Fungi (Patho) - Block 3 Flashcards
What type of organisms are fungi?
- Eukaryotic
- Heterotrophic
- Ubiquitous
- Obligate aerobes or facultative anaerobes
What are the morphologic forms of fungi?
- Yeasts (single cell)
- Mold (filamentous, multicellular)
- Dimorphic (switch between yeasts and molds)
Describe the components of a fungal cell structure?
- Membrane bound organelles
- Eukaryotic nucleus
- DNA
- Ribosomes are 80s (40s and 60s)
- Vacuole
- Enclosed by rigid cell wall
What is the function of vacuole?
Enclosed compartment containing water, nutrients, and enzymes that helps maintain pH and contain waste
What is the function of the cell wall?
Protects cells from osmotic shock, determine cell shape, and contains antigenic components
What are the components of a cell wall?
- Mannoproteins
- Glucans
- Chitin
- Cell membrane
- Ergosterol
What is the function of mannoproteins?
GLycosylated mannose allowing it to adhere to host cells
What is glucans?
Major component of cell wall: Branched b-(1,3)-glucan and b-(1,6)-glycan synthesized by b-(1,3)-glucan synthase in the cell membrane and exported to cell wall
What is chitin?
Long chain polymer of NAG -> produced by chitin synthase in cell membrane
What are the components of a cell membrane?
- Lipid bilayer that is selectively permeable
- Integral proteins
What is the dominant fungal sterol?
Ergosterol
How are yeast formed?
- Reproduce asexual budding or fission
- Mother cell elongates and pinches off forming a progeny cell
What is the structure of mold?
- Tubular (filamentous) multiceulluar
- spore formation (sexual or asexual resproduction)
- Long filaments (hyphae)
- Mycelium: matlike mass of hyphae
What is the difference between septate and non septate hyphae?
Septate: divided by cross walls
Non: lack cross walls, hollow
What are the functions of spores?
- Reproductive structures
- Help fungi spread and colonize
- Cause infection
- Provide resistance
- Metabolically dormant
What is a dimorphic fungi?
Capable of converting between yeast and mold forms in different temperatures
* Molds at ambient temp
* Yeast at body temp
Most damage due to fungal infection or indirect or direct?
Indirect:
1. Activation of macrophages and neutrophils
2. Activation of proinflammatory T helper cells
3. Antibodies are generated against cell wall components
What is the immune response to fungal infections?
Macrophages recognize PAMPS on fungal cell wall and secrete cytokines that activate T cells and neutrophils
What is cutaneous mycoses?
- Confined to epidermis
- Involved in keratinized tissue
- Dermatophytes
What is subcutaneous mycoses?
- Infection in the deeper layers of skin
- dermis, cornea, muscle, bone, and connective tissue
- Acquired from traumatic inoculation
- Localized
What is endemic mycoses?
- Caused by dimorphic fungi
- Confined to geographic regions
- Blastomyces, Histoplasma, Coccidioides
What are opportunistic mycoses?
- Caused by commensal fungi or fungi found within the environment
- Limited virulence
- Target IC patients
Mycoses that is caused by dermatophytes?
Cutaneous
How is cutaneuos mycoses transmissed?
Warm, moist environment transferred person to person
Presentation of dermatophytoses?
Itching, scaling skin patches that become inflamed and weeping
Tinea pedis
Atheletes foot
Tinea corporis
Ringworm
Tinea capitis
Scalp ringworm
Tinea cruris
jock itch
Tinea unguium
onychomycosis: nails to thicken, discolor, and become brittle
Describe the activity of Candidia?
Yeast that can become disseminated into the blood:
1. Breakdowns in mucosal barriers, biofilm formation
2. Cause infection in heart valves, liver, spleen, bones, kidney
3. Fever, chills, hypotension, altered mental status
Opportunistic fungi?
Candidia
Cryptococcus neoformans
Aspergillus
Pneumocystic jirovecii
Types of Candida albicans?
