enolase
    • Aspergillus fumigatus galactomannan
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11
Q

5 Types of Antifungal Drugs?

A

Antifungal Drugs

  • The azoles
  • The echinocandins
  • Amphotericin and derivatives
  • Flucytosine
  • Griseofulvin & Terbinafine
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12
Q

Antifungal Drugs

  • The azoles
A

Antifungal Drugs

  • The azoles
    • Ketoconazole: rarely used
    • Fluconazole: low toxicity, active against Cryptococcus , C. albicans , selected other Candida
    • Itraconazole: unreliable absorption, broad spectrum, esp vs dermatophytes
    • Posaconazole: oral only, broad spectrum; some anti-Zygomycete activity
    • Voriconazole: oral or IV, broad specturm, highly effective vs Aspergillus .
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13
Q

Antifungal Drugs

  • The echinocandins
A

Antifungal Drugs

  • The echinocandins
    • Expensive
    • very complete Candida coverage
    • good vs Aspergillus
    • limited coverage vs other fungi
    • Often used as second-line / salvage therapy.
    • Caspofungin, anidulafungin, micafungin, all IV only.
    • NO activity vs Cryptococcus.
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14
Q

Antifungal Drugs

  • Amphotericin and derivatives
A

Antifungal Drugs

  • Amphotericin and derivatives
    • Covers most Candida , Aspergillus , dimorphics with some specific exceptions.
    • IV only.
    • Nephrotoxic and infusion-related toxicities
    • liposomal and similar derivatives better tolerated.
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15
Q

Antifungal Drugs

  • Flucytosine
  • Griseofulvin & Terbinafine
A

Antifungal Drugs

  • Flucytosine: effective adjunctive agent vs Cryptococcus .
  • Griseofulvin & Terbinafine: good activity vs. dermatophytes.
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16
Q

Mold anatomy

A

Aspergillus

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17
Q

Aspergillosis

  • Yeast/Mold/Dimorph?
  • 3 Pathogenic species?
  • Common features?
A

Aspergillosis

  • Mold
  • Pathogenic species
    • A. fumigatus
    • A. flavus
    • A. niger
  • Common features
    • narrow septate hyphae that branch at 30-45o in tissue (acute-angle branching)
    • produce asexual spores in environment and in cultures, but not in mammalian tissues
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18
Q

What is it?

A

Aspergillus fumigatus

  • The most common pathogen
  • A. fumigatus has a dark-green colony
  • Flask-shaped vesicle with conidia swept away from stalk
  • Single row of phialides (uniseriate)
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19
Q

What is it?

A

Aspergillus flavus

  • Biseriate (2 rows of phialides)
  • Yellow colony
  • Phialides surround vesicle
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20
Q

What is it?

A

Aspergillus niger

  • White base with densely black conidia
  • Dark, rough conidia
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21
Q

Risks for Aspergillosis?

A

Aspergillosis: Epidemiology/ecology

  • Ubiquitous environmental saprophytes (dust, soil, on plants, etc).
  • Everyone is exposed to spores every day.
  • Neutropenia or phagocyte dysfunction (eg, CGD) is the key risk factor for invasive aspergillosis.
  • T-cell immunity is less important.
  • Environment influences incidence
    • decreases with filtered air
    • increased with construction/demolition
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22
Q

Aspergillosis Allergic Bronchopulmonary Disease

3 types?

A

Aspergillosis Allergic Bronchopulmonary Disease

  • hypersensitivity –> allergic pneumonitis or allergic bronchopulmonary aspergillosis (ABPA)
  • allergic aspergillosis
    • bronchospasm
    • fleeting pulmonary infiltrates
    • tends to be chronic or recurrent
  • refractory asthma
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23
Q

Aspergillosis Pulmonary colonization

Risks?

Symptoms?

A

Aspergillosis Pulmonary colonization

  • saprophytic colonization
    • usually no symptoms, but hemoptysis can result from local invasion
  • saprophytic colonization of preexisting lung lesions
    • superficial invasion
    • hemoptysis
24
Q

Invasive Aspergillosis

A

Invasive Aspergillosis

  • Invasive aspergillosis:
    • infection via inhalation of airborne spores
    • spores survive and germinate (produce hyphae) if local phagocytes are absent or dysfunctional
    • hyphae invade locally and spread via blood vessels
    • dissemination to distant organs via bloodstream
    • vascular invasion and occlusion produces extensive tissue necrosis and infarction
  • Pulmonary
  • Sinusitis
  • Other and disseminated disease
25
Q

How do you diagnose Aspergillosis?

