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Micro > Lecture 8 > Flashcards

Lecture 8 Flashcards

1
Q

MYCOLOGY

Myco=fungi ology=study of

A
  • Eukaryotic organisms
  • Have a true nucleus, nuclear membrane and organelles
  • Are Heterotrophs-depend on organic matter for carbon
  • yeasts
    -Unicellular but some species can form hyphe or pseudohyphae
    -White
  • asexual reproduction by budding
    -Form smooth round colonies
  • Most yeast are facultative anaerobes some are strict aerobes

*molds
-Multicellular and are organized into hyphae
-different colors
-reproduction sexual or asexual by spores
-fuzzy

  • Most fungi except yeast are obligate aerobes
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2
Q

FUNGAL CELL WALL

A
  • Thick cell wall made of chitin, glucan
    (polysaccharides) & mannan (protein)
  • Cell membrane contains ergosterol and zymosterol
  • Human cell membrane has cholesterol
  • Anti-fungals rely on this difference to target fungi & not affect human cells

Fungus are classified by the method of their sexual reproduction & type of sexual spore produced

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3
Q

FUNGAL ASEXUAL REPRODUCTION

A

Performed when conditions in environment are good – no genetic diversity
-mycelium form asexual spore forming bodies above the ground.
-haploid nucleus inside the fruiting body divides many times by mitosis forming many haploid spores that are genetically identical to the parent

  1. Use of a spore forming body
    Sporaniophore→sporangium – produce sporangiospores
    Conidiophore→phialides – produce conidia
  2. Splitting of hyphe→ produce arthroconidia
  3. Budding → producing blastoconidia
    * Cell swells and a bud breaks free
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4
Q

FUNGAL SEXUAL REPRODUCTION

A

Performed when environmental conditions are poor
-meiosis: results in daughter cells each with half the number of chromosomes of the parent cell- each cell is genetically different

3 Methods of sexual reproduction :
1. Mating of hyphae results in the creation of a zygospore
2. Production of an ascus sac that produces ascus spores
3. Basidium forming basidiospores

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5
Q

class Glomeromycota

A

sexual spore - zygospore (thick wall cell in between hyphae)

Asexual spore= sporangiospore in a sac like structure called
sporangium

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6
Q

class ASCOMYCOTA

A

Sexual spore- ascospores present in a Sac like structure called an ascus

Asexual spore- conidia on
conidiophor

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7
Q

class BASIDIOMYCETES

A

Sexual fusion- results in formation of a club shaped structure called basidium forming basidiospores

Asexual reproduction: occurs more rarely
* Budding
* Fragmentation
* Conidia formation

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8
Q

FUNGAL STRUCTURES

A
  • Multicellular = filamentous molds
  • Unicellular = microscopic yeasts
  • Molds have “hair” called mycelia - fuzzy or woolly appearance
  • Mycelia made up of hyphe
  • Hyphae grow at the tip and divide creating long and branching chains
  • Enzymes secreted from the hyphal tip -breakdown organic matter into smaller molecules which are used
    as food.
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9
Q

ASEPTATE HYPHAE

A
  • Initial hypha grows out from a spore
  • Non-septate or aseptate hyphae form one long cell with many nuclei
  • While they do not form septa between nuclei, they do form a septum at branch points that connect one
    filament to another, preventing the entire network from being compromised if one hypha is injured.
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10
Q

SEPTATE HYPHAE

A
  • Hyphae with dividers called septa between the cells
  • Pores between the cells let cytoplasm and nutrients flow throughout the mycelium
  • nucleus, can fit through the pores
  • When new cells bud septum does not form immediately
  • As the new cell matures, the cell wall grows down into the cytoplasm, forming the septum (singular form of septa)
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11
Q

HYPHAE MORPHOLOGY
Hyaline vs Phaeoid Hyphae

A

Hyaline- transparent no colour

Phaeoid (Dematiaceous)
Dark pigment due to melanin in the cell wall
* Pale brown to dark brown or black

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12
Q

FORMS FUNGI CAN EXIST IN

A

Monomorphic
* single type of growth
* ONLY yeast OR mold

Dimorphic
* Exists as a mold or a yeast or a spherule depending on the temperature
* Yeast in tissue 37 0C,
* Spherule 37 0C
* Mold phase (RT, O2)

Polymorphic
* Exists as yeast and mold at the same time
* Produces many forms, hyphae, pseudohyphae and budding yeast (called blastoconidia)