- Vulvovaginal candidiasis (vaginitis)
- Oral candidiaisis (thrush)
- Candida albicans develops pseudohyphae to invade tissues (dimorphic)
What is the cause of pseudomembranous candidiasis?
Overgrowth and development of pseudohyphae damaging stratified squamous epithelial layer
* Desaquamation and keratin protein buildup causing a psuedomembrane and red painful lesions
What is the structure of cyrptococcus?
Yeast surrounded by a polysaccharide capsule
How is cryptococcus transmitted?
Pigeon dropping and soil associated with eucalyptus:
* Inhalation of yeast
* Percutaneuos inoculation
* Opportunistic
What is the differenc between Cryptococcal pneumonia and meningitis?
Pneu: mild or asymptomatic contained in LN -> granulomas
Men: causes HA and photophobia, personality changes, fatal, Aid-defining condition
Describe the structure of Aspergillus?
Filamentous mold (septate mycelium with conidia)
Transmission of Aspergillus?
Inhalation of airborne spores from conidia and transferred to wounds by contaminated bandages
AIDs defining codnition
What is Aspergeillosis?
Opportunistic and systemic mycoses -> infection in skin, eyes, ears, sinuses
Presentations of allergic aspergillus sinusitis?
Chrnic rhinosinusitus that causes asymmetrical swelling around the orbit and nasal sinuses
What pathogen forms a fungal ball in the lungs?
Aspergillus (aspergilloma)
Populations that contract chronic pulmonary aspergillosis?
Chronic lung disease
What is the pathogen that lacks ergsterol?
Pneumocytis
Transmission of pneumocystis?
Portal of entry: respiratory tract
Opportunistic mycoses in IC patients (AIDs defining condition) -> PCP
How does pneumocystitis cause pneumonia?
Forms cysts in the lungs and ruptures releasing fungi:
1. Attach to alveolar epithelial cells
2. Induce inflammation -> foamy exudate blocking O2 exchange
3. Symmetrical bilateral interstitial infiltrates -> death from respiratory failure
What pathogen is known as Cavers?
Histoplasma capsulatum
What is the most common systemic mycoses in US?
Histoplasma capsulatum (Caver’s Disease)
Describe the strucutre of histoplasma?
Dimorphic fungal pathogen that forms spores
Transmission of histoplasma?
Inhalation of spores founds on feces
Presntation of histoplasmosis?
Pneumonia:
1. granuloma with calcifications
2. Acute infection
3. Aymptomatic
4. Disseminated liver, spleen, LN, BM (IC patients)
Clinical lab tests for histoplasmosis diagnosis?
- Antigen immunoassays
- Microscopy of fluids/tissue samples with narrow-based buds
Structure of Blastomyces?
Dimorphic pathogen in soil
Transmission of blasstomyces?
Inhalation of mold (conidia or hyphal fragments) infecting skin, bone, GU, CNS
How does blastomyces evade immune response?
- Adhere to resp mucosa and trasform to yeast
- Yeast sheds major surface antigen to avoid detection by macrophages
Dx caused by blastomyces?
- Pulmonary blastomycosis dx
- Disseminated dx in IC
Lab testing for blastomyces?
Culture of biopsy or sputum
Systemic pathogens can cause disease in healthy and immune-compromised individuals
Histoplasma
Blastomyces
Coccidioides
Opportunistic pathogens can cause mycoses in immune-compromised individuals
Aspergillus
Candida
Cryptococcus
Pneumocystis
What is the structure of coccidiodes?
Dimorphic
Transmission of coccidiodes?
Inhalation of mold carried to deep lungs producing endospores
How does coccidioides evade immune response?
- Phagocytosed by macrophages but escapes destruction by increasing pH of phagosome (urease)
- Produces proteases and collagenases -> breaching of mucosal barriers -> disseminated coccidioidomycosis
Lab testing used for coccidioides?
Detection of IgG and IgM antibodies and NAAT assays