A

Aspergillosis Diagnosis

  • Cultures
    • blood negative, even with disseminated
    • sputum/respiratory - colonization vs invasion
  • Biopsy & microscopy - KOH of fresh tissue or histopathology
  • Antibody testing seldom useful
  • Immunologic detection of cell surface antigens
    • Galactomannan test becoming more available,
  • PCR of rDNA sequences in blood and/or bronchial fluids
  • MORPHOLOGY
26
Q

Aspergillus size in tissue?

A

Aspergillus hyphae in tissue are 5-10 µm in diameter

27
Q

What is it?

A

Zygomycetes in Culture

  • Wooly, rapidly growing mold
  • Large, distinctive sporangium
28
Q

Mucormycosis (formerly Zygomycosis) Microbiology

  • Pathogenic species?
  • Common properties?
A

Mucormycosis (formerly Zygomycosis) Microbiology

  • Pathogenic species - Mucormycetes
    • Rhizopus sp.
    • Mucor sp.
    • Absidia sp.
  • Common properties
    • broad, aseptate hyphae, branching at 90o in tissue
    • produce sexual and asexual spores in the environment and in cultures, but not in mammalian tissues
29
Q

Mucormycosis

Where is it found?

6 major risk factors?

A

Mucormycosis Epidemiology/ecology

  • Ubiquitous environmental molds (decaying organic matter, fruits, etc)
  • Major risk factors include:
    • diabetic ketoacidosis
    • other metabolic acidoses (eg, uremia)
    • organ transplantation and abnormal CMI
    • neutropenia
    • burns
    • iron chelation therapy
30
Q

Mucormycosis 4 sites of involvement?

A

Mucormycosis

  • Rhinocerebral
  • Pulmonary
    • necrotizing pneumonitis with secondary blood vessel invasion, thrombosis & infarction
    • Dissemination to distant organs is common
  • Cutaneous
    • complication of extensive burns or other wounds
  • Gastrointestinal (rare)
    • invasion of gastrointestinal mucosa in malnourished children in developing countries
31
Q

How do you diagnose Mucormycosis?

A

Mucormycosis - Diagnosis

  • Cultures often negative, even in specimens containing visible fungal forms
  • Direct microscopy (KOH preps or histology) is most important diagnostic modality
  • No reliable serologic tests for antibodies or antigens, no DNA tests at this time.
32
Q

Mucormycosis size in tissue?

A

Mucormycosis hyphae in tissue are 10-30 µm in diameter

33
Q

How do you treat Mucormycosis?

A

Mucormycosis - Treatment

  • Multiple treatment modalities are essential
    • correct underlying host defense abnormality
    • surgical debridement/removal of necrotic tissues is essential
    • amphotericin B
    • posaconazole has some activity
    • Isavuconazonium approved specifically for Mucorales in 2015
34
Q

What is it?

Risk factor?

Common site of infection?

A

Fusarium

  • Opportunistic pathogen, esp in neutropenic patients
  • Common in fungal keratitis
  • Most commonly F. solani complex
  • Fusiform macroconidia; microconidia produced as well
  • Fluffy, white or colored colonies in culture
35
Q

Dermatophyte infections
3 major genera?

A

Dermatophyte infections

  • Taenia whatever…
    • Capitis; head and hair
    • Corporis, cruris, pedis; skin of body, groin, or feet
    • Onychomycosis – nail infections
  • Three major genera
    • Trichophyton
    • Epidermophyton
    • Microsporum
36
Q

What is it?

A

Trichophyton

  • Colonies
    • Slow to moderately rapid growth
    • Waxy, glabrous to cottony
    • Front, white to bright yellowish beige or red violet
    • Reverse pale, yellowish, brown, or reddish-brown
  • Microscopic
    • Microconidia, macroconidia, and arthroconidia
    • Miroconidia numerous; onecelled and round or pyriform in shape.
    • Macroconidia are multicellular smooth-walled and cylindrical, clavate or cigar-shaped. Produced in very few numbers or not at all.
37
Q

What is it?

A

Microsporum

  • Colonies
    • Glabrous, downy, wooly or powdery
    • Growth variable
    • Color varies depending on the species
      • Front: white to beige or yellow to cinnamon.
      • Reverse: yellow to red-brown.
  • Microconidia
    • Unicellular, solitary, oval to clavate in shape, smooth, hyaline and thin-walled.
  • Macroconidia
    • hyaline, echinulate to roughened, thin- to thickwalled, typically fusiform and multicellular, often with an annular frill.
38
Q

What is it?