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13
Q

MYCOSES

A

superficial
cutaneous
subcutaneous
systemic

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14
Q

SUPERFICIAL MYCOSES

A
  • Strictly confined to skin and hair
  • no overt symptoms
  • Fungus involved do not activate tissue responses or inflammatory reactions
  • Usually cosmetic concern rather than medical

Example of common superficial mycoses seen in North America
Tinea versicolor – caused my Malassezia furfur
* Causes hyperpigmentation or depigmentation of skin

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15
Q

TINEA VERSICOLOR

A
  • Malassezia furfur often normal flora on skin -opportunistic
  • Causes patchy lesions, scaling or varied pigments on skin most often face, chest trunk and abdomen
  • Can cause dandruff
  • Needs fat/oil to grow – found in areas with sebaceous glands
  • Can cause catheter acquired fungaemia in patients
    undergoing lipid replacement therapy
  • Lab Diagnosis: Microscopic exam of skin specimens in 10%KOH shows “spaghetti & meatballs” = budding yeast & hyphae
  • Shine a fluorescent woods lamp on skin and it will fluoresce
  • Will not grow on culture media unless covered with oil – w/o oil cultures will appear negative
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16
Q

CUTANEOUS MYCOSES

A
  • Caused most often by Dermatophytes – have only asexual reproduction
  • Involve keratinized area on host –skin, hair and nails
  • Causes a ring like lesion (ringworm) now named Tinea _location found
    -Tinea pedis = feet - athletes foot, Tinea capitis = hair,
    Tinea corporis = body skin Tinea unguium - Onychomycosis - deformed nails
  • Transmitted by direct/indirect contact with infected host
  • Symptoms: itching, scaling, lesions
  • Three genera of dermatophytes which infect different areas:
    Microsporum infects skin and hair (not nails)
    Epidermophyton infects skin and nails (not hair)
    Trichophyton infects hair, skin & nails
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17
Q

LAB DIAGNOSIS OF DERMATOPHYTES

A
  • risk 2 orgs work in level 2 lab with PPE and class 2 BSC

Specimens:
* Skin scraped from the margin of the lesion
* Hair plucked, not cut, from the edge of the lesion
* Nails scrapings are obtained from the nail bed

lab testing
1. Perform Microscopic examination:
In 10%KOH or Calcofluor white fluorescent stain
* Look for 2 sizes of asexual reproductive cells-each a distinct shape
Macroconidia & or Microconidia

  1. Culture the Specimen onto Agar Media:
    * portion of the specimen pressed into Dermatophyte test medium (DTM)
    * Basic agar with peptones, glucose, antibiotics & antifungals (chloramphenicol & Cycloheximide)
    * RT for up to 21 days
  2. Perform Macroscopic Exam of the mold growing on the plate (colonial morphology):
    * Description of color and texture of front of colony
    * Description of color only of back of colony
  3. Perform a Lactophenol cotton blue of the colony (staining)
    * Examine this preparation microscopically for
    characteristic macroconidia and or microconidia
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18
Q

Microsporum Microscopic Structures

A

Microsporum canis make:
-spindles shaped macroconidia with tapered pointed knob ends. Rough walled with small spines. more than 6 cells
- Microconidia that are found singly on septate hyphae and are club shaped

Microsporum gypseum make:
- Macroconidia with rough thin walls and rounded ends. less than 6 cells
-Microconidia that are club shaped

19
Q

Epidermophyton floccosum
Microscopic Structures

A
  • Septate hyphae
  • Makes Macroconidia that are smooth-walled, & “beaver tail” shaped
  • Made up of 2-4 cells
  • Macroconidia may be clustered at the end of a hyphae
  • Microconidia are absent
20
Q

Trichophyton rubrum Microscopic
Structures

A
  • Septate hyphae
  • Makes Microconidia that are teardrop shaped & Macroconidia may or may not be present
  • If present are long narrow thin, smooth walled with 2- 8 cell
21
Q

Trichophyton mentagrophytes
Microscopic Structures

A
  • Septate hyphae
  • Makes Microconidia that are round and clustered on branched conidiophores & Macroconidia that are
    thin- or thick-walled, 1- 6 cells
22
Q

