Exam 2: Intro to Fungi and Parasites Flashcards
1
Q
Fungi
Characteristics
A
- Kingdom ⇒ Myceteae
- Cell walls ⇒ chitin
- Cell membrane ⇒ ergosterol
- Classified as yeast or mycelium
- Yeast ⇒ unicellular
- Mycelium ⇒ multicellular
2
Q
Fungi cell walls are made mostly of…
A
chitin
(N-acetylglucosamine + glucan)
3
Q
Yeast
A
- Unicellular
- Replicate by budding, fission, or molds
4
Q
Mycelium
A
- Multicellular
- Formed from hyphae
- Each is unicellular
- Hollow or divided by crosswalls
- Non-septate vs septate
- Hyphae grow together forming a mat ⇒ mycelium
5
Q
Fungi
Reproduction
A
Occurs sexually or asexually.
-
Asexually
- Via production of various spores
- Conidia
- Sporangia
- Ascospores
- Spores disperse and start new colonies
- Via production of various spores
- Sexual process not well understood
6
Q
Fungi
Metabolism
A
- Most are free living
- Aerobic
-
Heterotrophs
- Obtains carbons from organic matter
- Most are saprophytic
- Obtain nutrients from dead organic matter
- Some are normal human flora
- Candida, Malassezia
- Some are highly adapted mammalian or human parasites
- Dermatophytes, Pneumocytis
7
Q
Fungi
Classification
A
May be organized based on tissues infected:
- Cutaneous
- Subcutaneous
- Systemic or endemic
- Opportunistic
8
Q
Cutaneous Fungi
A
- Cause infections of the keratinized layer of the skin, hair, and nails
- Termed dermatophytes
9
Q
Subcutaneous Fungi
A
- Infect the dermis, subcutaneous tissue, bone, or cornea
- Ex. Sporothrix
10
Q
Systemic or Endemic
Fungi
A
- Causes systemic disease
- Confined to specific geographic regions
-
Dimorphic
- Two lifecycle forms
- Usually cause primary infection in the lung with subsequent dissemination
- Transmission via inhalation of spores
11
Q
Opportunistic Fungi
A
- Human commensals or fungi found in the environment
- Affect immunocompromised individuals
- Can cause serious disease
- Ex. Candida
12
Q
Fungi
Transmission
A
Varied routes of infection.
Includes:
- Respiratory
- Direct contact
- Soil-contaminated wounds
13
Q
Fungi
Pathogenesis
A
-
Some are pathogenic to normal hosts
- Have overt virulent factors
- Ex.
- Coccidioides
- Histoplasma
-
Most are opportunists
- Minimal virulence
- Must have pre-disposing conditions to cause disease
- Loss of normal bacterial flora
- Iatrogenic immunosuppression
- Genetic or acquired immunodeficiencies
- DM
- Mechanical breach of skin/mucosal surfaces
- Indwelling catheter
- Serious disease is not common in immunocompetent host
14
Q
Fungal
Immunity
A
- Responses vary with type
-
Innate immunity to most fungi is very high
-
Neutrophil killing is the primary mechanism
- Esp. against hyphae
- Line up along hyphal surfaces and secrete lysosomal enzymes
- Conidia/spores requires Mφ ingestion
-
Neutrophil killing is the primary mechanism
-
Intracellular forms ⇒ yeast
- Requires cell mediated immunity for elimination
- CMI important in most fungal infections
- Impaired CMI / low T-cell counts ↑ susceptibility to invasive fungal infections
- Ab with minor role in resistance to fungi
15
Q
Fungi Propagation
A
- Can be propagated on any nutrient medium
-
Mold forms ⇒ Sabaraud’s Dextros Agar (SDA)
- Growth of mold forms
- ID of spores (conidia)
- Low pH inhibits bacterial colonization
- Also includes some anti-bacterial agents
- Commonly takes 1-4 weeks to grow @ 25° C
-
Yeast forms cultivated at 37° C on specialized media
- Cutaneous forms frequently visualized in tissue specimens w/ KOH
- Can use lactophenol cotton blue to stain
16
Q
Fungal
Treatments
A
- # of available treatments limited
- Due to common pathways and metabolic processes b/t fungi & mammalian cells
- Risk of toxicity high
17
Q
Aspergillus
Overview
A
-
Aspergillus fumigatus and Aspergillus flavus
- Most commonly associated with invasive disease
- Opportunistic fungi
- Disease usually associated with severe neutropenia
- Found ubiquitously in the environment
- Infection is acquired exogenously
18
Q
Aspergillus
Morphology
A
- Exist as molds
- Composed of septate hyphae
- Branches @ 45° angles ⇒ dichotomous branching
- Characteristic of Aspergillus
- Reproduce asexually by conidiaphore formation
19
Q
Aspergillus
Transmission
A
Spread by inhalation of conidiaspores
No person to person transmission
21
Q
Aspergilloma
A
-
Usually seen in those with underlying lung diease
- Particularly those with pre-existing cavities in the lung
- Non-allergic colonization
- Chronic process with development of pathological changes in the lung
- Formation of Aspergillus containing granulomas
- Causes “fungus ball” formations on CXR
- Granulomas must be surgically removed + antifulgal medications
22
Q
Systemic or Invasive
Aspergillosis
A
-
Only in immunocompromised individuals
- Risk factor ⇒ neutropenia
- May involve pulmonary, sinus, cerebral, or cutaneous sites
- Pathogenesis involves angioinvasion, thrombosis, and dissemination to other organs
- Damage caused by tissue infarcts, hemorrhage, and necrosis
31
Q
Trophozoite
A
Lifecycle form that grows and replicates by binary fission within the host.
33
Q
Protozoa
A
- Unicellular microbes
- Range in size from 2-100 microns
- Have a cell membrane and numerous organelles
- Organs of motility vary
- Includes:
- Flagellates
- Amoeba
- Ciliates
- Sporozoa
34
Q
Flagellates
A
- Cyst and trophozoite forms
- Have flagella
35
Q
Amoeba
A
- Cyst and trophozoite forms
- Form pseudopods
- Temporary arm-like projection of a eukaryotic cell membrane that are developed in the direction of movement
36
Q
Ciliates
A
- Cyst and trophozoite forms
- Have cilia
37
Q
Sporozoa
A
- Frequently intracellular pathogens
- Many forms:
- Trophozoite
- Sporozoite
- Motile spore-like stage in the life cycle
- Cysts
- Gametes
39
Q
Microsporidia
A
Obligate intracellular forms
41
Q
Nematodes
A
Round
Teeth or plates for attachment
42
Q
Trematodes
A
Flukes
Oral and ventral suckers
43
Q
Cestodes
A
Flat, segmented body (proglottids)
Hooks or suckers for attachment
Ex. hook worm