A

Epidermophyton

  • Colonies
    • Grow moderately rapidly (10d or so)
    • Front: brownish yellow to olive gray or khaki
    • Reverse: orange to brown with an occasional yellow border.
    • Flat and grainy initially; then radially grooved and velvety.
  • Microconidia are typically absent.
  • Macroconidia (10-40 x 6-12 µm), thin walled, 3- to 5- celled, smooth, and clavate-shaped with rounded ends
39
Q

Differences between Dermatophytes?

A

The Dermatophytes Compared

  • Trichophyton differs from Microsporum and Epidermophyton by having cylindrical, clavate to cigar-shaped, thin-walled or thick-walled, smooth macroconidia.
  • Epidermophyton is differentiated from Microsporum and Trichophyton by the absence of microconidia.
  • Microsporum differs from Trichophyton and Epidermophyton by having spindle-shaped macroconidia with echinulate to rough walls
40
Q

What is it?

A

Candida albicans

  • Budding spherical to ovoid blastoconidia
41
Q

What is it?

A

Candida dubliniensis

  • Morphologically identical to C. albicans
  • Germ-tube positive
  • More likely to develop fluconazole resistance
  • Distinguish by:
    • C. albicans growth at 45oC
    • C. dubliniensis dark-green colonies on Chromagar
    • C. dubliniensis reduction of 2,3,5-triphenyltetrazolium chloride
    • Molecular methods (other methods not entirely accurate)
42
Q

What is it?

A

Candida glabrata

  • No pseudohyphae – also seen with Cryptococcus , but capsule usually evident as space surrounding cell for Crypto
  • Frequently fluconazole resistant
43
Q

What is it?

A

Candida parapsilosis

  • Short, curving pseudohyphae with round to oval blastoconidia
44
Q

What is it?

A

Candida tropicalis

  • Multibranched pseudohyphae, blastoconidia borne singly or in chains from along pseudohyphae
45
Q

What is it?

A

Candida lusitaniae

  • Short, curved pseudohyphae with blastoconidia at or between septae.
  • Tends to develop Amphotericin B resistance
46
Q

What is it?

A

Candida krusei

  • Branching pseudohyphae with elongated blastoconidia.
  • Inherently resistant to fluconazole, but typically susceptible to voriconazole and posaconazole
47
Q

Candidiasis Treatment

  • C. glabrata and C. krusei are resistant to ____
  • C. lusitaniae is resistant to _____
A

Candidiasis Treatment

  • azoles (fluconazole, voriconazole, posaconazole)
    • Resistance to fluconazole in C. glabrata and C. krusei
  • Some Candida species resistant to specific antifungals
    • C. lusitaniae & Ampho B
48
Q

What is it?

What are the tests?

A

Cryptococcus - Biochemicals

  • Produces melanin on Birdseed Agar
  • Strongly urease positive
49
Q

Cryptococcosis ___ vs ____

Media?

A

Cryptococcosis gattii vs neoformans

  • Canavanine glycine bromthymol blue agar (CGB agar) can be used to distinguish between C. gattii and C. neoformans .
  • C. gattii is blue on this medium.
  • Requires genotyping for confirmation.
50
Q

Cryptococcosis Epidemiology/ecology

  • Where in the world?
  • C. ____ a/w ____ droppings
  • C. ____ a/w ____ trees in ____
  • Current epidemic?
  • __% a/w abnormal ____ immunity
A

Cryptococcosis Epidemiology/ecology

  • worldwide distribution
  • var. neoformans associated with pigeon droppings and soil.
  • var. gattii associated with Eucalyptus trees in Australia and Southern California; current epidemic evolving in British Columbia and Pacific Northwest
  • >80% of infections in people with serious abnormalities of cell-mediated immunity (eg, AIDS, transplantation, others).
51
Q

What is it?

Media?

A

Crypto on cornmeal agar

52
Q
A

Crypto histology

53
Q

Stains?

Size?

A

Crypto stains

5-10 microns

54
Q

Diagnosis?

Associate with?

Symptoms?

Diagnosis?

Treatment?

A

Malasessia furfur = Spagetti and Meatballs

  • lipophilic yeast
  • associated with catherter infections
  • neonates on extended courses of parenteral lipid.
  • adults with severe immunocompromise
  • Fever, signs of sepsis, catheter blockage.
  • Diagnosis requires lipid in culture; alert lab
  • Treated by catheter removal and D/C lipids if possible.
55
Q
A

Sporotrichosis Microbiology & Epidemiology

Sporothrix schenckii

  • dimorphic (hyphae at ambient temp, round to cigar-shaped yeast at 37oC and in tissues
  • natural habitat: soil and plant matter
  • Worldwide distribution
  • Most frequent in gardeners or others exposed to plant material.

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