SUBCUTANEOUS MYCOSES

A
  • Chronic infection of deeper skin layers spreading to muscle and bone but not usually to blood or organs
  • Fungus usually found in soil in tropical areas & enter through sites of skin trauma
  • Causes progressive non healing ulcers, may also see draining sinus tracts & tissue destruction
  • An example of a subcutaneous mycoses is Mycetoma
  • Characterized by formulation of melanotic granules containing the fungus being discharged onto the skin
    surface through multiple sinuses
  • You can express granules from draining lesions
23
Q

SYSTEMIC MYCOSES

A
  • A fungal infection that spreads throughout the body
  • Can affect multiple organs, blood, CSF
  • Can be fatal especially in immunocompromised individuals
  • Usually caused by dimorphic fungus, Aspergillus or a yeast
24
Q

DIMORPHIC FUNGI CAUSING
SYSTEMIC MYCOSES

A
  • Histoplasma capsulatum – spores found in bat or bird droppings
  • Coccidioides immitis - arthrospores found in soil
  • Blastomyces dermatitidis - Spores found in soil and wet, decaying wood
  • Paracoccidioides brasiliensis - Spores found in soil around coffee crops or armadillo dens
  • Sporothrix schenkii – spores found in soil & decomposing plant material especially roses (Rose handler’s disease)
  • Can also be carried by cats
25
Q

DIMORPHIC SYSTEMIC
MYCOSES how to get

A
  • Get infected by inhaling the spores, ingestion or by inoculation of spore into the skin
  • Healthy individuals usually have a limited acute respiratory or skin infection – some are asymptomatic
  • In immunocompromised the infection becomes chronic pulmonary infection or granulomatous skin lesions
  • lead to fatal systemic infections that
    affect the bones, internal organs, blood, CSF & lymphatic system
26
Q

LAB DIAGNOSIS OF DIMORPHIC
FUNGUS

A
  • Risk level 3 organisms in a Containment Level 3 Lab PPE & a class II bsc
  • Antigen or Antibody detection: using serological or immunodiagnostic techniques
  • Molecular tests like PCR: available for some dimorphs
  • Direct Specimen Microscopy: for detection of the yeast form in the body
  • Culture on fungal media at 25C & at 35C: may take up weeks to become positive
  • Microscopy from the culture: to see dimorphic yeast or mold structures
  • barrel shaped arthroconidia
    -tissue spherical
    -mariners wheel
    -rosette cluster of microconidia
27
Q

OPPORTUNISTIC SYSTEMIC
MYCOSES

A
  • Saprophytic fungi (naturally found in soil) or as normal flora – sometimes dismissed as non-pathogenic

Most Common Opportunistic Fungus:
Aspergillus spp., Mucor & Yeast (Candida)
* often as lab media contaminants
* But increasing cases of immunocompromised patients (especially AIDs) being infected by these organisms
* In order to be a true infection, there must be repeated isolation or isolation of the same organism from multiple specimens
* Or demonstration of the organism directly in the tissue

28
Q

Aspergillus spp.

A
  • Saprophytic fungus – found in soil or decomposing material
  • Conidia are inhaled.
    -common cause of allergies to mold or ear infections in healthy people
  • In immunocompromised, causes various respiratory infections, in lungs can be acute or chronic pneumonia
  • In the body the conidia continue to germinate hyphae causing fungal ball
  • Hyphae can spread via blood to other organs including brain -High mortality rate in this group
  • Organism is monomorphic → always a mold

Diagnosis:
* Direct specimen microscopy for characteristic mold structures
* Must have growth from multiple specimens
* Molecular testing

29
Q

Aspergillus vs Penicillium spp

A
  • Penicillium is not a pathogen
  • Has conidiophores with secondary branches called metula.
  • On metula are flask shaped phialides that bear the conidia – no vesicle

Aspergillus:
* Has conidiophores with a round vesicle at the end
* The vesicle has the metula & the phialides that bear the conidia

30
Q

MUCORMYCOSIS

A
  • Environmental fungus called Mucor causing infection in diabetics and immunocompromised
  • Infection is through inhalation, ingestion, or entering skin
  • Causes infections in the sinuses, eyes, lungs, skin & gastrointestinal tract
  • Invasion of blood vessels and blood clots causing rapid tissue necrosis
  • Disseminates throughout the body including the brain
  • Microscopic identification of characteristic fungal structures right from tissue biopsy
  • Growth from cultures from multiple specimens
  • Serology to detect antibodies
  • Molecular
31
Q

YEASTS

A
  • Found in the environment & as healthy normal flora of skin, genitals & intestine
  • Causes opportunistic infection in immunocompromised, those having antibiotic use or hormonal imbalances & malnutrition,
  • Candida is most common genus – C. albicans most common species of Candida – many more though
  • C. auris new species of importance – R to antifungals
  • Cryptococcus is another genus of yeast pathogenic to humans - C. neoformans causes serious infection in AIDs patients
32
Q

Forms Some Yeast can exist in:

A

Budding: Bud referred to as blastoconidium
Pseudohyphae: chains of buds that stay attached to the mother cell and to each other - have a constriction between adjacent cell
True hyphae or Germ tubes: long tube with parallel sides
and no constrictions
Chlamydospores: thick -walled survival spore made when the yeast is in adverse environmental conditions

33
Q

Candida albicans

A
  • Primary cause of yeast infections called Candidiasis
  • Causes 3 main types of infections

Muco-cutaneous :
* Oral (thrush), vaginal, upper respiratory, GI tract infections causing diarrhea

Cutaneous:
* Skin and nail infections

Systemic:
* Infections of inner organs and blood –serious & can be fatal

Presumptive identification of C.albicans:
* Is Polymorphic – exist as buds, true hyphae (germ tube), pseudohyphae & chlamydospores
* Chlamydospore & Germ tube test positive
* Urea test negative
Germ tube positive, grows well at 40– 42º C

34
Q

C. albicans vs C. dubliniensis

A

*C. dubliniensis is a separate species of Candida
* Causes infection in AIDS patients
* incorrectly identified as C. albicans because both Germ tube, chlamydospore positive & urea negative
* Need to differentiate because C. dubliniensis can be resistant to fluconazole which is used to treat C. albicans
* Differentiate by growth at 42 C
* C. albicans grows at 42
* C. dubliniensis does not grow at 42 C
* Can also do MALDI , PCR or other genetic testing

35
Q

Candida auris

A
  • fungus that is emerging as a serious global health threat & an infection control organism of concern
  • carried on the skin of colonized patients
  • can cause serious invasive disease
  • multidrug-resistant
  • Has caused outbreaks in healthcare settings
  • It is difficult to identify – easily misidentified as other Candida species when using traditional testing.
  • MALDI-TOF & Molecular methods are best ID methods
  • Must perform AST with antifungals to determine resistance

Germ tube negative, grows well at 40–42º C

36
Q

Other Clinically Significant
Candida spp.

A

C. tropicalis
C. glabrata
C. parapsilosis

  • All can cause outbreaks of nosocomial infections
  • Are resistant to numerous antifungals
37
Q

Cryptococcus neoformans

A
  • Found in nature (soil with pigeon droppings) - Route of entry is inhalation of yeast
  • Causes systemic infections meningitis, septicemia and pulmonary disease
  • Cryptococcus gattii also causes disease in immunocompromised & immunocompetent hosts
  • Important to distinguish two species since clinical course and treatment can be different
  • Special media available to differentiate the two – Canavanin Bromothymol blue agar
  • C. gattii uses glycine as a sole carbon and nitrogen source while C. neoformans does not
  • C. gattii turns the media from yellow to blue
38
Q

Cryptococcus Neoformans
Identification

A
  • Yeast-like, budding cells but no pseudohyphae or true hyphae or chlamydospores
  • mucoid colonies with capsule
  • India ink positive – tests for presence of capsule
  • Urea positive
  • Chlamydospore negative
  • Germ tube negative

Detection of cryptococcal capsular polysaccharide antigen
* Antigen detected directly from CSF or serum
* Method of choice for diagnosing patients with cryptococcal meningitis
* detected using latex agglutination, & lateral flow

39
Q

Treatment: fungus and yeast

A
  • Cell membrane contains ergosterol which some antifungals act upon
  • Primary antifungal amphotericin B
    (polyenes) & fluconazole (azole) –both broad-spectrum
  • Lethal to fungus but toxic to patient – now fungus have shown resistance
40
Q

Histoplasma capsulatum

A

spores found in bat or bird droppings

41
Q

Coccidioides immitis

A

arthrospores found in soil

42
Q

Blastomyces dermatitidis

A

Spores found in soil and wet, decaying wood

43
Q

Paracoccidioides brasiliensis

A

Spores found in soil around coffee crops or armadillo dens

44
Q

Sporothrix schenkii

A

spores found in soil & decomposing plant material especially roses (Rose handler’s disease)
* Can also be carried by cats

Micro (15 decks)

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